Intense terahertz pulses by four-wave rectification in air

TLDR

The authors propose a new four‑wave rectification technique to generate intense, ultrafast terahertz pulses from gases. They focus the fundamental and second‑harmonic outputs of an amplified Ti:sapphire laser to ~5×10¹⁴ W cm⁻² in air to drive the rectification process. The technique produces peak THz fields of ~2 kV cm⁻¹ with a spectrum centered at 2 THz, shows phase‑dependent coherence, and yields comparable signals in nitrogen, argon, and ambient air.

Abstract

We describe a new four-wave rectification method for the generation of intense, ultrafast terahertz (THz) pulses from gases. The fundamental and second-harmonic output of an amplified Ti:sapphire laser is focused to a peak intensity of ~5x10(14)W/cm (2) . Under these conditions, peak THz fields estimated at 2 kV/cm have been observed; the measured power spectrum peaks near 2 THz. Phase-dependent measurements show that this is a coherent process and is sensitive to the relative phases of the fundamental and second-harmonic pulses. Comparable THz signals have been observed from nitrogen and argon as well as from air.