Coherent anti-Stokes Raman scattering (CARS) microscopy imaging at interfaces: evidence of interference effects

D Gachet,N Sandeau,F Billard,H Rigneault

doi:10.1364/oe.15.010408

Abstract

We show in this paper that the contrast of the interface between resonant and nonresonant media imaged in Coherent anti-Stokes Raman scattering (CARS) microscopy strongly depends on the pump and Stokes fields spectral detuning. More specifically, when this detuning drives the vibrational resonance with the maximum phase difference, a spatial dip appears at the interface in the CARS image. This effect is studied both theoretically and experimentally and is an evidence of the coherent and resonant nature of the CARS contrast mechanism.

Highlights

Much attention has been given to coherent anti-Stokes Raman scattering (CARS) microscopy since its revival in 1999 [1], after it had been previously proposed by Duncan et al in 1982 [2]
CARS is at the same time a coherent and a resonant process, meaning that it differs in nature from one or two-photon excited fluorescence and from processes as nonresonant second (SHG) or third harmonic generation (THG)
Both aspects express in CARS image features: (i) the collected signal is proportional to the square of the coherent sum over the fields emitted within the excited volume; (ii) the collected signal is spectrally dependent as the technique probes specific vibrational resonances

Summary

Introduction

Much attention has been given to coherent anti-Stokes Raman scattering (CARS) microscopy since its revival in 1999 [1], after it had been previously proposed by Duncan et al in 1982 [2]. CARS is at the same time a coherent and a resonant process, meaning that it differs in nature from one or two-photon excited fluorescence (that are resonant and incoherent) and from processes as nonresonant second (SHG) or third harmonic generation (THG) (that are only coherent) Both aspects express in CARS image features: (i) the collected signal is proportional to the square of the coherent sum over the fields emitted within the excited volume; (ii) the collected signal is spectrally dependent as the technique probes specific vibrational resonances. Druet et al [13] showed that useful information may be extracted from CARS spectroscopy when exciting beams experience electronic absorption from the investigated medium This technique is not really suited for biological imaging, as it may damage the sample.

Methods

Discussion

Conclusion