Exploration of terahertz from time-resolved ultrafast spectroscopy in single-crystal Bi_2Se_3 topological insulator

摘要

In this article, we reconnoiter the differential reflection signal of a Bi_2Se_3 single-crystal flake, using ultrafast transient absorption spectroscopy in the femtosecond time domain and thereby explore the experimental data in terms of terahertz frequency generated in the sample. An exfoliated flake of a well-characterized self-flux grown bulk Bi_2Se_3 single crystal having rhombohedral structure and layered morphology is used in the present study. The kinetic profile of the same being generated through a reflection signal by a pump laser of 650 nm at an average power of 0.5 mW is studied utilizing time-resolved ultrafast technique. The silhouette as a function of probe delay predicting the capability of the terahertz generation is estimated. Here, two methods FFT (fast Fourier transformation) and FFD (filtering high-frequency component followed by fitting data) are performed to estimate the value of terahertz generated in the system. While comparing the two (FFT & FFD), it is found that a large amount of magnitude difference occurs in the prediction of terahertz frequency. Summarily, we not only report the generation of terahertz in Bi_2Se_3 flake, also but points out that the exact order of magnitude and the capability of the same depends upon the method of analysis. It is important to extract the vibration signal from the background one so that to find the exact order of magnitude and capability of terahertz generation by any quantum material.