# Observation of Kerr nonlinearity and Kerr-like nonlinearity induced by terahertz generation in LiNbO$_3$

## TL;DR

This paper demonstrates the coexistence of Kerr and Kerr-like nonlinearities in LiNbO3 induced by terahertz generation, revealing their dependence on interaction length and phase matching, supported by experimental and theoretical analysis.

## Contribution

It provides the first detailed experimental and theoretical investigation of Kerr and Kerr-like nonlinearities induced by terahertz waves in LiNbO3.

## Key findings

- Kerr and Kerr-like nonlinearities coexist in LiNbO3 during terahertz generation.
- Kerr-like nonlinearity contribution varies with interaction length due to phase mismatch.
- Low frequency phonon polaritons are excited during the process.

## Abstract

Femtosecond laser pulses interacting with LiNbO3 has been widely applied in intense terahertz generation, excitation and imaging of phonon polaritons and modulating light. It is of great importance to study the nonlinearities induced by femtosecond laser pulses in LiNbO3. Here, we demonstrate that both Kerr nonlinearity and Kerr-like nonlinearity induced by terahertz wave occur under the interaction between laser pulses and LiNbO3 using optical pump-probe techniques. We show that the contribution of Kerr-like nonlinearity to pump-probe spectra varies with the interaction length because of the phase mismatching between terahertz wave and laser pulse. We also observed the excitation of the low frequency phonon polaritons. Experimental results are in consistent with theoretical calculation.