Interpulse stimulation Fourier-transform coherent anti-Stokes Raman spectroscopy

Abstract

Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two ∼ 100 - fs pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research.