title: Wide-bandgap nonlinear crystal LiGaS2for femtosecond mid-infrared spectroscopy with chirped-pulse upconversion.
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 2000  cm-1. 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. LiGaS2is found to be an efficient crystal for the upconversion of MIR pulses in a wide frequency range of 1100-2700  cm-1, especially below 2000  cm-1. By using LiGaS2as an efficient upconversion crystal, we develop a MIR pump-probe spectroscopy system with a spectral resolution of 2.5  cm-1, a time resolution of 0.2 ps, and a probe window of 120  cm-1. Vibrational relaxation dynamics of CO stretching modes of Mn2(CO)10in cyclohexane and bovine serum albumin in D2O are demonstrated with a high signal-to-noise ratio.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Nakamura
authors.forename: Yoshizumi
authors.initials: Y
authors.lastname: Inagaki
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Hata
authors.forename: Norio
authors.initials: N
authors.lastname: Hamada
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Umemura
authors.forename: Tomosumi
authors.initials: T
authors.lastname: Kamimura