Mid-infrared laser phase-locking to a remote near-infrared frequency reference for high-precision molecular spectroscopy

B Chanteau,M Abgrall,C Chardonnet,O Lopez,D Nicolodi,Y Le Coq,F Auguste,G Santarelli,B Argence,W Zhang,B Darquié,A Amy-Klein

doi:10.1088/1367-2630/15/7/073003

Abstract

We present a method for accurate mid-infrared frequency measurements and stabilization to a near-infrared ultra-stable frequency reference, transmitted with a long-distance fibre link and continuously monitored against state-of-the-art atomic fountain clocks. As a first application, we measure the frequency of an OsO4 rovibrational molecular line around 10 μm with an uncertainty of 8 × 10−13. We also demonstrate the frequency stabilization of a mid-infrared laser with fractional stability better than 4 × 10−14 at 1 s averaging time and a linewidth below 17 Hz. This new stabilization scheme gives us the ability to transfer frequency stability in the range of 10−15 or even better, currently accessible in the near infrared or in the visible, to mid-infrared lasers in a wide frequency range.

Highlights

With their rich internal structure, molecules can play a decisive role in precision tests of fundamental physics
The frequency reference is a near-infrared cavity stabilized laser continuously monitored against primary standards and the coherent frequency link between near-infrared and mid-infrared frequencies is obtained by using an optical frequency comb. We demonstrate this stabilization scheme with a remote near-infrared frequency reference transferred via an optical fibre link from a national metrological institute (NMI)
We report a first application to high resolution molecular spectroscopy with a fractional uncertainty of 8x10-13 on the line centre

Summary

Introduction

With their rich internal structure, molecules can play a decisive role in precision tests of fundamental physics. The absolute frequency of the comb repetition rate 36th harmonic (9 GHz) is continuously measured against the primary standards of LNE-SYRTE, which includes an H-maser, a cryogenic oscillator and Cs-fountains [29,30] It enables real-time measurement of the ultra-stable laser frequency drift and its correction by applying to the driving frequency of an acousto-optic modulator an opposite linear drift (with a step every ms) updated every 100 s. This makes up an ultra-stable near-infrared reference, the frequency of which is currently traceable to primary standards with a 10-14 uncertainty after 100 s. The MIR frequency is directly linked to the near-infrared frequency reference, once the integers n and N and the signs have been determined

MIR frequency measurement and stabilisation

Conclusion