# Ultrafast nonlinear dynamics of indium tin oxide nanocrystals probed via fieldoscopy

## TL;DR

This study demonstrates ultrafast, reversible optical modulation of indium tin oxide nanocrystals using two-cycle pulses, revealing their potential for high-speed photonic switching and telecommunications.

## Contribution

First to use sensitive fieldoscopy to resolve the transient electric-field response of ITO nanocrystals during ultrafast modulation.

## Key findings

- Reversible modulation at fluences up to 1.2 mJ/cm2 with 10% depth
- Irreversible modulation occurs beyond 3.3 mJ/cm2 with up to 20% depth
- Modulation bandwidth spans from 2 to 2.5 micrometers

## Abstract

Scalable, high-speed, small-footprint photonic switching platforms are essential for advancing optical communication. An effective optical switch must operate at high duty cycles with fast recovery times, while maintaining substantial modulation depth and full reversibility. Colloidal nanocrystals, such as indium tin oxide (ITO), offer a scalable platform to meet these requirements. In this work, the transmission of ITO nanocrystals near their epsilon-near-zero wavelength is modulated by two-cycle optical pulses at a repetition rate of one megahertz. The modulator exhibits a broad bandwidth spanning from 2 um to 2.5 um. Sensitive fieldoscopy measurements resolve the transient electric-field response of the ITO for the first time, showing that the modulation remains reversible for excitation fluences up to 1.2 mJ/cm2 with a modulation depth of 10%, and becomes fully irreversible beyond 3.3 mJ/cm2, while reaching modulation depth of up to 20%. Field sampling further indicates that at higher excitation fluences, the relative contribution from the first cycle of the optical pulses is reduced. These findings are crucial for the development of all-optical switching, telecommunications, and sensing technologies capable of operating at terahertz switching frequencies.