129 research outputs found
Toward a Broadband Astro-comb: Effects of Nonlinear Spectral Broadening in Optical Fibers
We propose and analyze a new approach to generate a broadband astro-comb by
spectral broadening of a narrowband astro-comb inside a highly nonlinear
optical fiber. Numerical modeling shows that cascaded four-wave-mixing
dramatically degrades the input comb's side-mode suppression and causes
side-mode amplitude asymmetry. These two detrimental effects can systematically
shift the center-of-gravity of astro-comb spectral lines as measured by an
astrophysical spectrograph with resolution \approx100,000; and thus lead to
wavelength calibration inaccuracy and instability. Our simulations indicate
that this performance penalty, as a result of nonlinear spectral broadening,
can be compensated by using a filtering cavity configured for double-pass. As
an explicit example, we present a design based on an Yb-fiber source comb (with
1 GHz repetition rate) that is filtered by double-passing through a low finesse
cavity (finesse = 208), and subsequent spectrally broadened in a 2-cm,
SF6-glass photonic crystal fiber. Spanning more than 300 nm with 16 GHz line
spacing, the resulting astro-comb is predicted to provide 1 cm/s (~10 kHz)
radial velocity calibration accuracy for an astrophysical spectrograph. Such
extreme performance will be necessary for the search for and characterization
of Earth-like extra-solar planets, and in direct measurements of the change of
the rate of cosmological expansion.Comment: 9 pages, 6 figure
Laser cooling of trapped ytterbium ions with an ultraviolet diode laser
We demonstrate an ultraviolet diode laser system for cooling of trapped
ytterbium ions. The laser power and linewidth are comparable to previous
systems based on resonant frequency doubling, but the system is simpler, more
robust, and less expensive. We use the laser system to cool small numbers of
ytterbium ions confined in a linear Paul trap. From the observed spectra, we
deduce final temperatures < 270 mK.Comment: submitted to Opt. Let
Recommended from our members
Broadband Dispersion-Free Optical Cavities Based on Zero Group Delay Dispersion Mirror Sets
A broadband dispersion-free optical cavity using a zero group delay dispersion (zero-GDD) mirror set is demonstrated. In general zero-GDD mirror sets consist of two or more mirrors with opposite group delay dispersion (GDD), that when used together, form an optical cavity with vanishing dispersion over an enhanced bandwidth in comparison with traditional low GDD mirrors. More specifically, in this paper, we show a realization of such a two-mirror cavity, where the mirrors show opposite GDD and simultaneously a mirror reflectivity of 99.2% over 100 nm bandwidth (480 nm - 580 nm).Physic
High-order harmonic generation in Xe, Kr, and Ar driven by a 2.1-\mu m source: high-order harmonic spectroscopy under macroscopic effects
We experimentally and numerically study the atomic response and pulse
propagation effects of high-order harmonics generated in Xe, Kr, and Ar driven
by a 2.1-\mu m infrared femtosecond light source. The light source is an
optical parametric chirped-pulse amplifier, and a modified strong-field
approximation and 3-dimensional pulse propagation code are used for the
numerical simulations. The extended cutoff in the long-wavelength driven
high-harmonic generation has revealed the spectral shaping of high-order
harmonics due to the atomic structure (or photo-recombination cross-section)
and the macroscopic effects, which are the main factors of determining the
conversion efficiency besides the driving wavelength. Using precise numerical
simulations to determine the macroscopic electron wavepacket, we are able to
extract the photo-recombination cross-sections from experimental high-order
harmonic spectra in the presence of macroscopic effects. We have experimentally
observed that the macroscopic effects shift the observed Cooper minimum of Kr
from 80 eV to 60-70 eV and wash out the Cooper minimum of Ar. Measured
high-harmonic conversion efficiencies per harmonic near the cutoff are ~10^{-9}
for all three gases.Comment: 19 pages, 8 figure
Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz
A design for a compact x-ray light source (CXLS) with flux and brilliance
orders of magnitude beyond existing laboratory scale sources is presented. The
source is based on inverse Compton scattering of a high brightness electron
bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency
standing-wave linac and RF photoinjector powered by a single ultrastable RF
transmitter at x-band RF frequency. The high efficiency permits operation at
repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating
with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire
accelerator is approximately 1 meter long and produces hard x-rays tunable over
a wide range of photon energies. The colliding laser is a Yb:YAG solid-state
amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as
the accelerator. The laser pulse is frequency-doubled and stored for many
passes in a ringdown cavity to match the linac pulse structure. At a photon
energy of 12.4 keV, the predicted x-ray flux is
photons/second in a 5% bandwidth and the brilliance is in pulses with RMS pulse
length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic
energy, 10 microamp average current, 0.5 microsecond macropulse length,
resulting in average electron beam power of 180 W. Optimization of the x-ray
output is presented along with design of the accelerator, laser, and x-ray
optic components that are specific to the particular characteristics of the
Compton scattered x-ray pulses.Comment: 25 pages, 24 figures, 54 reference
- …