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Los Alamos National Laboratory Science Education Programs. Progress report, October 1, 1994--December 31, 1994

Description: During the 1994 summer institute NTEP teachers worked in coordination with LANL and the Los Alamos Middle School and Mountain Elementary School to gain experience in communicating on-line, to gain further information from the Internet and in using electronic Bulletin Board Systems (BBSs) to exchange ideas with other teachers. To build on their telecommunications skills, NTEP teachers participated in the International Telecommunications In Education Conference (Tel*ED `94) at the Albuquerque Convention Center on November 11 & 12, 1994. They attended the multimedia keynote address, various workshops highlighting many aspects of educational telecommunications skills, and the Telecomm Rodeo sponsored by Los Alamos National Laboratory. The Rodeo featured many presentations by Laboratory personnel and educational institutions on ways in which telecommunications technologies can be use din the classroom. Many were of the `hands-on` type, so that teachers were able to try out methods and equipment and evaluate their usefulness in their own schools and classrooms. Some of the presentations featured were the Geonet educational BBS system, the Supercomputing Challenge, and the Sunrise Project, all sponsored by LANL; the `CU-seeMe` live video software, various simulation software packages, networking help, and many other interesting and useful exhibits.
Date: February 1, 1995
Creator: Gill, D.H.
Partner: UNT Libraries Government Documents Department

Damage resistance of AR-coated germanium surfaces for nanosecond CO/sub 2/ laser pulses

Description: An evaluation of the state-of-the-art of AR coatings on gallium-doped germanium, used as a saturable absorber at 10.6 ..mu..m, has been conducted. Both 1-on-1 and N-on-1 laser damage thresholds were measured with 1.2 ns pulses on bare and coated surfaces. Only front surface damage was observed. With few exceptions, the thresholds for coated surfaces were centered at 0.49 +- 0.3 J/cm/sup 2/. Bare Ge had a threshold ranging from 0.65 to 0.70 J/cm/sup 2/. No significant differences due to substrate polish, crystallinity or doping level were evident and multiple-shot conditioning resulted in the same threshold as for single shot tests. From an analysis of standing-wave electric fields, damage for AR-coated Ge appeared to be limited by the surface properties of Ge. Measurements at both 1.2 and 70 ns indicated that the threshold (J/cm/sup 2/) of both coated and uncoated Ge increases as the square root of the pulse-width.
Date: January 1, 1977
Creator: Newnam, B.E. & Gill, D.H.
Partner: UNT Libraries Government Documents Department

Ultraviolet damage resistance of laser coatings

Description: The damage resistance of several thin-film materials used in ultraviolet laser optics was measured at 266 and 355 nm. The coatings included single, quarterwave (QW) layers of NaF, LaF/sub 3/, MgF/sub 2/, ThO/sub 2/, Al/sub 2/O/sub 3/, HfO/sub 2/, ZrO/sub 2/, Y/sub 2/O/sub 3/ and SiO/sub 2/, plus multilayer reflectors composed of some of these materials. The substrates were uv-grade fused silica. Single-shot thresholds were obtained with 22 ns and 27 ns (FWHM) pulses at 266 and 355 nm, respectively. One of the samples had previously been tested using 20-ps pulses, providing a pulsewidth comparison. At 266 nm the coating with the highest damage threshold was a QW layer of NaF at 10.8 J/cm/sup 2/ (450 MW/cm/sup 2/), whereas for a maximum reflector of Al/sub 2/O/sub 3//NaF the value was 3.6 J/cm/sup 2/ (154 MW/cm/sup 2/), and the threshold of the maximum reflector was 12.2 J/cm/sup 2/ (470 MW/cm/sup 2/). The results were analyzed to determine correlations with standing-wave electric fields and linear and two-photon absorption. Scaling relationships for wavelength, refractive index and atomic density, and pulsewidth were found.
Date: January 1, 1978
Creator: Newnam, B.E. & Gill, D.H.
Partner: UNT Libraries Government Documents Department

Picosecond-pulse damage studies of diffraction gratings

Description: Diffraction gratings are frequently used in dye-laser cavities as wavelength-tuning elements. These gratings often limit the maximum laser output energy because of their low damage thresholds. We have measured the damage characteristics of both ruled and holographically produced gratings, under a variety of conditions. Using the single-shot-per-site mode, the samples were irradiated by 30-ps, 1.064-..mu..m pulses having a spot size of 0.5-mm radius. It was found that holographic gratings have damage thresholds from 1.5 to 5.0 times higher than similar ruled gratings. Thresholds for S-polarized light (E parallel to grooves) were higher by factors of 1.5 to 6. For the same type grating, gold coatings yielded higher threshold than aluminum, although this is wavelength dependent. For holographic gratings, replicas have slightly higher thresholds than masters. Dependence upon groove spacing was weak. Data are presented to show a variety of comparisons between different types of gratings, including two different manufacturers and usage at higher orders of incidence.
Date: January 1, 1984
Creator: Gill, D.H. & Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Short-pulse CO/sub 2/-laser damage studies of NaCl and KCl windows

Description: The damage resistance of bare surfaces and the bulk interior of NaCl and KCl windows was measured with a short-pulse CO/sub 2/ laser at 10.6 ..mu..m. Parametric studies with 1.7-ns pulses indicated that adsorbed water was probably the limiting agent on surface thresholds in agreement with previous studies at long pulsewidths. Rear-surface thresholds up to 7 J/cm/sup 2/ were measured for polished NaCl windows, whereas KCl surfaces damaged at approximately 60% of this level. The breakdown electric-field thresholds of exit surfaces were only 50% of the value of the bulk materials. The pulsewidth dependence of surface damage from 1 to 65 ns, in terms of incident laser fluence, increased as t/sup 1/3/.
Date: January 1, 1979
Creator: Newnam, B.E.; Nowak, A.V. & Gill, D.H.
Partner: UNT Libraries Government Documents Department

Los Alamos National Laboratory Science Education Program. Annual progress report, October 1, 1995--September 30, 1996

Description: The National Teacher Enhancement program (NTEP) is a three-year, multi-laboratory effort funded by the National Science Foundation and the Department of Energy to improve elementary school science programs. The Los Alamos National Laboratory targets teachers in northern New Mexico. FY96, the third year of the program, involved 11 teams of elementary school teachers (grades 4-6) in a three-week summer session, four two-day workshops during the school year and an on-going planning and implementation process. The teams included twenty-one teachers from 11 schools. Participants earned a possible six semester hours of graduate credit for the summer institute and two hours for the academic year workshops from the University of New Mexico. The Laboratory expertise in the earth and environmental science provided the tie between the Laboratory initiatives and program content, and allowed for the design of real world problems.
Date: January 1, 1997
Creator: Gill, D.H.
Partner: UNT Libraries Government Documents Department

Angular dependence of multilayer-reflector damage thresholds

Description: The damage resistance of HfO/sub 2//SiO/sub 2/ multilayer dielectric reflectors was measured as a function of angle of incidence with 351-nm XeF-laser irradiation. The laser produced nominal 10-ns pulses at a repetition rate of 35 pps. A series of reflectors designed for 0/sup 0/, 30/sup 0/, 45/sup 0/, 60/sup 0/, 75/sup 0/, and 85/sup 0/ was tested with an S-plane polarized beam. To account for variations in the separate coating depositions, some of the coating designs were tested at two angles of incidence. At large angles of incidence, we did not observe the anticipated large increases in damage thresholds predicted theoretically on the basis of spatial dilution (1/costheta) of the intensity at the reflector surface and standing-wave electric fields. For example, the threshold for a reflector designed and tested at 85/sup 0/ was only a factor of 2.5 larger than that of normal-incidence reflectors tested at 0/sup 0/. Several possible mechanisms to explain this discrepancy were considered. 11 refs.
Date: January 1, 1984
Creator: Newnam, B.E.; Foltyn, S.R.; Gill, D.H. & Jolin, L.J.
Partner: UNT Libraries Government Documents Department