Plymouth Grating Laboratory (United States)

Falls are a leading cause of traumatic brain injury (TBI) in people 65 years of age and older. After a TBI, a person is at an increased risk of future falls due to related impairments such as vestibular and visual dysfunction, dual-tasking deficits, balance and coordination impairments, and cognitive and communication deficits, in addition to medical risk factors. Comprehensive assessments of TBI-related impairments that could contribute to falls should be considered by clinicians to reduce morbidity and mortality in this population. This article summarizes risk factors for falls after TBI and ideas to address each limitation.

Coating thickness variation affects the diffraction efficiency of MLD pulse compression gratings. Experimental coating data is examined. Simulations compare the sensitivity of different grating designs with narrow and broad bandwidths.

Maximum-recorded run-up estimates of six major nearfield paleotsunamis, dating from 0.3 to 2.8 ka, are compiled from reported studies at 12 reliable localities distributed over a north–south distance of 1000 km in the Cascadia subduction zone. The run-up estimates are based on surveyed elevations and positions of terminal sand sheet layers that were deposited by the dated paleotsunamis. Maximum terminal deposit elevations from open-coastal sites range from 3 to 12 m NAVD88. Paired proximal and distal run-up sites at four localities demonstrate landward vertical attenuation gradients (−2.5 to −4.2 m km−1) of decreasing terminal sand deposit elevation with increasing distance inland. An averaged attenuation gradient is reversed (3.0 m km−1) to project paleotsunami run-up elevations to adjacent ocean shorelines. The run-up projections are further adjusted by paleotsunami age and relative sea level curves to estimate shoreline inundation elevations under modern sea level conditions. The tsunami shoreline inundation elevations range from 3 ± 2 to 15 ± 2 m NAVD88, with the largest values occurring along the central Cascadia margin and the smallest values occurring in the eastern Juan de Fuca Strait. Contradictory to some numerical tsunami modeling assumptions, there is no apparent correlation between duration of interseismic strain accumulation or estimated upper-plate elastic flexure and corresponding paleotsunami run-up heights on the central Cascadia margin. The short duration since the last Cascadia megathrust rupture (0.3 ka) cannot be used to imply smaller run-up values for a near-future Cascadia tsunami. Coastal communities should plan for the maximum paleotsunami run-ups as recorded at the nearest reliable run-up localities.

Large aperture laser pulse compressor designs use several diffraction gratings in series and sometimes tiled together to compress an amplified 1 to 10 ns pulse to 0.1 to 10 ps. The wavefront of the compressed pulse must be well controlled to allow focusing to a small spot on a target. Traditionally, multilayer dielectric gratings (MLDG) have been fabricated onto high thermal expansion substrates such as BK7 glass to prevent crazing and excessive bending due to tensile coating stress when operated in high vacuum. However, the high CTE of the BK7 can cause wavefront distortion and changes in the period of the grating. This work uses ion-assisted deposition of HfO2/SiO2 films to increase the compressive stress in MLD layers to allow use of silica substrates in the compressor vacuum environment. Stress, coating uniformity, and damage results are reported. The process was scaled to full size (91cm × 42cm) MLD gratings for use in the Osaka University LFEX laser system. Diffracted wavefront results from the full scale gratings is presented.

We have developed large size diffraction gratings and flat mirrors for large size pulse compressor in LFEX laser system. The required size of grating is 1.8 m, and we use 2 segment system with 91 cm element gratings. The substrates of mirrors and gratings are made of newly developed fused synthetic silica glass for low thermal expansion. The coating on this fused silica substrates are made by the ion beam assisted deposition (IAD) process for low stress coating. The size of element grating is 91 × 42 × 9 cm, and the largest mirror is 86 × 43 × 9 cm. The grating was lured by a novel scanning beam interference lithography system (NanoRuler II) in Plymouth Grating Laboratory in USA. The diffraction efficiency of the grating is better than 95%, and the wave-front error is better than λ/3 at 632 nm.