17 research outputs found
A 12.5 GHz-Spaced Optical Frequency Comb Spanning >400 nm for near-Infrared Astronomical Spectrograph Calibration
A 12.5 GHz-spaced optical frequency comb locked to a Global Positioning
disciplined oscillator for near-IR spectrograph calibration is presented. The
comb is generated via filtering a 250 MHz-spaced comb. Subsequency nonlinear
broadening of the 12.5 GHz comb extends the wavelength range to cover 1380 nm
to 1820 nm, providing complete coverage over the H-band transmission widow of
Earth's atmosphere. Finite suppression of spurious sidemodes, optical linewidth
and instability of the comb have been examined to estmiate potential wavelength
biases in spectrograph calibration. Sidemode suppression varies between 20 db
and 45 dB, and the optical linewidth is ~350 kHz at 1550 nm. The comb frequency
uncertainty is bounded by +/- 30 kHz (corresponding to a radial velocity of +/-
5 cm/s), limited by the Global Positioning System disciplined oscillator
reference. These results indicate this comb can readily support radial velocity
measurements below 1 m/s in the near-IR.Comment: 16 pages, 12 figures, new file fixes some readability problems on
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Groups of diffeomorphisms and geometric loops of manifolds over ultra-normed fields
The article is devoted to the investigation of groups of diffeomorphisms and
loops of manifolds over ultra-metric fields of zero and positive
characteristics. Different types of topologies are considered on groups of
loops and diffeomorphisms relative to which they are generalized Lie groups or
topological groups. Among such topologies pairwise incomparable are found as
well. Topological perfectness of the diffeomorphism group relative to certain
topologies is studied. There are proved theorems about projective limit
decompositions of these groups and their compactifications for compact
manifolds. Moreover, an existence of one-parameter local subgroups of
diffeomorphism groups is investigated.Comment: Some corrections excluding misprints in the article were mad