Fast Low Frequency (Down to 10 cm −1 ) Multichannel Raman Spectroscopy Using an Iodine Vapor Filter

Abstract

We have constructed a multi-channel Raman spectrometer that is capable of recording the low frequency region down to 5 cm⁻¹ with a measurement time of a few tenths of a second. An iodine vapor filter, which uses a narrow (∼0.03 cm⁻¹) absorption line of iodine for Rayleigh scattering elimination, is combined with a multi-channel Raman spectrometer composed of a single polychromator and a charge-coupled device (CCD) camera. Thanks to the high Rayleigh scattering elimination efficiency of the filter, which is over 10⁶, Raman spectra of microcrystalline l-cystine from −300 cm⁻¹ to 1000 cm⁻¹ are simultaneously measurable with a small gap of 10 cm⁻¹ (–5 cm⁻¹ to 5 cm⁻¹). Although raw spectra contain many sharp spikes due to the fine structures of iodine absorption, they can be correctly compensated with the use of a transmittance spectrum measured under the same experimental conditions. Many Raman bands including the 9.8 cm⁻¹ band are measured with a high signal-to-noise ratio in both the Stokes and anti-Stokes sides with a measurement time as short as 0.2 s.