Single-shot broadband mid-IR spectra measured in the visible via upconversion

Researchers at the Institute for Molecular Science (Okazaki, Japan), National Chiao Tung University (Hsinchu, Taiwan), and Kagawa University (Takamatsu, Japan) have demonstrated single-shot broadband mid-IR spectroscopy using a conventional visible dispersive spectrometer; they do this by chirped-pulse upconversion of broadband IR spectra into the visible region. The results (red curves) compare well to results using a conventional mid-IR Fourier spectrometer (green curves) for analyzing films of polystyrene (a) and polyvinyl alcohol (b).

The entire mid-IR spectrum from 200 to 5500 cm^-1 (1.8 to 50 μm) was upconverted via four-wave difference-frequency generation (FWDFG) in xenon gas. First, a subcycle broadband mid-IR pulse was created from the fundamental and the second harmonic of a 30 fs pulse from a Ti:sapphire laser, while at the same time part of the fundamental was split off and chirped. The mid-IR pulse was passed through the medium to be analyzed; the chirped and mid-IR pulses were then combined in xenon to create a visible spectrum via FWDFG. The researchers say that the chirped-pulse upconversion method is especially applicable to mid-IR spectroscopy with attenuated total reflectance (ATR) because the temporal and spatial overlap of the mid-IR pulse and the chirped pulse would not be changed by exchanging the sample in the ATR region. Contact Takao Fuji at [email protected].