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

摘要

Single-shot recording of terahertz electric signals has recently becomepossible at high repetition rates, by using the photonic time-stretchelectro-optic sampling (EOS) technique. However the moderate sensitivity oftime-stretch EOS is still a strong limit for a range of applications. Here wepresent a variant enabling to increase the sensitivity of photonic time-stretchfor free-propagating THz signals. A key point is to integrate the ideapresented in Ref. [Ahmed et al., Rev. Sci. Instrum. 85, 013114 (2014)], forupgrading classical time-stretch systems. The method is tested using the highrepetition rate terahertz coherent synchrotron radiation source (CSR) of theSOLEIL synchrotron radiation facility. The signal-to-noise ratio of ourterahertz 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 tothe available laser power, potentially enabling further sensitivityimprovements when needed.