The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jan. 01, 1991
Filed:
Nov. 21, 1989
John J Ottusch, Malibu, CA (US);
Hughes Aircraft Company, Los Angeles, CA (US);
Abstract
A photodetector produces an output signal in response to irradiation by an optical beam from a pulsed laser. A delay unit delays the output signal for a period corresponding to one-half of one cycle of a beat frequency generated by interaction of two frequency components in the optical beam corresponding to two predetermined longitudinal modes of operation of the laser. A differential mixer subtractively combines the output of the photodetector with the output of the delay unit, to produce an output signal having the main profile of the laser pulses suppressed, and the beat frequency component, if present, amplified. A resonant circuit and amplifier may be provided to further amplify the beat frequency component. The output of the amplifier is integrated to produce a DC signal having a magnitude which corresponds to the amplitude of the beat frequency component. The DC signal is compared with a threshold value to discriminate between single and multimode operation of the laser. An optical shutter may be closed in response to sensed multi-longitudinal mode operation to block the laser beam and protect equipment which would otherwise be damaged thereby.