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Spectral redshift in harmonic generation from plasma dynamics in the laser focus
F Brandi1, F Giammanco, W Ubachs
1Physics Department, University of Pisa, Largo B. Pontecorvo 3, 56127-Pisa, Italy. brandi@df.unipi.it
Physical Review Letters
|April 12, 2006
Summary
High-harmonic generation in xenon gas reveals a new redshift mechanism. Ion dynamics influence harmonic intensity and spectral shifts, driven by ion repulsion and refractive index changes.
Area of Science:
- Nonlinear Optics
- Plasma Physics
- Atomic Physics
Background:
- High-harmonic generation (HHG) is a key process for producing extreme ultraviolet and X-ray light.
- Understanding the plasma dynamics in the laser focus is crucial for controlling HHG.
- Previous studies have focused on electron dynamics, with less attention to ion contributions.
Purpose of the Study:
- To investigate the spectral properties of high-harmonic generation in xenon.
- To identify the underlying plasma dynamics responsible for observed spectral shifts.
- To elucidate the role of ions in high-harmonic generation at specific laser parameters.
Main Methods:
- High-precision spectral measurements of the 9th harmonic generated in xenon.
- Comparison with theoretical calculations of plasma dynamics.
- Analysis of multiphoton ionization and subsequent ion behavior in the laser focus.
Main Results:
- A novel mechanism causing redshifts in high harmonics was identified for 300 ps pulses and above-saturation intensities.
- Ion nonlinear susceptibility significantly impacts harmonic intensity.
- Ion mutual repulsion and increased refractive index were determined to be the cause of the observed redshift.
Conclusions:
- Ion dynamics play a critical dual role in high-harmonic generation.
- The findings provide new insights into controlling harmonic spectra through plasma effects.
- This work advances the understanding of nonlinear phenomena in intense laser-matter interactions.