# Iris-assisted Terahertz Field-Induced Second Harmonic Generation in Air

## TL;DR

This paper demonstrates that inserting an iris into the interaction region significantly amplifies terahertz-induced second harmonic signals in air, enabling enhanced detection and study of nonlinear phase-matching in gases.

## Contribution

The study introduces an iris-assisted method to greatly enhance TFISH signals in air, providing a new platform for nonlinear phase-matching research in the gas phase.

## Key findings

- TFISH signal increases by tens of times with an iris in air.
- Amplification varies with air pressure and probe intensity.
- Platform enables detailed study of nonlinear phase-matching in gases.

## Abstract

Terahertz field-induced second harmonic generation (TFISH) is a technique for optical detection of broad-band THz fields. We show that by placing an iris at the interaction volume of the THz and optical fields, the TFISH signal increases by few ten-fold in atmospheric air. The iris-assisted TFISH amplification is characterized at varying air pressures and probe intensities and provides an elegant platform for studying nonlinear phase-matching in the gas phase.

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Source: https://tomesphere.com/paper/1906.10208