Search results for "OPTICS"
showing 10 items of 10033 documents
Orientation and Alignment Echoes
2015
We present one of the simplest classical systems featuring the echo phenomenon---a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation or alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by the kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of ${\mathrm{CO}}_{2}$ molecules excited by a pair of femtosecond laser pulses.
Resonance ionization spectroscopy of thorium isotopestowards a laser spectroscopic identification of the low-lying 7.6 eV isomer of 229Th
2011
International audience; In-source resonance ionization spectroscopy was used to identify an efficient and selective three step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in preparation of laser spectroscopic investigations for an identification of the low-lying 229 m Th isomer predicted at 7.6 ± 0.5 eV above the nuclear ground state. Using a sample of 232 Th, a multitude of optical transitions leading to over 20 previously unknown intermediate states of even parity as well as numerous high-lying odd parity auto-ionizing states were identified. Level energies were determined with an accuracy of 0.06 cm −1 for inte…
First-principles nonequilibrium Green's-function approach to transient photoabsorption: Application to atoms
2015
We put forward a first-principle NonEquilibrium Green's Function (NEGF) approach to calculate the transient photoabsorption spectrum of optically thin samples. The method can deal with pump fields of arbitrary strength, frequency and duration as well as for overlapping and nonoverlapping pump and probe pulses. The electron-electron repulsion is accounted for by the correlation self-energy, and the resulting numerical scheme deals with matrices that scale quadratically with the system size. Two recent experiments, the first on helium and the second on krypton, are addressed. For the first experiment we explain the bending of the Autler-Townes absorption peaks with increasing the pump-probe d…
Reversed Dark Resonance in Rb Atom Excited by a Diode Laser
2000
Origin of recently discovered reversed (opposite sign) dark resonances was explained theoretically and verified experimentally. It is shown that the reason for these resonances is a specific optical pumping of ground state level in a transition when ground state angular momentum is smaller than the excited state momentum.
Compact solid-state laser source for 1S-2S spectroscopy in atomic hydrogen
2005
We demonstrate a novel compact solid-state laser source for high-resolution two-photon spectroscopy of the $1S-2S$ transition in atomic hydrogen. The source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable 486 nm dye laser used in previous experiments and record 1S-2S spectra using both systems. With the solid-state laser system we demonstrate a resolution of the hydrogen spectrometer of 6 \times 10^{11} which is promising for a number of high-precision measurements in hydrogen-like systems.
Searching for alignment-to-orientation conversion in the ground state of atomic Cs with circularly polarized laser probe
2020
In this study we explored the possibilities for observing the angular momentum alignment-to-orientation conversion (AOC) in the ground state of various alkali metals: K, Rb, Cs. For theoretical analysis we used a model that is based on the Optical Bloch equations for the density matrix. Our model includes the interaction of all neighboring hyperfine levels with laser radiation, the mixing of magnetic sublevels in an external magnetic field, the coherence properties of the exciting laser radiation, and the Doppler effect. Additionally we simulated signals where the ground- or the excited-state coherent processes were numerically switched off in order to determine the origins of the features …
Magnetic field-induced mixing of hyperfine states of Cs 6 2^P_{3/2} level observed with a sub-micron vapor cell
2003
The fluorescence spectra of a sub-micron atomic cesium vapor layer observable under resonant excitation on D2 line have been studied in the presence of an external magnetic field. Substantial changes in amplitudes and frequency positions of the individual (resolved) hyperfine transitions have been recorded in moderate magnetic fields (up to ~ 50 Gauss). These features are caused by mixing of the hyperfine states of the upper level resulting from comparable values of the hyperfine splitting of the 62^P_{3/2} manifold and Larmor frequencies of the magnetic sublevels. The results of simulation show a good agreement with the experimental spectra. Possible application of the results for high spa…
Narrow-band pulsed electron source based on near-threshold photoionization of Cs in a magneto-optical trap
2019
The newly developed method of time-of-flight (ToF) momentum microscopy was used to analyse the cold electron emission from a Cs 3D magneto-optical trap (MOT). Three-step resonant photoionization was implemented via two intermediate states (6P3/2 pumped with 852 nm laser and 7S1/2 with 1470 nm) and a tuneable femtosecond Ti:sapphire laser for the final ionization step. The magnetic field of the MOT is switched off during the photoionization step. The natural bandwidth of the fs-laser is reduced to 4 meV using optical spectral filters. Precise tuning of the photon energy makes it possible to observe the transition regime between direct photoemission into the open continuum and field induced i…
Space-borne Bose–Einstein condensation for precision interferometry
2018
Space offers virtually unlimited free-fall in gravity. Bose-Einstein condensation (BEC) enables ineffable low kinetic energies corresponding to pico- or even femtokelvins. The combination of both features makes atom interferometers with unprecedented sensitivity for inertial forces possible and opens a new era for quantum gas experiments. On January 23, 2017, we created Bose-Einstein condensates in space on the sounding rocket mission MAIUS-1 and conducted 110 experiments central to matter-wave interferometry. In particular, we have explored laser cooling and trapping in the presence of large accelerations as experienced during launch, and have studied the evolution, manipulation and interf…
Optical Shielding of Destructive Chemical Reactions between Ultracold Ground-State NaRb Molecules
2020
Polar quantum gases represent promising platforms for studying many-body physics and strongly correlated systems with possible applications e.g. in quantum simulation or quantum computation. Due to their large permanent electric dipole moment polar molecules in electric field exhibit strong long-range anisotropic dipole-dipole interactions (DDIs). The creation and trapping of ultracold dipolar diatomic molecules of various species are feasible in many experimental groups nowadays. However long time trapping is still a challenge even in the case of the so called nonreactive molecules which are supposed to be immune against inelastic collisions in their absolute ground state [1] . Various hyp…