Lasers Al Fresco: Fun With Open-Cavity Lasers

Helium-neon lasers may be little more than glorified neon signs, but there’s just something about that glowing glass tube that makes the whole process of stimulated emission easier to understand. But to make things even clearer, you might want to take a step inside the laser with something like [Les Wright]’s open-cavity He-Ne laser.

In most gas lasers, the stimulated emission action takes place within a closed optical cavity, typically formed by a glass tube whose ends are sealed with mirrors, one of which is partially silvered. The gas in the tube is stimulated, by an electrical discharge in the case of a helium-neon laser, and the stimulated photons bounce back and forth between the mirrors until some finally blast out through the partial mirror to form a coherent, monochromatic laser beam. By contrast, an open-cavity laser has a gas-discharge tube sealed with the fully silvered mirror on one end and a Brewster window on the other, which is a very flat piece of glass set at a steep angle to the long axis of the tube and transparent to p-polarized light. A second mirror is positioned opposite the Brewster window and aligned to create a resonant optical cavity external to the tube.

To switch mirrors easily, [Les] crafted a rotating turret mount for six different mirrors. The turret fits in a standard optical bench mirror mount, which lets him precisely align the mirror in two dimensions. He also built a quick alignment jig, as well as a safety enclosure to protect the delicate laser tube. The tube is connected to a high-voltage supply and after a little tweaking the open cavity starts to lase. [Les] could extend the cavity to almost half a meter, although even a waft of smoke was enough obstruction to kill the lasing at that length.

If this open-cavity laser arrangement seems familiar, it might be because [Les] previously looked at an old-school particle counter with such a laser at its heart. Continue reading “Lasers Al Fresco: Fun With Open-Cavity Lasers”

Legit Hack Creates TEA Laser Power By Mr. Wimshurst

It’s a bit scary what you can make with stuff found in the average household, provided you know what you’re doing. How about a TEA laser? Don’t have a high-voltage power supply to run it? Do what [Steven] of rimstar.org did, and power it with a homemade Wimshurst machine.

TEA lasers give off ultraviolet light. In order to see the beam, [Steven] aims it through a glass of water tinted with highlighting-marker juice and onto a sheet of white paper. [Steven] originally used his homemade 30kV DC power supply to light up his TEA laser. He made the laser itself from aluminium foil, angled aluminium, transparency sheets, some basic hardware components, and a 100kΩ resistor.

Although the components are simple, adjusting them so that the laser actually works is quite a feat. [Steven] says he burned holes through several transparencies and pieces of foil before getting it right. Using a Wimshurst machine to power the TEA laser takes another level of patience. It takes about 25 cranks of the static electricity-producing machine to build up enough energy to attempt lasing.

Want to make your own TEA laser, perhaps in a different configuration? [Steven]’s design was based on one of [sparkbangbuzz]’s lasers, which we covered several years ago.

Continue reading “Legit Hack Creates TEA Laser Power By Mr. Wimshurst”