23 research outputs found
Femtosecond frequency comb measurement of absolute frequencies and hyperfine coupling constants in cesium vapor
We report measurements of absolute transition frequencies and hyperfine
coupling constants for the 8S_{1/2}, 9S_{1/2}, 7D_{3/2}, and 7D_{5/2} states in
^{133}Cs vapor. The stepwise excitation through either the 6P_{1/2} or 6P_{3/2}
intermediate state is performed directly with broadband laser light from a
stabilized femtosecond laser optical-frequency comb. The laser beam is split,
counter-propagated and focused into a room-temperature Cs vapor cell. The
repetition rate of the frequency comb is scanned and we detect the fluorescence
on the 7P_{1/2,3/2} -> 6S_{1/2} branches of the decay of the excited states.
The excitations to the different states are isolated by the introduction of
narrow-bandwidth interference filters in the laser beam paths. Using a
nonlinear least-squares method we find measurements of transition frequencies
and hyperfine coupling constants that are in agreement with other recent
measurements for the 8S state and provide improvement by two orders of
magnitude over previously published results for the 9S and 7D states.Comment: 14 pages, 14 figure
Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider
We present an optical frequency divider based on a 200 MHz repetition rate
Er:fiber mode-locked laser that, when locked to a stable optical frequency
reference, generates microwave signals with absolute phase noise that is equal
to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz
carrier, the phase noise is below -100 dBc/Hz, limited by the optical
reference. For offset frequencies > 10 kHz, the phase noise is shot noise
limited at -145 dBc/Hz. An analysis of the contribution of the residual noise
from the Er:fiber optical frequency divider is also presented.Comment: 4 pages, 3 figure
Frequency-stabilization to 6x10^-16 via spectral-hole burning
We demonstrate two-stage laser stabilization based on a combination of Fabry-
Perot and spectral-hole burning techniques. The laser is first pre-stabilized
by the Fabry-Perot cavity to a fractional-frequency stability of sigma_y(tau) <
10^-13. A pattern of spectral holes written in the absorption spectrum of
Eu3+:Y2SiO5 serves to further stabilize the laser to sigma_y(tau) = 6x10^-16
for 2 s < tau < 8 s. Measurements characterizing the frequency sensitivity of
Eu3+:Y2SiO5 spectral holes to environmental perturbations suggest that they can
be more frequency stable than Fabry-Perot cavities
Demonstration of a timescale based on a stable optical carrier
We report on the first timescale based entirely on optical technology. Existing timescales, including those incorporating optical frequency standards, rely exclusively on microwave local oscillators owing to the lack of an optical oscillator with the required frequency predictability and stability for reliable steering. We combine a cryogenic silicon cavity exhibiting improved long-term stability and an accurate
87
Sr
lattice clock to form a timescale that outperforms them all. Our timescale accumulates an estimated time error of only
48
±
94
 
 
ps
over 34 days of operation. Our analysis indicates that this timescale is capable of reaching a stability below
1
×
10
−
17
after a few months of averaging, making timekeeping at the
10
−
18
level a realistic prospect
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