Hydrogen maser development at Laval University

The physical construction of two hydrogen masers is described and results of measurements made on one of the masers are given. These include: cavity Q, thermal time constant, line Q, signal power output, magnetic shielding factor. Preliminary results indicate that the frequency stability will be mainly affected by the thermal of the cavity. The magnetic field and the barometric fluctuations should not affect the maser at the stability level above a few parts in 10 to the 15th power, which is the goal for averaging times of several hours

Pseudoresonance mechanism of all-optical frequency standard operation

We propose a novel approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of 10^-14/(\tau)^1/2. The physics beyond this approach is dark resonance splitting caused by interaction of the nuclear magnetic moment with the external magnetic field.Comment: revtex4, references adde

Combined quantum state preparation and laser cooling of a continuous beam of cold atoms

We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the F=4 ground state to pump the atoms toward F=3 while a second pi-polarized laser excites the F=3 -> F'=3 transition of the D2 line to produce Zeeman pumping toward m=0. To avoid trap states, we implement the first laser in a 2D optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the F=4 -> F'=4 and F=4 -> F'=5 transitions of the D2 line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second pi-polarized laser reveals the action of a new mechanism improving both laser cooling and state preparation efficiency. A physical interpretation of this mechanism is discussed.Comment: Minor changes according to the recommendations of the referee: - Corrected Fig.1. - Split the graph of Fig.6 for clarity. - Added one reference. - Added two remarks in the conclusion. - Results unchange

The mechanism and pattern of injuries of undocumented immigrants crossing the Texas-Mexico border along the Rio Grande Valley

Background Apprehensions of undocumented immigrants in the Rio Grande Valley sector of the U.S.-Mexico border have grown to account for nearly half of all apprehensions at the border. The purpose of this study is to report the prevalence, mechanism, and pattern of traumatic injuries sustained by undocumented immigrants who crossed the U.S.-Mexico border at the Rio Grande Valley sector over a span of 5 years and were treated at a local American College of Surgeons verified Level II trauma center. Methods A retrospective chart review was conducted from January 2014 to December 2019. Demographics, comorbidities, injury severity score (ISS), mechanism of injury, anatomical part of the body affected, hospital and ICU length of stay (LOS), and treatment costs were analyzed. Descriptive statistics for demographics, injury location and cause, and temporal trends are reported. The impact of ISS or surgical intervention on hospital LOS was analyzed using an analysis of covariance (ANCOVA). Results Of 178 patients, 65.2% were male with an average age of 31 (range 0–67) years old and few comorbidities (88.8%) or social risk factors (86%). Patients most commonly sustained injuries secondary to a border fence-related incident (33.7%), fleeing (22.5%), or motor vehicle accident (16.9%). There were no clear temporal trends in the total number of patients injured, or in causes of injury, between 2014 and 2019. The majority of patients (60.7%) sustained extremity injuries, followed by spine injuries (20.2%). Border fence-related incidents and fleeing increased risk of extremity injuries (Odds ratio (OR) \u3e 3; p \u3c 0.005), whereas motor vehicle accidents increased risk of head and chest injuries (OR \u3e 4; p \u3c 0.004). Extremity injuries increased the odds (OR: 9.4, p \u3c 0.001) that surgery would be required. Surgical intervention was common (64%), and the median LOS of patients who underwent surgery was 3 days more than those who did not (p \u3c 0.001). Conclusion In addition to border fence related injuries, undocumented immigrants also sustained injuries while fleeing and in motor vehicle accidents, among others. Extremity injuries, which were more likely with border fence-related incidents, were the most common type. This type of injury often requires surgical intervention and, therefore, a longer hospital stay for severe injuries

Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of $^{85}$Rb and $^{87}$Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers

Laser frequency stabilization to a single ion

A fundamental limit to the stability of a single-ion optical frequency standard is set by quantum noise in the measurement of the internal state of the ion. We discuss how the interrogation sequence and the processing of the atomic resonance signal can be optimized in order to obtain the highest possible stability under realistic experimental conditions. A servo algorithm is presented that stabilizes a laser frequency to the single-ion signal and that eliminates errors due to laser frequency drift. Numerical simulations of the servo characteristics are compared to experimental data from a frequency comparison of two single-ion standards based on a transition at 688 THz in 171Yb+. Experimentally, an instability sigma_y(100 s)=9*10^{-16} is obtained in the frequency difference between both standards.Comment: 15 pages, 5 figures, submitted to J. Phys.

Non-Destructive Probing of Rabi Oscillations on the Cesium Clock Transition near the Standard Quantum Limit

We report on non-destructive observation of Rabi oscillations on the Cs clock transition. The internal atomic state evolution of a dipole-trapped ensemble of cold atoms is inferred from the phase shift of a probe laser beam as measured using a Mach-Zehnder interferometer. We describe a single color as well as a two-color probing scheme. Using the latter, measurements of the collective pseudo-spin projection of atoms in a superposition of the clock states are performed and the observed spin fluctuations are shown to be close to the standard quantum limit.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

Parity nonconservation in Atomic Zeeman Transitions

We discuss the possibility of measuring nuclear anapole moments in atomic Zeeman transitions and perform the necessary calculations. Advantages of using Zeeman transitions include variable transition frequencies and the possibility of enhancement of parity nonconservation effects

Theoretical study of dark resonances in micro-metric thin cells

We investigate theoretically dark resonance spectroscopy for a dilute atomic vapor confined in a thin (micro-metric) cell. We identify the physical parameters characterizing the spectra and study their influence. We focus on a Hanle-type situation, with an optical irradiation under normal incidence and resonant with the atomic transition. The dark resonance spectrum is predicted to combine broad wings with a sharp maximum at line-center, that can be singled out when detecting a derivative of the dark resonance spectrum. This narrow signal derivative, shown to broaden only sub-linearly with the cell length, is a signature of the contribution of atoms slow enough to fly between the cell windows in a time as long as the characteristic ground state optical pumping time. We suggest that this dark resonance spectroscopy in micro-metric thin cells could be a suitable tool for probing the effective velocity distribution in the thin cell arising from the atomic desorption processes, and notably to identify the limiting factors affecting desorption under a grazing incidence.Comment: 12 pages, 11 figures theoretical articl