Method and apparatus for non-resonant background reduction in coherent anti-stokes raman scattering (CARS) spectroscopy

摘要

Embodiments of the invention provide a simple and robust system that allows non-resonant background to be removed from anti-Stokes signals generated during coherent anti-Stokes Raman spectroscopy (CARS) even when using cheaper laser systems, which do not have transform limited pulses. In particular, resonant CARS signals have a real and imaginary component. The imaginary component is directly related to the spontaneous Raman spectrum, for which there are already large spectral databases to allow chemical identification. The NRB signal, on the other hand, only has a real component. Within embodiments of the invention we recover the imaginary component of the entire CARS signal by simultaneously generating two CARS signals at orthogonal polarisations: one has the imaginary components destructively interfering with (i.e. subtracted from) the real components, the other has them constructively interfering. Measuring these two polarisations and subtracting them therefore cancels out the real part of the signal, leaving only the imaginary components.

主权项

1. A method for reducing a non-resonant background signal obtained during coherent anti-Stokes Raman scattering (CARS) spectroscopy, the method comprising:
generating a first beam having a linear polarisation, the first beam being one of a Stokes beam, or a pump/probe beam; generating a second beam having two orthogonal components one of which is delayed by λ/4 with respect to the other, the second beam being the other of the Stokes beam or the pump/probe beam; directing the Stokes beam and the pump/probe beam at a sample to be characterised, and obtaining two orthogonally polarised anti-Stokes beams therefrom; separating the two orthogonally polarised anti-Stokes beams each having real and imaginary components interfering and detecting the signals thereof; processing the anti-Stokes signals to obtain the imaginary components containing signals related to the Raman spectra of the sample, and to reduce the real components containing the non-resonant background signal.