Mid-infrared long-pass filter for high-power applications based on grating diffraction.

A gold-coated silicon grating has been developed, enabling efficient spatial separation of broadband mid-infrared (MIR) beams with wavelengths >5 mu m from collinearly propagating, broadband, high-power light in the near-infrared (NIR) spectral range (centered at 2 mu m). The optic provides spectral filtering at high powers in a thermally robust and chromatic-dispersion-free manner such as that necessary for coherent MIR radiation sources based on parametric frequency down-conversion of femtosecond MR lasers. The suppression of a > 20 W average-power, 2 mu m driving pulse train by three orders of magnitude, while retaining high reflectivity of the broadband MIR beam, is presented. (C) 2019 Optical Society of America