Upconversion time-stretch infrared spectroscopy

TL;DR

This paper introduces a high-resolution, ultrafast mid-infrared spectroscopy technique that significantly increases the number of spectral elements measured at high speed by using nonlinear upconversion, enabling new applications in molecular science.

Contribution

It presents a novel method that combines nonlinear upconversion with time-stretch infrared spectroscopy to measure over 1,000 spectral elements at high speed with high resolution.

Findings

Achieved measurement of more than 1,000 spectral elements.

Demonstrated high-resolution spectroscopy of methane at 0.017 cm-1.

Enabled high-speed vibrational spectroscopy for molecular science applications.

Abstract

High-speed measurement confronts the extreme speed limit when the signal becomes comparable to the noise level. In the context of broadband mid-infrared spectroscopy, state-of-the-art ultrafast Fourier-transform infrared spectrometers, in particular dual-comb spectrometers, have improved the measurement rate up to a few Mspectra/s, which is limited by the signal-to-noise ratio. Time-stretch infrared spectroscopy, an emerging ultrafast frequency-swept mid-infrared spectroscopy technique, has shown a record-high rate of 80 Mspectra/s with an intrinsically higher signal-to-noise ratio than Fourier-transform spectroscopy by more than the square-root of the number of spectral elements. However, it can measure no more than ~30 spectral elements with a low resolution of several cm-1. Here, we significantly increase the measurable number of spectral elements to more than 1,000 by incorporating a nonlinear upconversion process. The one-to-one mapping of a broadband spectrum from the mid-infrared to the near-infrared telecommunication region enables low-loss time-stretching with a single-mode optical fiber and low-noise signal detection with a high-bandwidth photoreceiver. We demonstrate high-resolution mid-infrared spectroscopy of gas-phase methane molecules with a high resolution of 0.017 cm-1. This unprecedentedly high-speed vibrational spectroscopy technique would satisfy various unmet needs in experimental molecular science, e.g., measuring ultrafast dynamics of irreversible phenomena, statistically analyzing a large amount of heterogeneous spectral data, or taking broadband hyperspectral images at a high frame rate.