Filtering Noise in Time and Frequency Domain for Ultrafast Pump-Probe Performed Using Low Repetition Rate Lasers

TL;DR

This paper introduces a combined time and frequency domain noise filtering technique for ultrafast pump-probe spectroscopy using low-repetition rate lasers, enhancing signal detection and reducing noise.

Contribution

It presents a novel detection scheme combining boxcar and lock-in amplifier techniques, along with a theoretical model and noise reduction methods for low-repetition laser measurements.

Findings

Enhanced signal-to-noise ratio in pump-probe measurements.

Optimal detection conditions for low-noise transient absorption signals.

Technique adaptable to other sensitive low-repetition rate measurements.

Abstract

Optical pump-probe spectroscopy is a powerful tool to directly probe the carrier dynamics in materials down to sub-femtosecond resolution. To perform such measurement, while keeping the pump induced perturbation to the sample as small as possible, it is essential to have a detection scheme with high signal to noise ratio. Achieving such high signal to noise ratio is easy with phase sensitive detection based on lock-in-amplifier when a high repetition rate laser is used as the optical pulse source. However such a lock-in-amplifier based method does not work well when a low repetition rate laser is used for the measurement. In this article, a sensitive detection scheme which combines the advantages of boxcar which rejects noise in time domain and lock-in-amplifier which isolates signal in frequency domain for performing pump-probe measurements using low-repetition rate laser system is proposed and experimentally demonstrated. A theoretical model to explain the process of signal detection and a method to reduce the pulse to pulse energy fluctuation in probe pulses is presented. By performing pump-probe measurements at various detection conditions the optimum condition required for obtaining transient absorption signal with low noise is presented. The reported technique is not limited to pump-probe measurements and can be easily modified to suite for other sensitive measurements at low-repetition rates.