Making Laser adjustments with an SNES gamepad

Gaming has infiltrated everything around us. It seems that any time a control interface is needed, the first thought to many current hacker’s minds are the familiar controls from the video games we grew up with. In this example, [eljaywasi] needed a way to control the wavelength of light coming out of a laser. We don’t know exactly how he’s actually changing the wavelength, but we do know he’s using an SNES gamepad as his interface. You can see a red and a blue LED located on the front of the pad, so it may be that two buttons would have sufficed. We don’t care, we like the SNES pad better.

Comments

  1. MrX says:

    He is probably just switching between lasers with different wavelengths. Unless he is using a acoustic-optic modulator which is really expensive. It is also possible to use passive optics to shift the frequency over a very limited range.

    • xeracy says:
      • medix says:

        Neither. “Switching between different lasers” is not really efficient, and will not provide you with a continuous tuning spectrum.

        AOM’s will only steer a beam, not change the color (that I know of). You need some type of nonlinear crystal for that. ;)

        The stepper is linked to what I’m guessing is a birefringent filter on the laser, which directly controls the lasing wavelength inside the cavity. I can’t tell which type of laser it is, so it’s difficult to say. Could be a diffraction grating as well.

        Perhaps [eljaywasi] can give us more information about the type of work he is doing and what lasers he’s using? I’d like to know more!

      • MrX says:

        medix see http://en.wikipedia.org/wiki/Acousto-optic_modulator
        they can indeed change frequency (by the Doppler effect due to moving planes), however don’t ask me if the frequency change is high enough for your eyes to even notice a change in color. I never used one of those to modulate frequency.

        I never heard a laser capable of changing the wavelength either!

    • Inc says:

      The laser he has there is a Spectra Physics Tsunami (i know as it is the same one i use).It has a tunable range from 675nm to 1100nm however you get into problems with the mirrors if you need to go over a large range. The centre wavelength of this laser is tunable in two ways. Either by moving a slit inside the cavity that site between the dispersion prisms while in femtosecond operation or changing the angle of a birefringent filter at the back of the cavity when in picosecond operation. Here he is attaching a stepper motor to the micrometer that controls the birefringent filter.

      • Inc says:

        a Tsunami is a Ti-Sapphire laser

      • MrX says:

        Thanks, that’s good information. By the way, you only find problems with mirrors if you have them coated for a particular wavelength.

      • Inc says:

        Laser cavity high reflector mirrors are normally always coated as they are Bragg mirrors. You can get broadband mirrors for this laser giving you a tunable range from 690-1025nm however the standard is for 720-850nm as Ti:Sapphs gain spectrum peaks at around 800nm and also modelocks best in this region.

      • medix says:

        Excellent! That’s what I wanted to know.. We’ve got a Mira 900 from Coherent which, from the sounds of it, has a similar cavity arrangement. Interesting though, since the mira does not have a slit between the dispersion prisms, but just a birefringent filter in the beam path. To switch to picosecond operation, you have to change out all the mirrors and re-align. >:o

        MrX, I had forgotten about the doppler shift, but you are correct that this likely won’t be enough to change the ‘color’ of the light (the term ‘color’ is relative here, since we could be talking about only picometers of wavelength shift).

        Now the question remains: How well does the laser take to tuning while in operation? The Mira is a pain in the ass. ;)

      • MrX says:

        I must say I’m impressed by the number of people both working on optics and reading HaD :) For a moment I thought HaD userbase were just xbox gamers.

        Keep up the good work HaD

      • Inc says:

        Medix,
        As with the Mira you also have to change the cavity and move mirrors around when going between ps and fs operation. The cavity of the two lasers are very similar however the cavity in the Tsunami also goes up and down rather than keeping it all in the same plane. Its actually quite a nice design with everything attaching to a central poll along the length and wrapping the cavity either side of it.
        I haven’t really needed to do any wavelength tuning with it and always need <100 fs pulses, however from playing with the slit i have never seen any real problems, it stays modelocked at least.

      • Inc says:

        pole not poll.. what is with my spelling today?

  2. bob says:

    Considering the military uses game controllers for their stuff, its not that surprising.

  3. aaron says:

    At a glance looks like a tunable laser maybe a dye laser by the size and position of the dial. It works by the stepper motor in one of the pictures turning a know on the laser. The know is then connected to a prism in the chamber which selects what wavelength gets bounced around the laser cavity and makes the beam.

  4. Amatol says:

    Seems like an extreme amount of circuitry just to turn a stepper motor.

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