Coherently controlled nonlinear raman spectroscopy and microscopy

Abstract

A method and system are presented for producing an output coherent anti-stokes Raman scattering (CARS) signal of a medium. The method comprises generation of a unitary optical excitation pulse that carries a pump photon, a Stokes photon and a probe photon; and inducing a CARS process in the medium by exciting the medium by the at least one such unitary optical excitation pulse.

Description

FIELD OF THE INVENTION [0001] The present invention relates to Raman spectroscopy and microscopy, and in particular, to coherent anti-stokes Raman spectroscopy and microscopy. BACKGROUND OF THE INVENTION [0002] In coherent nonlinear spectroscopy, the sample is probed by measuring processes of energy exchange between photons interacting with the sample. One of the most common nonlinear spectroscopy methods is coherent anti-stokes Raman scattering (CARS), a coherent four-wave mixing process involving the generation of a coherent vibration in the probed medium. In CARS, three laser photons, a pump photon (ωp) a probe photon (ωpr) and the Stokes photon (ωs), overlap in the medium under investigation. By nonlinear interaction with the molecules a fourth coherent photon (ωAS) with the anti-Stokes frequency ωAS=ωp−ωs+ωpr is generated. [0003] The CARS process can be visualized in a molecular energy level diagram as depicted in FIG. 1, where |i> and |g > are molecular rovibrational sta...

AI Technical Summary

Benefits of technology

The present invention provides a novel method and system for inducing a coherent anti-stokes Raman scattering (CARS) process in a medium by using a single laser source to generate a transform limited optical pulse carrying a pump photon, a Stokes photon, and a probe photon. This method allows for the use of a single laser source and a single coherent control technique, which is more efficient and cost-effective than conventional multi-beam nonlinear systems. The method also allows for the shaping of the optical pulse to induce a CARS signal with high spectral resolution and reduced detrimental background effects. The invention provides a solution for inducing a CARS process in a medium with a single laser source and offers a promising alternative to conventional multi-beam nonlinear systems.

Problems solved by technology

However, the these CARS microscopes also require two or three narrow-band sources that must be all tightly synchronized and also tunable within the Raman energy range.

However, the femtosecond CARS techniques suffer from two major difficulties.

The second difficulty is associated with a lack of selectivity between neighboring energy levels, due to the large bandwidth of the pulses.

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