Shot-Noise limited Time-encoded (TICO) Raman spectroscopy

TL;DR

This paper analyzes the detection sensitivity of a shot-noise limited broadband TICO-Raman system that uses a wavelength-swept FDML laser and dual-balanced detection to enhance Raman spectroscopy performance.

Contribution

It introduces a detailed analysis of shot-noise limited detection in broadband TICO-Raman spectroscopy using FDML lasers and dual-balanced detection techniques.

Findings

Achieves shot-noise limited detection sensitivity in broadband TICO-Raman.

Demonstrates the use of FDML lasers for broad spectral coverage.

Shows improved signal-to-noise ratio with dual-balanced detection.

Abstract

Raman scattering, an inelastic scattering mechanism, provides information about molecular excitation energies and can be used to identify chemical compounds. Albeit being a powerful analysis tool, especially for label-free biomedical imaging with molecular contrast, it suffers from inherently low signal levels. This practical limitation can be overcome by non-linear enhancement techniques like stimulated Raman scattering (SRS). In SRS, an additional light source stimulates the Raman scattering process. This can lead to orders of magnitude increase in signal levels and hence faster acquisition in biomedical imaging. However, achieving a broad spectral coverage in SRS is technically challenging and the signal is no longer background-free, as either stimulated Raman gain (SRG) or loss (SRL) is measured, turning a sensitivity limit into a dynamic range limit. Thus, the signal has to be isolated from the laser background light, requiring elaborate methods for minimizing detection noise. Here we analyze the detection sensitivity of a shot-noise limited broadband stimulated time-encoded Raman (TICO-Raman) system in detail. In time-encoded Raman, a wavelength-swept Fourier Domain Mode Locked (FDML) laser covers a broad range of Raman transition energies while allowing a dual-balanced detection for lowering the detection noise to the fundamental shot-noise limit.