MHz-repetition-rate, sub-mW, multi-octave THz wave generation in HMQ-TMS

Tobias Olaf Buchmann,Edmund J R Kelleher,Mojca Jazbinsek,Fabian Rotermund,Korbinian J Kaltenecker,O-Pil Kwon,Binbin Zhou,Seung-Heon Lee,Peter Uhd Jepsen

doi:10.1364/oe.386604

Abstract

We demonstrate the first megahertz (MHz) repetition-rate, broadband terahertz (THz) source based on optical rectification in the organic crystal HMQ-TMS driven by a femtosecond Yb:fibre laser. Pumping at 1035 nm with 30 fs pulses, we achieve few-cycle THz emission with a smooth multi-octave spectrum that extends up to 6 THz at -30 dB, with conversion efficiencies reaching 10-4 and an average output power of up to 0.38 mW. We assess the thermal damage limit of the crystal and conclude a maximum fluence of ∼1.8 mJ·cm-2 at 10 MHz with a 1/e2 pump beam diameter of 0.10 mm. We compare the performance of HMQ-TMS with the prototypical inorganic crystal gallium phosphide (GaP), yielding a tenfold electric field increase with a peak on-axis field strength of 7 kV·cm-1 and almost double the THz bandwidth. Our results further demonstrate the suitability of organic crystals in combination with fibre lasers for repetition-rate scaling of broadband, high-power THz sources for time-domain spectroscopic applications.

Highlights

Terahertz (THz) radiation is useful for a variety of applications covering the medical, security and scientific fields
We demonstrate the first megahertz (MHz) repetition-rate, broadband terahertz (THz) source based on optical rectification in the organic crystal HMQ-TMS driven by a femtosecond Yb:fibre laser
Our results further demonstrate the suitability of organic crystals in combination with fibre lasers for repetition-rate scaling of broadband, high-power THz sources for time-domain spectroscopic applications

Summary

Introduction

Terahertz (THz) radiation is useful for a variety of applications covering the medical, security and scientific fields. Time-domain methods (e.g. THz TDS), sensitive to both the wave amplitude and phase, can provide more information on the material properties compared to conventional Fourier-transform spectroscopy schemes [3]. Common to all these applications is the requirement for a stable, short-pulse, and broadband THz source. With the development and commercial availability of high-power fibre-based laser sources with repetition-rates in the MHz range, OR is becoming a promising technique to generate high repetition-rate, high average-power THz radiation.

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Conclusion