F. Mazza
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Hybrid fs/ps coherent anti-Stokes Raman CARS is a powerful laser diagnostic technique for thermometry and concentration measurements in chemically-reacting flows. The use of SHBC to generate the ps probe pulse is simple, robust, and relatively efficient. However, the presence of spectral sidebands in this pulse determines an additional modulation of the CARS spectrum, preventing comparisons to synthetic models. A solution is to employ a 4F-filter, to clean the spectrum, but dumps ~70% of the probe pulse energy. Fs/ps CARS thermometry can greatly benefit from an investigation of the spectrochronographic properties of the ps pulses, removing the filter. The probe pulse was characterized through frequency- and time-correlation measurements: its spectrum is discretized and the relative phase of each spectral segment is determined by measuring its arrival time. The fs pump/Stokes pulse is employed as an active temporal gate to perform time-correlation measurements. The phase information is further tuned using a genetic algorithm optimization. The resulting model is capable of rendering the additional modulation of experimental CARS spectra.
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Hybrid fs/ps coherent anti-Stokes Raman CARS is a powerful laser diagnostic technique for thermometry and concentration measurements in chemically-reacting flows. The use of SHBC to generate the ps probe pulse is simple, robust, and relatively efficient. However, the presence of spectral sidebands in this pulse determines an additional modulation of the CARS spectrum, preventing comparisons to synthetic models. A solution is to employ a 4F-filter, to clean the spectrum, but dumps ~70% of the probe pulse energy. Fs/ps CARS thermometry can greatly benefit from an investigation of the spectrochronographic properties of the ps pulses, removing the filter. The probe pulse was characterized through frequency- and time-correlation measurements: its spectrum is discretized and the relative phase of each spectral segment is determined by measuring its arrival time. The fs pump/Stokes pulse is employed as an active temporal gate to perform time-correlation measurements. The phase information is further tuned using a genetic algorithm optimization. The resulting model is capable of rendering the additional modulation of experimental CARS spectra.
For thermometry and concentration measurements in the gas-phase two-beam hybrid femtosecond/picosecond (fs/ps) coherent Raman spectroscopy (CRS) is the benchmark. To acquire additional information on major combustion species like for example carbon dioxide, oxygen and molecular hydrogen a supercontinuum is required. In this work in-situ femtosecond-laser-induced filamentation is proposed. This is a non-linear optical process where the pulse self-focusses. Through self-phase modulation and non-linear dispersion in the plasma medium a supercontinuum is created. In-situ generation of the supercontinuum allows for a great simplification of the experimental setup as no additional chirped mirrors are required to deliver a near-transform-limited ultrabroadband pulse to the probe volume. The work presents an experimental campaign split into three phases to characterise the filamentation process, the probe volume dimensions, and the effects of the filamentation process on thermometry.
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For thermometry and concentration measurements in the gas-phase two-beam hybrid femtosecond/picosecond (fs/ps) coherent Raman spectroscopy (CRS) is the benchmark. To acquire additional information on major combustion species like for example carbon dioxide, oxygen and molecular hydrogen a supercontinuum is required. In this work in-situ femtosecond-laser-induced filamentation is proposed. This is a non-linear optical process where the pulse self-focusses. Through self-phase modulation and non-linear dispersion in the plasma medium a supercontinuum is created. In-situ generation of the supercontinuum allows for a great simplification of the experimental setup as no additional chirped mirrors are required to deliver a near-transform-limited ultrabroadband pulse to the probe volume. The work presents an experimental campaign split into three phases to characterise the filamentation process, the probe volume dimensions, and the effects of the filamentation process on thermometry.