Two-colour high-speed asynchronous optical sampling based on offset-stabilized Yb:KYW and Ti:sapphire oscillators.

Area of Science:

• Ultrafast spectroscopy
• Solid-state physics
• Laser physics

Background:

• Coherent acoustic phonons play a crucial role in the thermal and electrical properties of semiconductor superlattices.
• Investigating these phonons requires high temporal resolution and sensitivity.

Purpose of the Study:

• To develop and demonstrate a high-speed asynchronous optical sampling system for ultrafast pump-probe measurements.
• To apply this system for the investigation of zone-folded coherent acoustic phonons in semiconductor superlattices.

Main Methods:

• Utilized two Kerr-lens mode-locked lasers (Yb:KYW and Ti:sapphire) synchronized in a master-slave configuration.
• Employed a repetition rate offset of a few kHz for asynchronous optical sampling.
• Performed two-colour pump-probe measurements in transmission geometry.

Main Results:

• Achieved noise floors below 10⁻⁶ at a 5-second data acquisition time.
• Obtained a temporal resolution below 350 fs with timing jitter less than 50 fs within a 1 ns window.
• Measured lifetimes of coherent acoustic phonon modes (100-500 GHz) in semiconductor superlattices at room temperature.

Conclusions:

• The developed system offers a powerful tool for high-resolution ultrafast spectroscopy.
• The study provides new insights into the dynamics of coherent acoustic phonons in semiconductor superlattices.
• Measured phonon lifetimes are compared with existing literature data.