Control of laser high-harmonic generation with counterpropagating light.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Optics
• Nonlinear Optics

Background:

• Laser high-harmonic generation (HHG) is a key process for producing extreme ultraviolet and X-ray light.
• Controlling HHG emission is crucial for advanced applications.
• The influence of counterpropagating laser fields on HHG is not fully understood.

Purpose of the Study:

• To investigate the effect of counterpropagating laser pulses on laser high-harmonic generation.
• To explore methods for controlling HHG emission using external laser fields.
• To understand the underlying mechanisms of disruption and enhancement in HHG.

Main Methods:

• Utilized a 30-femtosecond driving laser pulse interacting with a narrow argon jet.
• Introduced a chirped 1-picosecond counterpropagating laser pulse with lower intensity.
• Analyzed harmonic orders from the teens to the low thirties.
• Investigated conditions of both good and poor phase-matching.

Main Results:

• A weak, chirped counterpropagating pulse significantly disrupted HHG (up to 2 orders of magnitude reduction) under optimal phase-matching.
• Under poor phase-matching conditions, the counterpropagating pulse enhanced HHG (similar contrast) via quasiphase matching.
• Suppression of out-of-phase emission was observed during enhancement.

Conclusions:

• Counterpropagating laser light offers a controllable method to either suppress or enhance laser high-harmonic generation.
• The intensity and chirp of the counterpropagating pulse, along with phase-matching conditions, dictate the outcome.
• This provides a new pathway for tailoring extreme ultraviolet light generation for various applications.