Time-domain measurement of coherent transition radiation using a photoconductive antenna with micro-structured electrodes

K Kan,K Takano,I Nozawa,R Kuroda,J Yang,Y Yoshida,M Gohdo,H Kitahara,H Toyokawa

doi:10.1063/5.0067586

Abstract

The longitudinal electric field profile of coherent transition radiation (CTR), which is a radially polarized terahertz (THz) pulse from an electron bunch, was measured using a large-aperture photoconductive antenna (PCA) with a diameter of 8.8 mm and micro-structured concentric electrodes to detect THz light pulses. Photo-induced charge carriers were generated on the PCA by the irradiation of femtosecond laser pulses on the electrode plane. Pulsed light irradiation enabled time-resolved measurement of the THz light pulses, and time-domain measurement of CTR was conducted by measuring the electric-field-induced current output from the PCA by sweeping the timing of the laser irradiation. The frequency spectra obtained from the detected longitudinal electric field profiles of the CTR showed a reasonable response signal from the low-frequency region as low as 0.1 THz. In the present demonstration, the large-aperture PCA-detected THz wave from the CTR was from 0.1 to at least 1 THz. THz generation using the PCA was also performed and measured using a Michelson interferometer with a helium-cooled bolometer. Comparison of the THz pulse of the CTR detected using the PCA and that generated using the PCA revealed that time-domain measurement of the THz pulse using the PCA was limited by the response time of the charge carriers in the semiconductor. Enlargement of the aperture of the PCA enhanced the detectable frequency region toward a lower frequency.

Highlights

Ultra-short electron bunches with durations ranging from picoseconds to femtoseconds are widely used in accelerator physics applications for the generation of novel light pulses, such as freeelectron lasers[1,2] and laser-Compton x rays.[3]
In ultrafast electron diffraction (UED), an electron bunch is used as a probe source, and the ultrafast phenomena are analyzed through electron diffraction patterns
This paper presents an analysis of the longitudinal electric field profile of coherent transition radiation (CTR) using a large-aperture photoconductive antenna (PCA) with micro-structured electrodes

Summary

Introduction

Ultra-short electron bunches with durations ranging from picoseconds to femtoseconds are widely used in accelerator physics applications for the generation of novel light pulses, such as freeelectron lasers[1,2] and laser-Compton x rays.[3] A short electron bunch is a key element for the direct use of electron bunches in timeresolved studies of ultrafast phenomena and reactions, including ultrafast electron diffraction (UED)[4,5] and pulse radiolysis.[6–9] The time resolutions of these measurements depend on the electron bunch length. In UED, an electron bunch is used as a probe source, and the ultrafast phenomena are analyzed through electron diffraction patterns. Pulse radiolysis is a critical technique that involves an electron bunch and is a valuable and effective tool for observing ultrafast radiation-induced phenomena and understanding the kinetics of these mechanisms. The generation and diagnostics of ultra-short electron bunches are essential for novel light generation and improving the time resolution of these techniques

Methods

Results

Conclusion