Scanning micro-resonator direct-comb absolute spectroscopy.

Alessio Gambetta,Davide Gatti,Gianluca Galzerano,Paolo Laporta,Marco Cassinerio

doi:10.1038/srep35541

Alessio Gambetta, Davide Gatti + Show 3 more

Open Access

https://doi.org/10.1038/srep35541

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Abstract

Direct optical Frequency Comb Spectroscopy (DFCS) is proving to be a fundamental tool in many areas of science and technology thanks to its unique performance in terms of ultra-broadband, high-speed detection and frequency accuracy, allowing for high-fidelity mapping of atomic and molecular energy structure. Here we present a novel DFCS approach based on a scanning Fabry-Pérot micro-cavity resonator (SMART) providing a simple, compact and accurate method to resolve the mode structure of an optical frequency comb. The SMART approach, while drastically reducing system complexity, allows for a straightforward absolute calibration of the optical-frequency axis with an ultimate resolution limited by the micro-resonator resonance linewidth and can be used in any spectral region from UV to THz. We present an application to high-precision spectroscopy of acetylene at 1.54 μm, demonstrating performances comparable or even better than current state-of-the-art DFCS systems in terms of sensitivity, optical bandwidth and frequency-resolution.

Highlights

Matched to the optical frequency comb-mode spacing in order to achieve the desired Vernier ratio
The proposed approach can be seen as a cavity Vernier spectroscopy with a Vernier ratio, the ratio between the cavity free-spectral range and the comb repetition rate, extremely large, which corresponds to the useful condition that only one comb mode resonates with the cavity[12,30]
By combining in an efficient way the unique characteristics of the optical frequency combs (OFCs) source with the flexibility of a scanning FP interferometer, we demonstrate a compact and versatile Direct frequency comb spectroscopy (DFCS) method with a resolution of ~20 MHz and a single-scan bandwith of ~1 THz, capable of absolute frequency measurements with a noise-equivalent-absorption level per comb mode of 2.7 · 10−9 cm−1 Hz−1/2 in the near-infrared

Summary

Introduction

Matched to the optical frequency comb-mode spacing in order to achieve the desired Vernier ratio This makes the design of the detection stage tightly connected to the characteristics of the laser source employed, feature that may be undesirable in remote sensing applications. The resolution limit of FTS has been overcome by cutting the interferogram length in such a way that the measurement points in frequency domain overlap with position of the comb modes. This last approach allows spectroscopic measurements with acquisition time and interferometer length reduced by orders of magnitude and with frequency scale accuracy given by the comb[35]. A further spectral extension down to THz region will be feasible in the years when high-finesse THz resonators will be available

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