Laser energy absorption prediction of silicon substrate surface from a mid- and high-spatial frequency error.

Additional laser energy absorption of optical elements limits the further development of high-energy laser systems. In engineering, inexpensive and precise absorption test technology is essential. We attempt to predict energy absorption via surface spatial error value based on the roughness-induced absorption (RIA) theory. However, the absorption coefficients cannot match roughness values measured with an atomic force microscope or white light interferometer. We find three influencing factors and optimize the definition of RIA to spatial error-induced absorption (SEIA). SEIA is proportional to δ2 of a mid- and high-spatial frequency error in a certain frequency range. This range depends on laser diameter, wavelength, and coating. Excluding the absorption induced by fabrication defects, the total absorption can be classified into SEIA and background absorption (BGA). BGA is decided by material and process technology, which can be obtained by calculations. The sum of SEIA and BGA is predictable because both can be estimated. The substrate absorption of high-energy optics can be semi-quantificationally predicted. SEIA provides a new angle to research element-absorbed laser energy for high-power laser technologies.

Enrollment Length, Service Category, and HIV Health Outcomes Among Low-Income HIV-Positive Persons Newly Enrolled in a Housing Program, New York City, 2014-2017.

Objectives. To evaluate the impact of duration and service category on HIV health outcomes among low-income adults living with HIV and enrolled in a housing program in 2014 to 2017.Methods. We estimated relative risk of engagement in care, viral suppression, and CD4 improvement for 561 consumers at first and second year after enrollment to matched controls through the New York City HIV surveillance registry, by enrollment length (enrolled for more than 1 year or not) and service category (housing placement assistance [HPA], supportive permanent housing [SPH], and rental assistance [REN]).Results. The SPH and REN consumers were enrolled longer and received more services, compared with HPA consumers. Long-term SPH and REN consumers had better engagement in care, viral suppression, and CD4 count than controls at both first and second year after enrollment, but the effect did not grow bigger from year 1 to 2. HPA consumers did not have better outcomes than controls regardless of enrollment length.Conclusions. Longer enrollment with timely housing placement and a higher number and more types of services are associated with better HIV health outcomes for low-income persons living with HIV with unmet housing needs.

Housing Subsidies and Housing Stability are Associated with Better HIV Medical Outcomes Among Persons Who Experienced Homelessness and Live with HIV and Mental Illness or Substance Use Disorder.

Among 958 applicants to a supportive housing program for low-income persons living with HIV (PLWH) and mental illness or a substance use disorder, we assessed impacts of housing placement on housing stability, HIV care engagement, and viral suppression. Surveillance and administrative datasets provided medical and residence information, including stable (e.g., rental assistance, supportive housing) and unstable (e.g., emergency shelter) government-subsidized housing. Sequence analysis identified a "quick stable housing" pattern for 67% of persons placed by this program within 2 years, vs. 28% of unplaced. Compared with unplaced persons not achieving stable housing quickly, persons quickly achieving stable housing were more likely to engage in care, whether placed (per Poisson regression, ARR: 1.14;95% CI 1.09-1.20) or unplaced (1.19;1.13-1.25) by this program, and to be virally suppressed, whether placed (1.22;1.03-1.44) or unplaced (1.26, 1.03-1.56) by this program. Housing programs can help homeless PLWH secure stable housing quickly, manage their infection, and prevent transmission.

RESUMEN: Unas 958 personas de bajos recursos y quienes viven con VIH y enfermedades mentales o bien presentan problemas de abuso de sustancias solicitaron a un programa de vivienda complementada con servicios de apoyo. Entre ellas, se evaluó los impactos de la colocación en viviendas sobre la estabilidad en la misma, así como la participación en los cuidados médicos para el VIH, y la supresión de la carga viral. Las bases de datos administrativas y del registro de vigilancia brindaron información médica y domiciliar, incluyendo información sobre vivienda estable (por ejemplo, asistencia de pago de renta a largo plazo, o vivienda complementada con servicios de apoyo) y vivienda inestable (por ejemplo, alojamiento de emergencia temporal) subsidiada por el gobierno. El método "análisis de secuencia" permitió identificar una pauta caracterizada por estabilidad domiciliar conseguida de modo ligero (es decir, de forma oportuna) en el 67% de las personas quienes fueron colocadas por este programa dentro de un lapso de dos años, comparado con 28% de las personas quienes no fueron colocadas. En comparación con las personas quienes no fueron colocadas y no lograron estabilidad de vivienda de modo ligero, las personas quienes lograron estabilidad de vivienda de modo ligero tuvieron una mayor probabilidad de participar en cuidados médicos, ya sea que fueran colocadas (según regresión de Poisson, cociente de riesgo ajustado: 1.14; intervalo de confianza de 95%: 1.09-1.20) o no fueran colocadas (1.19, 1.13-1.25) por este programa, así como de lograr la supresión de la carga viral, ya sea que fueran colocadas (1.22, 1.03-1.44) o no fueran colocadas (1.26, 1.03-1.56) por este programa. Los programas que facilitan la colocación en o el pago de vivienda y apoyo en el mismo pueden ayudar a las personas con VIH y sin hogar obtener vivienda estable de modo ligero, controlar su infección, y prevenir la transmisión.

Detailed near-surface nanoscale damage precursor measurement and characterization of fused silica optics assisted by ion beam etching.

Near-surface nanoscale damage precursor generated from the fabrication process has great influence on laser-induced damage threshold improvement of fused silica. In this work, high-resolution transmission electron microscopy (HRTEM) is used to characterize the arrangement of material particles near surface. The nanoscale defects in the Beilby layer could be clearly distinguished. And we find ion beam etching (IBE) has little effect on the arrangement of material particles. This microscopic phenomenon makes IBE a promising technique for the detection of nanoscale near-surface damage precursors. To further investigate the nanoscale near-surface damage after chemical mechanical polishing, a trench is generated by ion sputtering to contain the nature and characteristics of nanoscale precursors in different depths. The evolutions of chemical structure defects and nanoparticles are measured and their laser-induced absorption performance are tested. The results show that there is a nanoscale defect layer (~360nm) beneath the Beilby layer. A model for nanoscale defect layer of fused silica after CMP is offered. In the model, the quantitative density of nanoparticles falls exponentially with increasing the depth and the contents of ODC and NBOHC decreases linearly, respectively. Research results can be a reference on characterizing nanoscale defects near surface and conducting post-processing technologies to improve the laser damage resistance property of fused silica.

A Randomized Controlled Trial of a Rapid Re-housing Intervention for Homeless Persons Living with HIV/AIDS: Impact on Housing and HIV Medical Outcomes.

We conducted a randomized controlled trial to determine whether, for homeless persons living with HIV/AIDS (PLWHA), rapid re-housing can improve housing and HIV viral suppression more than standard housing assistance. We recruited 236 PLWHA from HIV emergency housing in New York City (NYC) and randomized them to: (1) Enhanced Housing Placement Assistance (EHPA), i.e., immediate assignment to a case manager to rapidly re-house the client and provide 12 months of case management or (2) usual services, i.e., referral to an NYC housing placement program for which all HIV emergency housing residents were eligible. We compared time to stable housing placement and percentage virally suppressed from baseline to 12 months. EHPA clients were placed faster than usual services clients (p = 0.02; 25% placed by 150 days vs. 243 days, respectively), more likely to be placed [adjusted hazards ratio = 1.8; 95% confidence interval(CI) 1.1-2.8], and twice as likely to achieve or maintain suppression (adjusted odds ratio 2.1; 95% CI 1.1-4.0).

Multilevel Factors Associated with a Lack of Viral Suppression Among Persons Living with HIV in a Federally Funded Housing Program.

Persons with HIV who are receiving housing services often have high rates of engagement in care, yet many are not virally suppressed. We linked data from the New York City Housing Opportunities for Persons with AIDS (HOPWA) program to electronically reported laboratory tests from the HIV surveillance registry to examine factors associated with a lack of viral suppression. Of 1491 HOPWA consumers, 523 (35.1%) were not durably suppressed, and 253 (17.0%) were unsuppressed at their last viral load test. Substance use, age < 27 years, and emergency housing all independently predicted lack of durable viral suppression and lack of viral suppression at last viral load test.

Unimorph deformable mirror with an integrated strain feedback layer.

The correction accuracy of a pint-sized unimorph deformable mirror (DM) is significantly influenced by the nonlinear hysteresis error of piezoelectric ceramics, especially in an open-loop state. Moreover, the control bandwidth is also reduced by the nonlinearity. In this paper, we fabricated a three-unit pint-sized unimorph DM with strain gauges integrated on the actuators as a feedback layer for the first time. An experimental platform was built and utilized to test each electrode's strain signal. Testing results show that, under quasi-static condition, the hysteresis curve of the mirror's central displacement is corrected and the hysteresis rate could be reduced from 11% to less than 2% by adopting the strain feedback signal. More specifically, the DM's initial surface, Zernike defocus, together with spherical aberration can also be corrected by this method, and the correction accuracy is improved more than 20% compared to the open-loop state. By introducing a closed-loop control the gaps of the DMs under open loop are supplied. This demonstrates that adding a strain feedback layer is promising to enhance the performance of a unimorph DM.

Laser absorption precursor research: microstructures in the subsurface of mono-crystalline silicon substrate.

In high-energy laser systems, the energy absorption coefficient of silicon optical elements is one of the most critical performance indicators. The absorption coefficient of substrate limits the absorption of the overall elements. Since mono-crystalline silicon is transparent in working wavelength range, the subsurface absorption precursors also influence the entire absorption dramatically. In this paper, the subsurface of a super-polished silicon substrate is exposed by ion beam etching (IBE) as deep as 4.6 µm. In different depth layers, morphology and energy absorption are measured with an atom force microscope and photothermal instrument, respectively. In the 100 nm layer, microstructures are found, and their heights decrease while widths increase with IBE. Finally, structures are diminished below the 1.12 µm layer. Absorption increases with the structures' appearance. When the structures are fully exposed, absorption reaches the peak value, 327.5% of the unremoved surface. Once structures are removed, the absorption value falls down to the lowest point, 67.5%, which verifies that structures influence the absorption significantly. According to the structure depth and energy dispersive spectrometer results, the structures are most likely the densificated micro zones, generated by fabrication processes. In practical fabrication, a subsurface layer of 1.12 µm thick needs to be removed by stress-less processes, to obtain a low-absorption element.

Investigation of surface damage precursor evolutions and laser-induced damage threshold improvement mechanism during Ion beam etching of fused silica.

Surface damage precursor evolution has great influence on laser-induced damage threshold improvement of fused silica surface during Ion beam etching. In this work, a series of ion sputtering experiment are carried out to obtain the evolutions of damage precursors (dot-form microstructures, Polishing-Induced Contamination, Hertz scratches, and roughness). Based on ion sputtering theory, surface damage precursor evolutions are analyzed. The results show that the dot-form microstructures will appear during ion beam etching. But as the ion beam etching depth goes up, the dot-form microstructures can be mitigated. And ion-beam etching can broaden and passivate the Hertz scratches without increasing roughness value. A super-smooth surface (0.238nm RMS) can be obtained finally. The relative content of Fe and Ce impurities both significantly reduce after ion beam etching. The laser-induced damage threshold of fused silica is improved by 34% after ion beam etching for 800nm. Research results can be a reference on using ion beam etching process technology to improve laser-induced damage threshold of fused silica optics.

High-Efficiency Chemical-Mechanical Magnetorheological Finishing for Ultra-Smooth Single-Crystal Silicon.

To improve the material removal efficiency and surface quality of single-crystal silicon after magnetorheological finishing, a novel green chemical-mechanical magnetorheological finishing (CMMRF) fluid was developed. The main components of the CMMRF fluid are nano-Fe3O4, H2O2, CH3COOH, nanodiamond, carbonyl iron powder, and deionized water. The novel CMMRF fluid can simultaneously achieve Ra 0.32 nm (0.47 mm × 0.35 mm measurement area), Ra 0.22 nm (5 µm × 5 µm measurement area), and 1.91 × 10-2 mm3/min material removal efficiency. Comprehensive studies utilizing a scanning electron microscope and a magnetic rheometer show that the CMMRF fluid has a high mechanical removal effect due to the well-dispersed nanodiamond and nano-Fe3O4 particles. The results of Fourier transform infrared spectra and Young's modulus test reveal the mechanism of the chemical reaction and the mechanical characteristics deterioration of the modified layer. Under co-enhanced chemical and mechanical effects, an ultra-smooth and highly efficient MRF technology for single-crystal silicon is realized.

Homelessness and housing assistance among persons with HIV, and associations with HIV care and viral suppression, New York City 2018.

OBJECTIVES: To measure housing assistance and homelessness among persons living with HIV (PLWH) and their association with health. METHODS: Exposure categories were: experiencing homelessness (per emergency shelter use or self-report), receiving housing assistance (per housing subsidy) without homelessness, or neither homelessness nor receiving housing assistance. Outcomes were: engagement (≥1 visit) and retention (≥2 visits ≥90 days apart) in HIV-related medical care and one-time (latest viral load) and durable (≥1 viral load test, all suppressed) HIV viral suppression (<200 copies/mL). Among PLWH in New York City (NYC), we calculated and conducted modified Poisson regressions of the four outcomes according to exposure category. RESULTS: During 2018, 45% of NYC's 84,053 PLWH received housing assistance, and 8% experienced homelessness. Relative to homelessness, receipt of assistance without homelessness was associated with 3-7% higher adjusted relative risk (ARR) of engagement and retention in care and 31-64% higher ARR of one-time and durable viral suppression. Relative to not receiving assistance, receipt of assistance without homelessness was associated with 6-18% higher ARR of care and 2-5% lower ARR of viral suppression. CONCLUSIONS: Programs promoting housing stability may support HIV care and viral suppression, particularly if preventing homelessness. These may help improve HIV care and suppression rates.

Effects of Ion Beam Etching on the Nanoscale Damage Precursor Evolution of Fused Silica.

Nanoscale laser damage precursors generated from fabrication have emerged as a new bottleneck that limits the laser damage resistance improvement of fused silica optics. In this paper, ion beam etching (IBE) technology is performed to investigate the evolutions of some nanoscale damage precursors (such as contamination and chemical structural defects) in different ion beam etched depths. Surface material structure analyses and laser damage resistance measurements are conducted. The results reveal that IBE has an evident cleaning effect on surfaces. Impurity contamination beneath the polishing redeposition layer can be mitigated through IBE. Chemical structural defects can be significantly reduced, and surface densification is weakened after IBE without damaging the precision of the fused silica surface. The photothermal absorption on the fused silica surface can be decreased by 41.2%, and the laser-induced damage threshold can be raised by 15.2% after IBE at 250 nm. This work serves as an important reference for characterizing nanoscale damage precursors and using IBE technology to increase the laser damage resistance of fused silica optics.

Research on the Surface Evolution of Single Crystal Silicon Mirror Contaminated by Metallic Elements during Elastic Jet Polishing Techniques.

Metallic elements can contaminate single crystal silicon mirror during ion beam etching (IBE) and other postprocessing methods, which can affect the performance of components in an infrared laser system. In this work, scanning electron microscope (SEM) and atomic force microscope (AFM) were used to characterize the distribution of contaminant represented by aluminum (Al). After characterizing contaminated area, elastic jet polishing (EJP), EJP, and static alkaline etching (SAE) combined technique were used to process the mirror. The morphology and laser-induced absorption were measured. Results show that metallic elements can mix with silicon and generate bulges due to the sputtering effect. In addition, SAE and EJP combined technique can remove metallic contaminant and stabilize the surface quality. Research results can be a reference on conducting postprocessing technologies to improve laser damage resistance property of single crystal silicon mirror in infrared laser system.