Coupled resonators employing phase-conjugating and ordinary mirrors

We calculate the oscillation conditions and the eigen-frequencies for phase-conjugating-resonator-normal-resonator coupled optical systems. With an eye toward applications to interferometry, we choose specific examples for which it is shown that the conditions for oscillation and the eigenfrequencies depend on the normal-resonator path length. The examples include both linear displacement and rotation sensing (Sagnac) resonant interferometers. Our results suggest that if the distortion-correcting and self-aligning properties of the phase-conjugating resonator are retained in the more complicated system, then these hybrid resonators may offer some advantages over their conventional counterparts

Alignment of resonant optical cavities

When an input Gaussian beam is improperly aligned and mode-matched to a stable optical resonator, the electric field in the resonator couples to off-axis spatial eigenmodes. We show that a translation of the input axis or a mismatch of the beam waist to the resonator waist size causes a coupling of off-axis modes which is inphase with the input field. On the other hand, a tilt of the input beam or a mismatch of the beam waist position to cavity waist position couples to these modes in quadrature phase. We also propose a method to measure these coupling coefficients and thereby provide a means to align and mode-match a resonant optical cavity in real time

Anterior cruciate ligament injury incidence across sex, sport, and level: a systematic review and meta-analysis

Well controlled Anterior Cruciate Ligament (ACL) injury prevention neuromuscular training reduces the risk of ACL injury by 50%, but despite the efficacy of these programs, ACL injury rates have not decreased. This lack of decrease in injury incidence may be due in part to limited knowledge on who is most at risk for sustaining an ACL injury, and there is no formal clinical tool available to estimate the personalized or group risk of ACL injury. The purpose of this study was to better understand what groups of athletes are most at risk of sustaining a primary ACL injury, as the first step in mitigating risk and decreasing the substantial public health and financial burden of ACL injuries. To accomplish this goal, we conducted a systematic review and meta-analysis using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and through specific inclusion/exclusion criteria to analyze specific subgroupings of athletes. 7,038 studies were identified in the initial database search and 80 studies were included in the final subgroup meta-analysis. Analyses revealed that female athletes had a greater risk of ACL injury compared to male athletes. However, this project pointed out gaps in the current epidemiological prevalence of ACL injuries and the extra precaution people should take about the overgeneralization of sex and sport types for risk assessment. For example, it is well known that for sex comparable sports, females are at greater risk for ACL injury compared to males – however, the absolute risk level for various female sports is substantially low (e.g., female high school volleyball and female college lacrosse). In addition, female professional sports have overall higher ACL injury rates and prevention programs appear less effective for this group warranting more rigorous and targeted prevention efforts. Future studies should also utilize rigorous epidemiological approaches to assess injury rates as there are many sports, sex, and levels that do not have sufficient data to determine absolute prevalence or risk level. When more information is discovered, a personalized risk assessment tool can then be developed to then determine the most at-risk populations to allocate resources and prevention efforts to reduce the number of ACL injuries

Transistor-Like Behavior of a Bose-Einstein Condensate in a Triple Well Potential

In the last several years considerable efforts have been devoted to developing Bose-Einstein Condensate (BEC)-based devices for applications such as fundamental research, precision measurements and integrated atom optics. Such devices capable of complex functionality can be designed from simpler building blocks as is done in microelectronics. One of the most important components of microelectronics is a transistor. We demonstrate that Bose-Einstein condensate in a three well potential structure where the tunneling of atoms between two wells is controlled by the population in the third, shows behavior similar to that of an electronic field effect transistor. Namely, it exhibits switching and both absolute and differential gain. The role of quantum fluctuations is analyzed, estimates of switching time and parameters for the potential are presented.Comment: 12 pages, 12 figure

Mirror reflectometer based on optical cavity decay time

Described is a reflectometer capable of making reflectivity measurements of low-loss highly reflecting mirror coatings and transmission measurements of low-loss antireflection coatings. The technique directly measures the intensity decay time of an optical cavity comprised of low-loss elements. We develop the theoretical framework for the device and discuss in what conditions and to what extent the decay time represents a true measure of mirror reflectivity. Current apparatus provides a decay time resolution of 10 nsec and has demonstrated a cavity total loss resolution of 5 ppm

The Arecibo HII Region Discovery Survey

We report the detection of radio recombination line emission (RRL) using the Arecibo Observatory at X-band (9GHz, 3cm) from 37 previously unknown HII regions in the Galactic zone 66 deg. > l > 31 deg. and |b| < 1 deg. This Arecibo HII Region Discovery Survey (Arecibo HRDS) is a continuation of the Green Bank Telescope (GBT) HRDS. The targets for the Arecibo HRDS have spatially coincident 24 micron and 20 cm emission of a similar angular morphology and extent. To take advantage of Arecibo's sensitivity and small beam size, sources in this sample are fainter, smaller in angle, or in more crowded fields compared to those of the GBT HRDS. These Arecibo nebulae are some of the faintest HII regions ever detected in RRL emission. Our detection rate is 58%, which is low compared to the 95% detection rate for GBT HRDS targets. We derive kinematic distances to 23 of the Arecibo HRDS detections. Four nebulae have negative LSR velocities and are thus unambiguously in the outer Galaxy. The remaining sources are at the tangent point distance or farther. We identify a large, diffuse HII region complex that has an associated HI and 13CO shell. The ~90 pc diameter of the G52L nebula in this complex may be the largest Galactic HII region known, and yet it has escaped previous detection.Comment: Accepted to ApJ Data can be found here: http://go.nrao.edu/hrd