105 research outputs found
Phase noise characterization of sub-hertz linewidth lasers via digital cross correlation
Phase noise or frequency noise is a key metrics to evaluate the short term
stability of a laser. This property is of a great interest for the applications
but delicate to characterize, especially for narrow line-width lasers. In this
letter, we demonstrate a digital cross correlation scheme to characterize the
absolute phase noise of sub-hertz line-width lasers. Three 1,542 nm
ultra-stable lasers are used in this approach. For each measurement two lasers
act as references to characterize a third one. Phase noise power spectral
density from 0.5 Hz to 0.8 MHz Fourier frequencies can be derived for each
laser by a mere change in the configuration of the lasers. This is the first
time showing the phase noise of sub-hertz line-width lasers with no reference
limitation. We also present an analysis of the laser phase noise performance.Comment: 4 pages, 5 figure
Excess noise and photo-induced effects in highly reflective crystalline mirror coatings
Thermodynamically induced length fluctuations of high-reflectivity mirror
coatings put a fundamental limit on sensitivity and stability of precision
optical interferometers like gravitational wave detectors and ultra-stable
lasers. The main contribution - Brownian thermal noise - is related to the
mechanical loss of the coating material. Owing to their low mechanical losses,
Al\textsubscript{0.92}Ga\textsubscript{0.08}As/GaAs crystalline mirror coatings
are expected to reduce this limit. At room temperature they have demonstrated
lower Brownian thermal noise than with conventional amorphous coatings.
%However, no detailed study on the noise constituents from these coatings in
optical interferometers has been conducted. We present a detailed study on the
spatial and temporal noise properties of such coatings by using them in two
independent cryogenic silicon optical Fabry-Perot resonators operated at 4 K,
16 K and 124 K. We confirm the expected low Brownian thermal noise, but also
discover two new noise sources that exceed the Brownian noise: birefringent
noise that can be canceled via polarization averaging and global excess noise
(10 dB above Brownian noise). These new noise contributions are a barrier to
improving ultra-stable lasers and the related performance of atomic clocks, and
potentially limit the sensitivity of third-generation gravitational wave
detectors. Hence, they must be considered carefully in precision interferometry
experiments using similar coatings based on semiconductor materials
Quantum cascade laser frequency stabilisation at the sub-Hz level
Quantum Cascade Lasers (QCL) are increasingly being used to probe the
mid-infrared "molecular fingerprint" region. This prompted efforts towards
improving their spectral performance, in order to reach ever-higher resolution
and precision. Here, we report the stabilisation of a QCL onto an optical
frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and
10-14, respectively. The comb is stabilised to a remote near-infrared
ultra-stable laser referenced to frequency primary standards, whose signal is
transferred via an optical fibre link. The stability and frequency traceability
of our QCL exceed those demonstrated so far by two orders of magnitude. As a
demonstration of its capability, we then use it to perform high-resolution
molecular spectroscopy. We measure absorption frequencies with an 8x10-13
relative uncertainty. This confirms the potential of this setup for ultra-high
precision measurements with molecules, such as our ongoing effort towards
testing the parity symmetry by probing chiral species
Optical Atomic Clock Comparison through Turbulent Air
We use frequency comb-based optical two-way time-frequency transfer (O-TWTFT)
to measure the optical frequency ratio of state-of-the-art ytterbium and
strontium optical atomic clocks separated by a 1.5 km open-air link. Our
free-space measurement is compared to a simultaneous measurement acquired via a
noise-cancelled fiber link. Despite non-stationary, ps-level time-of-flight
variations in the free-space link, ratio measurements obtained from the two
links, averaged over 30.5 hours across six days, agree to ,
showing that O-TWTFT can support free-space atomic clock comparisons below the
level
Automatic control of amplitude-to-phase conversion in photo-detection of femto-second pulses for low phase-noise microwave generation
International audienc
Automatic control of amplitude-to-phase conversion in photo-detection of femto-second pulses for low phase-noise microwave generation
International audienc
Optical and microwave frequency synthesis with optical frequency combs
International audienc
Optical and microwave frequency synthesis with optical frequency combs
International audienc
Accurate control of optoelectronic amplitude to phase noise conversion in photodetection of ultra-fast optical pulses
International audienc
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