Surpassing the Path-Limited Resolution of a Fourier Transform Spectrometer with Frequency Combs

TL;DR

This paper introduces a method combining Fourier transform spectroscopy with optical frequency combs to achieve higher spectral resolution than traditional limits, enabling faster and more precise molecular measurements.

Contribution

The authors demonstrate surpassing the Fourier transform spectrometer resolution limit by using frequency combs and matching the maximum delay to the comb line spacing.

Findings

Achieved resolution beyond the traditional Fourier limit.

Reduced measurement time and instrument size significantly.

Enabled high-resolution spectra without instrumental ringing effects.

Abstract

Fourier transform spectroscopy based on incoherent light sources is a well-established tool in research fields from molecular spectroscopy and atmospheric monitoring to material science and biophysics. It provides broadband molecular spectra and information about the molecular structure and composition of absorptive media. However, the spectral resolution is fundamentally limited by the maximum delay range ({\Delta}$_{max}$) of the interferometer, so acquisition of high-resolution spectra implies long measurement times and large instrument size. We overcome this limit by combining the Fourier transform spectrometer with an optical frequency comb and measuring the intensities of individual comb lines by precisely matching the {\Delta}$_{max}$ to the comb line spacing. This allows measurements of absorption lines narrower than the nominal (optical path-limited) resolution without ringing effects from the instrumental lineshape and reduces the acquisition time and interferometer length by orders of magnitude.