Photo: Home-built helium-neon laser
A photo from last year’s lab course: In “Build Your Own Laser”, students learned to align the components of a simple helium-neon laser, and characterize its properties.
In the photo above, you see the (noncoherently) glowing He-Ne-tube, enclosed in a transparent box for safety (high voltage!). It is sandwiched between a high-reflective mirror and a 98% reflective output coupler (both barely visible in this photo). Good alignment provided, the arrangement leads to a coherent narrow red laser beam propagating to the right/front. I blocked this beam with a piece of paper to make it visible, leading to the rightmost red spot on the photo.