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San Antonio, TX, United States

Hokr B.H.,Texas A&M University | Hokr B.H.,TASC Inc | Bixler J.N.,Texas A&M University | Elpers G.,Nanohmics, Inc. | And 6 more authors.
CLEO: QELS - Fundamental Science, CLEO_QELS 2015 | Year: 2015

simple method for accurately simulating focusing beams, which obey Gaussian optics, in the context of traditional Monte Carlo simulations is presented. This technique will allow rapid implementation into existing Monte Carlo codes. © OSA 2015. Source

Bixler J.N.,Optical Radiation Branch | Hokr B.H.,Texas A&M University | Winblad A.,ENGILITY | Elpers G.,Nanohmics, Inc. | And 2 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2016

Monte Carlo simulations are widely considered to be the gold standard for studying the propagation of light in turbid media. However, due to the probabilistic nature of these simulations, large numbers of photons are often required in order to generate relevant results. Here, we present methods for reduction in the variance of dose distribution in a computational volume. Dose distribution is computed via tracing of a large number of rays, and tracking the absorption and scattering of the rays within discrete voxels that comprise the volume. Variance reduction is shown here using quasi-random sampling, interaction forcing for weakly scattering media, and dose smoothing via bi-lateral filtering. These methods, along with the corresponding performance enhancements are detailed here. © 2016 SPIE. Source

Schmidt M.S.,Optical Radiation Branch | Kennedy P.K.,Optical Radiation Branch | Vincelette R.L.,TASC Inc | Denton M.L.,TASC Inc | And 4 more authors.
Journal of Biomedical Optics | Year: 2014

Thresholds for microcavitation of bovine and porcine melanosomes were determined using nanosecond laser pulses in the near-infrared (1000 to 1319 nm) wavelength regime. Isolated melanosomes were irradiated by single pulses (10 or 50 ns) using a Q-switched Spectra Physics Nd:YAG laser coupled with an optical parametric oscillator (1000 to 1200 nm) or a continuum laser at 1319 nm. Time-resolved nanosecond strobe photography after the arrival of the irradiation beam allowed imaging of microcavitation events. Average fluence thresholds for microcavitation increased nonlinearly with increasing wavelength from ~0.5 J/cm2 at 1000 nm to 2.6 J/cm2 at 1319 nm. Fluence thresholds were also measured for 10-ns pulses at 532 nm and found to be comparable to visible nanosecond pulse values published in previous reports. Calculated melanosome absorption coefficients decreased from 925 cm-1 at 1000 nm to 176 cm-1 at 1319 nm. This trend was found to be comparable to the decrease in retinal pigmented epithelial layer absorption coefficients reported over the same wavelength region. Estimated corneal total intraocular energy retinal damage threshold values were determined in order to compare to current and proposed maximum permissible exposure (MPE) safe levels. Results from this study support recently proposed changes to the MPE levels. © The Authors. Source

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