Secondly, we introduced a dispersion-free long-pass filter for the MIR spectral region based on a gold grating. It is suitable for higher average powers than conventional filters and beyond the cut-on wavelength the usability is only limited by the gold reflectivity. By using three gratings, we kept 66 % of the desired MIR power while suppressing the generating NIR power (>20W) by more than three orders of magnitude. This enables higher average powers to be used for MIR generation and shorter MIR pulses in this spectral region.
Figure: Difference between using the Mach-Zehnder configuration and just measuring the stage position for 40 scans in air (left). (a) Concept of dispersion-free separation of the MIR (red) from the fundamental beam (blue) via a grating and (b) the corresponding diffraction efficiency and sample spectra (right).
Schweinberger, W. et al., Interferometric delay tracking for low-noise Mach-Zehnder-type scanning measurements. Optics Express 27, 4789-4798 (2019).
Gerz, D. et al., Mid-infrared long-pass filter for high-power applications based on grating diffraction. Optics Letters 44, 3014-3017 (2019)