Single-Beam Coherent Raman Spectroscopy and Microscopy via Spectral Notch Shaping

TL;DR

This paper introduces a simplified single-beam coherent Raman spectroscopy technique using spectral notch shaping, enabling high-resolution vibrational imaging with a single femtosecond pulse, reducing experimental complexity.

Contribution

The work presents a novel single-beam CARS method employing a tunable spectral notch filter, eliminating the need for multiple laser sources and complex pulse shaping.

Findings

Achieved high-resolution vibrational spectra in a single shot.

Demonstrated vibrational imaging of various samples.

Resolved the entire vibrational spectrum in the 300-1000 cm^{-1} range.

Abstract

Raman spectroscopy is one of the key techniques in the study of vibrational modes and molecular structures. In Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy, a molecular vibrational spectrum is resolved via the third-order nonlinear interaction of pump, Stokes and probe photons, typically using a complex experimental setup with multiple beams and laser sources. Although CARS has become a widespread technique for label-free chemical imaging and detection of contaminants, its multi-source, multi-beam experimental implementation is challenging. In this work we present a simple and easily implementable scheme for performing single-beam CARS spectroscopy and microscopy using a single femtosecond pulse, shaped by a tunable narrowband notch filter. As a substitute for multiple sources, the single broadband pulse simultaneously provides the pump, Stokes and probe photons, exciting a broad band of vibrational levels. High spectroscopic resolution is obtained by utilizing a tunable spectral notch, shaped with a resonant photonic crystal slab filter, as a narrowband, time-delayed probe. Using this scheme the entire vibrational spectrum can be resolved in a single-shot multiplexed measurement, circumventing the need for a multi-source configuration or a complex pulse-shaping apparatus. We demonstrate high-resolution single-beam micro-spectroscopy and vibrational imaging of various samples in the 300cm^{-1}-1000cm^{-1} spectral range.