Picosecond time resolved opto-acoustic imaging with 48 MHz frequency resolution

Area of Science:

• Optics and Photonics
• Acoustics
• Materials Science

Background:

• Pump-probe spectroscopy is crucial for studying ultrafast dynamics.
• Asynchronous optical sampling (AOS) offers high spectral resolution and fast acquisition rates.
• Opto-acoustic imaging requires precise control over temporal and spectral resolution.

Purpose of the Study:

• To present a compact femtosecond dual-oscillator pump-probe setup.
• To achieve high temporal and spectral resolution for broadband opto-acoustic imaging.
• To investigate the opto-acoustic response of thin films with unprecedented detail.

Main Methods:

• Utilized a femtosecond dual-oscillator laser system with a 48 MHz repetition rate.
• Employed asynchronous optical sampling (AOS) for precise timing control.
• Achieved relative timing jitter of 500 fs or lower between oscillators.
• Performed broadband opto-acoustic imaging from 300 MHz to 150 GHz.

Main Results:

• Demonstrated picosecond temporal resolution and 48 MHz spectral resolution.
• Successfully imaged opto-acoustic responses across a broad frequency spectrum.
• Observed high-frequency acoustic echoes and GHz surface acoustic waves in a thin film.
• Experimental results were validated by semi-analytical calculations.

Conclusions:

• The developed setup enables high-resolution, broadband opto-acoustic imaging.
• The system's capabilities are suitable for characterizing acoustic phenomena in materials.
• Accurate modeling of acoustic wave dispersion was achieved.