Two-dimensional, optical temporal bandpass filter using four-wave mixing in a BSO crystal: dynamic schlieren imaging system

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Abstract
In four-wave mixing in BSO crystal, the frequency of the reference wave is changed to construct a 2-D optical temporal bandpass filter with arbitrary center frequency. This filter achieves real-time precise observation of the spectral components of an oscillating object field, or it converts the frequency of the time-varying phase object field into intensity. In comparison with the traditional schlieren method imaging static states of the object, this novel method may be called the dynamic schlieren method. The principle and experimental results are given, showing the basic filtering characteristics and demonstrating two typical uses of the filter.