Hybrid high spectral resolution broadband mid-infrared SFG spectrometer development and demonstration

In this work, we present the development of a femtosecond tunable middle infrared (mid-IR) radiation source for the realization of a hybrid concept compact broadband high-resolution sum-frequency generation (SFG) spectroscopy system. For the realization of the new concept, we used a two-channel picosecond fiber laser as a seed for narrowband (∼1.5 cm^-1) and broadband ultrafast radiation sources operating at 1 kHz repetition rate. In order to achieve >500 cm^-1 bandwidth widely tunable microjoule level pulses in the mid-IR spectral region (2-10 µm), broadband femtosecond source optimization was performed. Numerical simulations with different nonlinear crystals and optical parametric amplification layouts at given fixed initial conditions paved a way to experimentally realize an optimal scheme for a femtosecond mid-IR channel. Fully operating SFG spectrometer setup was assembled and tested. The developed SFG spectrometer demonstrates a unique combination of parameters: excellent spectral resolution (<3 cm^-1) similar to a narrowband scanning picosecond spectrometers and fast simultaneous acquisition of broadband spectra up to more than 850 cm^-1.