Below gap optical absorption in GaAs driven by intense, single-cycle coherent transition radiation

Area of Science:

• Physics
• Materials Science
• Optics

Background:

• Terahertz (THz) fields offer unique capabilities for probing material properties.
• High-field interactions in semiconductors are crucial for advanced electronic and photonic devices.
• Accelerator-based light sources provide intense, synchronized electromagnetic fields.

Purpose of the Study:

• To investigate the nonlinear optical response of gallium arsenide (GaAs) under intense, single-cycle terahertz fields.
• To demonstrate a synchronized pump-probe technique using transition radiation for dynamic optical property measurements.
• To explore strong-field-induced electroabsorption in semiconductors.

Main Methods:

• Generation of single-cycle terahertz fields via coherent transition radiation from a relativistic electron beam.
• Utilizing transition radiation from the same electron bunch to create a synchronized broadband optical probe beam.
• Measuring dynamic changes in sub-band-gap optical absorption of single-crystal GaAs.

Main Results:

• Observed large amplitude changes in the sub-band-gap optical absorption of GaAs.
• Demonstrated dynamic modification of optical properties consistent with strong-field electroabsorption.
• Established a synchronized pump-probe methodology for studying ultrafast light-matter interactions.

Conclusions:

• Single-cycle terahertz fields can induce significant nonlinear optical effects in GaAs.
• Strong-field electroabsorption is a key mechanism governing the observed optical property changes.
• These findings are relevant for nonlinear THz-driven light-matter interactions at accelerator-based light sources.