Broadband THz spectroscopy system beyond 25 THz using BNA crystals and a tunable single-ring-fiber compressor

TL;DR

This paper introduces a broadband THz spectroscopy system that extends beyond 25 THz using BNA crystals and a tunable fiber compressor, enabling access to the challenging THz gap with ultrafast NIR pulses.

Contribution

The system combines BNA nonlinear interactions with a gas-filled fiber compressor to achieve broadband THz spectroscopy beyond 25 THz, covering the new THz gap.

Findings

Successfully generated and detected THz radiation beyond 25 THz.

Achieved pulse durations as short as 31 fs in the NIR pump.

Demonstrated broadband spectroscopy in previously inaccessible THz regions.

Abstract

We present a terahertz time-domain spectroscopy (THz-TDS) system which accesses a broadband spectrum, efficiently covering the so-called "new THz gap" between 5 and 15 THz and extending beyond 25 THz. The system exploits nonlinear interactions within the organic crystal BNA (N-benzyl-2-methyl-4-nitroaniline) to generate and detect THz radiation upon excitation by a near-infrared (NIR) pulse centered at 1.03 $\mu$m. To enable broadband THz spectral monitoring, the NIR pulse from a Yb-based solid-state laser undergoes spectral broadening in a gas-filled single-ring hollow-core photonic crystal fiber, followed by a pulse compression to achieve durations as short as 31 fs. This approach paves the way for broadband spectroscopy in hard-to-access THz regions using widely available near-infrared ultrafast sources.