Analysis of Q-switch in a CO2 laser with saturable absorber

Intracavity experiments with an SF₆ saturable absorber have been performed with a CO₂ infrared laser. Accurate measurements of the passive Q-switch pulses versus the laser parameters have been made. A comparison with theoretical models is presented, discussing the involved approximations.     

Atomic gallium laser spectroscopy with violet/blue diode lasers

We describe the operation of two GaN-based diode lasers for the laser spectroscopy of gallium at 403 nm and 417 nm. Their use in an external cavity configuration has enabled us to investigate of absorption spectroscopy in a gallium hollow cathode. We have analyzed the Doppler-broadened profiles, accounting for hyperfine and isotope structure and extracting both the temperature and density of the neutral atomic sample produced in the glow discharge. We have also built a setup to produce a thermal atomic beam of gallium. By using the GaN-based diode lasers, we have studied the laser-induced fluorescence and hyperfine-resolved spectra of gallium. PACS 42.55.Px; 42.60.-v; 32.30.-r; 03.75.Be     

Collective effects on ionization of Rydberg sodium atoms by blackbody radiation

Ionization by blackbody radiation of a beam of sodium atoms, prepared in Rydberg states by two-step laser excitation, has been investigated. Ionization by absorption of an additional laser photon was also present, although these ionization channels take place on very different time scales. For atom densities in the range 1–4 x 10¹¹ cm^-3 and power density of the laser used for the second step excitation of the order of MW/cm², we have found evidence of space-charge interactions in the laser-light focus region.     

Laser ionization and time-resolved ion collection in cesium vapor

Cesium atoms are ionized by resonant two-photon pulsed laser absorption. The ion collection is investigated when the application of the collecting electric field is time delayed with respect to the laser pulse. It is shown that the time evolution of the atomic ion density is governed by a conversion of atomic ions to molecular ones. Owing to the large molecular recombination coefficient the ion density decreases exponentially. The conversion rate constants for collisions with cesium or argon atoms have been determined.     

Shortcut-to-Adiabatic Controlled-Phase Gate in Rydberg Atoms

A shortcut-to-adiabatic protocol for the realization of a fast and high-fidelity controlled-phase gate in Rydberg atoms is developed. The adiabatic state transfer, driven in the high-blockade limit, is sped up by compensating nonadiabatic transitions via oscillating fields that mimic a counterdiabatic Hamiltonian. High fidelities are obtained in wide parameter regions. The implementation of the bare effective counterdiabatic field, without original adiabatic pulses, enables to bypass gate errors produced by the accumulation of blockade-dependent dynamical phases, making the protocol efficient also at low blockade values. As an application toward quantum algorithms, how the fidelity of the gate impacts the efficiency of a minimal quantum-error correction circuit is analyzed.     

Dark Energy： Relating the Evolutions of the Universe from the Past to the Future

Using the evolution history of the universe, one can make constraint on the parameter space of dynamic dark energy models. We discuss two different parameterized dark energy models. Our results further restrict the combined constraints obtained from supernova and the first-year Wilkinson-microwave-anisotropy-probe observations. From the allowed parameter space, it is found that our universe will experience an eternal acceleration. We also estimate the bound on the physically relevant regions both in the re-inflationary and inflationary phases.