36 research outputs found
Radiative and collisional processes in translationally cold samples of hydrogen Rydberg atoms studied in an electrostatic trap
Supersonic beams of hydrogen atoms, prepared selectively in Rydberg-Stark
states of principal quantum number in the range between 25 and 35, have
been deflected by 90, decelerated and loaded into off-axis electric
traps at initial densities of atoms/cm and translational
temperatures of 150 mK. The ability to confine the atoms spatially was
exploited to study their decay by radiative and collisional processes. The
evolution of the population of trapped atoms was measured for several
milliseconds in dependence of the principal quantum number of the initially
prepared states, the initial Rydberg-atom density in the trap, and the
temperature of the environment of the trap, which could be varied between 7.5 K
and 300 K using a cryorefrigerator. At room temperature, the population of
trapped Rydberg atoms was found to decay faster than expected on the basis of
their natural lifetimes, primarily because of absorption and emission
stimulated by the thermal radiation field. At the lowest temperatures
investigated experimentally, the decay was found to be multiexponential, with
an initial rate scaling as and corresponding closely to the natural
lifetimes of the initially prepared Rydberg-Stark states. The decay rate was
found to continually decrease over time and to reach an almost -independent
rate of more than (1 ms) after 3 ms. To analyze the experimentally
observed decay of the populations of trapped atoms, numerical simulations were
performed which included all radiative processes, i.e., spontaneous emission as
well as absorption and emission stimulated by the thermal radiation. These
simulations, however, systematically underestimated the population of trapped
atoms observed after several milliseconds by almost two orders of magnitude,
although they reliably predicted the decay rates of the remaining atoms in the
trap. TheComment: 36 pages, 18 figure
Slow and velocity-tunable beams of metastable He by multistage Zeeman deceleration
Metastable helium molecules (He) have been generated by striking a
discharge in a supersonic expansion of helium gas from a pulsed valve. When
operating the pulsed valve at room temperature, 77K, and 10K, the mean velocity
of the supersonic beam was measured to be 1900m/s, 980m/s, and 530m/s,
respectively. A 55-stage Zeeman decelerator operated in a phase-stable manner
was then used to further reduce the beam velocity and tune it in the range
between 100 and 150m/s. The internal-state distribution of the decelerated
sample was established by photoionization spectroscopy.Comment: 10 pages, 7 figure
Fluorescence-lifetime-limited trapping of Rydberg helium atoms on a chip
Metastable (1s)(2s) helium atoms produced in a supersonic beam
were excited to Rydberg-Stark states (with in the range) in a
cryogenic environment and subsequently decelerated by, and trapped above, a
surface-electrode decelerator. In the trapping experiments, the Rydberg atoms
were brought to rest in 75~s and over a distance of 33~mm and kept
stationary for times in the ~s range, before
being re-accelerated for detection by pulsed field ionization. The use of a
home-built valve producing short gas pulses with a duration of about 20~s
enabled the reduction of losses arising from collisions with atoms in the
trailing part of the gas pulses. Cooling the decelerator to 4.7~K further
suppressed losses by transitions induced by blackbody radiation and by
collisions with atoms desorbing from the decelerator surface. The main
contribution (60\%) to the atom loss during deceleration is attributed to the
escape out of the decelerator moving traps of atoms having energies higher than
the trap saddle point, spontaneous emission and collisions with atoms in the
trailing part of the gas pulses causing each only about 20\% of the atom loss.
At 4.7 K, the atom losses in the trapping phase of the experiments were found
to be almost exclusively caused by spontaneous emission and the trap lifetimes
were found to correspond to the natural lifetimes of the Rydberg-Stark states.
Increasing the temperature to 100 K enhanced the trap losses by transitions
stimulated by blackbody radiation
Metrology of Rydberg states of the hydrogen atom
We present a method to precisly measure the frequencies of transitions to
high- Rydberg states of the hydrogen atom which are not subject to
uncontrolled systematic shifts caused by stray electric fields. The method
consists in recording Stark spectra of the field-insensitive Stark states
and the field-sensitive Stark states, which are used to calibrate the
electric field strength. We illustrate this method with measurements of
transitions from the hyperfine levels in the
presence of intentionally applied electric fields with strengths in the range
between and Vcm. The slightly field-dependent level
energies are corrected with a precisely calculated shift to obtain the
corresponding Bohr energies . The energy
difference between and obtained with our method agrees with
Bohr's formula within the kHz experimental uncertainty. We also
determined the hyperfine splitting of the state by taking the
difference between transition frequencies from the levels to the Stark states. Our results demonstrate the
possibility of carrying out precision measurements in high- hydrogenic
quantum states
Imaging-assisted single-photon Doppler-free laser spectroscopy and the ionization energy of metastable triplet helium
Skimmed supersonic beams provide intense, cold, collision-free samples of
atoms and molecules are one of the most widely used tools in atomic and
molecular laser spectroscopy. High-resolution optical spectra are typically
recorded in a perpendicular arrangement of laser and supersonic beams to
minimize Doppler broadening. Typical Doppler widths are nevertheless limited to
tens of MHz by the residual transverse-velocity distribution in the
gas-expansion cones. We present an imaging method to overcome this limitation
which exploits the correlation between the positions of the atoms and molecules
in the supersonic expansion and their transverse velocities - and thus their
Doppler shifts. With the example of spectra of
(1\mathrm{s})(n\mathrm{p})\,^3\mathrm{P}_{0-2}\leftarrow
(1\mathrm{s})(2\mathrm{s})\,^3\mathrm{S}_1 transitions to high Rydberg states
of metastable triplet He, we demonstrate the suppression of the residual
Doppler broadening and a reduction of the full linewidths at half maximum to
only about 1 MHz in the UV. Using a retro-reflection arrangement for the laser
beam and a cross-correlation method, we determine Doppler-free spectra without
any signal loss from the selection, by imaging, of atoms within ultranarrow
transverse-velocity classes. As an illustration, we determine the ionization
energy of triplet metastable He and confirm the significant discrepancy between
recent experimental (Clausen et al., Phys. Rev. Lett. 127 093001 (2021)) and
high-level theoretical (Patk\'os et al., Phys. Rev. A 103 042809 (2021)) values
of this quantity
Multistage Zeeman deceleration of metastable neon
A supersonic beam of metastable neon atoms has been decelerated by exploiting
the interaction between the magnetic moment of the atoms and time-dependent
inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91
deceleration solenoids, the atoms were decelerated from an initial velocity of
580m/s to final velocities as low as 105m/s, corresponding to a removal of more
than 95% of their initial kinetic energy. The phase-space distribution of the
cold, decelerated atoms was characterized by time-of-flight and imaging
measurements, from which a temperature of 10mK was obtained in the moving frame
of the decelerated sample. In combination with particle-trajectory simulations,
these measurements allowed the phase-space acceptance of the decelerator to be
quantified. The degree of isotope separation that can be achieved by multistage
Zeeman deceleration was also studied by performing experiments with pulse
sequences generated for Ne and Ne.Comment: 16 pages, 15 figure
New method to study ion-molecule reactions at low temperatures and application to the H + H H + H reaction
Studies of ion-molecule reactions at low temperatures are difficult because
stray electric fields in the reaction volume affect the kinetic energy of
charged reaction partners. We describe a new experimental approach to study
ion-molecule reactions at low temperatures and present, as example, a
measurement of the
reaction with the ion prepared in a single rovibrational state at
collision energies in the range -60 K. To reach such
low collision energies, we use a merged-beam approach and observe the reaction
within the orbit of a Rydberg electron, which shields the ions from stray
fields. The first beam is a supersonic beam of pure ground-state H
molecules and the second is a supersonic beam of H molecules excited to
Rydberg-Stark states of principal quantum number selected in the range
20-40. Initially, the two beams propagate along axes separated by an angle of
10. To merge the two beams, the Rydberg molecules in the latter beam
are deflected using a surface-electrode Rydberg-Stark deflector. The collision
energies of the merged beams are determined by measuring the velocity
distributions of the two beams and they are adjusted by changing the
temperature of the pulsed valve used to generate the ground-state
beam and by adapting the electric-potential functions to the electrodes of the
deflector. The collision energy is varied down to below K, i.e., below meV, with an energy resolution of 100
eV. We demonstrate that the Rydberg electron acts as a spectator and does
not affect the cross sections, which are found to closely follow a
classical-Langevin-capture model in the collision-energy range investigated.
Because all neutral atoms and molecules can be excited to Rydberg states, this
method of studyingComment: 39 pages, 10 figure
High-resolution laser spectroscopy between 0.9 and 14.3 THz in a supersonic beam: Rydberg-Rydberg transitions of atomic Xe at intermediate n values
ISSN:0021-9606ISSN:1089-769
Deceleration and trapping of a fast supersonic beam of metastable helium atoms with a 44-electrode chip decelerator
ISSN:1094-1622ISSN:0556-2791ISSN:1050-294
PFI-ZEKE-photoelectron spectroscopy of N<inf>2</inf>O using narrow-band VUV laser radiation generated by four-wave mixing in Ar using a KBBF crystal
ISSN:0021-9606ISSN:1089-769