Abstract
We demonstrate two complementary types of microscopy using an identical setup for single-pulse coherent anti-Stokes Raman scattering (CARS) imaging, which employs an ultrabroadband laser pulse with a spectral bandwidth of 4800 cm(-1) and enables the suppression of nonresonant CARS signals. One is a novel type of microscopy that uses spectral phase modulation for the selective excitation of a single Raman mode. The selective excitation is achieved by the modulated pulse focusing its difference-frequency spectrum into a narrow spectral region. Another type is Fourier-transform CARS (FT-CARS) microspectroscopy based on the measurement of the CARS spectrum obtained from the Fourier-transform of the interferometric autocorrelation (IAC) signal. Vibrational spectral imaging of chemical and biological samples is demonstrated using the two types of microscopy.
Highlights
Coherent anti-Stokes Raman scattering (CARS) is a nonlinear Raman process in which pulsed light of at least two frequencies is mixed within a sample
Multi-spectral coherent anti-Stokes Raman scattering (CARS) images of a polystyrene bead in acetone were obtained by Fourier-transform CARS (FT-CARS) microspectroscopy
We demonstrated that with FT-CARS microspectroscopy the nonresonant CARS signal can be suppressed, a spectral resolution of 60 cm−1 can be achieved and a CARS spectrum with a bandwidth of 4000 cm−1 can be obtained in a single measurement
Summary
Coherent anti-Stokes Raman scattering (CARS) is a nonlinear Raman process in which pulsed light of at least two frequencies is mixed within a sample. The nonresonant signal decreases, while the resonant signals of the Raman mode with wave number NΩR, where N is an integer, is present Another technique is single-pulse multiplex CARS spectroscopy where phase shifting of a narrow spectral band enables an effective narrow probing of the vibrational mode [12,13]. We show that the difference between CARS spectra can be quantified by a normalized spectral correlation (NSC) technique, with which identification of specific organella can be achieved
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