100mW Burning Red Laser

Now that the laser diodes are everywhere, I wonder how many of you remember how a HeNe laser looks like. For me it was the first laser I’ve seen, and it was at the age of 14 (back in April 1997).

Up to that point, I was aware of lasers only from SciFi movies. In 1997, I finally had one right in front of me. It was in a physics laboratory, at the Mihai Eminescu Highschool, Satu Mare. There I’ve spent the next 4 years of my life.

This laser was a HeNe laser. Big, somehow noisy, and for the 1mw output used a big power source. But it was a laser and followed the guidelines!

A laser (Light Amplification by Stimulated Emission of Radiation) is a device which uses a quantum mechanical effect, stimulated emission, to generate a coherent beam of light from a lasing medium of controlled purity, size, and shape. The output of a laser may be a continuous, constant-amplitude output (known as CW or continuous wave), or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved. A laser medium can also function as an optical amplifier when seeded with light from another source. The amplified signal can be very similar to the input signal in terms of wavelength, phase, and polarisation; this is particularly important in optical communications. The verb “to lase” means “to produce coherent light” or possibly “to cut or otherwise treat with coherent light”, and is a back-formation of the term laser.

Common light sources, such as the incandescent light bulb, emit photons in almost all directions, usually over a wide spectrum of wavelengths. Most light sources are also incoherent; i.e., there is no fixed phase relationship between the photons emitted by the light source. By contrast, a laser generally emits photons in a narrow, well-defined, polarized, coherent beam of near-monochromatic light, consisting of a single wavelength or hue.

Over the time solid state lasers have been developed: these devices emit coherent light, at the cost of very little electrical power. Now laser diodes can be found almost everywhere, so I thought it is time to try to get one myself.

So I’ve purchased a 100mW laser diode from ebay. It came with the driver circuit, ready for power up. Using that, I’ve created a simple aluminum housing, to keep the device packed together with the batteries, for easier use. I’m going to show that here:

Materials used:

1. The laser diode with its driver circuit (~26$)

This is a 100mw Pulsed red (655nm) laser diode.
2. Rechargeable 2700mAh 4 Battery pack (~20$)

This pack provides 4×1.2V = 4.8V @ 2700mAh
3. Suitable shape metal piece (free)
4. Long shape aluminum can with top removed (free)
5. Adhesive tape, some screws and some tools

A few steps and we are done

I’ve packed all the laser components on the small metal board. Under the laser driver and the batteries I’ve added a plastic layer to prevent the electronic components from getting in contact with the metal surface.
Next I drilled a few holes in the aluminum can to be able to fix some screws, and I covered it in black tape so it would look better and would get an extra strength. I’ve also added a switch between the batteries and the laser driver circuit. The laser diode got an improvised support, from a small plastic pipe as seen in the picture. This also has a screw to fix it to the metal surface.

I pushed the components inside the aluminum housing, and fixed the screws.

Now that everything is done, we can test the overall look and feel of this little device.
Adjusting the output lens, allows focusing the beam to a tiny spot, hot enough to instantly burn black colored materials. Why black? Because black materials do not reflect light, they absorb it. The result is accumulated energy in the form of heat.

To the right there are several other hires photos with my red laser. All the pictures are real, as recorded with my camera. I’ve also added some pictures with a 5mW green laser, even if it’s not related to this project.

Just a little light show, hope you like it.

Radu Motisan

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