Femtosecond CARS For The Study Of Temperature Measurement

Coherent anti-Stokes Raman scattering, CARS，with the advantages of nointerference with the flow field, high signal intensity, and high spatial spectralresolution, was used in combustion temperature measurement wildly.With thedevelopment of ultra-short pulse laser technology, the time-resolved femtosecondCARS technique, which used the femtosecond laser as source, could reduce thenon-resonant background noise and ignore the effect of pulse shake, then improvesthe spatial and temporal resolution of combustion temperature measurement.Because of its high-frequency signal acquisition, single-shot femtosecond CARS,which could realize the millisecond and transient dynamic monitoring and analysisof the turbulent and transient combustion temperature, has played a uniqueadvantage in the combustion field of work.The time-resolved femtosecond CARS formula was derived from Maxwell’sequations and material equation, introducing the time variable.In order to explorethe effects of the unknown laser parameters (pulse width and shape), the delay of thepump pulse and the Stokes pulse at the zero time, and the shake of the pulse energyintensity to the time-resolved CARS signals, we simulated time-resolvedfemtosecond CARS signal at300K in theory, respectively, to search for a morereliable fitting of programs to reduce the effect of unknown variables to theexperimental accuracy.After building a set of femtosecond CARS temperature measurement system,we accessed to the femtosecond CARS signal.In order to solve the effect of opticalpath drift to CARS signal, we introduced two diaphragms before and after the delaysystem;To ensure the three pulses to overlap in time and space completely, we tookthe use of an oscilloscope and coverslip to assist the coverslip regulation;In order toimprove the signal to noise ratio of CARS, we introduced a spatial and frequencydomain filtering device collected before the signal acquisition system;To reduce theaberration of spherical lens, we designed a phase-matching scheme. Finally, theobtained femtosecond CARS signal was compared with the theoretical simulation,then we obtained the temperature of combustion,by using the OPA laser of Coherentltd.In addition, we carried out a single-shot femtosecond CARS work, based on asingle-shot femtosecond CARS linear temperature measurement theory, by using thetime-resolved femtosecond CARS experimental system, we made an initial progressin the experimental part.In order to improve the signal to noise ratio of single-shotfemtosecond CARS, we carried out the chirped-probe-pulse CARS. The original single-shot femtosecond CARS theoretical model was improved. We obtained aninitial CARS signal in the chirped-probe-pulse CARS experiment by using thedispersive material (ZF-4) to broad the probe pulse.