Open AccessCharacterization of the frequency stability of an optical frequency standard at 139 µm based upon noise-immune cavity-enhanced optical heterodyne molecular spectroscopy
Author(s) -
Hemanth Dinesan,
Eugenio Fasci,
A D'Addio,
Antonio Castrillo,
L. Gianfrani
Publication year - 2015
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.23.001757
Subject(s) - optics , laser linewidth , finesse , heterodyne (poetry) , optical cavity , resonator , materials science , physics , laser , noise (video) , free spectral range , fabry–pérot interferometer , artificial intelligence , computer science , acoustics , image (mathematics)
Frequency fluctuations of an optical frequency standard at 1.39 µm have been measured by means of a highly-sensitive optical frequency discriminator based on the fringe-side transmission of a high finesse optical resonator. Built on a Zerodur spacer, the optical resonator exhibits a finesse of 5500 and a cavity-mode width of about 120 kHz. The optical frequency standard consists of an extended-cavity diode laser that is tightly stabilized against the center of a sub-Doppler H(2) (18)O line, this latter being detected by means of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. The emission linewidth has been carefully determined from the frequency-noise power spectral density by using a rather simple approximation, known as β-line approach, as well as the exact method based on the autocorrelation function of the laser light field. It turns out that the linewidth of the optical frequency standard amounts to about 7 kHz (full width at half maximum) for an observation time of 1 ms. Compared to the free-running laser, the measured width corresponds to a line narrowing by a factor of ~220.