Impact of laser-contaminant interaction on the performance of the protective capping layer of 1 ω high-reflection mirror coatings.

High dielectric constant multilayer coatings are commonly used on high-reflection mirrors for high-peak-power laser systems because of their high laser-damage resistance. However, surface contaminants often lead to damage upon laser exposure, thus limiting the mirror's lifetime and performance. One plausible approach to improve the overall mirror resistance against laser damage, including that induced by laser-contaminant coupling, is to coat the multilayers with a thin protective capping (absentee) layer on top of the multilayer coatings. An understanding of the underlying mechanism by which laser-particle interaction leads to capping layer damage is important for the rational design and selection of capping materials of high-reflection multilayer coatings. In this paper, we examine the responses of two candidate capping layer materials, made of SiO2 and Al2O3, over silica-hafnia multilayer coatings. These are exposed to a single oblique shot of a 1053 nm laser beam (fluence ∼10 J/cm2, pulse length 14 ns), in the presence of Ti particles on the surface. We find that the two capping layers show markedly different responses to the laser-particle interaction. The Al2O3 cap layer exhibits severe damage, with the capping layer becoming completely delaminated at the particle locations. The SiO2 capping layer, on the other hand, is only mildly modified by a shallow depression. Combining the observations with optical modeling and thermal/mechanical calculations, we argue that a high-temperature thermal field from plasma generated by the laser-particle interaction above a critical fluence is responsible for the surface modification of each capping layer. The great difference in damage behavior is mainly attributed to the large disparity in the thermal expansion coefficient of the two capping materials, with that of Al2O3 layer being about 15 times greater than that of SiO2.

Dynamics of transient absorption in bulk DKDP crystals following laser energy deposition.

The transient changes in the optical properties of bulk DKDP material arising from its exposure to high temperatures and pressures associated with localized laser energy deposition are investigated. Two methods for initiation of laser-induced breakdown are used, intrinsic, involving relatively large energy deposition brought about by focusing of the laser beam to high intensities, and extrinsic, arising from more localized deposition due to the presence of pre-existing absorbing damage initiating defects. Each method leads to a very different volume of material being affected, which provides for different material thermal relaxation times to help better understand the processes involved.

Factors influencing rat survival in a warm renal ischemia model: time to adapt the protocols.

INTRODUCTION: Survival in warm renal ischemia models is not only dependent on the treatment or surgical technique being evaluated, but also on factors inherent to the model itself. Use of rats of various strains in previous studies makes interstudy comparison difficult when trying to design an appropriate model control that would yield intermediate survival. In this study, impact of rat strain on survival after prolonged warm renal ischemia in the setting of delivery-controlled inhalational anesthesia was evaluated. MATERIALS AND METHODS: Under general delivery-controlled inhalation anesthesia with isoflurane, Dahl salt-sensitive, Wistar-Furth, Sprague-Dawley, and spontaneously hypertensive rats (n = 66 rats) were subjected to 150 minutes of unilateral renal warm ischemia time, subsequent reperfusion, and contralateral nephrectomy. Animals were followed up for 1 month, after which survivors were euthanized and morphologic changes in kidneys were scored. RESULTS: Thirty-day survival was: Dahl salt sensitive, 78%; Wistar-Furth, 67%; Sprague-Dawley, 55%; and spontaneously hypertensive rats, 0% (P < .0001). Histologic acute injury scores were higher for non-survivors versus 30-day survivors (P < .0001). CONCLUSION: Our data strongly suggest that rat strain is a major factor influencing survival and that strain and warm ischemia time selections must be considered together when designing a model control yielding intermediate survival. Further study is warranted in order to compare the effect of delivery-controlled inhalational versus historical anesthesia methods on animal survival.