# Giant Nonlinear Optical Absorption of Freestanding Graphene Oxide Films for Femtosecond Pulse Compression

## TL;DR

Researchers created freestanding graphene oxide films that show strong nonlinear optical absorption and help compress femtosecond laser pulses.

## Contribution

The study introduces freestanding graphene oxide films with enhanced nonlinear optical properties for efficient femtosecond pulse compression.

## Key findings

- Freestanding GO films exhibit significant nonlinear optical absorption at low excitation fluence.
- These films enable femtosecond pulse compression around 800 nm by suppressing chirp effects.
- The pulse shortening is attributed to saturable absorption and an inflection point in the refractive index.

## Abstract

We have successfully
produced an ultrathin freely suspended GO
film, which is a biomimetic structure inspired by the transparent
dragonfly wing structure. Based on a colloidal self-assembly process
over a large area, solvent evaporation was applied within a limited
opening geometry. The free-standing GO film shows a significant enhancement
of the nonlinear optical absorption, where saturable absorption and
photoinduced absorption were observed at dramatically decreased excitation
fluence compared with other work on GO films dispersed on substrates.
Surprisingly, we also found that free-standing GO films are beneficial
for compressing femtosecond pulses around 800 nm. Using a frequency-resolved
optical gating as well as an open aperture Z-scan method, the origin
was found to be associated with two effects. While the pulse shortening
results from saturable absorption, the chirp effect is also suppressed
due to the presence of an inflection point around 800 nm in the refractive
index spectrum of free-standing GO film.