Variable Frequency Laser Using Shaken Ball Bearings

Lasers normally emit only one color, or frequency of light. This is true for laser pointers or the laser diodes in a DVD player. [Kevin] caught wind of state-of-the-art research into making variable wavelength lasers using shaken grains of metal and decided to build his own.

When [Kevin] read a NewScientist blog post on building variable frequency lasers built with shaken metallic grains, he knew he had to build on. He dug up the arxiv article and realized the experimental setup was fairly simple and easily achievable with a bit of home engineering.

[Kevin]’s device works by taking thousands of small ball bearings and putting them in a small vial with Rodamine B laser dye. To vibrate the particles in the dye, [Kevin] mounted his container of dye and bearings on an audio speaker and used a frequency generator to shake the ball bearings.

When a small 30mW green laser shines through the vial of ball bearings and dye, the laser changes color to a very bright yellow. By vibrating the vial at 35 to 45 Hz, [Kevin] can change the frequency, or color of the laser.

[Kevin] can only alter the frequency of the laser by about 30 nm, or about the same color change as a reddish-orange and an orangish-yellow. Still, it’s pretty amazing that [Kevin] was able to do state-of-the-art physics research at home.

Sadly, we couldn’t find any videos of [Kevin]’s variable frequency laser. If you can find one send it in to the tip line and we’ll update this post.

22 thoughts on “Variable Frequency Laser Using Shaken Ball Bearings

  1. Rhodamine is really cool, I’ve done some research with it… And you can find it in all kinds of places. Pink and orange highlighters and other fluorescent stuff of similiar shades usually contain it – if you have a green laser pointer shine it on some of this.stuff and you should see the effect in action.

    1. this is definitely not something that should have anything to do with that.

      You would need a good filter to differentiate between different wavelengths. (not sure how good of a filter, and if they even make IR filters that specific [i.e. a common ir diode frequency ± 30nm]. It might work, but is nowhere near the best solution.

      There are already at least 2 or 3 different wavelengths of IR laser diodes commonly in use (780, 980, 1064, see for more. Keep in mind anything that’s not semiconductor or solid state probably has a significantly higher cost and large size). (if it doesn’t use a laser / lasers, I’m sure an IR LED will exist for any of those wavelengths that are semiconductors and solid state).

      Also, someone already found a very very good and cheap (almost trivial even) solution for point clouds interfering with each other: put a vibration motor on the device. That way it introduces (semi) random vibration into both the projector and the camera. Thus, the camera has a much easier time tracking its own point cloud compared to others vibrating differently.

  2. Correct me if I’m wrong, but isn’t the unit nM a measure of Wavelength and not Frequency?

    The unit of Frequency is usually in Hertz. I believe Watts may also be appropriate as it is a measure of Force in Time, but I doubt this device would manipulate the Power of the laser.

  3. I read somewhere that with variable frequency lasers you can send data over them using FM instead of AM so you have higher throughput, what do you think that data through increase could be with this laser?

      1. while the current setup probably wouldn’t do, i can see a way to improve it drastically – use iron filings, and rather than use the speaker to vibrate the iron you could just mount a voice coil around the vial and vibrate them directly. Then again, the filings would probably clump around the walls of the vial, but hey. i’m a musician not a physicist.

    1. Using audio for the modulation and physical vibration of metal balls would make that much too slow for professional use.

      And they are other ways to do it, this is just an interesting phenomena.

  4. Shaking grains of metal…

    That’s a radio wave detector from before the age of vacuum tubes. It had to be combined with a decoherer, which originally was a device which struck or shook the coherer.

    That system made it possible to receive Morse code sent from a spark gap transmitter.

    120-ish years and the state of the art is again a shaking tube filled with fine grains of metal. ;)

  5. I don’t think the Dye is actually lasing. For one there is no resonator/cavity in place and for two 30mW CW isn’t nearly enough power for a Dye laser. Typical dye lasers pumped with 532nm lasers use a high powered ( 40W average or so ) pulsed ( q-switched ) frequency doubled Nd:YAG laser.

    Still impressive, even if it isn’t lasing. The principle is there.

    1. I suspect you are correct about the lasing. At 30mW I am still only seeing spontaneous emission instead of stimulated emission, however I did have some safety concerns about taking anything more powerful than 30mW to a Maker Faire. The original paper mentions using a Nd:YAG laser however doesn’t state the power of the pump source.

      As for the lack of a resonator the family of lasers this belongs to does not require one, at least not in the traditional sense. Random lasers were discovered in 1999 and were first described in the paper “Laser-like emission in opal photonic crystals”. In a random laser the mirrors are embed within the lasing material with the spaces between them acting as lots of tiny resonators.

      1. The pump laser power is indicated in the paper. Page 2, last two paragraphs laser as t=7ns pulse and per pulse energy of E=3.7mJ used in the experiment. This means the laser peak power P=E/t is likely in excess of ~1kW.

        Beam waist used was large though (6mm), maybe you could reach the pump intensity used in the paper by focusing a less powerful laser.

  6. This is great, people should have to access to all experiments, for other experimenters to replicate for that is the purpose.
    I haven’t read the original article or the original experiment article, so I am just speculating but perhaps higher wavelengths could be obtained with an ultrasonic frequency generator.

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