Mid-infrared broadband long-pass filter based on grating diffraction

In recent years, the development of high-power, near-infrared (NIR) femtosecond lasers has enabled a new class of broadband mid-infrared (MIR) radiation sources that combine the spectral coverage of the molecular fingerprint region, a brilliance exceeding even that of 3 rd -generation synchrotrons, and outstanding temporal coherence. One of the challenges that arises in the development of these sources is the need to separate a tens-of-Watts NIR beam from the broadband MIR beam arising out of a parametric process such as intra-pulse difference frequency generation (IPDFG) in a suitable nonlinear crystal. Conventional coated optics face the issues of adding significant amount of dispersion to a temporally well-compressed pulse and the linear and nonlinear absorption restrict the usable NIR power in many MIR-transparent materials, such as germanium.