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Measuring Of Power In Each Beam Of A Dual Beam Laser Scanner

IP.com Disclosure Number: IPCOM000048680D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Froess, RJ: AUTHOR

Abstract

A method is provided for measurement of power in individual beams of a multiple-beam laser scanner system by directing the beams to the same photodetector, sensing the sum of the beam intensities, and adjusting the power in the beams until the sum of the beam intensities reaches the desired value.

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Measuring Of Power In Each Beam Of A Dual Beam Laser Scanner

A method is provided for measurement of power in individual beams of a multiple-beam laser scanner system by directing the beams to the same photodetector, sensing the sum of the beam intensities, and adjusting the power in the beams until the sum of the beam intensities reaches the desired value.

A single laser beam 10 is directed to an acousto-optic modulator 12, and the modulator is driven with a discrete RF frequency for each output beam to be produced. As a specific example, when the modulator 12 is driven by two RF frequencies, two first-order beams are produced, beam 14 produced by frequency F1 and beam 16 produced by frequency F2. The intensity of each optical beam depends on the magnitude of both RF signals and, since the beams are physically very close together, it is difficult to measure the intensity of each beam individually.

The measurement of power can be facilitated by utilizing the change in optical frequency of each beam caused by its interaction with the acoustic wave inside the modulator. The optical frequency of each of the beams 14 and 16 is shifted by its respective RF drive frequency. If both beams are directed to the same photodetector 18, a beat frequency is produced. The bottom figure shows the resultant electrical signal from the photodetector. The waveform is produced by the beating together of the optical frequencies, and has a frequency equal to the difference between the...