Abstract
Femtosecond time-resolved mid-infrared (MIR) spectroscopy based on chirped-pulse upconversion is a promising method for observing molecular vibrational dynamics. A quantitative study on nonlinear media for upconversion is still essential for wide applications, particularly at the frequencies below . We evaluate wide-bandgap nonlinear crystals of Li-containing ternary chalcogenides based on their performance as the upconversion medium for femtosecond MIR spectroscopy. The upconversion efficiency is measured as a function of the MIR pulse frequency and the chirped pulse energy. is found to be an efficient crystal for the upconversion of MIR pulses in a wide frequency range of , especially below . By using as an efficient upconversion crystal, we develop a MIR pump–probe spectroscopy system with a spectral resolution of , a time resolution of 0.2 ps, and a probe window of . Vibrational relaxation dynamics of CO stretching modes of in cyclohexane and bovine serum albumin in are demonstrated with a high signal-to-noise ratio.
© 2016 Optical Society of America
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