Time-stretch infrared spectroscopy

Improving the spectral acquisition rate of broadband mid-infrared spectroscopy promises further advancements of molecular science and technology. Unlike pump-probe spectroscopy, which requires repeated measurements with different pump-probe delays, continuous spectroscopy running at a high spectral acquisition rate enables transient measurements of fast non-repeating phenomena or statistical analysis of a large amount of spectral data. Recently, Fourier-transform infrared spectrometers with rapid delay scan mechanisms including dual-comb spectrometers have significantly improved the measurement rate up to ~1 MSpectra s⁻¹ that is fundamentally limited by the signal-to-noise ratio. Here, we overcome the limit and demonstrate the fastest continuous broadband mid-infrared spectrometer running at 80 MSpectra s⁻¹ by implementing a wavelength-swept time-stretch spectroscopy technique. Our proof-of-concept experiment demonstrates broadband absorption spectroscopy of phenylacetylene from 4.4 to 4.9 µm (2040–2270 cm⁻¹) at a resolution of 15 nm (7.7 cm⁻¹) with a signal-to-noise ratio of 85 without averaging and a shot-to-shot fluctuation of 1.3%.