Compact frequency-comb Fourier-transform infrared spectrometer

We demonstrate a Fourier-transform infrared (FTIR) spectrometer without moving parts based on frequency-combs where the interference of two coherent frequency-comb beams occurs via wavefront combination, thereby eliminating the need of a dielectric combiner. This enables dispersionless operation over eventually the complete THz-to-visible spectrum in a single instrument. Furthermore we demonstrate the use of a single GaSe crystal for generating both beams, in an implementation for the 22–36 THz mid-infrared range. Spurious cross-modulation effects and a way to eliminate them are experimentally demonstrated. The compact comb-FTIR can be equally well applied for spectroscopic microscopy as for long-path standoff chemical monitoring.