Yujie Shen

Low wavenumber efficient single-beam coherent anti-Stokes Raman scattering using a spectral hole

We demonstrate an approach to detect low wavenumber vibrational signals based on single-beam coherent anti-Stokes Raman scattering (CARS) with a spectral hole. Using a 4f pulse shaper for both pulse shaping and signal collection, we achieve an enhanced efficiency in collecting back-reflected CARS signals.

A versatile setup using femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman scattering.

We report a versatile setup based on the femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman scattering. The setup uses a femtosecond Ti:Sapphire oscillator source and a folded 4f pulse shaper, in which the pulse shaping is carried out through conventional optical elements and does not require a spatial light modulator. Our setup is simple in alignment, and can be easily switched between the collinear single-beam and the noncollinear two-beam configurations. We demonstrate the capability for investigating both transparent and highly scattering samples by detecting transmitted and reflected signals, respectively.

Single-beam heterodyne FAST CARS microscopy

We demonstrate, for the first time, single-beam heterodyne FAST CARS imaging without data post-processing and with nonresonant background subtraction in a simple setup via the real-time piezo modulation of the probe delay. Our fast signal acquisition scheme does not require a spatial light modulator in the pulse shaper, and is suitable for high-resolution imaging and time-resolved dynamics. In addition, the spectral detection of the back-scattered FAST CARS signal is incorporated into the pulse shaper, allowing for a compact and more efficient design. Such epi-detection capability is demonstrated by imaging Si and MoS2 microstructures.

Picosecond supercontinuum generation in large mode area photonic crystal fibers for coherent anti-Stokes Raman scattering microspectroscopy

We perform a detailed theoretical and experimental investigation of supercontinuum generation in large-mode-area photonic crystal fibers pumped by a high-energy, high-repetition rate picosecond Nd:YVO4 laser, with the goal of using it as the Stokes beam in coherent anti-Stokes Raman scattering setup. We analyze the influence of fiber structure and length on the supercontinuum power, spectral shape, and group delay dispersion. We identify the experimental conditions for stable supercontinuum generation, with microjoule-level pulse energy and the spectrum extending beyond 1600 nm, which allows excitation of Raman frequencies up to 3000 cm−1 and beyond. We demonstrate reliable and efficient operation of a coherent anti-Stokes Raman spectroscopy and microscopy setup using this supercontinuum source.

Controlled supercontinua via spatial beam shaping

Abstract Recently, optimization techniques have had a significant impact in a variety of fields, leading to a higher signal-to-noise and more streamlined techniques. We consider the possibility for using programmable phase-only spatial optimization of the pump beam to influence the supercontinuum generation process. Preliminary results show that significant broadening and rough control of the supercontinuum spectrum in the visible region are possible without loss of input energy. This serves as a proof-of-concept demonstration that spatial effects can controllably influence the supercontinuum spectrum, leading to possibilities for utilizing supercontinuum power more efficiently and achieving excellent spectral control.

Supercontinuum generation in large-mode-area photonic crystal fibers for coherent Raman microspectroscopy

We study supercontinuum (SC) generation in large-mode-area (LMA) photonic crystal fibers with various core sizes and lengths, pumped by a picosecond Nd:YVO4 laser. Micro-joule level SC pulse energy is achieved, and the spectrum extends beyond 1600 nm, corresponding to an effective Raman detection range over 3000 wavenumbers. A multiplex CARS setup based on the SC source is constructed, and we demonstrate CARS acquisition in air, and compare the signal obtained with different LMA fiber parameters.

Wide-field coherent anti-Stokes Raman scattering microscopy based on picosecond supercontinuum source

We present a wide-field coherent anti-Stokes Raman scattering microscopy setup based on picosecond-laser-pumped supercontinuum and use it to demonstrate video-rate imaging with chemical specificity. The broadband excitation allows simultaneous imaging of a wide range of Raman modes, and chemically selective imaging is achieved by applying filters corresponding to the anti-Stokes Raman bands.We present a wide-field coherent anti-Stokes Raman scattering microscopy setup based on picosecond-laser-pumped supercontinuum and use it to demonstrate video-rate imaging with chemical specificity. The broadband excitation allows simultaneous imaging of a wide range of Raman modes, and chemically selective imaging is achieved by applying filters corresponding to the anti-Stokes Raman bands.