263 research outputs found
Sub-Doppler frequency metrology in HD for test of fundamental physics
Weak transitions in the (2,0) overtone band of the HD molecule at m were measured in saturated absorption using the technique of
noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Narrow
Doppler-free lines were interrogated with a spectroscopy laser locked to a
frequency comb laser referenced to an atomic clock to yield transition
frequencies [R(1) = kHz; R(2) =
kHz; R(3) = kHz] at three
orders of magnitude improved accuracy. These benchmark values provide a test of
QED in the smallest neutral molecule, and open up an avenue to resolve the
proton radius puzzle, as well as constrain putative fifth forces and extra
dimensions.Comment: 5 pages, 4 figure
UV frequency metrology on CO (a3Pi); isotope effects and sensitivity to a variation of the proton-to-electron mass ratio
UV frequency metrology has been performed on the a3Pi - X1Sigma+ (0,0) band
of various isotopologues of CO using a frequency-quadrupled injection-seeded
narrow-band pulsed Titanium:Sapphire laser referenced to a frequency comb
laser. The band origin is determined with an accuracy of 5 MHz (delta \nu / \nu
= 3 * 10^-9), while the energy differences between rotational levels in the
a3Pi state are determined with an accuracy of 500 kHz. From these measurements,
in combination with previously published radiofrequency and microwave data, a
new set of molecular constants is obtained that describes the level structure
of the a3Pi state of 12C16O and 13C16O with improved accuracy. Transitions in
the different isotopologues are well reproduced by scaling the molecular
constants of 12C16O via the common mass-scaling rules. Only the value of the
band origin could not be scaled, indicative of a breakdown of the
Born-Oppenheimer approximation. Our analysis confirms the extreme sensitivity
of two-photon microwave transitions between nearly-degenerate rotational levels
of different Omega-manifolds for probing a possible variation of the
proton-to-electron mass ratio, \mu=m_p/m_e, on a laboratory time scale
Novel techniques in VUV high-resolution spectroscopy
Novel VUV sources and techniques for VUV spectroscopy are reviewed.
Laser-based VUV sources have been developed via non-linear upconversion of
laser pulses in the nanosecond (ns), the picosecond (ps), and femtosecond (fs)
domain, and are applied in high-resolution gas phase spectroscopic studies.
While the ns and ps pulsed laser sources, at Fourier-transform limited
bandwidths, are used in wavelength scanning spectroscopy, the fs laser source
is used in a two-pulse time delayed mode. In addition a Fourier-transform
spectrometer for high resolution gas-phase spectroscopic studies in the VUV is
described, exhibiting the multiplex advantage to measure many resonances
simultaneously.Comment: 17 Pages, 8 figures, Conference proceedings of the VUV/X-ray 2013 at
Hefei, Chin
XUV frequency comb metrology on the ground state of helium
The operation of a frequency comb at extreme ultraviolet (XUV) wavelengths
based on pair-wise amplification and nonlinear upconversion to the 15th
harmonic of pulses from a frequency comb laser in the near-infrared range is
reported. Following a first account of the experiment [Kandula et al., Phys.
Rev. Lett. 105, 063001 (2010)], an extensive review is given of the
demonstration that the resulting spectrum at 51 nm is fully phase coherent and
can be applied to precision metrology. The pulses are used in a scheme of
direct-frequency-comb excitation of helium atoms from the ground state to the
1s4p and 1s5p 1P_1 states. Laser ionization by auxiliary 1064 nm pulses is used
to detect the excited state population, resulting in a cosine-like signal as a
function of the repetition rate of the frequency comb with a modulation
contrast of up to 55%. Analysis of the visibility of this comb structure yields
an estimated timing jitter between the two upconverted comb laser pulses of 50
attoseconds, whch indicates that extension to even shorter wavelengths should
be feasible. The helium metrology investigation results in transition
frequencies of 5740806993(10) MHz and 5814248672(6) MHz for excitation of the
1s4p and 1s5p 1P_1 states, respectively. This constitutes the first absolute
frequency measurement in the XUV, attaining unprecedented accuracy in this
windowless part of the electromagnetic spectrum. From the measured transition
frequencies an eight-fold improved 4He ionization energy of 5945204212(6) MHz
is derived. Also a new value for the 4He ground state Lamb shift is found of
41247(6) MHz. This experimental value is in agreement with recent theoretical
calculations up to order m\alpha^6 and m^2/(M\alpha^5), but with a six times
higher precision, therewith providing a stringent test of quantum
electrodynamics in bound two-electron systems.Comment: 18 pages, 13 figure
Frequency metrology on the 4s 2S1/2 - 4p 2P1/2 transition in the calcium ion for a comparison with quasar data
High accuracy frequency metrology on the 4s 2S1/2 - 4p 2P1/2 transition in
calcium ions is performed using laser cooled and crystallized ions in a linear
Paul trap. Calibration is performed with a frequency comb laser, resulting in a
transition frequency of f=755222766.2(1.7) MHz. The accuracy presents an
improvement of more than one order of magnitude, and will facilitate a
comparison with quasar data in a search for a possible change of the fine
structure constant on a cosmological time scale.Comment: Corrected typos (including one on the axis of figure 6
Bounds on fifth forces from precision measurements on molecules
Highly accurate results from frequency measurements on neutral hydrogen
molecules H_2, HD and D_2 as well as the HD^+ ion can be interpreted in terms
of constraints on possible fifth-force interactions. Where the hydrogen atom is
a probe for yet unknown lepton-hadron interactions, and the helium atom is
sensitive for lepton-lepton interactions, molecules open the domain to search
for additional long-range hadron-hadron forces. First principles calculations
in the framework of quantum electrodynamics have now advanced to the level that
hydrogen molecules and hydrogen molecular ions have become calculable systems,
making them a search-ground for fifth forces. Following a phenomenological
treatment of unknown hadron-hadron interactions written in terms of a Yukawa
potential of the form V_5(r)=\beta exp(-r/\lambda)/r current precision
measurements on hydrogenic molecules yield a constraint \beta < 1 \times
10^{-7} eV\AA for long-range hadron-hadron interactions at typical force ranges
commensurate with separations of a chemical bond, i.e. \lambda ~1 \AA and
beyond.Comment: 7 pages, 3 figures, 1 tabl
Dissociation energy of the hydrogen molecule at 10 accuracy
The ionization energy of ortho-H has been determined to be
cm
from measurements of the GK(1,1)--X(0,1) interval by Doppler-free two-photon
spectroscopy using a narrow band 179-nm laser source and the ionization energy
of the GK(1,1) state by continuous-wave near-infrared laser spectroscopy.
(H) was used to derive the dissociation energy of
H, (H), at cm with a
precision that is more than one order of magnitude better than all previous
results. The new result challenges calculations of this quantity and represents
a benchmark value for future relativistic and QED calculations of molecular
energies.Comment: 6 pages, 5 figure
Ion distribution and ablation depth measurements of a fs-ps laser-irradiated solid tin target
The ablation of solid tin surfaces by an 800-nanometer-wavelength laser is
studied for a pulse length range from 500 fs to 4.5 ps and a fluence range
spanning 0.9 to 22 J/cm^2. The ablation depth and volume are obtained employing
a high-numerical-aperture optical microscope, while the ion yield and energy
distributions are obtained from a set of Faraday cups set up under various
angles. We found a slight increase of the ion yield for an increasing pulse
length, while the ablation depth is slightly decreasing. The ablation volume
remained constant as a function of pulse length. The ablation depth follows a
two-region logarithmic dependence on the fluence, in agreement with the
available literature and theory. In the examined fluence range, the ion yield
angular distribution is sharply peaked along the target normal at low fluences
but rapidly broadens with increasing fluence. The total ionization fraction
increases monotonically with fluence to a 5-6% maximum, which is substantially
lower than the typical ionization fractions obtained with nanosecond-pulse
ablation. The angular distribution of the ions does not depend on the laser
pulse length within the measurement uncertainty. These results are of
particular interest for the possible utilization of fs-ps laser systems in
plasma sources of extreme ultraviolet light for nanolithography.Comment: 8 pages, 7 figure
Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers
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