# Femtosecond imbalanced time-stretch spectroscopy for ultrafast gas detection

## TL;DR

This paper introduces a compact, robust femtosecond imbalanced time-stretch spectroscopy system for ultrafast gas detection, simplifying dual-comb spectroscopy with a straightforward optical setup.

## Contribution

It presents a novel, simplified femtosecond imbalanced time-stretch spectroscopy method that enables ultrafast gas detection with a compact and robust design.

## Key findings

- Successfully encoded hydrogen cyanide absorption lines.
- Achieved wide-range spectral analysis using a simple optical layout.
- Demonstrated effective mapping from optical frequency to radio frequency domain.

## Abstract

Dual-comb spectroscopy is a promising method for precise optical spectrum analysis with fast data acquisition speed. However, its implementation and applications are often hindered by the complexity of optical comb systems. Here, as a compact and robust system, femtosecond imbalanced time-stretch spectroscopy (FITSS) with simple optical layout is proposed and demonstrated. The time-stretch interferometry from one femtosecond laser builds a mapping from the optical frequency domain to the radio frequency regime. In experiment, the absorption line of a hydrogen cyanide cell is encoded in the probing arm of a Mach-Zehnder interferometer (MZI). The down-converted radio frequency comb is transformed from a periodically chirped waveform, which is the interferogram of the MZI with different dispersion values on two arms. By turning the optical filter, the spectrum over a wide range is analyzed.

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Source: https://tomesphere.com/paper/1907.08007