1,232 research outputs found
Coherent, multi-heterodyne spectroscopy using stabilized optical frequency combs
The broadband, coherent nature of narrow-linewidth fiber frequency combs is
exploited to measure the full complex spectrum of a molecular gas through
multi-heterodyne spectroscopy. We measure the absorption and phase shift
experienced by each of 155,000 individual frequency comb lines, spaced by 100
MHz and spanning from 1495 nm to 1620 nm, after passing through a hydrogen
cyanide gas. The measured phase spectrum agrees with Kramers-Kronig
transformation of the absorption spectrum. This technique can provide a full
complex spectrum rapidly, over wide bandwidths, and with hertz-level accuracy.Comment: 4 pages, 3 figure
The determination of shock ramp width using the noncoplanar magnetic field component
We determine a simple expression for the ramp width of a collisionless fast
shock, based upon the relationship between the noncoplanar and main magnetic
field components. By comparing this predicted width with that measured during
an observation of a shock, the shock velocity can be determined from a single
spacecraft. For a range of low-Mach, low-beta bow shock observations made by
the ISEE-1 and -2 spacecraft, ramp widths determined from two-spacecraft
comparison and from this noncoplanar component relationship agree within 30%.
When two-spacecraft measurements are not available or are inefficient, this
technique provides a reasonable estimation of scale size for low-Mach shocks.Comment: 6 pages, LaTeX (aguplus + agutex);
packages:amsmath,times,graphicx,float, psfrag,verbatim; 3 postscript figures
called by the file; submitted to Geophys. Res. Let
Phonological characteristics of the lexicon at 2;0 years predict language outcomes at 3;6 years
Poster session 3 - Early speech production: no. 7Toddlers’ first words are of higher mean phonological neighborhood density (ND) than words learned later. The words of children with delayed lexical development are of significantly higher mean ND than those of typically developing children. A relationship between a higher mean ND value at 2;0 years and expressive language skills at 3;6 years may indicate that early word processing difficulties inhibit ongoing development ...postprin
Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers
We present full phase stabilization of an amplified Yb:fiber femtosecond
frequency comb using an intra-cavity electro-optic modulator and an
acousto-optic modulator. These transducers provide high servo bandwidths of 580
kHz and 250 kHz for frep and fceo, producing a robust and low phase noise fiber
frequency comb. The comb was self-referenced with an f - 2f interferometer and
phase locked to an ultra-stable optical reference used for the JILA Sr optical
clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors
(over 1 mHz - 1 MHz) respectively. Alternatively, the comb was locked to two
optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of
integrated phase errors respectively
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