Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating.

We investigate an approach for the recycling of laser-damaged large-aperture deuterated potassium dihydrogen phosphate (DKDP) crystals used for optical switching (KDP) and for frequency conversion (DKDP) in megajoule-class high-power laser systems. The approach consists of micromachining the surface laser damage sites (mitigation), combined with multiple soaks and ultrasonication steps in a coating solvent to remove, synergistically, both the highly adherent machining debris and the laser-damage-affected antireflection coating. We identify features of the laser-damage-affected coating, such as the "solvent-persistent" coating and the "burned-in" coating, that are difficult to remove by conventional approaches without damaging the surface. We also provide a solution to the erosion problem identified in this work when colloidal coatings are processed during ultrasonication. Finally, we provide a proof of principle of the approach by testing the full process that includes laser damage mitigation of DKDP test parts, coat stripping, reapplication of a new antireflective coat, and a laser damage test demonstrating performance up to at least 12 J/cm2 at UV wavelengths, which is well above current requirements. This approach ultimately provides a potential path to a scalable recycling loop for the management of optics in large, high-power laser systems that can reduce cost and extend lifetime of highly valuable and difficult to grow large DKDP crystals.

Fracture-induced subbandgap absorption as a precursor to optical damage on fused silica surfaces.

The optical damage threshold of indentation-induced flaws on fused silica surfaces was explored. Mechanical flaws were characterized by laser damage testing, as well as by optical, secondary electron, and photoluminescence microscopy. Localized polishing, chemical leaching, and the control of indentation morphology were used to isolate the structural features that limit optical damage. A thin defect layer on fracture surfaces, including those smaller than the wavelength of visible light, was found to be the dominant source of laser damage initiation during illumination with 355 nm, 3 ns laser pulses. Little evidence was found that either displaced or densified material or fluence intensification plays a significant role in optical damage at fluences >35 J/cm(2). Elimination of the defect layer was shown to increase the overall damage performance of fused silica optics.

Changes in the relative amounts of endogenous and exogenous fatty acids in sebaceous lipids during early adolescence.

Skin surface lipid samples were collected from the scalps of 40 males, aged 9-15, and the lipid class composition of each was analyzed by quantitative thin layer chromatography. The ratio of wax esters/[cholesterol + cholesterol esters] (WE/[CH + CE]) increased with age. The wax ester, cholesterol ester, triglyceride, and free fatty acid classes were isolated from each sample and the fatty acid compositions were determined by capillary gas chromatography of fatty acid methyl esters (FAME) prepared from each lipid class. The concentrations of most of the different types of fatty acids were found to be correlated with the WE/[CH + CE] ratio. Those straight chain fatty acids that are thought to be synthesized mainly within the sebaceous glands, such as 14:0, 14:1, 16:1, and 18:2 delta 5, 8 tended to increase with increasing WE/[CH + CE], while fatty acids which circulate in the blood, such as 18:0, 18:1, and 18:2 delta 9, 12, tended to decrease with increasing WE/[CH + CE]. For the majority of straight chain fatty acid types, the data could be fitted to the equation y = a + b/[x + 1], which can be derived from simple assumptions concerning the origins of the various sebum components. The FAME from the wax esters were separated into saturated and monounsaturated fractions and analyzed by capillary gas chromatography to determine the concentrations of the different types of branched chain FAME present. In the wax esters, straight chain fatty acids tended to increase with increasing WE/[CH + CE], while terminally branched (iso and anteiso) fatty acids tended to decrease. Other branched chain fatty acids increased up to a WE/[CH + CE] ratio of about 2 and then decreased at higher ratios.

Effects of pharmacological autonomic blockade upon cardiac rate and blood pressure conditioned and unconditioned responses in Macaca mulatta.

Heart rate, systolic and diastolic blood pressures were recorded during classical delay conditioning of rhesus macaque monkeys. When portions of the autonomic nervous system were selectively blocked by pharmacological agents, it appeared that the initial increases in heart rate and blood pressures in response to the conditioned stimulus were the result of increased sympathetic activity and a concomitant decrease in parasympathetic activity. Towards the end of the conditioned stimulus, an increase in parasympathetic activity was indicated. Blockade of the autonomic system which produced total elimination of the conditioned cardiac rate response and substantial reduction or elimination of the conditioned blood pressure response, was not necessarily or always accompanied by a corresponding elimination of the respective unconditioned responses. Such a finding suggests a different underlying neural mediation of these conditioned and unconditioned responses.

Classical conditioning of heart rate and blood pressure in Macaca mulatta.

Classical delay conditioning of heart rate, and of systolic and diastolic blood pressures, was carried out in 16 rhesus monkeys. Blood pressure and inter-systolic interval were measured from an in-dwelling arterial catheter; recordings were taken prior to conditioned stimulus (CS) on each trial, during a 20 sec visual stimulus that filled the conditioned-unconditioned stimulus (CS-UCS) interval, and following UCS (a brief electric tail-shock). The heart rate response both to CS and to UCS was biphasic (acceleration followed by deceleration); the blood pressure response functions were more complex, and were different for the CS and post-UCS periods. Comparison of the patterns of cardiac and blood pressure responses on any trial indicates a possible sequence of baroreceptor reflex activity.