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    Home-Built Diode Pumped Solid State (DPSS) Laser

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    Basic Home-Built DPSS Laser Information

    Introduction to Home-Built DPSS Laser

    Constructing a Diode Pumped Solid State (DPSS) laser at home is becoming an increasingly attractive project as the availability of the major components increases and their price drops to affordable levels. While there are many types of DPSS lasers, what we will concentrate on are those using Nd:YAG (Neodymium doped Yttrium Aluminum Garnet) or Nd:YVO4 (Neodymium doped Yttrium orthoVanadate) for the lasing medium with a KTP (Potassium Titanyl Phosphate, KTiOPO4) crystal for intracavity second harmonic generation. This generates green light at 532 nm which is not a bad shade of green and quite close to the eye's peak sensitivity. This is the approach used in modern green laser pointers and most modern DPSS green lasers. While other materials can be used to obtain other wavelengths (blue being the most common), (1) these are much less efficient and getting them to work well is more difficult and (2) they are much less common and thus the components are likely to be much more expensive. So, while the same basic principles apply, the details differ. If you have a healthy budget, after successfully completing a green DPSS laser, you can set your sights on one of these. :)

    High power DPSS lasers use lasing crystals in the form of rods pumped by radially arranged arrays of high power laser diodes. Since just one of the diode arrays alone would likely break the budget of an individual, what we consider primarily in this chapter are much more modest - typically a chip of Nd:YVO4 a few mm on a side and a mm or so in thickness pumped by a single bare (on heatsink), packaged, or fiber-coupled laser diode. Intracavity frequency doubling is done with a small block of KTP with the various mirrors either combined with, or separate from these. This basic configuration can easily generate over 100 mW of green light. The Nd:YVO4 and KTP are available individually or in 'hybrid' modules (also called composite crystals or composite crystal assemblies) from suppliers such as CASIX. Their "DPM" series combine the Nd:YVO4, KTP, and mirrors into a single unit for as little as $49 (quantity 1). See the sections starting with: Green DPSS Lasers using Hybrid Crystals.) Just add a pump diode and collimating lens and you will have the equivalent of a green laser pointer. Components may also be obtained from various laser surplus outfits and also show up on eBay from time-to-time.

    Depending on sophistication, the pump laser diode may be mounted directly on the lasing crystal or have its beam passed through correction and collimating optics first. Thermo Electric (TE) devices may be used to regulate the temperature of the pump diode for general cooling and to temperature tune its wavelength to the optimum for the absorption band of the Nd in the lasing crystal (around 808 nm). Temperature control of the vanadate to keep it cool and happy) and KTP to keep it warm and happy to further optimize output power may also be desirable. If you are determined to generate more than a few mW of green light, all of these will be needed.

    However, note that like the home-built pulsed solid state laser, constructing a DPSS laser truly from scratch is way out of the question onless you work for laser diode and laser crystal companies simultaneously. :) So, you may feel that a DPSS laser doesn't offer enough of a challenge or reward without being able to say you did everything from the the ground up. Building one for $10 is also probably not realistic unless you can salvage crystals and optics from a broken laser - the major components are still expensive (though slowly coming down in price). Having said all that, I do consider a DPSS laser to be worthy of home-built laser status - else I wouldn't have created this chapter!

    Home-Built DPSS Laser Safety

    There are two areas of safety considerations for the home-built DPSS laser (and other similar lasers, for that matter):

    Provide proper warning signs for both the laser radiation and high voltage. Keep pets and small children out of the area and make sure everyone present is instructed as to the dangers. The use of proper laser safety goggles for the specific wavelength(s) of your laser or indirect viewing methods such as the use of a CCD camera are highly recommended. Relatively inexpensive goggles designed specifically for the 3 relevant wavelengths of the green DPSS laser are available from many companies. One possible source is Spectronika. Ltd.. However, they are likely to be more expensive laser safety goggles for many other lasers. The primary reason is probably that they do have to be triple coated to cover the 3 relevant wavelengths - 808 nm, 1,064 nm, and 532 nm. The best ones will have high quality narrow band coatings to maximize the transmission of non-laser wavelengths and thus brightness. Simple dye-absorption type materials would not work well. You get what you pay for!

    For more information, see the chapter: Laser Safety. Sample safety labels which can be edited for this laser can be found in the section: Laser Safety Labels and Signs.

    DPSS Laser Construction References and Links

    Some Photos of Home-Built DPSS Lasers

    OK, not all these are actually home-built but are of the general design that could be constructed using available components and modest machining skills.

    Home-Built DPSS Laser Description

    Unlike most of the other (non solid state) home-built lasers, no specific design is presented here. A wide variety of crystal and cavity sizes will work and which one you use may end up depending on the cost and availability of crystals and optical components. Home-built DPSS lasers can have design goal green (532 nm) power outputs of anywhere from a few mW to several watts. I say "design goal" here because if all the planets don't align your way, in the end, all you may get is a fraction of a mW no matter what the design intended! As has been noted before, while constructing a green DPSS is easy in principle, getting it to perform to anywhere near spec requires attention to detail, painstaking parts fabrication and assembly, and precise alignment. And, it's all too easy to damage the soft crystals or their coatings or blow a laser diode. That can get discouraging and expensive very quickly.

    See Organization of Basic Green DPSS Lasers for examples of the major components of typical green laser pointers and a medium power (50 to 100 mW) green DPSS laser system similar to the 80 mW unit shown in the Laser Equipment Gallery (Version 1.74 or higher) under: "Miscellaneous Diode Pumped Solid State Lasers". Either of these would be a suitable home-built DPSS laser. The second generation pointer (upper right diagram) is not much more than a CASIX DPM hybrid crystal positioned next to an 808 nm pump diode with a microlens to improve the pump beam shape (but that could be left out for the a first version). An IR filter and collimating lens completes the unit. Such an approach may be the best choice for your first green DPSS laser. See the section: Super Simple Green DPSS Laser using Hybrid Crystal.

    The medium power green DPSS laser uses closed loop TEC control of both pump diode and cavity temperature and a possibly overly complex set of pump beam correction optics (actual lenses shown are basically just guesses!) which could be simplified considerably. See the section: A HREF="lasercds.htm#cdsrd801">Description of the 80 mW Green DPSS Laser for a listing of the specifications for the major components.

    For an example of a higher power and more challenging laser, see the very preliminary diagram of a Typical Home-Built DPSS Laser Assembly. This should be capable of between 100 mW and 2 W of green output. However, any of the higher power versions, at least, would be quite complex and expensive projects. In addition to all the precision machining, the cost of the pump diode, large vanadate and KTP crystals, and optics, there would need to be considerable electronics: The driver for the pump diode, the pump and vanadate TECs with their controllers, and the KTP heater and its controller. Note that while the beam correction optics shown in this diagram use anamorphic prisms, that approach will only work for up to perhaps a 2 to 4 W pump diode. For higher power using a wide stripe pump diode, bar, or array of bars, either a fiber-coupled or fiber bundled diode laser source with output focusing optics, or the use of a lens duct and HR mirror on the vanadate crystal would be needed.

    To see how the "big boys" do it, check out Coherent Verdi Description. The cavity configuration can be seen at the bottom of the page. I have edited the diagram as Ring Cavity Resonator of Coherent, Inc. Verdi Green DPSS Laser. The ring cavity provides robust single mode operation at high power levels as well as nearly 100 percent efficient extraction of the doubled (green) output due to the unidirectional beam circulation.

    Photos of the interior of an actual Coherent Compass 532-200, a lower power green DPSS laser than the Verdi also using a ring cavity can be found in the Laser Equipment Gallery (Version 1.86 or higher) under "Coherent Diode Pumped Solid State Lasers". The 532-200 is rated 200 mW, but can produce at least 400 mW by increasing current to the pump diode (at the expense of diode life expectancy). The last photo in the sequence is a closeup of the cavity and output optics showing the actual beam path.

    Here is the general description covering low, medium, and high power DPSS lasers. See the section: Component Selection Chart for Home-Built DPSS Lasers for an idea of what is required based on output power.

    For something to rival the pros, see Typical High Power Green DPSS Laser Optical Path, a side-pumped YAG based Green DPSS laser capable of truly show stopping power. Finally, information on cavity construction of high power DPSS YAG laser with a linear resonator is provided by Bob and hosted by LaserFX in Laser Construction - Pump Cavity. I expect this page to be added to on a regular basis.

    However, perhaps, building one of the more modest designs first would be a good idea - this would set you back the price of a nice used car just for the pump diode arrays, crystals, and optics. Throw in the resonator machining, electronics, and what else is required to turn it into a useful laser and you could be motoring around in style. :)

    Green DPSS Lasers using Hybrid Crystals

    Before undertaking what is going to be a relatively complex and expensive project, it might be worth seeing if you really have caught the "DPSS Bug". :) Here are some systems that will get you some green light without either expensive crystals or the need for complex mounting and infinite alignment fiddling. I am, of course, talking about the use of a hybrid (also called composite) vanadate-KTP crystal such as the CASIX DPM series. It shouldn't take much more than an above average flashlight to make any of these lase. OK, maybe just a bit more. :) A 100 to 500 mW, 808 nm pump diode will be needed. The resulting laser should be capable of 5, maybe 10 mW of green light with the DPM010X or up to 60 mW or more with the DPM110X hybrid crystals (more on these below). Now, it won't produce a perfect Gaussian beam shape or be super efficient because there is no pump beam correction and no separate control of pump, vanadate, and KTP temperature. But, it will lase bright green without too much effort. Adding a lens or two for collimation and an IR blocking filter will get you the equivalent of a green diode laser module or fancy green laser pointer (with the major components in full view!). And, it should be possible to improve the things further with careful shaping of the pump beam though achieving the same beam quality as with discrete crystals and optics will be difficult or impossible with the short flat-flat cavity design of these composite crystals. Most laser companies either decided not to pursue the composite crystal approach despite its simplicity and obvious cost advantages or gave up trying to achieve satisfactory performance.

    However, Melles Griot's low-to-medium power high quality green DPSS lasers now use composite crystals similar to CASIX's but of their own design optically contacted without any glue between the crystals (the DPM010X crystals are glued), so there is nothing to degrade. Unfortunately, there is no chance of getting these crystals for home use. :( VLOC also manufactures composite crystals that may be capable of very high output power - over 1 WATT of green - but you don't want to ask the price. :) So, what about somehow separating the two crystals by dissolving or softening the glue to eliminate that problem? Even if this could be done, just handling the individual pieces would be a challenge. The larger of the two CASIX composite crystals is 2x2x2.5 mm total dimensions; the smaller, 1x1x1.5 mm. I'm not about to try separating my CASIX crystal but attempting this with other types of composite crystals using an acetone soak was not promising. By the time the glue softened enough for the crystals to come apart, the mirrors had deteriorated to the point of being useless. Also, assuming you could get the two pieces apart without damaging them, what remains are two surfaces which aren't AR coated. Without index matching of some kind, there would be excessive loss and instability from the reflections at the two uncoated surfaces. See the section: Joachim's Comments on Lasers Using Composite Crystals, below.

    (Note: Should you acquire an optically contacted crystal (possible sources: Cristal Laser and VLOC), while there is no glue in between the crystals to be damaged by excessive intracavity power, there can still be problems with handling and excessive pump power popping the crystals. Since only the edges are glued, very small optically contacted crystals tend to fall apart either on their own or when pumping causes the central parts to expand. Thus, there still may be an upper limit below the damage threshold of the vanadate. The only way to determine it non-destructively is to check the specifications.)

    CASIX has now started selling composite crystals that may be optically contacted rather than glued at about the same prices as they were previously charging for the glued crystals. The DPM1101 and DPM1102 ($99 and $129, respectively, but these prices will no doubt drop quickly) should not have the stability problems and power limitations caused by the face glue of the DPM010X composite crystals. See CASIX High Power DPM Crystal and Casix Optical Bonding. I have done some preliminary tests on the DPM1101 and DPM1102. See the sections below.

    Note that originally, the CASIX Web site stated that the DMP110X composite crystals were diffusion bonded but it is not known if this is true of all of these crystals. Some have been shipped with "splints" on two sides, presumably to hold them together more securely, something that shouldn't be needed with diffusion bonding. Other information has also suggested that they are optically contacted.

    Super Simple Green DPSS Laser

    The design of this bare-bones laser is similar to the approach described in the section: The Short Life of Greenie #1 but there, the crystal is being pushed way beyond its capabilities (though what failed was the pump diode, not the crystal). The following has much more modest goals. I can't stop you from pumping it harder than recommended - just don't say you weren't warned!

    See Super Simple Green DPSS Laser. (The magnifications - 1X, 3X, 8X - assume a 100 dpi display or printer.) The mounting shown for the pump diode and crystal are just suggestions - you don't have to use the same really tiny plates and screws that are shown. Note the size of this laser at 1X! Almost anything that puts the output facet of the pump diode almost in contact (but not touching) the vanadate will work.

    For experimentation, a very simple power supply is sufficient for the laser diode driver (though a proper driver should be added to make them more user friendly and fool-proof if put to actual use, even if for demonstrations or as that green laser pointer with visible guts. :) My test power supply consists of a low voltage power transformer, rectifier, and filter capacitor, controlled by a Variac with an 8 ohm power resistor in series with the laser diode and a meter to monitor current. With care (always turn the current down before powering up/down, make sure all connections are secure), this can safely drive these diodes with no possibility of overshoot/reverse polarity on power cycling and good immunity to power spikes. Compared to our "killer laser diode driver", a very expensive commercial unit that has obliterated more than one very expensive diode laser due to some intermittent circuit problem, this bare bones driver is quite reliable!

    My initial tests of the DPM0101 and DPM0102 were using a fiber-coupled 808 nm pump. In a nutshell, they work great! With the fiber's 100 um core diameter and no beam correction, the thresholds for both were similar and slightly higher than with my discrete (green laser pointer guts) setup using a GRIN lens. However, it was possible to obtain much higher output power - probably 10 or 15 mW - at a pump power of around perhaps 300 or 400 mW (this with the non-polarized output of the multimode fiber which reduced efficiency by about 50 percent compared to a polarized pump beam that matches the preferred axis of the vanadate). The beam shape was actually quite decent even with the planar-planar resonator of the hybrid crystals. (More below.)

    One interesting characteristic for the DPM0102 was that as the pump power was increased, output power climbed slowly for awhile and then increased after a time delay rapidly to a much higher level. I suspect that this may be due to heating effects - either thermal lensing of the crystal or improved phase matching at higher temperature - but don't know for sure. The DPM0101 didn't exhibit this behavior - output power increased smoothly with pump power. But it didn't sustain the highest power for more than a couple seconds - the power decayed to a lower level. However, this was reversible by shutting down and letting the crystal cool off. Both these effects may have been related to alignment - my setup, or lack thereof, couldn't really be adjusted precisely.

    I expect that even simple pump beam shaping to reduce its diameter in the vanadate will result in higher efficiency and greater output for the same pump power. I haven't done any precise measurements as yet but will do so soon. However, I don't intend to push my luck on output power though knowing the problems that others have experienced with damage to the glue used to bond the two crystals together.

    Even Simpler Instant Green DPSS Laser

    Since my initial experiments, I found a bare (but mounted) 808 nm pump diode laying around that was just screaming to be put to a good use. So, I installed it on a heatsink with the CASIX DPM0102 and presto: Instant green DPSS laser. Later, I added an adjustable platform with mounting bracket for the crystal. This setup isn't nearly as compact and cute as the one in the diagram, above, but works quite well. At the modest current required for reasonable power, the heatsink alone is more than sufficient for cooling and no TEC is needed - which is my justification for calling it "even simpler". :)

    Even Simpler Instant Green DPSS Laser is a photograph of this unit lasing with a power output of about the 10 mW. (For an idea of size, the threaded holes of the optical table are 1 inch apart.) The closeup shows the major components. The pump diode is at the left wired with a reverse polarity protection diode and bypass capacitor. The DPM0102 hybrid crystal is mounted on a miniature three screw adjustable platform which provides for fine control of pitch, roll, and height. It is held snugly, but gently, under the aluminum bracket amidships with its rear face positioned as close to the pump diode as possible without touching. The "pitch" (I.e., tilt) adjustment is for vertical alignment; loosening the bracket and/or the screws that fasten the pump diode to the baseplate allows horizontal alignment of the pump beam with the crystal. The screws marked "roll" are really only to allow the entire crystal/platform to be raised or lowered - slight rotation about the beam axis has no effect of any consequence (but may come in handy for future applications). Although the laser cavity is formed by the faces of the crystal and thus there are no adjustments (!!) for actual mirror alignment, it's still important for the crystal to be fairly well aligned with the diode's output beam (though a huge $500 Newport mount isn't needed). Due to reflection of the backward going green beam from the front facet of the pump diode, there will be ghost spots when alignment isn't correct. The orientation and distance between the spots provide a clear indication of which direction to move. In the case of my diode, the chip appears not be mounted particularly perpendicular to the plate's centerline so it needs to be skewed to make the output beam come out straight when the ghosts spots merge!

    An interesting characteristic of this setup is that above some minimum power level, not very much green light seems to come out the back of the crystal (unlike my green DPSS laser using discrete crystals and optics where everything behind the vanadate literally lights up like a Christmas tree). At low power, there appears to be significant back scattered green light. This actually appears to reduce in intensity as the pump power is increased - but only if the crystal is oriented so that the polarization of the vanadate matches the pump diode. Otherwise, the back scattered green light continues to increase in brightness. In reality, the back scattered light is probably just not increasing in brightness as fast as the main beam so it appears to decrease. Got that? :) I don't know whether this is some non-linear effect with respect to the relative amount of forward/backward conversion in the KTP, simply changes in mode structure resulting in more of the backward green hitting the front facet of the pump diode and being reflected forward, or something else.

    Even without any pump beam shaping, the output beam profile is still TEM00 and reasonably circular at low power. At higher power it may split into 2 or three modes though I haven't really determined the conditions for this to occur. Since my pump diode is quite high power (probably good for 2 W at least with a large stripe width), its threshold is much higher (about 700 mA) than the 100 to 250 mW diode recommended for use with these composite crystals, so I don't really know how the efficiency of this rig compares to using the fiber-coupled pump but it seems to lase green with very little pump power (checked by the brightness of the pump light) and output power increases quite rapidly with increasing pump power.

    Another incredibly super simple instant design is shown in Green DPSS Demo Laser using CASIX DPM0101 Composite Crystal. The pump diode is a bare chip soldered to a brass plate with the top contact attached using silver conductive Epoxy. The DPM0101 is glued into a slot in its own brass plate with 4 screws and lock-washers for adjustment. I have built a unit similar to this for somone who needs to show non-laser types how a basic diode pumped microchip laser works. It will be mounted in a Plexiglas box with a magnifier. For the power supply, I used the Roithner EU38 laser diode driver with a filtered 4 V linear voltage regulator preceeding it. Input power is from a 6-9 V wall adapter. See: Green Demo Laser Power Supply Using EU38. The complete system is shown in Green Demo Laser With Power Supply. The dimensions aren't quite identical to the diagram, above, but close enough for government work. :) The reason for the ghost spot is that the laser diode chip is mounted a bit skewed on its heatsink so the reflection of backward going green beam from the KTP doesn't reflect on-axis.

    The CASIX DPM0101 and DPM0102

    The use of hybrid or composite crystals like the CASIX DPM series represents by far the easiest way to construct a low power green DPSS laser. They virtually eliminate fiddling as a pastime since the HR, Nd:YVO4 (vanadate), KTP, and OC mirrors are all permanently aligned. For many applications, no additional optics are required. And, the cost can't be beat especially once the cost and time of fabricating suitable mounts for separate vanadate, KTP, and OC mirrors is taken into consideration. See the section: Super Simple Green DPSS Laser using Hybrid Crystal.

    There are some disadvantages to this approach. With the batch fabrication technique (see below), both mirrors are planar which means there is little control of transverse mode structure (though with a well shaped pump beam, this doesn't seem to be a problem). And there is that problematic glue used to bond the vanadate and KTP together which is one of the prime limitations on extended operation at high output power. (This only applies to the DPM010X; the new physically similar DPM110X hybrid crystals are optically contacted which should eliminate this problem and allow for much higher continuous output power operation.) However, these deficiencies are more than made up for by the immediate gratification of getting bright green light with without the hassles of handling, mounting, and aligning individual fragile crystals and optics.

    DPM crystal specifications:

    These are based on my expectations and observations. I have not actually made precise measurements:

    Maximum output power:

    This is one of those things where there are apparently no hard answers (or at least no one is talking) so much of the following is just my opinion. According to CASIX, the maximum recommended input pump power is around 300 mW resulting in a lifetime of at least 5,000 hours (whatever that really means). The first person I asked at CASIX didn't specify output power but someone else suggested that 10 mW max was a good number. Given that both of these DPM crystals are intended for green DPSS laser pointers, I would assume that a continuous output power of 2 or 3 mW for the DPM0101 and 5 mW for the DPM0102 will be safe for long term reliability. I know it's tempting to drive these things much harder - I've seen over 35 mW (limited only because I didn't wont to fry my samples) and others have achieved 100 mW or more. However, there are both thermal considerations as well as damage to the cement used to glue the vanadate and KTP which may limit use of such high power for more than short periods of time. From conversations with other crystal venders (but not CASIX) using similar adhesives, operating at a 30 mW level may result in damage after a few hours while at 5 mW, there may not be any damage after thousands of hours. Note that since intracavity power density also depends on factors like pump spot size and shape, there won't be a single number for maximum output power. Until more is known, just assume your mileage may vary and don't press your luck too much. :) Please send me mail via the Sci.Electronics.Repair FAQ Email Links Page if you have any additional information or personal experiences using these or similar crystals.

    Operational considerations:

    Which one to get? While the DPM0102 is more expensive than the DPM0101 ($49 versus $99 in November, 2002) it is easier to handle and may possibly be more robust, and is potentially easier to cool and thus may be capable of higher output power. And, should one spot of the glue become damaged from overzealous experiments in pushing the envelope, there are plenty of alternative areas to use just by shifting the pump beam location. However, with the introduction of the DPM110X optically bonded hybrid crystals at reasonable prices (see below), the use of glued crystals will only be justified in extremely cost sensitive applications. So, go for the DPM1101 or DPM1102 instead.

    The CASIX DPM1101 and DPM1102

    As of November, 2002, CASIX has started selling optically bonded hybrid crystals that should provide significant benefits compared to the DPM010X glued crystals. Most notable is the total lack of glue to degrade when run at high power. Thus, the performance of these crystals will be limited by thermal considerations resulting in continuous green output power of at least 60 mW and possibly much more. The DPM010X crystals were limited to a continuous green output power of 5 to 10 mW due to degradation of the glue from intracavity photon flux. Another possible improvement is that the input mirror is also coated HR@532nm so the nearly 50 percent of the backward traveling green light normally wasted is reflected to the output (though this, of course, could also be done for the glued crystals).

    When the DMP110X crystals were introduced, the following (slightly paraphrased) appeared on the CASIX product announcement page:

    "Optical bonding is based on diffusion. The crystals are permanently bonded by heating to a high temperature under pressure resulting in a chemical exchange of molecules at the interface. The resulting monolithic unit should be stable with respect to high and low temperature storage, temperature cycling, impact and shearing, solvents and other chemical attack. They can work in high vacuum and under intense radiation."

    Since these hybrid crystals can be fabricated in large pieces and then diced up into their final size, costs should be much closer to those of glued crystals. The cost of optically contacted crystals will never be very low since they must be assembled individually. In fact, the initial prices for the DPM1101 and DPM1102 ($99 and $129) are similar to the previous prices of the DPM0101 and DPM0102 (which have now dropped to $49 and $99). Given the advantages of the optically bonded approach, there is little reason to even consider glued crystals unless price is the absolutely overriding concern.

    However, it now appears as though the DPM110X crystals are indeed optically contacted and not diffusion bonded. This is somewhat confirmed by the existence of the reinforcing strips. If so, most of the advantages are still present, but how they can be fabricated at low cost is a mystery. And, even with the reinforcing strips, the robustness of optically contacted composite crystals is questionable since delamination from the stresses induced by thermal stress (in particular, thermal lensing) can be a problem with this approach.

    See the section: Some Tests of the DPM1101 and DPM1102 for some more info.

    Some Tests of the DPM0101

    I actually have an interest in using this type of composite crystal for an application other than making a nice pretty bright green light bulb which I will describe in the future when I have more information. For now, I did some more detailed tests on the CASIX DPM0101 to see if it would be useful. (I would expect the DPM0102 to behave similarly but its larger size wasn't as convenient for my test jig.) The following was done using a 1.6 W max 808 nm fiber-coupled laser diode with a 150 um core diameter on a very expensive ILX Lightwave laser diode driver and TEC controller (e.g., at work, not at home!). The pump diode was temperature tuned to produce 808 nm +/- 0.5 nm. The fiber tip was mounted in a 5 axis Newport mount as was the collimated single mode fiber with focusing lens feeding an Ando optical spectrum analyzer. The DPM0101 was sitting in a 1 mm wide groove on a platform that could be also be adjusted in 4 axes.

    Note that the output of the multimode fiber is non-polarized. Thus, the portion of the pump light that matches the preferred polarization axis of the vanadate will be absorbed in a shorter distance (100 or 200 um assuming 3 percent doping for the DPM0101) of the vanadate while the other light will have a much deeper penetration - possibly resulting in a significantly higher threshold and lower output power (for a given pump power) if a substantial portion doesn't get absorbed at all.

    Here are some observations using the fiber-coupled pump, far from complete:

    I later tested the same crystal with a Spectra-Physics SCT100-808-Z1-01 open heatsink laser diode (1 W, 100 um stripe width) temperature tuned for 808 nm. The diode was positioned just short of touching the DPM0101 with the crystal oriented for optimal absorption. The lasing threshold came down to about 100 mW with good beam quality. I did not look at the spectral behavior but assume it to be similar.

    Some Tests of the DPM1101 and DPM1102

    I ordered 1 each of the DPM1101 and DPM1102 and received them in about a week. The following are very preliminary tests of both crystals. So far, results are mixed but generally positive.

    I would have expected the diffusion bonding technique (which is what I assumed these to be based on the CASIX Web site) to yield a very robust composite crystal. However, the samples I received had pieces of glass or other material glued on two sides apparently to provide reinforcement so they don't fall apart. This is why the size specification has a smaller clear aperture than that of the glued crystals. So, the top view looks something like this:

                         ________________________
                       _|________________________|_
                      |       |                    |
                      |       |                    |
                      | Van-  |                    |
             Pump --> | adate |         KTP        | --> Green Output
                      |       |                    |
                      |       |                    |
                      |_______|____________________|
                        |________________________|
    
    

    Apparently, some samples of the DPM1101 and DPM1102 received by other people do not have the splints. Perhaps CASIX was being overly careful on the first few batches. I did order mine just after the product announcement. However, since they are actually optically contacted, this makes sense. The CASIX Web site no longer lists the method used. If this is so, whether for technical reasons or something else, I don't know. I have my suspicions though.

    The lasing tests on the DPM1102 were initially performed using a Sony SLD322V pump diode (808 nm, 500 mW max, 50 um stripe width) with a pair of 12 mm f/1 lenses for beam focusing. The pump assembly was mounted on a Newport XYZ micropositioner.

    The lasing threshold was relatively low (about 200 mA). However, a nice TEM00 beam was produced only near the top of the crystal - the classic "sweet spot problem".

    Increasing pump power didn't produce proportionately more output power as would be expected (or at least desired). The power seemed to remain steady at a few mW. Granted, I'm not doing anything yet to cool the crystal.

    I next tried a DPM1101 (1x1 clear aperture) with a fiber-coupled 808 nm pump (100 um core) whose output fiber was mounted on a Newport XYZ micropositioner. The performance of this estup was much better than that of the DPM1102 producing a nice TEM00 beam from lasing threshold to 50 mW or so which was the maximum I have pumped it so far. (I do not know the exact pump power but expect it to be around 500 mW at the fiber tip.) There was only a slight variation in output power with respect to pump position on the crystal (minimal "sweet spot problem"). The output power increased smoothly with respect to pump power (which is not something I've seen in most of Casix's glued crystals). When pumped to produce about 20 to 30 mW, the output remained quite constant over the course of an hour (eyeballed).

    After better success with the DPM1101, I replaced it with the DPM1102 but used the same fiber-coupled pump setup. In this case, the results were somewhat better than with the Sony diode. While there was still some non-uniformity of power output with respect to pump position, it didn't seem nearly as severe. The output power increased smoothly with pump power and was of similar intensity to that from the DPM1101. I've run this setup now for at least 10 hours at a 50 mW output power level with no significant change in behavior. The only cooling is from being in contact with an aluminum plate on which it is loosely clamped.

    So, my opinion is that the two crystals do behave in a somewhat similar manner when the pump is the same.

    More to follow.

    Improving the Performance of Simple Green DPSS Lasers

    Here are some thoughts on dealing with the deficiencies of this or any DPSS laser. Thses should go a long way in converting a quick experiment into a decent performing laser:

    For more, see the next two sections.

    Substituting High Power Laser Diodes in DPSS Lasers

    So you have heard that replacing the 500 mW laser diode (LD) in your green DPSS laser pointer or module with a 2 W unit can boost its output power to 100 mW. Probably not. Aside from issues of quality of the vanadate and KTP and cooling, the reason has to do with LD brightness. The stripe width determines how tightly the slow axis can be focused for a given set of beam shaping optics (or none) and thus the available power density inside the lasing medium for a given total LD output power. Only if the maximum LD output power increases faster than stripe width, will there be a significant benefit to using a higher power LD unless the beam shaping optics are modified - which is usually not an option. The performance may actually get worse. Now it's true that even with the larger stripe width, more output power from the laser may be possible but it will likely be in higher order modes (which are likely not wanted in any case) due to the wider pump beam. If there is an aperture inside the cavity to confine a TEM00 mode, then the extra power will be totally wasted and only result in additional heating of the vanadate.

    Therefore, attempting to swap in some undocumented high power diode found on eBay to boost power of a DPSS laser is at best a crap shoot even if its wavelength and electrical parameters are known. :)

    The typical stripe width of a LD is roughly proportional to its maximum output power. The beam from a 2 W LD will be 4 times as bright as one from a 500 mW unit only if their stripe widths are the same. However, the typical stripe width for a 500 mW LD is 50 um while that of a 2 W LD is 200 um or even 400 um. The stripe width can be determined experimentally by projecting the LD beam onto a screen through a short focal length positive lens producing a focused image of the stripe. The stripe width of the LD will be the ratio of the distance from the lens to the LD and from the lens to the screen multiplied by the image size on the screen.

    Joachim's Comments on Lasers Using Composite Crystals

    The following includes experience with both the parts of these modules separated to avoid the glue problem as well as microchip lasers in general. (Note: The terms: "composite crystal", "hybrid module", and "microchip laser" are used interchangeably and all mean about the same thing.)

    (From: "Joachim Mueller" (JoachimMueller@swol.de).)

    I have tried to work with the parts from CASIX. I ordered some of the DPM-crystals from casix separated (not glued together) and did some experiments with them. The middle surfaces, which normally are bonded together, are only polished - there are no coatings. When only sticking them together, the optical loss resulting from reflections is too high. Only a very weak green beam was visible. One solution is using index matching gel (used in fiber optic technology). This material is able to operate under very high power-density with no damage. The problem is handling the 2 small crystals and keeping the matching gel free from air-bubbles. Also the 2 parts have to be aligned to the proper angle to match the polarization. It was a a lot of work putting the 2 parts together. Another problem is that CASIX can not test the crystals like they do with complete modules. If the polish is not perfect to form a parallel resonator, the result in green light is bad. After spending a lot of time on this approach, I came to the conclusion, that it is not a good way to save money. I think using discrete standard crystals is the better way to build a good working laser.

    In fact, I worked for 2 years trying all kinds of microchip modules from $99 to $1,000 each. The result is, that I stopped all work in this direction. Nearly all manufacturers (and users) of microchip lasers had trouble with it. Most of the laser manufacturers went back to using traditional spherical resonators. One of the problems of the modules is, that the beam quality is never quite as good and that there is no second source for such a part. Getting a good module is like playing the lottery. The chance to get the next module with the same characteristic as one you've tested is low.

    And, except for the special case of mass produced green laser pointers, microchip technology is expensive. For the same amount of money you can get the parts for a laser made from discrete parts. The vanadate + KTP + OC mirror will cost below $200. Beam quality of a discrete is better. Modules work with a very short cavity, a few millimeters. This increases divergence. It is nearly impossible to get a beam of diameter of 1 mm and less than 1 mR using a microchip module. Pumping a CASIX module with 1 W or more gives a divergence of 10 to 15 mR. Reducing this to 1 to 1.5 mR requires a 10X telescope which enlarges the beam to 2 mm or more. There are some modules with better beams, like the LSB-modules from Russia. They have about half the divergence of a CASIX module but cost at least double the price. (More below.) The only advantage of a module is getting relative high output power the easy way. But what is better: 100 mW of a 2 mm thick 1.5 mR beam or 50 mW of a 1 mm at 0.5 mR? When I see a thin low-divergence DPSS-laser beam, I know that this is NOT microchip technology. If make the effort and spend the time making a stable mechanics for adjusting the optics the results with using discrete parts will be much better.

    Im currently working on a discrete plane-parallel resonator (using HR@1064-coated KTP). It is like using a separated crystal module with the inner surfaces AR coated. My cooperation with a Chinese crystal manufacturer allows me to optimize coatings, materials and other characteristics. First results: 100 mW at 5 mR divergence without any beam optics. This configuration will lower the number of parts and makes me free from adjusting the orientation of the KTP inside the cavity. Moving the pump spot in XY direction does not affect the cavity alignment (This is a big problem when using a spherical resonator). Once adjusted, the cavity is a kind of "big module" and is replaceable inside the laser without the need of readjusting all parts. I'm now thinking about a simple and reliable mechanical adjustment-stage. Then it could be possible to offer the cavity without diode ready-to-use, just mount the thing to a TE-cooler, pump it and add output optics. Like a module! I think this cavity will cost a user around $350 and will allow building a powerful DPSS-laser without the trouble of mounting crystals and glued modules.

    There are 2 companies I know making LSB based microchip lasers. One is in Germany and the other is in Russia. The Russian version (from Science and Technology Center FIRN is in a metal housing constructed for low pump power (1 to 2 W). The German version (I forget who it is from) is 3x3x2.5 mm unmounted and better to cool. I tested both versions, but was not happy with the quality and the price ($400 to $500). The LSB itself has a very high efficiency. With the Russian parts, 200 mW at 1 W of pump power was possible. It could be more, if they would use higher quality KTP. The manufacturers told me a maximum pump power of about 3 to 5 W, so 1 W output is theoretically possible. But in reality, trouble starts at pump power greater than about 1.5 W. It had some coating defects and thermal management is also critical. LSB is a very bad thermal conductor. I know that a group of scientists reached 1 W green with a module under optimum conditions but they didn't say anything about the lifetime of their microchips. I think LSB is a good solution for a maximum output at low pump power (1 W). It would be interesting to use LSB-chips in a standard setup with discrete crystals. Unfortunately, I have no single piece of coated Nd:LSB available. :-(

    (From: Joe Farina (nospam@newsranger.com).)

    There is a paper which might be worth mentioning. It was published in Optics Letters, Volume 19, Number 18, September 15, 1994: "Intracavity frequency doubling of a continuous-wave, diode-laser-pumped neodymium lanthanum scandium borate laser." Here is part of the abstract:

    "...A simple plane-plane 3-mm-long resonator is formed by a coated Nd(10%):LaSc3(BO3)4 crystal and a coated potassium titanyl phosphate (KTP) crystal. The second-harmonic output power at 531 nm is 522 mW at 2.05 W incident pump power of the diode laser... The well-known chaotic power fluctuations of intracavity frequency-doubled lasers (green problem) are avoided by use of a short KTP crystal, between 0.5 and 2 mm in length."

    Component Selection Chart for Home-Built DPSS Lasers

    Here is a chart of general design choices and specifications for the major components of typical possible home-built green DPSS lasers. The specifics shouldn't be taken as fixed in optical cement. :) These are just to provide an idea of what is involved. This chart will evolve as more information becomes available. These lasers all are end-pumped. Perhaps, there will be a similar chart for your basic 100 W to 10 kW output side-pumped DPSS lasers in the future. :) (For the even simpler design using a combined vanadate/KTP crystal with integral mirrors, see the sections starting with: Green DPSS Lasers using Hybrid Crystals.)

     Power Output:          5 mW       20 mW      100 mW       1 W         5 W
    -------------------------------------------------------------------------------
     Pump Diode (1)
      Maximum Power       100 mW      500 mW        1 W       10 W        50 W
      TEC Thermal Power     --          1 W         3 W       30 W       150 W
      Beam Correction     <-- uLens or None -->   Prisms    <-- Fiber-coupled -->
    
     Resonator (2)
      Type               <-------- Hemispherical ------->   <--- Long Radius --->
      Length                7 mm       15 mm       40 mm       80 mm     150 mm
    
     HR Mirror (3)
      Diameter              ---         ---         ---        10 mm      15 mm
      RoC                   ---         ---         ---       250 mm     500 mm
    
     Vanadate:
      Overall Size       2x2x0.5mm  3x3x1.2 mm  3x3x1.2 mm   3x3x3 mm   4x4x4 mm
      Doping Level          3%          1%          1%         0.7%       0.7%
      Side 1 Coatings    HT@808nm    HT@808nm    HT@808nm    HT@808mn   HT@808nm
                         HR@1064nm   HR@1064nm   HR@1064nm   AR@1064nm  AR@1064nm
      Side 2 Coatings    AR@1064nm   AR@1064nm   AR@1064nm   AR@1064nm  AR@1064nm
      TEC Thermal Power     ---        0.5 W        1 W         4 W       20 W
    
     KTP (4)
      Overall Size        2x2x3 mm    2x2x5 mm    2x2x5 mm    3x3x7 mm   3x3x7 mm
      Type               <------------ Flux Grown -------->  <-- Hydrothermal -->
      Side 1 Coating     AR@1064nm   AR@1064nm   AR@1064nm   AR@1064nm  AR@1064nm
      Side 2 Coating     AR@1064nm   AR@1064nm   AR@1064nm   AR@1064nm  AR@1064nm
      Heater Power           ---        0.5 W       0.5 W       1 W        2 W
    
     OC Mirror (5)
      Diameter              5 mm         5 mm         5 mm      10 mm      15 mm
      RoC                  10 mm        20 mm        50 mm     100 mm     200 mm
      Side 1 Coatings     HR@1064nm   HR@1064nm   HR@1064nm   HR@1064nm  HR@1064nm
                          AR@532nm    AR@532nm    AR@532nm    AR@532nm   AR@532nm
      Side 2 Coatings     AR@532nm    AR@532nm    AR@532nm    AR@532nm   AR@532nm
    

    Notes:

    1. Pump diode power value is with everything optimal. Losses in beam shaping optics will increase this as well. I would recommend 1.5X to 2X as a safe margin. Any of these lasers may use fiber-coupled pumping but at up to a 50 percent loss in efficiency due to the polarization sensitive nature of the vanadate crystal. (When using a non-polarized pump, a higher doping percentage in the vanadate can be used to compensate for the increase in effective absorption length.) For lower power lasers, using no beam ld correction at all may be acceptable. For medium power lasers, cylindrical lens based correction may be used instead of (anamorphic) prisms. For the very high power lasers, an alternative to fiber-coupled pumps is to use a lens duct with stacked laser diode bars but that would require having the HR mirror on the rear of the vanadate since the working distance between a lens duct and lasing crystal must be short.

      For up to 10 mW (possibly even a bit higher), the use of a single mode pump diode with a GRIN lens or conventional beam correction optics may result in the highest efficiency. In one test I did, the same vanadate microchip laser (similar to a green laser pointer) that required 50 to 75 mW to reach threshold with a bare or fiber-coupled 1 W multimode laser diode would lase at something like 10 mW of pump power using a focused single mode diode! However, single mode diodes are only available up to 100 or 150 mW and are very expensive.

    2. A hemispherical resonator may be used in all cases if the HR mirror is on the rear surface of the vanadate. This puts the intra-cavity mode beam waist there as well.

    3. HR mirror diameter is not critical except that where it is not on rear of vanadate, it must be large enough for pump beam. HR RoC should be selected to control intra-cavity beam diameter inside vanadate and KTP crystals.

    4. KTP X and Y size is not critical as long as the clear aperture is at least 3 or 4 times the 1/e intracavity beam diameter at optimal orientation (to minimize diffraction losses).

    5. OC mirror diameter is not critical. OC mirror RoC should be selected to control intra-cavity beam diameter inside vanadate and KTP crystals.

    Basic Description of 100 mW-Class Cavity and Suggested Parts

    The following should get you enough green photons to impress your cat at least. :) This configuration would be suitable for a laser easily up to 100 mW, perhaps 200 mW on a good day.

    The effective cavity length should be just a bit smaller than the RoC of the OC (output) mirror to assure stability in this hemispherical resonator. Since the intracavity beam is diffracted when entering and leaving the vanadate and KTP crystals (and these have a high index of refraction of around 2.2 and 1.9, respectively) the actual cavity length will be slightly longer than if they weren't present, about 2 or 3 mm in this case. So, start with the distance from the pump-side of the vanadate to the OC mirror of about 48 to 50 mm for a 50 mm RoC OC. The KTP should be close to the vanadate to take advantage of the small beam waist (and maximum power density for best doubling efficiency).

    Sources of Special Parts and Supplies for the Home-Built DPSS Laser

    Laser Pump Diodes

    No, you can't get these out of a CD player (even 1,000 CD players). :)

    Laser surplus places like MWK Laser Products may sell high power laser diodes. However, in many cases, they are pulls from equipment near end-of-life with output power that is way down from new part specifications. For example, a diode spec'd at 20 W may only produce 0.5 W at some ridiculous maximum current. These are probably not terribly useful for incorporation into a serious DPSS laser. (A 20 W diode also has a very long emitting aperture which would make beam shaping very difficult especially if all you can get out of it is a half watt!)

    High power laser diodes also turn up on eBay from time-to-time (some are from MWK who goes by the eBay ID hene1). Without a guarantee, there is really no way to know for sure about the output power, remaining life, or if the device works at all. Search for "laser" and "diode".

    The companies below are all manufacturers or suppliers of high power laser diodes, laser diode arrays, laser diode bars, etc. But the chances of a private individual getting any free samples or diodes at a discount from them are slim to none (probably none).

    It appears as though Thorlabs sells some IMC high power laser diode bars (20 and 40 W at least). What's interesting are the prices. Boston Laser, Roithner, and others also list some prices. The prices are all somewhat depressing. :(

    Here is info on some manufacturers/suppliers known to be willing to sell in small quantities:

    When ordering laser diodes, if possible, specify a center wavelength range which results in optimal absorption in your laser crystal (typically 808 to 810 nm for vanadate and YAG). Otherwise, they may just send you diodes that are 804 nm at full power - even shorter wavelength for lower power. They may cost a bit more but is well worth not having to heat them significantly (which also reduces their life expectancy) to center the wavelength at 808 nm for maximum absorption. A longer wavelength is almost always better since cooling to shift it 2 or 3 nm is no problem (0.3 nm/°C). Also keep in mind that the wavelength spec is usually listed for rated power. If run at reduced power, it will be somewhat shorter.

    Also see: K3PGP's Laser Diode Manufacturers and K3PGP's Laser Diode Specifications maintained by K3PGP (Email: k3pgp@qsl.net). (This is a listing of the database that used to be on the Thorlabs Web site.)

    Laser diode drivers:

    While it's possible to build your own laser diode driver, given that the laser diode (or array or bar or bars) probably represents the single most expensive component of your laser, buying a reliable driver is probably the best option. Laser diodes are very finicky and unless you can afford to blow a few in developing a home-built driver, a commercial unit is really best.

    However, I plan to provide a design for a bare bones but reliable (I hope) constant current driver (2.5 A max) as well as a complete power supply using it in the near future. Stay tuned to this FAQ. :)

    Various laser resellers and surplus dealers have low cost no-frill driver boards capable of 1 to 1.5 A at prices from around $10 to $50. These are almost certainly far-East imports which may or may not meet advertized specs. I probably wouldn't trust them to drive a $1,000 fiber-coupled laser diode without some testing to make sure they work properly.

    The B&W Tek driver (BWD800) looks identical to the one from Roithner (EU38) so it's probably sourced elsewhere. I have used one of these to power the green demo laser described in the section: Even Simpler Instant Green DPSS Laser.

    For higher quality modules and lab-style (and expensive) controllers, see:

    The Wavelength Electronics modules have a good reputation (although I do have a blown one, cause unknown!) but are relatively expensive: around $300 for a 2.5 A driver. Lab style instruments from places like ILX Lightwave can run upwards of $10,000! And, they can still blow multi-$K laser diodes! Don't ask me know I know. :(

    Laser and non-linear crystals and optics:

    The following are some possible sources for laser crystals (e.g., Nd:YAG, Nd:YVO4), non-linear crystals (e.g., KTP, LBO), hybrid modules combining the lasing and doubling crystals, and optics (HR and OC mirrors, filters, etc.). Most probably won't give you the time of day unless you can convince them you are are associated with a company or university with deep pockets but others like CASIX and Roithner have prices for some items on their Web sites. These companies may have many more products than those listed below but these are the most relevant to the home-built DPSS laser. (Legend: LC=laser crystals, CC=composite crystals, NC=non-linear crystals, OP=optics, HM=hybrid modules. An HM is a CC mounted in a case with or without a driver.)

    The following are manufacturers:

    The following are resellers:

    CASIX can provide everything but the pump diode for composite and discrete green DPSS lasers. The authorized distributor in the USA for CASIX is U-Oplaz Technologies, Inc. whose prices are the same as those listed on the CASIX Web site. I ordered the DPM0101 and DPM0102 from U-Oplaz with very responsive courteous service but watch out for the $15 S&H charge. The DPM0102 even came in a cute cloth covered Chinese box. :) Lasershoppe is also selling CASIX crystals and optics (but apparently not their hybrid modules) at a moderate markup ($40 to $50/item). However, they do list prices for the higher power crystals (which are not present on the CASIX Web site or in their catalog). See the Lasershoppe Diode Pumped Laser Optics Kits Page.

    Roithner sells everything needed for a 100 mW-class green DPSS laser including pump beam focusing optics (required for use with their packaged laser diodes).

    Optics component companies like Melles Griot, Newport, and others will have the various lenses and prisms needed for pump beam shaping.

    Laser (resonator) mirrors:

    While there are many sources of laser mirrors including places like CVI and Newport, their cost can run several hundred to over $1,000 - for a single mirror using ion beam sputtered super polished fused silica substrates. However, there may be no choice for use with higher power (e.g., Laserscope class) lasers. For low power DPSS lasers, the only reasonably priced source I know of at the present time for cavity mirrors is CASIX (see contact info, above). They have some of the types of planar and concave small radius mirrors required for low to medium power green and IR DPSS lasers.

    Thermal control devices and supplies:

    Large electronics distributors may have some of these items, like TECs but their selection is probably limited. And, they certainly won't have supplies like indium foil (for cushioning laser crystals while providing good thermal contact) and low temperature solder (for mounting bare laser diodes, laser diode bars, and submodules). Some of this stuff shows up on eBay from time-to-time (Doesn't almost everyting? :) I recently came across some sheets of indium there but they were way too thick and the quantity was HUGE! Apparently, indium sheets, wire, gaskets, and other forms are common for cryogenic sealing applications but what you need is really just a fraction of a square inch of 0.001" thick indium foil). So, I wouldn't recommend holding your breath while waiting for the perfect deal at an auction. For these specific items, after reading what they would cost if purchased in the micro-sized quantities needed for DPSS lasers, see the special arrangement we have made, a few paragraphs from here.

    (From: Richard Everett (reverett@newtonlabs.com).)

    "I just got ten new surplus TEC devices in from BG Micro (Spring, 2002). These are NEW Marlow Industries DT12-4 (roughly 12 V at 4 A) 1.2x1.2 inch modules for about $6.75 each. This is really not a bad price, but here is the neat thing: You can buy the same module mounted on a heatsink with a little fan for $9.95. The cold side has a gold anodized metal plate with a prism shaped part sticking out of the middle of it with a hole tapped in on the flat of the metal prism shaped thing. It *almost* looks like this thing was designed for bolting on a c-mount diode. It is kind of funky, but it looks like it could possibly be made to cool a C-mount diode almost as-is."

    Here are some sources for TECs, controllers, temperature sensors, accessories, and supplies, as well as application information on-line. However, some of these companies probably have a $100 or so minimum order and small quantities of specialty items like indium foil and low temp solder are bound to be exhorbitantly priced.

    However, at least one company, Melcor has an on-line store with relatively reasonably prices for small quantities (linked from their homepage).

    A couple of notes about benefits of indium over silicone heat sink compound: First, although indium's thermal conductivity is much lower than copper, it is still much higher than silicone or other types of grease-type fillers or pads. Another advantage is that it doesn't make a mess of everything, which is a definite plus in the middle of precision optics. :)

    If indium foil isn't readily available but wire or another shape is, transform these non-planar shapes into foil is easy and quick. Dig out a smooth steel plate and rod from your junk drawer. Put a small piece of indium on the plate and use the rod as a rolling pin. In under a minute, this should produce a reasonable facsimile of foil since indium is very soft. It doesn't have to be perfect. You'll also wonder how they can charge so much for so little. :-) I assume tools made from something other than steel will also work but indium does stick to some, especially textured, materials.

    Additional suppliers of TEC controllers (both lab style and modules):

    There are also TEC controller ICs if you want to roll your own and would rather not design it from scratch. For example, check out:

    National Semiconductor has an app note on using an audio amplifier as a TEC controller. See their: Application Brief 118.

    For more information and suppliers than you could possibly want, see the Peltier Device Information Directory.

    (From: joefarina@my-deja.com.)

    LakeShore has 2" x 2" sheets of indium foil (apparently a pack of 5) for $93 (LakeShore - Indium and Solder.)

    They also have a very low temperature (70 °C) solder called "Ostaloy 158" for $57. I don't know if there's a minimum order. (These items seem rather difficult to obtain in small quantity from other sources.)

    I recently received some of Melcor's low temperature (93 °C) solder Melcor - Solder), but there was a $100 minimum order from them. I also got a couple of TE coolers and some thermally conductive epoxy. My order didn't quite make it to $100, but they let it slide.

    (From: Bob.)

    There is a HUGE increase in price when you buy in small quantity. If you spent $1,000 with an indium supplier you may get 1,000 times as much material as if you spent $100, no exaggeration! When I called around for quotes on low temp solder I got back numbers like $50 a foot for a 10 to 50 foot quantity. I then asked for a quantity of 500 feet, and got quotes of around $5 a foot I don't know of any vendor willing to supply small quantities at a fair price. And, while there is a lot of indium floating around on eBay, unfortunately, pure indium has much too high a melting point (157 °C) for use in soldering assembled diodes, as the diodes themselves are often assembled with either indium solder or an alloy with an even lower melting point.

    (From: Sam.)

    Through an arrangement with Bob and Sterling Resale Optics, we will be able to provide small quantities of indium foil (for cushioning laser crystals with good thermal contact) and low temperature solder (for mounting laser diode bars and bare laser diodes on heatsinks). And, perhaps other similarly hard to find items in the future.