Abstract

A comparison of three different infrared detectors in the 10.6-μm region is presented. A method for measuring the frequency response from dc up to 100 MHz in a continuous way is developed. We show that the flatness of the frequency response does not only depend on the electronic circuit following the detector, matching the impedance between the detector and the preamplifier, but also on the parallelism of the local oscillator and the signal beam. The signal-to-noise ratio of the detector signal is improved and reaches the theoretical limit by chopping only the signal beam and detecting the spectral analyzed intermediate frequency signal with the lock-in technique. Detecting the signal in this new way suppresses externally detected noise, which is omnipresent in weak signal detection.

© 1988 Optical Society of America

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