Three-dimensional modeling of electric-field enhancement in multilayer dielectric gratings arising from inadvertent flaws.

Pulse-compression gratings for high-power, short-pulse laser systems are exposed to high electric fields that are further enhanced locally due to their 2D nanostructured surface. This makes them vulnerable to laser-induced damage. The present work considers the effect on electric-field modulation caused by an array of commonly found inadvertent flaws in gratings including fabrication defects, contamination particles, and laser-induced-damage initiation. These defects affect the laser-damage performance characteristics of the grating. To understand the local field-enhancement distribution due these imperfections, 3D modeling of the electric-field distribution is performed with a sufficiently high resolution of 1/74 of the laser wavelength (λ) while considering a volume of ≈489 λ3. The results provide estimates for the ensuing electric-field intensification and projected reduction of the laser-damage thresholds, as well as the anticipated pattern of damage growth initiation.

Manufacturing-induced contamination in common multilayerdielectric gratings.

Contamination of pulse compression gratings during the manufacturing process is known to give rise to reduced laser damage performance and represents an issue that has not yet been adequately resolved. The present work demonstrates that the currently used etching methods introduce carbon contamination inside the etched region extending to a 50- to 80-nm layer below the surface. This study was executed using custom samples prepared in both, a laboratory setting and by established commercial vendors, showing results that are very similar. The laser-induced-damage performance of the etched and unetched regions in the grating-like samples suggest that contaminants introduced by etching process are contributing to the reduction of the laser-induced damage threshold.

Arizona Study of Aging and Neurodegenerative Disorders and Brain and Body Donation Program.

The Brain and Body Donation Program (BBDP) at Banner Sun Health Research Institute (http://www.brainandbodydonationprogram.org) started in 1987 with brain-only donations and currently has banked more than 1600 brains. More than 430 whole-body donations have been received since this service was commenced in 2005. The collective academic output of the BBDP is now described as the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND). Most BBDP subjects are enrolled as cognitively normal volunteers residing in the retirement communities of metropolitan Phoenix, Arizona. Specific recruitment efforts are also directed at subjects with Alzheimer's disease, Parkinson's disease and cancer. The median age at death is 82. Subjects receive standardized general medical, neurological, neuropsychological and movement disorders assessments during life and more than 90% receive full pathological examinations by medically licensed pathologists after death. The Program has been funded through a combination of internal, federal and state of Arizona grants as well as user fees and pharmaceutical industry collaborations. Subsets of the Program are utilized by the US National Institute on Aging Arizona Alzheimer's Disease Core Center and the US National Institute of Neurological Disorders and Stroke National Brain and Tissue Resource for Parkinson's Disease and Related Disorders. Substantial funding has also been received from the Michael J. Fox Foundation for Parkinson's Research. The Program has made rapid autopsy a priority, with a 3.0-hour median post-mortem interval for the entire collection. The median RNA Integrity Number (RIN) for frozen brain and body tissue is 8.9 and 7.4, respectively. More than 2500 tissue requests have been served and currently about 200 are served annually. These requests have been made by more than 400 investigators located in 32 US states and 15 countries. Tissue from the BBDP has contributed to more than 350 publications and more than 200 grant-funded projects.

Monolayer organic thin films as particle-contamination-resistant coatings.

Three organic monolayers coatings were developed and tested for their effectiveness to increase cleaning efficiency of attached microscale particles by air flows. The experiments were performed using silica substrates coated with these organic thin films and subsequently exposed to stainless-steel and silica microparticles as a model of contamination. Laser-induced-damage tests confirmed that the coatings do not affect the laser-induced-damage threshold values. The particle exposure results suggest that although the accumulation of particles is not significantly affected under the experimental conditions used in this work, the coated substrates exhibit significantly improved cleaning efficiency with a gas flow. A size-distribution analysis was conducted to study the adsorption and cleaning efficiency of particles of different sizes. It was observed that larger size (> 5-µm) particles can be removed from coated substrates with almost 100% efficiency. It was also determined that the coatings improve the cleaning efficiency of the smaller particles (≤ 5 µm) by 17% to 30% for the stainless steel metal and 19% to 38% for the silica particles.

Performance characterization of freeform finished surfaces of potassium dihydrogen phosphate using fluid jet polishing with a nonaqueous slurry.

Potassium dihydrogen phosphate (KDP) and its deuterated analog (DKDP) are unique nonlinear optical materials for high power laser systems. They are used widely for frequency conversion and polarization control by virtue of the ability to grow optical-quality crystals at apertures suitable for fusion-class laser systems. Existing methods for freeform figuring of KDP/DKDP optics do not produce surfaces with sufficient laser-induced-damage thresholds (LIDT's) for operation in the ultraviolet portion of high-peak-power laser systems. In this work, we investigate fluid jet polishing (FJP) using a nonaqueous slurry as a sub-aperture finishing method for producing freeform KDP surfaces. This method was used to selectively polish surface areas to different depths on the same substrate with removals ranging from 0.16 µm to 5.13 µm. The finished surfaces demonstrated a slight increase in roughness as the removal depth increased along with a small number of fracture pits. Laser damage testing with 351 nm, 1 ns pulses demonstrated excellent surface damage thresholds, with the highest values in areas devoid of fracture pits. This work demonstrates, for the first time, a method that enables fabrication of a waveplate that provides tailored polarization randomization that can be scaled to meter-sized optics. Furthermore, this method is based on FJP technology that incorporates a nonaqueous slurry specially designed for use with KDP. This novel nonaqueous FJP process can be also used for figuring other types of materials that exhibit similar challenging inherent properties such as softness, brittleness, water-solubility, and temperature sensitivity.

Increased Risk of Autopsy-Proven Pneumonia with Sex, Season and Neurodegenerative Disease.

There has been a markedly renewed interest in factors associated with pneumonia, a leading cause of death worldwide, due to its frequent concurrence with pandemics of influenza and Covid-19 disease. Reported predisposing factors to both bacterial pneumonia and pandemic viral lower respiratory infections are wintertime occurrence, older age, obesity, pre-existing cardiopulmonary conditions and diabetes. Also implicated are age-related neurodegenerative diseases that cause parkinsonism and dementia. We investigated the prevalence of autopsy-proven pneumonia in the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND), a longitudinal clinicopathological study, between the years 2006 and 2019 and before the beginning of the Covid-19 pandemic. Of 691 subjects dying at advanced ages (mean 83.4), pneumonia was diagnosed postmortem in 343 (49.6%). There were 185 subjects without dementia or parkinsonism while clinicopathological diagnoses for the other subjects included 319 with Alzheimer's disease dementia, 127 with idiopathic Parkinson's disease, 72 with dementia with Lewy bodies, 49 with progressive supranuclear palsy and 78 with vascular dementia. Subjects with one or more of these neurodegenerative diseases all had higher pneumonia rates, ranging between 50 and 61%, as compared to those without dementia or parkinsonism (40%). In multivariable logistic regression models, male sex and a non-summer death both had independent contributions (ORs of 1.67 and 1.53) towards the presence of pneumonia at autopsy while the absence of parkinsonism or dementia was a significant negative predictor of pneumonia (OR 0.54). Male sex, dementia and parkinsonism may also be risk factors for Covid-19 pneumonia. The apolipoprotein E4 allele, as well as obesity, chronic obstructive pulmonary disease, diabetes, hypertension, congestive heart failure, cardiomegaly and cigarette smoking history, were not significantly associated with pneumonia, in contradistinction to what has been reported for Covid-19 disease.

Mechanisms of picosecond laser-induced damage in common multilayer dielectric coatings.

The physical mechanisms and ensuing material modification associated with laser-induced damage in multilayer dielectric high reflectors is investigated for pulses between 0.6 and 100 ps. We explore low-loss multilayer dielectric SiO2/HfO2 mirrors which are commonly employed in petawatt-class laser systems. The spatial features of damage sites are precisely characterized, enabling the direct correlation of the observed damage morphology to the location of energy deposition and the corresponding standing-wave electric-field intensities within the layer structure. The results suggest that there are three discrete damage-initiation morphologies arising from distinctly different mechanisms: the first prevailing at laser pulse lengths shorter than about 2.3 ps, while the other two are observed for longer pulses. Modeling of the thermomechanical response of the material to localized laser-energy deposition was performed for each type of damage morphology to better understand the underlying mechanisms of energy deposition and subsequent material response.

Tau immunoreactivity in peripheral tissues of human aging and select tauopathies.

Many studies have been directed at understanding mechanisms of tau aggregation and therapeutics, nearly all focusing on the brain. It is critical to understand the presence of tau in peripheral tissues since this may provide new insights into disease progression and selective vulnerability. The current study sought to determine the presence of select tau species in peripheral tissues in elderly individuals and across an array of tauopathies. Using formalin fixed paraffin embedded sections, we examined abdominal skin, submandibular gland, and sigmoid colon among 69 clinicopathologically defined cases: 19 lacking a clinical neuropathological diagnosis (normal controls), 26 progressive supranuclear palsy (PSP), 21 Alzheimer's disease (AD), and 3 with corticobasal degeneration (CBD). Immunohistochemistry was performed using antibodies for "total" tau (HT7) and two phosphorylated tau species (AT8 and pT231). HT7 staining of abdominal skin revealed immunoreactivity of potential nerve elements in 5% of cases (1 AD, 1 AD/PSP, and 1 CBD out of 55 cases examined); skin sections lacked AT8 and pT231 immunoreactive nerve elements. Submandibular glands from all cases had HT7 immunoreactive nerve elements; while pT231 was present in 92% of cases, and AT8 in only 3 cases (2 AD and one AD/PSP case). In sigmoid colon, HT7 immunoreactivity was present in all but 2 cases (97%), pT231 in 54%, and AT8 was present in only 5/62 cases (8%). These data suggest select tau species in CNS tauopathies do not have a high propensity to spread to the periphery and this may hold clues for the understanding of CNS tau pathogenicity and vulnerability.

Prevalence of Submandibular Gland Synucleinopathy in Parkinson's Disease, Dementia with Lewy Bodies and other Lewy Body Disorders.

BACKGROUND: Clinical misdiagnosis, particularly at early disease stages, is a roadblock to finding new therapies for Lewy body disorders. Biopsy of a peripheral site might provide improved diagnostic accuracy. Previously, we reported, from both autopsy and needle biopsy, a high prevalence of submandibular gland synucleinopathy in Parkinson's disease (PD). Here, we report on an extension of these studies to subjects with dementia with Lewy bodies (DLB) and other Lewy body disorders in 228 autopsied subjects from the Arizona Study of Aging and Neurodegenerative Disorders. OBJECTIVE: To provide an estimate of the prevalence of histological synucleinopathy in the submandibular glands of subjects with PD and other Lewy body disorders. METHODS: Submandibular gland sections from autopsied subjects were stained with an immunohistochemical method for α-synuclein phosphorylated at serine 129. Included were 146 cases with CNS Lewy-type synucleinopathy (LTS), composed of 46 PD, 28 DLB, 14 incidental Lewy body disease (ILBD), 33 Alzheimer's disease with Lewy bodies (ADLB) and 2 with progressive supranuclear palsy and Lewy bodies (PSPLB). Control subjects included 79 normal elderly, 15 AD, 12 PSP, 2 conticobasal degeneration (CBD) and 2 multiple system atrophy (MSA). RESULTS: Submandibular gland LTS was found in 42/47 (89%) of the PD subjects, 20/28 (71%) DLB, 4/33 (12%) ADLB and 1/9 (11%) ILBD subjects but none of the 110 control subjects. CONCLUSIONS: These results provide support for further clinical trials of in vivo submandibular gland diagnostic biopsy for PD and DLB. An accurate peripheral biopsy diagnosis would assist subject selection for clinical trials and could also be used to verify other biomarkers.