Abstract: A laser system for measuring dimensional aberrations across a target surface includes a laser diode for producing a diverging beam of laser emission. A mask spaced from the diode in the beam has an aperture therein and can be moved so as to translate the aperture to selected locations laterally with respect to the beam. The mask blocks emission from impinging on the target except for emission transitting the aperture. Emission reflected from a segment to the target returns through the aperture back into the laser diode. An AC current is added to the driver current to modulate the emission. A lock-in amplifier of a photodetector signal adds feedback current to the driver current to lock in phase angle, so that the feedback current is a measure of the aberrations.

Abstract: An optical transmitter includes at least one single-mode type laser diode for producing laser emission, and an external cavity with a partial reflector for reflecting a portion of the emission back into the laser. A DC current operates the laser in a first mode with a first frequency of emission. The laser is pulsed with a predetermined sequence of signal pulses each shifting the laser to a second mode with a second frequency different than the first frequency. The frequency shifting thereby constitutes information in a laser beam corresponding to the sequence of signal pulses. The laser system may be formed of a plurality of laser diodes in an array, so that the reflector reflects emission back into the diodes to lock them in the alternate modes of operation.

Abstract: A time of flight velocimeter wherein a radiation source projects two parallel beams into an air mass. Each of the parallel beams converges into a waist portion. As an aerosol particle moves through the waist portion, part of the radiation of each of the beams is backscattered. This backscattered radiation is focused onto two detectors, one for each beam. Signals from the detectors, generated in response to the backscattered radiation, are processed to determine the velocity of the particle which has passed through the waist portion of the two beams.