buffo
Rick, the inverse square law assumes a divergent light source. (Either a point source or a spherical one.) :?Originally Posted by LaserLover
A laser beam has extremely low divergence. You will still have 400 mw at 12 feet from the laser. In fact, assuming that you've got less than 2 mrad of divergence, you'll still have 400 mw at around 50 feet from the laser. Beyond that, the beam may have widened just enough that it won't all fit on the aperature of your power meter. (Hard to tell from the picture, but it looks like the opening is around 1 cm in diameter.)
Still, even when the beam has expanded to larger than 1 cm, most of the power is concentrated in the center of the beam, so you won't loose all that much power if you loose a few mm around the edges.
The most likely reason that the beam looks dim in the picture is that 1) the lighs were on, 2) the air is clean, and 3) the beam is moving away from the camera. (# 2 and # 3 work together. Small particles, ie fog and haze, tend to scatter in shallow angles along the propagation path, while larger particles, ie visible dust, tend to scatter in wider angles up to and including 180 degrees from the propagation path. If you lived in a dusty warehouse, then the beam would have looked better from the vantage point you took the picture from.)
Nonetheless, I thought it looked pretty cool. I especially like the idea of mounting the two modules side by side like that. Looks like you nailed the alignment of the two perfectly!
Adam
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