Temperature Measurement With Femtosecond/picosecond CARS

CARS, namely Coherent Anti-Stokes Raman Spectroscopy, is one kind of spectroscopy technology for temperature measurement of combustion conditions with many advantages such as little friction for combustion conditions, high result resolution, and good collection efficiency. The development of femtosecond laser popularizes the application of femtosecond CARS and femtosecond/picosecond CARS for temperature measurement. Femtosecond CARS can efficiently restrain the non-resonant noise, realize high time and space resolution while femtosecond/picosecond CARS can explore the changes of temperature instantaneously.Based on the Maxwell equation and Matter equation, this paper obtained the intensity expression and phase matching of CARS by deriving nonlinear effect quation and three order nonlinear susceptibility. After introducing the concept of femtosecond/picosecond CARS, this paper derived the electric field of three pulses and CARS intensity with molecular responses. According to the CARS intensity expression above, the parameters for fitting were decided based on the analyses of the influential factors for amplitude and shape of spectroscopy. After the design of phase matching by calculation, the construction of system was finished by using femtosecond laser for light resource, stepping motor translation table for delay time and spectrograph system for collection of signals. Finally CARS signals of different combustion temperatures were obtained.Based on the calculation results above, the fitting for experimental data and theretical results was realized by the strategy of reducing the step length and span of temperature gradually. Accurate measured instantaneous combustion temperatures were gained and result error was within the anticipated range. Then this paper made a detailed analysis of the result error and provided improved resolution and advice for future research.