An air-spaced virtually imaged phased array with 94 MHz resolution for precision spectroscopy

TL;DR

This paper introduces an air-spaced VIPA spectrometer achieving 94 MHz resolution for mid-infrared frequency combs, enabling high-precision, broad-spectrum molecular spectroscopy with fast data acquisition.

Contribution

The work presents a novel air-spaced VIPA spectrometer with record spectral resolution, demonstrating its capability for high-resolution, broad spectral coverage in mid-infrared spectroscopy.

Findings

Achieved 94 MHz spectral resolution with VIPA spectrometer.

Successfully measured high-resolution spectra of methane, HCN, and ammonia.

Demonstrated broad spectral coverage over 290 cm$^{-1}$ (8.7 THz).

Abstract

We report on an air-spaced virtually imaged phased array (VIPA) spectrometer that resolves the modes of a mid-infrared frequency comb with a repetition rate of 250 MHz, without an optical filter cavity. With a record spectral resolution of 94 MHz for VIPA, the spectrometer enables precision molecular spectroscopy with high resolution, broad spectral coverage and fast data acquisition. We demonstrate the capabilities of the spectrometer by measuring the absorption spectra of molecular species generated in plasmas. Using plasmas of a mixture of nitrogen, hydrogen, and methane at a low pressure of 1.5 mbar, we obtained high-resolution spectra of methane, around 3017 cm$^{-1}$, as well as hydrogen cyanide and ammonia, around 3240 cm$^{-1}$, demonstrating a wide spectral coverage over 290 cm$^{-1}$ (equivalent to 8.7 THz). The spectrometer performance in terms of Allan-Werle deviation and noise-equivalent absorption is discussed. The air-spaced VIPA concept offers a compact and practical spectrometer that harnesses the full potential of a stabilized frequency comb, making it suitable for a wide range of high-precision spectroscopic applications.