Executive Summary : | The proposed project aims to develop a transient absorption measurement system using a femtosecond laser pump beam and a supercontinuum probe to characterize laser-produced plasmas with nanosecond time resolution. This system can measure electron density, atomic density, excitation temperature, and kinetic temperature, similar to Laser-Induced Breakdown Spectroscopy for emission spectrum analysis. The system has the potential to achieve a temporal resolution of 12.5 ns over microsecond delays, and upon successful completion, it has the potential to be patented. The ultrafast laser with 7 mJ pulse energy, 1 kHz repetition rate, and 35 fs pulse duration is used to produce the plasma. A special delay line is designed to probe the plasma with delays up to several microseconds in the cooling phase. The probe pulse is circulated between two mirrors in an arrangement similar to a regenerative amplifier. A two-component Pockels cell system is used to allow the laser pulse into the cavity and let it out after the desired time delay. A Faraday Isolator is necessary to avoid back reflections from the regenerative type delay line going back into the femtosecond laser amplifier, which could damage crystals and other optics. The external compressor pulse has a pulse duration of 50 fs and is used to produce a supercontinuum by focusing it on a Sapphire block of 1 mm thickness. The continuum beam probes the plasma in a direction orthogonal to the plasma expansion direction, and a spectrometer with resolution better than 0.1 nm equipped with a CCD camera will measure single shot absorption in the plasma over a wide spectral range. |