Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios

TL;DR

This paper demonstrates efficient terahertz radiation generation using two-color laser schemes with uncommon frequency ratios, challenging existing theories and expanding understanding of THz generation mechanisms.

Contribution

It introduces new frequency ratios for THz generation in the two-color scheme and provides experimental evidence supporting the gas-ionization model over multi-wave mixing theory.

Findings

Efficient THz generation with frequency ratios 1:4 and 2:3.

THz polarization can be controlled by rotating the longer-wavelength laser.

Energy scaling laws are similar across different frequency ratios.

Abstract

In the widely-studied two-color laser scheme for terahertz (THz) radiation from a gas, the frequency ratio of the two lasers is usually fixed at $\omega_2/\omega_1=$1:2. We investigate THz generation with uncommon frequency ratios. Our experiments show, for the first time, efficient THz generation with new ratios of $\omega_2/\omega_1=$1:4 and 2:3. We observe that the THz polarization can be adjusted by rotating the longer-wavelength laser polarization and the polarization adjustment becomes inefficient by rotating the other laser polarization; the THz energy shows similar scaling laws with different frequency ratios. These observations are inconsistent with multi-wave mixing theory, but support the gas-ionization model. This study pushes the development of the two-color scheme and provides a new dimension to explore the long-standing problem of the THz generation mechanism.