Time-dependent ionization models designed for intense and short laser pulse propagation in dielectric materials

Area of Science:

• Physics
• Optics
• Materials Science

Background:

• Intense, short laser pulses can generate conduction electrons via multiphoton absorption (MPA) in dielectric materials.
• The MPA process is sensitive to the laser's frequency spectrum, which can change during propagation.

Purpose of the Study:

• To develop and validate simple models for MPA that account for time-dependent laser frequency spectrum evolution.
• To assess the impact of spectral changes on MPA and electron generation.

Main Methods:

• Development of two MPA models: one based on Bloch-Volkov states, the other on adapted density matrix formalism.
• Integration of these models into a propagation code.
• Validation through simulations considering harmonic generation and pulse chirping.

Main Results:

• Both models accurately simulate MPA across various laser frequency spectrum characteristics.
• Presence of a second harmonic significantly enhances the ionization rate.
• Chirped pulses are correctly modeled, accounting for dynamic changes in multiphoton order.

Conclusions:

• The developed models provide a reliable framework for studying MPA under evolving spectral conditions.
• These models are suitable for incorporation into laser-material interaction propagation codes.
• Understanding spectral evolution is crucial for predicting laser-induced electron production.