877 research outputs found
Mid-infrared upconversion spectroscopy based on a Yb:fiber femtosecond laser
We present a system for molecular spectroscopy using a broadband mid-infrared
laser with near infrared detection. Difference frequency generation of a
Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from
2100-3700 cm^-1 (2.7-4.7 microns) with average power up to 40 mW. The MIR
spectrum was upconverted to near-infrared wavelengths for broadband detection
using a two-dimensional dispersion imaging technique. Absorption measurements
were performed over bandwidths of 240 cm^-1 (7.2 THz) with 0.048 cm^-1 (1.4
GHz) resolution, and absolute frequency scale uncertainty was better than 0.005
cm^-1 (150 MHz). The minimum detectable absorption coefficient per spectral
element was determined to be 4.4 x 10^-7 cm^-1 from measurements in low
pressure CH_4, leading to a detection limit of 2 parts-per-billion. The
spectral range, resolution, and frequency accuracy of this system show promise
for determination of trace concentrations in gas mixtures containing both
narrow and broad overlapping spectral features, and we demonstrate this in
measurements of air and solvent samples.Comment: 8 pages, 7 figure
Hybrid Electro-Optically Modulated Microcombs
Optical frequency combs based on mode-locked lasers have proven to be
invaluable tools for a wide range of applications in precision spectroscopy and
metrology. A novel principle of optical frequency comb generation in
whispering-gallery mode microresonators ("microcombs") has been developed
recently, which represents a promising route towards chip-level integration and
out-of-the-lab use of these devices. Presently, two families of microcombs have
been demonstrated: combs with electronically detectable mode spacing that can
be directly stabilized, and broadband combs with up to octave-spanning spectra
but mode spacings beyond electronic detection limits. However, it has not yet
been possible to achieve these two key requirements simultaneously, as will be
critical for most microcomb applications. Here we present a key step to
overcome this problem by interleaving an electro-optic comb with the spectrum
from a parametric microcomb. This allows, for the first time, direct control
and stabilization of a microcomb spectrum with large mode spacing (>140 GHz)
with no need for an additional mode-locked laser frequency comb. The attained
residual 1-second-instability of the microcomb comb spacing is 10^-15, with a
microwave reference limited absolute instability of 10^-12 at a 140 GHz mode
spacing.Comment: 8 pages, 4 figures; accepted for publication in Physical Review
Letter
Parametric seeding of a microresonator optical frequency comb
We have investigated parametric seeding of a microresonator frequency comb
(microcomb) by way of a pump laser with two electro-optic-modulation sidebands.
We show that the pump-sideband spacing is precisely replicated throughout the
microcomb's optical spectrum, and we demonstrate a record absolute line-spacing
stability for microcombs of at 1 s. The spectrum of a
parametric comb is complex, and often non-equidistant subcombs are observed.
Our results demonstrate that parametric seeding can not only control the
subcombs, but can lead to the generation of a strictly equidistant microcomb
spectrum.Comment: 10 pages, 5 figure
Martin Buber\u27s I and Thou: Implications for Reclaiming the Soul in Organizations
2006/04/20. Discusses how businesses can reclaim their souls in relation to Martin Buber\u27s ideas about how people treat each other. The Winifred E. Weter Lecture
Offset frequency dynamics and phase noise properties of a self-referenced 10 GHz Ti:sapphire frequency comb
This paper shows the experimental details of the stabilization scheme that
allows full control of the repetition rate and the carrier-envelope offset
frequency of a 10 GHz frequency comb based on a femtosecond Ti:sapphire laser.
Octave-spanning spectra are produced in nonlinear microstructured optical
fiber, in spite of the reduced peak power associated with the 10 GHz repetition
rate. Improved stability of the broadened spectrum is obtained by
temperature-stabilization of the nonlinear optical fiber. The carrier-envelope
offset frequency and the repetition rate are simultaneously frequency
stabilized, and their short- and long-term stabilities are characterized. We
also measure the transfer of amplitude noise of the pump source to phase noise
on the offset frequency and verify an increased sensitivity of the offset
frequency to pump power modulation compared to systems with lower repetition
rate. Finally, we discuss merits of this 10 GHz system for the generation of
low-phase-noise microwaves
Selecting surface features for accurate multi-camera surface reconstruction
This paper proposes a novel feature detector for selecting local textures that are suitable for accurate multi-camera surface reconstruction, and in particular planar patch fitting techniques. This approach is in contrast to conventional feature detectors, which focus on repeatability under scale and affine transformations rather than suitability for multi-camera reconstruction techniques. The proposed detector selects local textures that are sensitive to affine transformations, which is a fundamental requirement for accurate patch fitting. The proposed detector is evaluated against the SIFT detector on a synthetic dataset and the fitted patches are compared against ground truth. The experiments show that patches originating from the proposed detector are fitted more accurately to the visible surfaces than those originating from SIFT keypoints. In addition, the detector is evaluated on a performance capture studio dataset to show the real-world application of the proposed detector
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