Study Of Femtosecond Carstechnology Based On The Measurement Of Flame Temperature

Coherent anti-Stokes Raman scattering (CARS) spectrum technology is a widely used spectral measurement technology to measure the temperature. With the advantages of non-invasive and no interference to the flow field and with the features of remote control, short response time,high resolution, CARS adapts to various of harsh conditions of combustion diagnostic research. In recent years,with the progress of ultrafast laser pulse technology,the femtosecond CARS and femtosecond time-resolved CARS spectrum has successfully used to burn the field temperature measurement. It can greatly improve the measuring time resolution capability, reduce the effects of the non-resonant background signal, so widening the application range and improving the temperature measurement precision of the CARS.With the femtosecond CARS spectrum technology to temperature measurement as the research focus, this paper first introduced the basic concepts of femtosecond CARS. Then, from the basic equations of nonlinear effect, we described the basic theory of CARS and gave the calculation model of femtosecond time-resolution, deduced the light intensity expression of CARS and its main influence factors. In the third order nonlinear polarization rate, we calculated the molecule density difference and Raman line width factor of different energy level. Based on these theories, we calculated the Q vibration CARS theory spectrum of nitrogen and carbon monoxide and the S rotation CARS theory spectrum of nitrogen and hydrogen. We discussed the influence of pump laser line width and temperature to the linear of spectral line. At the same time, we analyzed and discussed the calculation model of femtosecond time-resolution CARS spectrum in depth. Using this model, we simulated time-resolution spectrum of nitrogen in different temperature.In experiment, we set up a set of femtosecond time-resolved CARS spectra measurement system and carried out the early verification experiment by measuring the time-resolved CARS spectra of BBO crystal and Rhodamine-590. By adjusting the delay time between probe beam and pump-Stokes beams,we got the time-resolved CARS spectra of the sample, validated the feasibility of this system to conduct time-resolution CARS.