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Thread: Hologram on a Bicycle

  1. #1
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    Default Hologram on a Bicycle

    The theme for San Jose Bike Party's July ride was "Science", so I decided to make a hologram for it and mount in on my bike. I've wanted to find a use for the Wicked Arctic Spyder blue laser pointer I have, and this could be it. I'd make a laser lit transmission hologram, mount it on the rack and light it with the blue laser.

    To avoid the mess of processing silver halide plates at home, I decided to use some of the new Bayer photopolymer we have at work for testing. I would build the exposure system on a breadboard at home, and take the pieces in and set them up on available space on a table we have that sports a new Coherent Verdi V-6 laser. I used a he-ne laser to do the set up in my kitchen as shown below.

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    The he-ne laser in the top right corner sends its beam to a mirror in the top left corner. The beam goes down through a half wave plate, the beamsplitter, another half wave plate, reflects off the a mirror in the bottom left corner, is spread by a spatial filter and illuminates the recording plane in the bottom right corner. That's the "reference" beam.

    The "object" beam is reflected off the beamsplitter, spread by a spatial filter and bounces off three large mirrors before rear-illuminating the "object" diffuser. The picture below shows the system set up on the exposure table, with green light going through it. I set the beam ratio at 20:1 to give me a clean first shot, and the power at maximum (33mW/cm^2) to give me the best chance of getting a hologram I could use for building the playback system for the bike.

    Click image for larger version. 

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    After doing a sketch of the space available on the bike rack, I decided to use a reference beam angle of 50 degrees, diverging from a point about 20 inches away from the plate. The object was a 2-D graphic cut out of black vinyl on a glass plate, mounted in front of a ground glass diffuser. The image is a peace sign with a gear for the outer ring, both gender symbols and a set of pedals on the periphery, and a reducing lens in the bottom left corner to balance it out.

    The first shot was a mixed result. The image was real bright around the edges, a lot dimmer but still quite bright in the center, and there was a big fringe all around. But it was useable to continue, so I built the replay system seen below.

    Click image for larger version. 

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    I used a 6x12" breadboard to hold my blue handheld laser, which has an output of 150mW (on the low setting) at 445nm. The beam goes through two diffusers to spread it out, then reflects off two mirrors before illuminating the hologram from the top. The components are all from Thorlabs. The hologram was tilted so its image was the best compromise of visibility from typical positions of viewers riding behind me and those standing to look at it up close.

    After the replay system was completed, I went for a better hologram on the day of the ride (which started for me at 6:30pm). I figured the big fringe in the first hologram was caused by movement of the plate because the backer was absorbing too much light during the exposure, while it was clamped in the plateholder with the recording plate. For the second exposure, I went for the minimum power I thought would give an image, at 1.5mW/cm^2. This was still three times the dosage quoted in the literature, but my meter readings were taken in the central "hot spot" of the beams and I thought I'd have a good chance at exposing the whole plate. Wrong! Only about the central half had an image.

    Increased the power to about 7mW/cm^2 and the third shot was the worst of the three, with a big black fringe spot right in the middle. Damn. Out of time. An hour before I have to leave and I still have to mount the hologram on a piece of plexiglas for use on the ride, as i didn't want to risk a thin glass plate breaking with all those tires right behind.

    First hologram to mount was #1, seen below. Right away the film got twisted as it fed into the laminator onto the adhesive covered panel. I had no time for THAT, and the result of the subsequent stress test on the tile covered concrete floor can be seen. Luckily though, the second hologram mounted well.

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    The picture below shows the resulting hologram on the bike, a 1982 custom built Bruce Gordon framed 10-speed. The photopolymer material fluoresces green with illumination by the 445nm wavelength. The color of this fluorescence is distorted by the street lighting here and my cheap camera settings. The reflection off the incident surface of the hologram is seen as blue patches on the ground under my pedals. There is also a large blue patch on the ground behind the bike, from the undiffracted zeroth order.

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    The picture below shows the finished display, but exposure artifacts with the camera used to take the picture makes it look much weirder than it really is. Although only the central half of the plate has an exposure, most of the image is visible through it. Some anamorphic distortion can be seen in the image, making the gear look oval instead of round. This is because I didn't adequately compensate for the shift in distance to the replay source caused by using blue light instead of green, as was used for exposure.

    The breadboard of the display was secured to the rack by a single clamp underneath, and it held tight throughout the ride and another ride the following night. It weighs 9 pounds. The single 18650 battery lasted the whole ride (from about 8:30 to 11:30) on the low setting.

    This was a fun project for me, taking about four full days to complete, spread out over seven. The image is just what was on my mind that week, and easy to make in the time I had.

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  2. #2
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    Looking good; not sure I would trust it all to a bungie though, but maybe I am nost seeing the bike mounting method well. I do cringe a bit seeing the blue 445 used; I think a nice red would be better as it is on the back of your bike. Maybe hook it up to your brakes to increase the power some when you slow down.
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  3. #3
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    Very, very cool, Bob! As-usual, well-executed, great story, Cinco estrellas!

    j

    PS - whatever happened to your X-Y lissajous ground-scanner on-a-bike project? That sounded cool...
    cya
    ....and armed only with his trusty 21 Zorgawatt KTiOPO4...

  4. #4
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    COOL. I Need one of those for my Trek 700.

    Steve

  5. #5
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    Bob,

    Nice work! It is nice to see such a great write-up. Next time I am in town I would love to see it and the setup in person.

    -Adam
    Support your local Janitor- not solicited .

    Laser (the acronym derived from Light Amplification by Stimulated Emissions of Radiation) is a spectacular manifestation of this process. It is a source which emits a kind of light of unrivaled purity and intensity not found in any of the previously known sources of radiation. - Lasers & Non-Linear Optics, B.B. Laud.

  6. #6
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    Fantastic project Bob, thanks for sharing

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

  7. #7
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    Yes indeed a very Sweet Ride Bob and i like the image too!

  8. #8
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    Very Cool Bob!!!

  9. #9
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    Two of my very favorite things: Bikes and lasers!

    I really wish I could have seen this in person; as a rider approaching a strange blue luminosity ahead of me, my curiosity turning to wonder as a hologram appeared. Inspiring project!

  10. #10
    swamidog's Avatar
    swamidog is offline Jr. Woodchuckington Janitor III, Esq.
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    bob,

    plus 1 million points for the best use (outside of a hammer) of a wicked lasers arctic.
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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