Efficient generation and heterodyne detection of 4.75-µm light with second-harmonic generation

Second-harmonic generation energy conversion efficiencies of CO(2) laser radiation as high as 56% have been measured in 2-cm-long AgGaSe(2) crystals with 30-ns pulses. The value of the nonlinear coefficient d(36), which best fits the measured data, is (32 ± 4) x 10(-12) m/V. Continuous-wave second-harmonic generation in tellurium generated up to 0.27 mW with an efficiency of 6.8(10)(-5). These pulsed and continuous beams were combined to demonstrate heterodyne detection at 4.75 µm, which increased the signal strength of weak signals by at least a factor of 25 over direct detection. Simultaneous heterodyne detection of 5- and 10-µm light is demonstrated by use of both the pump and second-harmonic beams from the cw laser as independent local oscillators.