Broadband micro-transient absorption spectroscopy enabled by improved lock-in amplification

Abstract

Recent breakthroughs in material development have increased the demand for characterization methods capable of probing nanoscale features on ultrafast time scales. As the sample reduces to atomically thin levels, an extremely low-level signal limits the feasibility of many experiments. Here, we present an affordable and easy-to-implement solution to expand the maximum sensitivity of lock-in detection systems used in transient absorption spectroscopy by multiple orders of magnitude. By implementation of a tuned RC circuit to the output of an avalanche photodiode, electric pulse shaping allows for vastly improved lock-in detection. Furthermore, a carefully designed “peak detector” circuit provides additional pulse shaping benefits, resulting in even more lock-in detection signal enhancement. We demonstrate the improvement of lock-in detection with each of these schemes by performing benchmark measurements of a white-light continuum signal and micro-transient absorption spectroscopy on a few-layer transition metal dichalcogenide sample. Our results show the practicality of ultrafast pump–probe spectroscopy for many high-sensitivity experimental schemes.

Research progress of lock-in amplifiers

“…10 kHz [58,59] ; 当光源部分的控制光, 能通过高速半 导体器件耦合进光路系统, 即可实现1 MHz以上 的高速调制, 配置宽带锁相放大器, 同样的测量时 间内可实现20 dB的信噪比提升 [59][60][61] . 随着锁相放 大器应用带宽的进一步提升, 日本Tanaka研究 组 [62] 近期报道了一种不同于这两类调制的信噪比 增强新方案, 利用超快激光的80 MHz重复频率,…”