Ultrafast laser-inscribed mid-infrared transmission gratings in IG2: modelling and high-resolution spectral characterization

The ultrafast laser inscription technique was used to fabricate mid-infrared volume gratings in the bulk of chalcogenide glass IG2 (Ge₃₃As₁₂Se₅₅). These gratings are spectrally characterized using a Fourier transform infrared spectrometer, by measuring the transmission spectrum over the entire transmission band of the IG2 substrate. The gratings exhibit first order diffraction across the entire 2–5 μm spectral band, with the specific transmission band tuned by changing the angle of incidence. Higher diffraction orders are also observed. High-resolution spectral data is presented alongside detailed modelling and analysis. This work provides the basis for future design of mid-infrared transmission gratings; ULI provides a low-cost, robust alternative to mid-infrared reflection gratings, with the added capability to engineer the grating response to a specific application.