Development of mid-infrared solid state lasers for spaceborne lidar

Laser performance of Ho(3+):Tm(3+):Cr(3+):YAG crystals was investigated under both Cr:GSAG laser and flashlamp pumping. A flashlamp pumped Cr:GSAG laser was built to simulate high power quasi-CW laser diode pumping of a 2.1 micrometer holmium laser. The 2.1 micrometer output laser energy exceeded more than 14 mJ, the highest value reported to date under laser pumping near 785 nm. This was obtained in a pulse length of nearly 650 microsec from a 3 x 3 mm Ho:Tm:Cr:YAG rod by using the flashlamp-pumped Cr:CSAG laser as a pumping source at the diode laser wavelength, 785 micrometers. In addition, Ho:Tm:Cr:YAG crystals with various Tm(3+) concentrations were evaluated for flashlamp-pumped normal mode and Q-switched 2.1 micrometer laser operations under a wide variety of experimental conditions in order to understand internal dynamic processes among the ions and to determine an optimum lasing condition. An increase of the laser slope efficiency was observed with the increase of the Tm(3+) concentration from 2.5 to 4.5 atomic percent. The thermal dependence of the laser performance was also investigated. Q-switched laser output energies corresponding to nearly 100 percent of the normal-mode laser energies were obtained in a strong single spike of 200 ns pulse length by optimizing the opening time of a lithium niobate Q-switch

Development of mid-infrared solid state lasers for spaceborne lidar

This semiannual progress report covers work performed during the period from April 13, 1988 to October 13, 1988 under NASA grant number NAG-1-877 entitled, Development of mid-infrared solid state lasers for spaceborne lidar. We have designed a flashlamp-pumped Cr3(+);GSAG laser of pulsed laser energy greater than 200 mJ and of pulse width of 1 ms FWHM to simulate a high-power laser diode in pumping mid-infrared laser crystals such as Tm3(+), Er3(+), and/or Ho3(+)-ion doped YAG, YLF or other host materials. This Cr3(+);GSAG laser will be used to determine optimum conditions for laser diode pumped mid-infrared lasers, maximum energy extraction limit with longitudinal pumping, thermal damage limit, and other problems related to high power laser diode pumping. We have completed a modification of an existing flashlamp-pumped and liquid nitrogen cooled rare earth laser system for 60 J electrical input energy and a 500 micron pulse width, and have carried out preliminary experiments with a Ho(+):Er3(+):Tm3(+):YAG crystal to test the system performance. This flashlamp-pumped rare earth laser system will be used to determine optimum Tm3(+)-ion concentration in Ho3(+):Cr3(+):Tm3(+):YAG crystal in the remaining research period

Development of mid-infrared solid state lasers for spaceborne lidar

The laser performance of a Ho(3+):Tm(3+):Cr(3+):YAG crystal was measured under flashlamp pumping at various operating temperatures. The normal mode laser thresholds of a Ho(3+)(0.45 at. percent):Tm(3+)(2.5 at. percent):Cr(3+)(1.5 at. percent ):YAG crystal were found to range from 26 to 50 J between 120 and 200 K with slope efficiencies up to 0.36 percent with a 60 percent reflective output mirror. From the Q-switched operations a slope efficiency corresponding to 90 percent of the normal mode operation was observed. Laser wavelengths were measured for various operating conditions and fluorescence spectra were obtained at various temperatures in order to help understand the dynamic energy processes among the Ho(3+), Tm(3+), and Cr(3+) ions. A pulse forming network for a flashlamp pumped Cr:GSAG laser, which is to be used as a high power laser diode simulator in rare earth laser pumping, was completed and tested. The network provided critically damped, 1 ms FWHM, square pulses with a rise time of about 160 micrometers at an input electrical energy of 300 J

On invariant sets in Lagrangian graphs

In this exposition, we show that a Hamiltonian is always constant on a compact invariant connected subset which lies in a Lagrangian graph provided that the Hamiltonian and the graph are smooth enough. We also provide some counterexamples for the case that the Hamiltonians are not smooth enough.Comment: 4 page

Faking an Implicit Measure of Addiction Proneness

Self-report measures are known to be susceptible to faking, and response distortion is a particularly critical issue in the context of assessing job applicants (Holden & Kroner, 1992; Hough, Eaton, Dunnette, Kamp, & McCloy, 1990). However, the advent of conditional reasoning methodology makes it possible to assess personality more objectively by focusing on implicit rather than explicit cognitions. Previous research has suggested that the conditional reasoning methodology is resistant to faking. This study evaluates the fakability of a new measure of addiction, the Conditional Reasoning Test of Addiction Proneness, which was developed specifically to assess the implicit cognitions that justify engaging in addictive behavior (Bowler, Bowler, & James, 2011). This study examined whether respondents could successfully distort their responses on the Conditional Reasoning Test for Addiction Proneness as well as a self-report measure of addiction, the Self-Assessment of Behavior. Results indicate that the self-report measure is susceptible to faking but the conditional reasoning measure is resistant to response distortion, thus providing further support that Conditional Reasoning Test of Addiction Proneness does in fact assess implicit cognitions

A student's history of the town of Norton in Massachusetts

Thesis (Ed.M.)--Boston Universit

Examining the Relationship of Race on Students’ Perceptions of Safety and Concealed Campus Carry on a University Campus

Previous literature suggests that students who feel unsafe in their academic settings experience harmful academic, social, and psychological ramifications. With an alarming increase in school shootings, violence, and media coverage, the political discourse surrounding gun violence and strategies to ensure safety on college campuses has become increasingly polarized. States like Texas, Georgia, and Colorado have passed bills allowing students to carry concealed handguns on university campuses. At the time of this study, the state legislature in West Virginia passed a similar bill known as the Campus Self-Defense Act (Senate Bill 246, 2021). College students who identify as Black, Indigenous, People of Color (BIPOC) face unique stressors compared to their White student peers when it comes to perceptions of safety on campus. At primarily White institutions (PWIs), students identifying as BIPOC have reported feeling less safe, likely contributing to higher attrition rates and other barriers to success (Gummadam et al., 2015). This study aimed to address a gap in the literature by investigating perceptions of safety regarding concealed carry gun policies among undergraduate students identifying as BIPOC. In the present study, 226 undergraduate students (Mage = 19.6, 85.4% women-identifying, 11.9% BIPOC) reported their gun beliefs and behaviors, fear of on-campus crime victimization, and attitudes toward campus carry. Controlling for gender identity, sexual identity, age, in-state residence, and years of undergraduate education, participants identifying as BIPOC reported feeling significantly less safe with campus carry gun policies, compared to their White counterparts. Future research directions and clinical implications are discussed