Related to MAKE 20, Lunchbox Laser Shows

Hobby Laser and Materials Buying Advice

October 29, 2009

Let There Be More Light - Lasers

With the advent of the diode laser, coherence is finally available at a hobbyist price. Search eBay for “laser module” and you will find lasers from $5.00 and up. There are basically two kinds of laser displays: screen effects, where the laser shines on a screen (which is what we are doing here), and beam effects, where the laser’s path though the air is visible. Beam effects require much more powerful lasers than we are dealing with here, fog machines, and have all sorts of legal regulatory ramifications (see below).

There are 2 different kinds of lasers to look for, diode lasers, and DPSS (diode pumped solid state). The red and violet lasers are diode lasers; the laser light is produced directly by a diode, much like an LED. Green lasers are Diode-Pumped Solid State (DPSS): an IR laser diode pumps a YAG crystal that lases at 1064 nanometer. This passes through another crystal that doubles the frequency emitting the 532nm (green) output. DPSS lasers are available in many colors, but only the green ones are affordable to folks like us. Green will get you the best output for your buck. Not because they are inherently more powerful than reds, but because the human eye is more sensitive to that color range. So a 5mw greenie will be perceived about as bright at a 10mw red laser. The violet lasers are problematic. They are often referred to as “blue” lasers, because they were removed from Blu-Ray players. Their color is almost into the ultra-violet range, and is hard to see at low power. They work best projected onto a fluorescent material such as cloth screens and to a certain extent, photo background paper.

Start small; get a 5 or 10mw module and do all your initial experimenting with that. That way if the laser accidently gets a taste of house current, you’re not out a lot of money. Once you have small lasers under your belt (not recommended literally), you can move up to more powerful units. Just be aware that bigger lasers have heat management issues. And bigger lasers can be dangerous as hell. It is scary to think that Amazon will sell anyone a 100mw green laser pointer for $45.00; I see a lot of half-blind kids in the future. Good news for us laser enthusiasts, though. For some odd reason, you can currently buy a pointer for less than a module right now. There are instructions on the Internet for cutting the guts out of a pointer to use as a module in a device: you need a pipe cutter, a Dremel tool and lots of patience.

Also be aware that as you get into higher power lasers (>5mw), there is a paperwork minefield of government and industry certification awaiting you if you want to perform legally in larger venues. Go to www.laserist.org/Laserist/Safety_7.html for a taste of this. I have a meeting with a lawyer later this week to find out if we want to proceed with this professionally.

For the Lumia we used a big 250mw red diode laser from Sunclan (clantechlaser.com). This power level meant the box also needed a heatsink and fan.

The laser for the Diffracterator was based on a pointer, as you can see in LunchBoxen_28.

The pointer was cut down and the outer paint scrapped off to make a better thermal bond to the copper support for passive heat dissipation. As laser pointers contain lasers that were designed for intermittent use, they need heat sinking in order to work continuously. As this laser was just a bit too small to fit snugly in its mount, Wayne added a strip of copper around it to bulk it out.

Basic laser hygiene: stick to lasers under 5mw until you know what you are doing. Don’t point any laser at anybody, ever. Aim your completed lunch boxen at walls and ceilings, not at your audience. Be very careful with lasers outside; the FAA takes a dim view of blinding pilots with over-powered pointers.

Materials

For each lunchbox:

• Metal lunchbox around $12 on eBay. We searched for “science fiction lunchbox” and found a variety. Older ones (like Pigs In Space) are larger and sturdier than new ones (like Wall-E), so they’re better for the Diffracterator, which is more complex. Dome boxes that hold a thermos in the lid provide even more room.
• 3/8" plywood, sized to fit bottom of box for the base plate
• Small laser module, or disassembled laser pointer
• Heat sinks (optional) for more powerful lasers (over 10mW), if used, and their voltage regulators. For one 250mW laser we used, Wayne had a stud rectifier heat sink lying around, which he drilled out to fit around the laser and secured to the base plate.
• 12V DC cooling fans (optional) if you use powerful lasers. We found some at a ham radio swap.
• Diode, 1N4003
• Phillips screws
• Perforated metal pipe hanger strap, about 3'
• Pipe hangers
• 12V DC power supply wall-wart or bench supply
• Connectors for power supply
• Capacitors: 10µF electrolytic, 0.1 µF ceramic Paint, matte black

For each voltage circuit (1 per laser and motor):

• LM317 voltage regulator
• Capacitors: 10µF electrolytic, 0.1 µF
• Resistor, 240Ω
• Potentiometer, 2kΩ We used micro pots, but regular pots with knobs would let you control motor speed more easily. You can also use a 1kΩ pot, for a narrower output range of 1.25V–6V.
• Insulated hookup wire
• Small piece of perf board

For the Lumia:

• Voltage circuits (2) using parts specified above
• Mabuchi RF-500T DC gearmotor about $5 from Skycraft Parts & Surplus (skycraftsurplus.com), or other motor that runs about 1rpm with 3V DC. Regular (non-geared) motors spin too fast.
• Transparent disk, plastic or glass for the rotating disk. Use a clear plastic protective cover disk from a pack of CD-Rs or DVD-Rs, or cut a glass disk 4½" diameter with a 1/8" hole in the center. If you use glass, take a laser pointer to a glass store and shine it through various kinds of patterned or stained glass, such as shower-door glass, to see how it affects the beam. You can have the store cut the disk (mine cost around $20), or else you’ll need a glass circle cutter and glass drill bit.
• Plastic model glue or 5-minute epoxy, clear
• Washer sized to match the motor shaft
• Front-surface (aka first surface) mirror, around 1½" square $4 from Edmund Scientific (scientificsonline.com), part #3052323, or you can find one inside a View-Master toy (the binocular style, where the reel sits horizontally).

For Diffracterator:

• Voltage circuits (4) as above; 3 motors, 1 laser
• DC gearmotors (3) as above
• Transmissive diffraction grating, matrix (aka double axis) We used some old (now discontinued) film from Edmund Scientific, but Rainbow Symphony (rainbowsymphony.com) has sheets for about $3.
• Reflective diffraction grating, matrix, 1¼" round I bought a 57mm x 42mm piece for $12, part #DGRM from Dragon Lasers (dragonlasers.com); it’s solid plastic, not flexible, so I had it cut by my local glass store (Diamond Glass in Ann Arbor, Mich.).
• 5½" round piece of 1/8" plexiglass I also had the glass store cut this.
• Small scrap of plastic
• White nylon rod, ½" diameter, ¾" length

For Motiondizer:

• Voltage circuit for laser
• Small matched speakers and amplifier Find a used set of powered computer speakers for $5 or so (or buy a new set) and remove them from their cases; I pulled mine from surplus Apple speakers that went with the Mac Cube.
• Front-surface mirrors: 1" round (2), 2" square (1) For the round ones, get the lightest-weight mirrors you can, to improve sensitivity. See above for sources, and if anyone knows an inexpensive source for these, I’d appreciate hearing from them.
• Flat piece of cork, 2" square I cut this from a drink coaster.
• Thin rubber membrane from a rubber glove or a heavy balloon
• DC power jack (optional) to match the wall-wart from the powered speakers
• Panel-mount RCA jacks (2) (optional)

Tools

• Pliers
• Tinsnips or hacksaw
• Hammer
• Pop rivet tool and rivets
• Bench vise doubles as an anvil to pound out the curvature of the strap hangers
• Saw to cut the plywood base plate
• Hand sander (optional) prevents splinters when handling the base plate
• Drill and bits
• 8-32 tap and drill set, with tap handle - for Diffracterator
• Propane torch to melt plastic, for Lumia and Diffracterator
• Paintbrush if not using spray paint
• Soldering station: iron, solder, damp sponge
• Tweezers or needlenose pliers
• Voltmeter
• Wire cutter/stripper
• Luxo illuminated magnifier (optional) if your vision is as lousy as mine
• Phillips screwdriver
• Pipe cutter to cut apart laser pointers to extract their modules
• Toothpick
• Band-Aids, iodine, aspirin just in case