Transient absorption microscopy setup with multi-ten-kilohertz shot-to-shot subtraction and discrete Fourier analysis

Area of Science:

• Spectroscopy
• Microscopy
• Materials Science

Background:

• Transient absorption microscopy demands rapid detection of subtle optical density changes.
• Conventional methods often rely on high-repetition-rate lasers and lock-in detection.

Purpose of the Study:

• To present a flexible, cost-efficient alternative detection scheme for transient absorption microscopy.
• To achieve benchmark sensitivity without complex lock-in setups.

Main Methods:

• Utilized a conventional photodiode and a MHz-bandwidth USB oscilloscope.
• Implemented shot-to-shot evaluation of pump-probe and probe-only data.
• Developed a custom Fourier transform-based evaluation algorithm and a low-pass amplified photodetector circuit.

Main Results:

• Achieved sensitivity comparable to established methods, with the detection scheme contributing negligibly.
• Demonstrated the system's capability to monitor multiple modulation frequencies and expand to parallel detection channels.
• Laser pulse fluctuations were identified as the primary sensitivity limitation.

Conclusions:

• The proposed photodiode and oscilloscope-based scheme offers a viable, sensitive, and versatile alternative for transient absorption microscopy.
• The method is suitable for 2-D imaging of micro-crystalline molecular thin films.
• This approach provides flexibility for advanced experimental designs, including multi-channel and multi-frequency detection.