New energy-transfer upconversion process in Er(3+):ZBLAN mid-infrared fiber lasers

Abstract not availableOri Henderson-Sapir, Jesper Munch, and David J. Ottawa

Effect of hydrogen additive on the evolution of beam divergence incopper bromide lasers

©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.We present a systematic study of the effect of hydrogen additive on the beam quality of copper bromide lasers. It is a well-established fact that the addition of small amounts of hydrogen to the neon buffer gas of this class of laser will dramatically increase their average output power and efficiency. Our results show that the partial pressure of hydrogen used to maximize the total output power is not the same as that which optimizes the power density in the drilling plane of a copper bromide laser based micro-machining systemPeter Graham Foster, Peter Eric Davis, Donald McCoy, and Jesper Munc

Persistent Homology of Coarse Grained State Space Networks

This work is dedicated to the topological analysis of complex transitional networks for dynamic state detection. Transitional networks are formed from time series data and they leverage graph theory tools to reveal information about the underlying dynamic system. However, traditional tools can fail to summarize the complex topology present in such graphs. In this work, we leverage persistent homology from topological data analysis to study the structure of these networks. We contrast dynamic state detection from time series using CGSSN and TDA to two state of the art approaches: Ordinal Partition Networks (OPNs) combined with TDA, and the standard application of persistent homology to the time-delay embedding of the signal. We show that the CGSSN captures rich information about the dynamic state of the underlying dynamical system as evidenced by a significant improvement in dynamic state detection and noise robustness in comparison to OPNs. We also show that because the computational time of CGSSN is not linearly dependent on the signal's length, it is more computationally efficient than applying TDA to the time-delay embedding of the time series

Feedback control of thermal lensing in a high optical power cavity

This paper reports automatic compensation of strong thermal lensing in a suspended 80 m optical cavity with sapphire test mass mirrors. Variation of the transmitted beam spot size is used to obtain an error signal to control the heating power applied to the cylindrical surface of an intracavity compensation plate. The negative thermal lens created in the compensation plate compensates the positive thermal lens in the sapphire test mass, which was caused by the absorption of the high intracavity optical power. The results show that feedback control is feasible to compensate the strong thermal lensing expected to occur in advanced laser interferometric gravitational wave detectors. Compensation allows the cavity resonance to be maintained at the fundamental mode, but the long thermal time constant for thermal lensing control in fused silica could cause difficulties with the control of parametric instabilities.This research was supported by the Australian Research Council and the Department of Education, Science and Training and by the U.S. National Science Foundation, through LIGO participation in the HOPF

Stabilization of injection-locked lasers using spatial mode interference

We report the use of spatial-mode-interference, or tilt-locking, for the active stabilization of injection-locking of a Nd:YAG laser. We show that this control scheme is robust and adds negligible frequency noise to the injection-locked laserOttaway, D.J.; Gray, M.B.; Shaddock, D.A.; Hollitt, C.; Veitch, P.J.; Munch, J.; McClelland, David Ernes

Power scalable TEM(oo) CW Nd: YAG laser with thermal lens compensation

We present finite-element analyzes and experimental results to validate our approach for building high-power single-mode Nd:YAG lasers. We show that the thermooptical and thermomechanical properties of a slab laser can be controlled. This is essential for the use of the proposed unstable resonator. We include demonstration of an efficient subscale laser operating at 20 W TEM00.D. Mudge, M. Ostermeyer, P. J. Veitch, J. Munch, B. Middlemiss, D. J. Ottaway and M. W. Hamilto

Green, Yellow, and Red risk perception in everyday life - a communication tool

Background: Adolescents have the highest risk for food allergy-related fatalities. Our main aim was to investigate the level of risk in everyday social situations as perceived by adolescents/young adults with peanut allergy, their families, and their friends. Methods: The web-based ‘Colours Of Risks’ (COR) questionnaire was completed by 70 patients (aged 12–23 years), 103 mothers and fathers, 31 siblings (aged 12–26 years), and 42 friends (aged 12–24 years). COR deals with six main contexts (home, school/university, work, visiting/social activities, special occasions/parties, and vacations), each with 1-12 items. Response categories are green (I feel safe), yellow (I feel uncertain), or red (I feel everything is risky). Results: There was a high level of agreement between participants in defining situations as safe, uncertain, or risky, but female patients and mothers rated fewer situations as safe compared to male patients and fathers. Being with close friends and family, and attending planned parties without alcohol were perceived as situations of low risk. While 94% of patients took an epinephrine auto-injector (EAI) into risky situations, only 65% took it into safe situations. In contrast to the close family, 31% of the friends did not know the patient had an EAI, and fewer knew how to administer the EAI. Conclusion: Young adults with peanut allergy face challenges when moving from the safe home with ready assistance if needed, to independence with unpredictable surroundings and less certain help. Perceived ‘safe’ situations may in fact be the riskiest, as patients often do not take the EAI with them

Quality of life in childhood, adolescence and adult food allergy: patient and parent perspectives

Background: Studies of children with food allergy typically only include the mother and have not investigated the relationship between the amount of allergen needed to elicit a clinical reaction (threshold) and health-related quality of life (HRQL). Our aims were (i) to compare self-reported and parent-reported HRQL in different age groups, (ii) to evaluate the impact of severity of allergic reaction and threshold on HRQL, and (iii) to investigate factors associated with patient-reported and parent-reported HRQL. Methods: Age-appropriate Food Allergy Quality of Life Questionnaires (FAQLQ) were completed by 73 children, 49 adolescents and 29 adults with peanut, hazelnut or egg allergy. Parents (197 mothers, 120 fathers) assessed their child's HRQL using the FAQLQ-Parent form. Clinical data and threshold values were obtained from a hospital database. Significant factors for HRQL were investigated using univariate and multivariate regression. Results: Female patients reported greater impact of food allergy on HRQL than males did. Egg and hazelnut thresholds did not affect HRQL, but lower peanut threshold was associated with worse HRQL. Both parents scored their child's HRQL better than the child's own assessment, but whereas mother-reported HRQL was significantly affected by limitations in the child's social life, father-reported HRQL was affected by limitations in the family's social life. Severity of allergic reaction did not contribute significantly to HRQL. Conclusion: The risk of accidental allergen ingestion and limitations in social life are associated with worse HRQL. Fathers provide a unique perspective and should have a greater opportunity to contribute to food allergy research

A highly efficient computational framework for fast scan-resolved simulations of metal additive manufacturing processes on the scale of real parts

This article proposes a novel high-performance computing approach for the prediction of the temperature field in powder bed fusion (PBF) additive manufacturing processes. In contrast to many existing approaches to part-scale simulations, the underlying computational model consistently resolves physical scan tracks without additional heat source scaling, agglomeration strategies or any other heuristic modeling assumptions. A growing, adaptively refined mesh accurately captures all details of the laser beam motion. Critically, the fine spatial resolution required for resolved scan tracks in combination with the high scan velocities underlying these processes mandates the use of comparatively small time steps to resolve the underlying physics. Explicit time integration schemes are well-suited for this setting, while unconditionally stable implicit time integration schemes are employed for the interlayer cool down phase governed by significantly larger time scales. These two schemes are combined and implemented in an efficient fast operator evaluation framework providing significant performance gains and optimization opportunities. The capabilities of the novel framework are demonstrated through realistic AM examples on the centimeter scale including the first scan-resolved simulation of the entire NIST AM Benchmark cantilever specimen, with a computation time of less than one day. Apart from physical insights gained through these simulation examples, also numerical aspects are thoroughly studied on basis of weak and strong parallel scaling tests. As potential applications, the proposed thermal PBF simulation framework can serve as a basis for microstructure and thermo-mechanical predictions on the part-scale, but also to assess the influence of scan pattern and part geometry on melt pool shape and temperature, which are important indicators for well-known process instabilities

Compensation of Strong Thermal Lensing in High Optical Power Cavities

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plates, and that the cavity mode structure can be maintained by thermal compensation. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.Comment: 8 page