Difference frequency spectromete

While generation of sum frequencies yields tunable ultraviolet radiation by mixing the output from two lasers in the visible range, the phase-matched generation of difference frequencies allows one to construct tunable coherent infrared sources. One early example is the difference-frequency spectrometer of Pine [5.277], which has proved to be very useful for high-resolution infrared spectroscopy. 

The spectral linewidth of the infrared radiation is determined by that of the two pump lasers. With frequency stabilization of the pump lasers, a linewidth of a few megahertz has been reached for the difference-frequency spectrometer. In combination with a multiplexing scheme devised for calibration, monitoring, drift compensation, and absolute stabilization of the difference spectrometer, a continuous scan of 7.5 cm has been achieved with a reproducibility of better than 10MHz [5.278]. 

Fig. 5.117. Difference-frequency spectrometer based on mixing a cw Ti sapphire ring laser with a single-frequency III-V diode laser in the nonlinear crystal AgGaS2 [5.280J...

The spectral linewidth of the infrared radiation is determined by that of the two pump lasers. With frequency stabilization of the pump lasers, a linewidth of a few megahertz has been reached for the difference-frequency spectrometer. In... 

Figure 6.23 Difference-frequency spectrometer with diode lasers [569]...

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