471 research outputs found
Sub-Hz line width diode lasers by stabilization to vibrationally and thermally compensated ULE Fabry-Perot cavities
We achieved a 0.5 Hz optical beat note line width with ~ 0.1 Hz/s frequency
drift at 972 nm between two external cavity diode lasers independently
stabilized to two vertically mounted Fabry-Perot (FP) reference cavities.
Vertical FP reference cavities are suspended in mid-plane such that the
influence of vertical vibrations to the mirror separation is significantly
suppressed. This makes the setup virtually immune for vertical vibrations that
are more difficult to isolate than the horizontal vibrations. To compensate for
thermal drifts the FP spacers are made from Ultra-Low-Expansion (ULE) glass
which possesses a zero linear expansion coefficient. A new design using Peltier
elements in vacuum allows operation at an optimal temperature where the
quadratic temperature expansion of the ULE could be eliminated as well. The
measured linear drift of such ULE FP cavity of 63 mHz/s was due to material
aging and the residual frequency fluctuations were less than 40 Hz during 16
hours of measurement. Some part of the temperature-caused drift is attributed
to the thermal expansion of the mirror coatings. High-frequency thermal
fluctuations that cause vibrations of the mirror surfaces limit the stability
of a well designed reference cavity. By comparing two similar laser systems we
obtain an Allan instability of 2*10-15 between 0.1 and 10 s averaging time,
which is close to the theoretical thermal noise limit.Comment: submitted to Applied Physics
Frequency Metrology on single trapped ions in the weak binding limit: The 3s1/2-3p3/2 transition in 24-Mg+
We demonstrate a method for precision spectroscopy on trapped ions in the
limit of unresolved motional sidebands. By sympathetic cooling of a chain of
crystallized ions we suppress adverse temperature variations induced by the
spectroscopy laser that usually lead to a distorted line profle and obtain a
Voigt profile with negligible distortions. We applied the method to measure the
absolute frequency of the astrophysically relevant D2 transition in single
24-Mg+ ions and find 1072082934.33(16)MHz, a nearly 400fold improvement over
previous results. Further, we find the excited state lifetime to be 3.84(10)
ns.Comment: 4 pages, 5 figure
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
Injection Locking of a Trapped-Ion Phonon Laser
We report on injection locking of optically excited mechanical oscillations of a single, trapped ion. The injection locking dynamics are studied by analyzing the oscillator spectrum with a spatially selective Fourier transform technique and the oscillator phase with stroboscopic imaging. In both cases we find excellent agreement with theory inside and outside the locking range. We attain injection locking with forces as low as 5(1)×10^(-24)  N so this system appears promising for the detection of ultraweak oscillating forces
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
Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap
We report on observations of thermal motion of a single, Doppler-cooled ion
along the axis of a linear radio-frequency quadrupole trap. We show that for a
harmonic potential the thermal occupation of energy levels leads to Gaussian
distribution of the ion's axial position. The dependence of the spatial thermal
spread on the trap potential is used for precise calibration of our imaging
system's point spread function and sub-milliKelvin thermometry. We employ this
technique to investigate the laser detuning dependence of the Doppler
temperature.Comment: 5 pages, 4 figure
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
Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel
We investigate a new scheme for astronomical spectrograph calibration using
the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our
concept is based upon a single-mode fiber channel, that simultaneously feeds
the spectrograph with comb light and sunlight. This yields nearly perfect
spatial mode matching between the two sources. In combination with the absolute
calibration provided by the frequency comb, this method enables extremely
robust and accurate spectroscopic measurements. The performance of this scheme
is compared to a sequence of alternating comb and sunlight, and to absorption
lines from Earth's atmosphere. We also show how the method can be used for
radial-velocity detection by measuring the well-explored 5-minute oscillations
averaged over the full solar disk. Our method is currently restricted to solar
spectroscopy, but with further evolving fiber-injection techniques it could
become an option even for faint astronomical targets.Comment: 21 pages, 11 figures. A video abstract for this paper is available on
youtube. For watching the video, please follow
https://www.youtube.com/watch?v=oshdZgrt89I . The video abstract is also
available for streaming and download on the related article website of New
Journal of Physic
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
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