研究目的
Investigating the correlation between the HHG conversion efficiency and the driving laser spectral features to identify optimized HHG conditions by monitoring the driving field spectral features in real time.
研究成果
The study demonstrates a clear correlation between the driving IR spectral shift and optimal HHG conditions for different noble gases. The HHG conversion efficiency is highest when the ionization level is optimal for phase-matching, before significant plasma-induced spectral shifts occur. Monitoring the IR spectral shift can serve as a method to maintain optimal HHG conditions, beneficial for applications requiring high photon flux and unaffected spatiotemporal beam characteristics.
研究不足
The study is limited by the one-dimensional model used, which may not fully account for three-dimensional nonlinear propagation effects of the laser field in the medium. Additionally, the model overestimates the ionization degree in the high-intensity region, leading to discrepancies between calculated and experimental spectral shifts.
1：Experimental Design and Method Selection:
The study involves analyzing the HHG conversion efficiency dependence on the driving laser intensity and the conditions for optimal phase-matching in a loose focusing configuration using a Ti:Sapphire laser.
2：Sample Selection and Data Sources:
The experiment uses noble gases (argon, neon, or helium) as the generation medium, with varying laser intensities and gas pressures.
3：List of Experimental Equipment and Materials:
A Ti:Sapphire laser, spherical mirror, gas cell, pressure gauge, needle valve, iris, metallic transmission filter, fiber spectrometer, and back-illuminated CCD camera.
4：Experimental Procedures and Operational Workflow:
The laser is focused into a gas cell to produce high-order harmonics. The gas cell position and pressure are adjusted to optimize harmonic output. The IR beam size and energy are tuned by varying the iris diameter. The driving laser spectrum after interaction and the harmonic beam distribution are recorded.
5：Data Analysis Methods:
The HHG conversion efficiency is defined as the ratio of harmonic beam energy to driving laser energy. The spectral shift of the driving laser is analyzed to correlate with HHG efficiency.
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