A far-infrared broadband (8.5–37 μm) autocorrelator with sub-picosecond time resolution based on cadmium telluride

A background-free autocorrelator has been developed for measuring the duration of far-infrared laser pulses in the spectral range from 8.5 to 37 μm by using an 840-μm-long wedged cadmium telluride crystal as the second-harmonic generator. Typical intensity second-harmonic autocorrelation traces are given for the wavelengths of 19.7 and 37 μm, indicating FWHM pulse duration of 0.90 and 1.5 ps respectively. An interferometric autocorrelation trace at 18.2 μm has been measured for the first time, and the distortion of autocorrelation traces due to the absorption and re-emission of ambient water vapor is shown at 28 μm.