Study On Multi-Wavelength Lasers For Fluorescence-Rejected Raman Spectrometers

Food safety,drug safety,environmental pollution,terrorist attacks and other issues are not only the threats to people's life safety and health,but also directly affect the social stability,economic development and international cooperation.Therefore,there is an urgent need to promote the use of advanced detection technology.In many detection methods,Raman spectroscopy has advantages of simple sample preparation,fast and non-contact detection,and is widely used in airport,customs,on-site law enforcement and other fields.However,Raman spectroscopy,especially portable Raman spectroscopy,has the problem of fluorescence interference in the application process.Using shift-excitation Raman difference spectroscopy(SERDS)can effectively eliminate the fluorescence background physically without any artificial error.The key to SERDS technology is a special light source.Therefore,it's necessary to develop a multi-wavelength excitation light source with narrow line width and narrow wavelength.And the development of SERDS technology is very important for the fluorescence suppression of portable Raman spectroscopy.In this thesis,a dual-wavelength external-cavity semiconductor laser device based on Littrow structure is designed,which includes three parts: laser drive,wavelength tuning and coupling output.The laser drive can provide constant current output of 0-250 mA and can implement constant temperature control using predictive control algorithm,with the longterm temperature stability better than 0.01 ?;The other two parts of wavelength tuning and coupling output include a double-LD module,a three-dimensional adjustment structure and a dual-wavelength coupling output device.In this thesis,the relevant experiments were conducted on the home-made dualwavelength external cavity semiconductor laser device.We explored the influences of LD output facet reflectivity,grating first-order diffraction efficiency,injection current,divergence angle and other factors on the ECDL output performance.Without output coupling structure,the output wavelengths of 778.4nm and 779.3nm were obtained.The wavelength difference is 0.9nm,the line width is less than 0.2nm,the output power reaches 110 mW at 190 mA and the wavelength stability is better than 0.2nm within 6 hours.After adding the output coupling elements,the maximum power of 107 mW can be obtained,and the wavelength stability is better than 0.1nm within 3 hours.