Finally…

.. I found time and will to put together laser diode driver, TEC controller, data conditioning circuitry and USB interface in one case. One of the DAC’s had been damaged when cleaning up the mess of circuits and loose wires, and the prospect of replacing that tiny SMD device (with the danger of making the whole PCB unusuable) had reduced my incentive to go on with this project since two years…well there were other reasons too. But it wasn’t that bad after all. So now everything works again and I go on developing a stable single mode red diode laser suitable for holography.

Next thing was to rebuild Colin’s laser head with extra emphasis on thermal stability. Just right now automated scans are performed for determining the best operating point (current and temperature). On the pic above you see the laser head in front of my universal diode controller incl digital measurement machinery.

I now also performed long term stability measurements, and posted the results on my revamped web site. After a few minutes warm-up time, the laser runs stable single mode without jumps for hours; the price is a moderate 32mW output compared to the 100mW+ the Rohm diode can do.

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9 Responses to “Finally…”

  1. holo2008 Says:

    Hello,

    great that you found time to do lasers again! I’d love to see some plan for building a diode laser myself. When do you expect to have something more concrete? Or perhaps even one for sale?

    Thank you
    Dave

  2. rxlaser Says:

    Hi Dave,

    thanks for asking. Well, I still need get back to speed and next
    I will do some more measurements of other laser diodes; esp. the kinds you see on ebay now, ie. the Sony SLD1239JL and SLD1239JL-54, the 200mW+ open can diodes, and then some blue ray 405nm ones, and perhaps also with an improved ECDL design. Depending on the findings I may put together something, but I am not sure, what precisely.

    While I have collected a number of high quality components for ultra-stable diode and TEC drivers and so on, I don’t have that much time and incentive to sit down and build things for other people, esp. do mechanical work. So I could offer some kits incl the circuits, but as far as I can see, it is quite hard if not impossible to optimally adjust a higher power diode laser for single mode operation without some mesasurement equipment, and this can be done only for the completed laser. Thus selling just parts kits would send a few people into frustration and I don’t like to be held responsible for that. Maybe I will sell off some protypes I don’t need any more, at some point.

    I’ll keep you posted!
    -W

  3. holo2008 Says:

    Hello, I like to try to build a laser myself, so do you have concrete schematics for laser drivers and peltier coolers ? I could not find them on your site.

    Thank you
    Dave

  4. rxlaser Says:

    Hi Dave, as for schematics, for the laser diode driver I have a setup under development which should be even better than the proven Thorlabs driver LD1255 (incidentally the latter can easily be converted to do more than just 200mA). But I still need to spend more time on protection features, and then design a PCB and so on, this will take a few more months given the limited time I have.

    For the TEC driver, so far I was using left-over prototypes from my Coherent 315-M project based on MAX1968. Originally I was thinking to use a design based on the Hytek HY5600 controller (of which I happen to have a load). But it isn’t yet clear whether that can achieve the required stability (it works unidirectional only), and since this is a special, not generally available part I think it doesn’t make much sense to base a “production” version on it. I also like to avoid PWM controllers like the MAX1968 since these SMD devices are painful to use for non-experienced people, while size and efficiency play no role for holography purposes, so it is actually pretty pointless to use those (I learned this lesson in my Coherent 315 project; I also see, somewhat amused, other people falling into this trap, esp light show people who use lasers just as better collimated lamps for which a temp stability of one degree would be more than sufficient).

    So I tend to a design based on a cheap and readily available power opamp or audio amplifier, together with a high precision opamp frontend and a precision voltage source for stability (and of course a carefully designed PID control loop). Since the needed cooling power is low, probably even a one-dollar device like the LM4860, LM4871or TEA2025B can drive the peltier element. Look for example here:
    http://www.national.com/appbriefs/files/AppBrief118.pdf Otherwise, for more power, consider TDA7240A or similar, alle these can be obained via ebay.

  5. holo2008 Says:

    I see, thank you. And what do you think of the popular Die4Drive driver for the diode?

  6. rxlaser Says:

    Dave,

    this and other constructions are made for uses (“blanking”) that are pretty much the opposite of what we need. I am not sure how good or bad this may work, and you always hear stories where people have successfully done holograms with this and that, but they might have been just lucky or done one good hologram out of 20 attempts, while you never hear about failures.

    There is no stabilization whatsoever in this circuit, so at the very least put in a good voltage reference such as REF02. The point is to exclude as many potential failure modes as possible, in holography there are always plenty of less controllable ones left 😉

    Otherwise, this driver does not seem reliable to me, especially putting the diode to the positive voltage line (rather than against ground) invites for trouble.

    All the best,
    -W

  7. RGB Says:

    W, I look forward to read about your work. Now and then I browse your web pages to see if you´ve come up with something new. I will also try to build a diode laser suitable for holographic work, but I will use equipment from Wavelength Electronics. I have not decided whether to use the MI-Lasers diode mount or build something like a Newport or ILX diode mount. You wrote somewhere that it is important to isolate the collimator lens from the mount. How important is this?

    I do not have any fancy measuring equipment so I hope it will be enough to use Hans´DVD test to find a stable region.

    D

  8. rxlaser Says:

    Hi “D number 2”,

    isolating the mount and having the diode sealed off in a closed housing would protect the diode from air currents, but I think that one can equally well just put the whole mount/collimator combination in a closed box with just a little hole for the beam. I think Colin’s design is the easiest way to go. And putting the diode and lens in the same metal brick makes adjustment much easier, and in fact I am thinking about changing my Newport setup for this reason. Another is that I like to use a standard 9mm thread for easier exchanging the collimator lens (to a 405nm one, that is).

    Thanks for your interest,
    W

  9. rxlaser Says:

    PS:

    I have added the schematics for my current laser diode driver, but I still need to perform various measurements so it is preliminary. A PCB is being made as well. See http://pagesperso-orange.fr/redlum.xohp/laser/red_diodelasers.html#LDdrv

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