Inhibition of linear absorption in opaque materials using phase-locked harmonic generation.

Area of Science:

• Nonlinear optics
• Solid-state physics
• Materials science

Background:

• Second- and third-harmonic generation (SHG and THG) are crucial nonlinear optical processes.
• Strongly absorbing materials like GaAs typically exhibit high optical losses above their absorption edge.
• Phase and group velocity mismatch often limit harmonic generation efficiency and propagation in such materials.

Purpose of the Study:

• To theoretically predict and experimentally demonstrate the inhibition of linear absorption for SHG and THG.
• To investigate harmonic generation in strongly absorbing materials, specifically GaAs.
• To explore the underlying physical mechanisms responsible for absorption inhibition.

Main Methods:

• Theoretical prediction of nonlinear optical processes.
• Experimental setup utilizing a 100-fs pump pulse at 1300 nm.
• Propagation of generated second (650 nm) and third (435 nm) harmonic pulses through a 450-microm-thick GaAs substrate.

Main Results:

• Demonstrated inhibition of linear absorption for SHG and THG in GaAs above the absorption edge.
• Observed propagation of 650 nm and 435 nm harmonic pulses through the GaAs substrate without significant absorption.
• Identified a phase-locking mechanism responsible for trapping harmonics and imparting pump's dispersive properties.

Conclusions:

• Linear absorption can be inhibited for SHG and THG in strongly absorbing materials like GaAs.
• The demonstrated phase-locking mechanism offers a novel approach for efficient harmonic generation and propagation.
• This finding has potential applications in optical devices and frequency conversion technologies.