Development Of Broadband Light Source And Spectrometer For B-CARS System

Coherent anti-Stokes Raman scattering(CARS)microscope is an emerging optical imaging technology based on Raman scattering.Label-free CARS is unique in chemical analysis,much faster than spontaneous Raman microscopy in molecular imaging speed.It opens the door for applications of vibrational microscopic imaging in life science and clinical diagnosis.Broadband coherent anti-Stokes Raman scattering(B-CARS)system covers both fingerprint and carbon-hydrogen(C-H)vibration region,a wider spectral range than traditional CARS systems,and thus provides richer chemical information.This thesis focuses on the broadband pulse laser source and spectrometer required for the construction of the B-CARS system.The nonlinear effect in the optical fiber is an effective means of spectral conversion.In this work,a highly nonlinear photonic crystal fiber(HNL-PCF),possessing multiple nonlinear effects,including self-phase modulation effect,Raman self-frequency shift,fourwave mixing,cross-phase modulation and self-steeping effect,etc,was employed to obtain super-continuum broadband spectrum for B-CARS.Meanwhile,a high-resolution spectrometer was built for measurement of Raman spectra.Rapid and accurate Raman spectra acquisition is highly desired for CARS system.Based on the results of Zemax simulation,the structure of CARS spectrometer was optimized.In this new design,achromatic lens instead of the traditional concave mirror was applied to eliminate the chromatic aberration of the focal spot.At the same time,the optimized optical path occupies a smaller space volume,which was benifical for further integrated system.In order to achieve automatic control,the STM32 single-chip microcomputer,as the main control chip in the spectrum acquisition system,was developed.Based on the Lab VIEW,VS platforms and serial communication mode,the control program was coded for automatic spectrum acquisition via stepping motor and rotational stage.After persisitant optimization,both acquisition speed and signal-to-noise ratio of the spectrometer were significantly improved.The Raman spectra of dimethyl sulfoxide(DMSO)samples were tested and compared with that obtained by commercial spectrometers,and the results proved that the homebuilt system achieved the same performances as the commercial spectrometers in signal-to-noise ratio.