Large Attenuation Measurement for Laser Beam by Intermediate Frequency Substitution Method

An intermediate frequency substitution method in the optical region is studied experimentally for attenuation measurement of laser beams. A frequency shifting technique with an acoustooptic modulator is used to obtain test and local oscillator signals for heterodyne detection. A 30-MHz waveguide-below-cutoff attenuator is adopted as a standard attenuator. Attenuations up to 70 dB can be measured with an accuracy of 0.2 dB.