High sensitivity photonic time-stretch electro-optic sampling of terahertz pulses

TL;DR

This paper introduces an enhanced photonic time-stretch electro-optic sampling method that significantly improves the sensitivity for detecting terahertz pulses, enabling more precise measurements at high repetition rates.

Contribution

The authors develop a novel variant of time-stretch EOS that increases sensitivity by integrating a previously proposed upgrade, tested on a synchrotron source, achieving a 6.5-fold SNR improvement.

Findings

Signal-to-noise ratio improved by a factor of 6.5

Achieved noise-equivalent electric field below 1.25 V/cm

Sensitivity scalable with laser power

Abstract

Single-shot recording of terahertz electric signals has recently become possible at high repetition rates, by using the photonic time-stretch electro-optic sampling (EOS) technique. However the moderate sensitivity of time-stretch EOS is still a strong limit for a range of applications. Here we present a variant enabling to increase the sensitivity of photonic time-stretch for free-propagating THz signals. A key point is to integrate the idea presented in Ref. [Ahmed et al., Rev. Sci. Instrum. 85, 013114 (2014)], for upgrading classical time-stretch systems. The method is tested using the high repetition rate terahertz coherent synchrotron radiation source (CSR) of the SOLEIL synchrotron radiation facility. The signal-to-noise ratio of our terahertz digitizer could thus be straightforwardly improved by a factor $\approx 6.5$, leading to a noise-equivalent input electric field below $1.25$~V/cm inside the electro-optic crystal, over the 0-300~GHz band (i.e, 2.3~$\mu$V/cm/$\sqrt{\text{Hz}}$). The sensitivity is scalable with respect to the available laser power, potentially enabling further sensitivity improvements when needed.