307 research outputs found
Testing the Dirac equation
The dynamical equations which are basic for the description of the dynamics
of quantum felds in arbitrary space--time geometries, can be derived from the
requirements of a unique deterministic evolution of the quantum fields, the
superposition principle, a finite propagation speed, and probability
conservation. We suggest and describe observations and experiments which are
able to test the unique deterministic evolution and analyze given experimental
data from which restrictions of anomalous terms violating this basic principle
can be concluded. One important point is, that such anomalous terms are
predicted from loop gravity as well as from string theories. Most accurate data
can be obtained from future astrophysical observations. Also, laboratory tests
like spectroscopy give constraints on the anomalous terms.Comment: 11 pages. to appear in: C. L\"ammerzahl, C.W.F. Everitt, and F.W.
Hehl (eds.): Gyros, Clocks, Interferometers...: Testing Relativistic Gravity
in Space, Lecture Notes in Physics 562, Springer 200
Astronomical spectrograph calibration with broad-spectrum frequency combs
Broadband femtosecond-laser frequency combs are filtered to
spectrographically resolvable frequency-mode spacing, and the limitations of
using cavities for spectral filtering are considered. Data and theory are used
to show implications to spectrographic calibration of high-resolution,
astronomical spectrometers
Precision spectroscopy of the 3s-3p fine structure doublet in Mg+
We apply a recently demonstrated method for precision spectroscopy on strong
transitions in trapped ions to measure both fine structure components of the
3s-3p transition in 24-Mg+ and 26-Mg+. We deduce absolute frequency reference
data for transition frequencies, isotope shifts and fine structure splittings
that are in particular useful for comparison with quasar absorption spectra,
which test possible space-time variations of the fine structure constant. The
measurement accuracy improves previous literature values, when existing, by
more than two orders of magnitude
Ultra-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
Absolute Frequency Measurements of the Hg^+ and Ca Optical Clock Transitions with a Femtosecond Laser
The frequency comb created by a femtosecond mode-locked laser and a
microstructured fiber is used to phase coherently measure the frequencies of
both the Hg^+ and Ca optical standards with respect to the SI second as
realized at NIST. We find the transition frequencies to be f_Hg=1 064 721 609
899 143(10) Hz and f_Ca=455 986 240 494 158(26) Hz, respectively. In addition
to the unprecedented precision demonstrated here, this work is the precursor to
all-optical atomic clocks based on the Hg^+ and Ca standards. Furthermore, when
combined with previous measurements, we find no time variations of these atomic
frequencies within the uncertainties of |(df_Ca/dt)/f_Ca| < 8 x 10^{-14}
yr^{-1}, and |(df_Hg/dt)/f_Hg|< 30 x 10^{-14} yr^{-1}.Comment: 6 pages, including 4 figures. RevTex 4. Submitted to Phys. Rev. Let
Laser frequency combs for astronomical observations
A direct measurement of the universe's expansion history could be made by
observing in real time the evolution of the cosmological redshift of distant
objects. However, this would require measurements of Doppler velocity drifts of
about 1 centimeter per second per year, and astronomical spectrographs have not
yet been calibrated to this tolerance. We demonstrate the first use of a laser
frequency comb for wavelength calibration of an astronomical telescope. Even
with a simple analysis, absolute calibration is achieved with an equivalent
Doppler precision of approximately 9 meters per second at about 1.5 micrometers
- beyond state-of-the-art accuracy. We show that tracking complex, time-varying
systematic effects in the spectrograph and detector system is a particular
advantage of laser frequency comb calibration. This technique promises an
effective means for modeling and removal of such systematic effects to the
accuracy required by future experiments to see direct evidence of the
universe's putative acceleration.Comment: Science, 5th September 2008. 18 pages, 7 figures (7 JPG files),
including Supporting Online Material. Version with higher resolution figures
available at http://astronomy.swin.edu.au/~mmurphy/pub.htm
Recoil Correction to Hydrogen Energy Levels: A Revision
Recent calculations of the order (Z\alpha)^4(m/M)Ry pure recoil correction to
hydrogen energy levels are critically revised. The origins of errors made in
the previous works are elucidated. In the framework of a successive approach,
we obtain the new result for the correction to S levels. It amounts to -16.4
kHz in the ground state and -1.9 kHz in the 2S state.Comment: 15 pages, Latex, no figure
A Frequency Comb calibrated Solar Atlas
The solar spectrum is a primary reference for the study of physical processes
in stars and their variation during activity cycles. In Nov 2010 an experiment
with a prototype of a Laser Frequency Comb (LFC) calibration system was
performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla
during which high signal-to-noise spectra of the Moon were obtained. We exploit
those Echelle spectra to study the optical integrated solar spectrum . The
DAOSPEC program is used to measure solar line positions through gaussian
fitting in an automatic way. We first apply the LFC solar spectrum to
characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and
Th-Ar calibrated spectra reveals S-type distortions on each order along the
whole spectral range with an amplitude of +/-40 m/s. This confirms the pattern
found by Wilken et al. (2010) on a single order and extends the detection of
the distortions to the whole analyzed region revealing that the precise shape
varies with wavelength. A new data reduction is implemented to deal with CCD
pixel inequalities to obtain a wavelength corrected solar spectrum. By using
this spectrum we provide a new LFC calibrated solar atlas with 400 line
positions in the range of 476-530, and 175 lines in the 534-585 nm range. The
new LFC atlas improves the accuracy of individual lines by a significant factor
reaching a mean value of about 10 m/s. The LFC--based solar line wavelengths
are essentially free of major instrumental effects and provide a reference for
absolute solar line positions. We suggest that future LFC observations could be
used to trace small radial velocity changes of the whole solar photospheric
spectrum in connection with the solar cycle and for direct comparison with the
predicted line positions of 3D radiative hydrodynamical models of the solar
photosphere.Comment: Accept on the 15th of October 2013. 9 pages, 10 figures. ON-lINE data
A&A 201
Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock
Over a two-year duration, we have compared the frequency of the 199Hg+ 5d106s
2S 1/2 (F=0) 5d9 6s2 2D 5/2 (F=2) electric-quadrupole transition at 282 nm
with the frequency of the ground-state hyperfine splitting in neutral 133Cs.
These measurements show that any fractional time variation of the ratio
nu(Cs)/nu(Hg) between the two frequencies is smaller than +/- 7 10^-15 / yr (1
sigma uncertainty). According to recent atomic structure calculations, this
sets an upper limit to a possible fractional time variation of g(Cs) m_e / m_p
alpha^6.0 at the same level.Comment: 4 pages with 3 figures. RevTeX 4, Submitted to Phys. Rev. Let
One-loop corrections of order (Z alpha)^6m_1/m_2, (Z alpha)^7 to the muonium fine structure
The corrections of order (Z alpha)^6m_1/m_2 and (Z alpha)^7 from one-loop
two-photon exchange diagrams to the energy spectra of the hydrogenic atoms are
calculated with the help of the Taylor expansion of corresponding integrands.
The method of averaging the quasipotential over the wave functions in the
d-dimensional coordinate space is formulated. The numerical values of the
obtained contributions to the fine structure of muonium, hydrogen and
positronium are presented.Comment: Talk given at the XVIth International Workshop High-Energy Physics
and Quantum Field Theory (QFTHEP2001), Moscow, Russia, 6-12 Sep 2001, 12
pages, REVTE
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