Abstract. 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∕cm 2 at 1000 nm to 2.6 J∕cm 2 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.
Currently, no light source exists which is both narrow-band and speckle-free with sufficient brightness for full-field imaging applications. Light emitting diodes (LEDs) are excellent spatially incoherent sources, but are tens of nanometers broad. Lasers on the other hand can produce very narrow-band light, but suffer from high spatial coherence which leads to speckle patterns which distort the image. Here we propose the use of random Raman laser emission as a new kind of light source capable of providing short-pulsed narrow-band speckle-free illumination for imaging applications.
Abstract. Thresholds for microcavitation of bovine and porcine melanosomes were previously reported, using single nanosecond (ns) laser pulses in the visible (532 nm) and the near-infrared (NIR) from 1000 to 1319 nm. Here, we report average radiant exposure thresholds for bovine melanosome microcavitation at additional NIR wavelengths up to 1540 nm, which range from ∼0.159 J∕cm 2 at 800 nm to 4.5 J∕cm 2 at 1540 nm. Melanosome absorption coefficients were also estimated, and decreased with increasing wavelength. These values were compared to retinal pigment epithelium coefficients, and to water absorption, over the same wavelength range. Corneal total intraocular energy retinal damage threshold values were estimated and compared to the previous (2007) and recently changed (2014) maximum permissible exposure (MPE) safe levels. Results provide additional data that support the recent changes to the MPE levels, as well as the first microcavitation data at 1540 nm, a wavelength for which melanosome microcavitation may be an ns-pulse skin damage mechanism. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
Identifying and implementing techniques for carbon management has become an important endeavor in the mitigation of global climate change. Two important techniques being pursued are geologic and terrestrial carbon sequestration. With regard to terrestrial sequestration, in order to accurately monitor changes in soil carbon potentially induced by sequestration practices, rapid, cost-effective, and accurate measurements must be developed. Spark-induced breakdown spectroscopy (SIBS) has the potential to be used as a field-deployable method to monitor changes in the concentration of carbon in soil. SIBS spectra in the 248 nm region of eight soils were collected, and the neutral carbon line at 247.85 nm was compared to total carbon concentration determined by standard dry combustion techniques. Additionally, Fe and Si emission lines were evaluated in a multivariate statistical model to evaluate their impacts on the model's predictive power for total carbon concentrations. The preliminary results indicate that SIBS is a viable method to quantify total carbon levels in soils, obtaining a correlation of (R(2)=0.972) between measured and predicated carbon in soils. These results show that multivariate analysis can be used to construct a calibration model for SIBS soil spectra.
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