96 research outputs found
Spectrally resolved single-shot wavefront sensing of broadband high-harmonic sources
Wavefront sensors are an important tool to characterize coherent beams of
extreme ultraviolet radiation. However, conventional Hartmann-type sensors do
not allow for independent wavefront characterization of different spectral
components that may be present in a beam, which limits their applicability for
intrinsically broadband high-harmonic generation (HHG) sources. Here we
introduce a wavefront sensor that measures the wavefronts of all the harmonics
in a HHG beam in a single camera exposure. By replacing the mask apertures with
transmission gratings at different orientations, we simultaneously detect
harmonic wavefronts and spectra, and obtain sensitivity to spatiotemporal
structure such as pulse front tilt as well. We demonstrate the capabilities of
the sensor through a parallel measurement of the wavefronts of 9 harmonics in a
wavelength range between 25 and 49 nm, with up to lambda/32 precision.Comment: 12 pages, 6 figure
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
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
Direct frequency comb spectroscopy of trapped ions
Direct frequency comb spectroscopy of trapped ions is demonstated for the
first time. It is shown that the 4s^2S_(1/2)-4p^2P_(3/2) transition in calcium
ions can be excited directly with a frequency comb laser that is upconverted to
393 nm. Detection of the transition is performed using a shelving scheme to
suppress background signal from non-resonant comb modes. The measured
transition frequency of f=761 905 012.7(0.5) MHz presents an improvement in
accuracy of more than two orders of magnitude.Comment: 4 pages, 5 figur
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
Deep-Ultraviolet Frequency Metrology of H2 for Tests of Molecular Quantum Theory
Molecular hydrogen and its isotopic and ionic species are benchmark systems for testing quantum chemical theory. Advances in molecular energy structure calculations enable the experimental verification of quantum electrodynamics and potentially a determination of the proton charge radius from H2 spectroscopy. We measure the ground state energy in ortho-H2 relative to the first electronically excited state by Ramsey-comb laser spectroscopy on the EF1Σg+-X1Σg+(0,0) Q1 transition. The resulting transition frequency of 2 971 234 992 965(73) kHz is 2 orders of magnitude more accurate than previous measurements. This paves the way for a considerably improved determination of the dissociation energy (D0) for fundamental tests with molecular hydrogen
Diffractive shear interferometry for extreme ultraviolet high-resolution lensless imaging
We demonstrate a novel imaging approach and associated reconstruction
algorithm for far-field coherent diffractive imaging, based on the measurement
of a pair of laterally sheared diffraction patterns. The differential phase
profile retrieved from such a measurement leads to improved reconstruction
accuracy, increased robustness against noise, and faster convergence compared
to traditional coherent diffractive imaging methods. We measure laterally
sheared diffraction patterns using Fourier-transform spectroscopy with two
phase-locked pulse pairs from a high harmonic source. Using this approach, we
demonstrate spectrally resolved imaging at extreme ultraviolet wavelengths
between 28 and 35 nm
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
Demonstration of Ramsey-Comb Precision Spectroscopy in Xenon at Vacuum Ultraviolet Wavelengths Produced with High-Harmonic Generation
The remarkable progress in the field of laser spectroscopy induced by the
invention of the frequency-comb laser has enabled many new high-precision tests
of fundamental theory and searches for new physics. Extending frequency-comb
based spectroscopy techniques to the vacuum (VUV) and extreme ultraviolet (XUV)
spectral range would enable measurements in e.g. heavier hydrogen-like systems
and open up new possibilities for tests of quantum electrodynamics and
measurements of fundamental constants. The main approaches rely on
high-harmonic generation (HHG), which is known to induce spurious phase shifts
from plasma formation. After our initial report (Physical Review Letters 123,
143001 (2019)), we give a detailed account of how the Ramsey-comb technique is
used to probe the plasma dynamics with high precision, and enables accurate
spectroscopy in the VUV. A series of Ramsey fringes is recorded to track the
phase evolution of a superposition state in xenon atoms, excited by two
up-converted frequency-comb pulses. Phase shifts of up to 1 rad induced by HHG
were observed at ns timescales and with mrad-level accuracy at nm. Such
phase shifts could be reduced to a negligible level, enabling us to measure the
transition frequency in at 110
nm (seventh harmonic) with sub-MHz accuracy. The obtained value is times
more precise than the previous determination and the fractional accuracy of
is times better than the previous best
spectroscopic measurement using HHG. The isotope shifts between and
two other isotopes were determined with an accuracy of kHz. The method
can be readily extended to achieve kHz-level accuracy, e.g. to measure the
transition in . Therefore, the Ramsey-comb method shows great
promise for high-precision spectroscopy of targets requiring VUV and XUV
wavelengths
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