10:00 〜 10:15
▲ [16a-Z08-5] High-speed low-frequency vibrational spectroscopy using a Sagnac interferometer
キーワード：Raman spectroscopy, Nonlinear optics
High-speed vibrational spectroscopy, by virtue of its chemical specificity and label-free nature, as well as its suitability to imaging or capturing short-lived phenomena, has many applications in biological, medicinal, and material sciences. One powerful such technique is Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) spectroscopy, based on a third-order nonlinear process where Raman-active vibrational modes are coherently excited and read out by pump and probe pulses, respectively. It is a promising technique due to its broadband Raman spectral range, rapid spectral acquisition rate, and its relatively simple optical setup. However, rapid-scan FT-CARS is limited by inherent poor sensitivity in the information-rich low-frequency Raman region (typically below ~200 cm-1). This weakness is a result of 2 factors: (1) FT-CARS detection typically occurs at probe frequencies far from the probe center, where low-frequency Raman signals are strongest; and (2) optical shortpass filtering in FT-CARS disproportionately attenuates low-frequency Raman modes.
In order to push high-speed vibrational spectroscopy beyond these limitations, we demonstrate rapid-scan Sagnac-enhanced impulsive stimulated Raman scattering (SE-ISRS) spectroscopy, a technique for high-speed vibrational spectroscopy based on a common-path Sagnac interferometer (SI). The SI provides two benefits: (1) probe background reduction by destructive interference and (2) low-frequency vibration sensitivity enhancement by detection of Raman vibrations at the probe center frequency. Comparing Raman power spectra of bromoform acquired at 24 kHz using both SE-ISRS and FT-CARS spectroscopies, we demonstrate improvements of the signal-to-noise ratios of the 157 cm-1, 222 cm-1, and 539 cm-1 vibrational modes by factors of 7.6, 2.5, and 4.3, respectively. This technique is a step towards more sensitive and versatile low-frequency vibrational spectroscopy.
In order to push high-speed vibrational spectroscopy beyond these limitations, we demonstrate rapid-scan Sagnac-enhanced impulsive stimulated Raman scattering (SE-ISRS) spectroscopy, a technique for high-speed vibrational spectroscopy based on a common-path Sagnac interferometer (SI). The SI provides two benefits: (1) probe background reduction by destructive interference and (2) low-frequency vibration sensitivity enhancement by detection of Raman vibrations at the probe center frequency. Comparing Raman power spectra of bromoform acquired at 24 kHz using both SE-ISRS and FT-CARS spectroscopies, we demonstrate improvements of the signal-to-noise ratios of the 157 cm-1, 222 cm-1, and 539 cm-1 vibrational modes by factors of 7.6, 2.5, and 4.3, respectively. This technique is a step towards more sensitive and versatile low-frequency vibrational spectroscopy.