High Spectral Resolution Broadband Coherent Anti-Stokes Raman Scattering Spectroscopy

Coherent anti-Stokes Raman scattering(CARS)microscopy is a recently developed nonlinear technique based on molecular vibration or rotation.Therefore the nonlinear signal is generated by the interaction between light and matter without invaded labels.CARS has exhibited their prospective applications in spectral detection and live-cell imaging for its distinct characteristics,including high sensitivity and spatial resolution,label-free chemical specificity,three-dimension sectioning capability.Traditional CARS can resonant only single or few molecular bonds due to the limitation of the spectral bandwidth.Obviously it is not adequate to recognition and mapping of an unknown biomolecule or that with complex components with few molecular.In order to recognizing an unknown biomolecule or that with complex components,a broadband CARS spectrum detection technology with high spectrum resolution is needed.So this paper presents a broadband CARS spectroscope with high spectral resolution.In this scheme,the ultrashort laser beam is divided into two arms,one being used to pump a photonic crystal fiber to generate super-continuum as Stokes.Another one passes through a narrow band filter with bandwidth about 0.7nm as the pump and probe beam.The pump and Stokes beams are then combined with a collinear structure and focused onto the sample with a micro-objective,generating a broadband CARS spectrum with high spectral resolution.The main innovations of the paper are as follows: 1.A high spectral resolution broadband CARS spectrum detection method is proposed,and the theoretical analysis and numerical simulation are carried out to prove the feasibility of the method.2.A high resolution broadband CARS spectral detection system,Six CARS characteristic peaks of the benzonitrile sample molecule in the range of 500-3500 cm-1 were obtained at one time.The main contributions of this paper are summarized as:(1)Based on the comparison of traditional CARS and broadband CARS,a broadband CARS spectroscopy with high spectral resolution is developed.(2)The symmetric split-step Fourier method is used to solve the generalized nonlinear schrodinger equation,simulating the pulse evolution in time and frequency domain when it travels along the photonic crystal fiber.This provides a theoretical basis forthe supercontinuum generation used in high spectral resolution broadband CARS spectroscopy.(3)Using the high spectral resolution broadband CARS spectroscopy,we simulated the CARS spectrum generation based on several molecular vibrations of polystyrene,and obtained all their CARS spectrum with high spectral resolution as the same time.(4)broadband CARS spectral detection system with high spectral resoution,we also obtained all their CARS spectrum within 500-3500 cm-1 of the sample molecular vibration with high spectral resolution as the same time.