| abstract |
A multipass cavity system employs a beam of light that is reflected back and forth between reflective surfaces a plurality of times, illuminating a different portion of the field of view with each pass until the light exits the reflection cavity. The “recycling” of the light beam substantially improves the SNR of the detection system. The present invention is a beam alignment system for use in such a multipass cavity, correcting misalignment in four degrees of freedom; the horizontal and vertical axes, and angle in each of the vertical and horizontal axes. Angular or positional errors lateral to the direction of the beam can dramatically affect performance. The present invention enables the measurement and adjustment of each degree of freedom independently, in order to make beam steering corrections and maintain optical alignment. This is accomplished in an automated, closed-loop feedback control system. |