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Advances in fiber laser technology have resulted in the increased use and availability of several high-power laser systems operating in the mid-infrared band with short switching times and high modulation rates. The current American National Standard for the Safe Use of Lasers (ANSI Z136.1-2014) defines the calculation of the maximum permissible exposure (MPE) on the skin in terms of the exposure duration a single pulse or the total exposure time limit, and is based on continuous-wave laser skin exposure minimum visible lesion (MVL) data. This study determined the MVL data thresholds in Yucatan miniature pig skin for multiple-pulse 1940-nm laser exposures with pulse repetition frequencies (PRFs) of 100, 200, and 1000 Hz, and trains of 300, 1000, or 3000 pulses. The individual pulse duration in each exposure train was 500 µs. We report the MVL thresholds as the median effective dose (ED50) based on varying individual pulse energy. The results highlight the effect of PRF on the thresholds for multiple-pulse cases. Comparison with the existing ANSI Z136.1 MPE limits provides a calculation of the safety margin for each parameter case.

Pulsed high-energy lasers operating in the near-infrared (NIR) band are increasingly being used in medical, industrial, and military applications, but there are little available experimental data to characterize their hazardous effects on skin tissue. The current American National Standard for the Safe Use of Lasers (ANSI Z136.1-2014) defines the maximum permissible exposure (MPE) on the skin as either a single-pulse or total exposure time limit. This study determined the minimum visible lesion (MVL) damage thresholds in Yucatan miniature pig skin for the single-pulse case and several multiple-pulse cases over a wide range of pulse repetition frequencies (PRFs) (10, 125, 2,000, and 10,000 Hz) utilizing nanosecond-scale pulses (10 or 60 ns). The thresholds are expressed in terms of the median effective dose (ED50) based on varying individual pulse energy with other laser parameters held constant. The results confirm a decrease in MVL threshold as PRF increases for exposures with a constant number of pulses, while also noting a PRF-dependent change in the threshold as a function of the number of pulses. Furthermore, this study highlights a change in damage mechanism to the skin from melanin-mediated photomechanical events at high irradiance levels and few numbers of pulses to bulk tissue photothermal additivity at lower irradiance levels and greater numbers of pulses. The observed trends exceeded the existing exposure limits by an average factor of 9.1 in the photothermally-damaged cases and 3.6 in the photomechanicallydamaged cases.

Laser-induced microcavitation refers to the rapid formation and expansion of a vapor bubble inside the bio-tissue when it is exposed to intense, pulsed laser energy. With the associated microscale dissection occurring within the tissue, laserinduced microcavitation is a common approach for high precision bio-surgeries. For example, laser-induced microcavitation is used for laser in-situ keratomileusis (LASIK) to precisely reshape the midstromal corneal tissue through excimer laser beam. Multiple efforts over the last several years have observed unique characteristics of microcavitions in biotissues. For example, it was found that the threshold energy for microcavitation can be significantly reduced when the size of the biostructure is increased. Also, it was found that the dynamics of microcavitation are significantly affected by the elastic modules of the bio-tissue. However, these efforts have not focused on the early events during microcavitation development. In this study, a direct numerical simulation of the microcavitation process based on equation of state of the biotissue was established. With the direct numerical simulation, we were able to reproduce the dynamics of microcavitation in water-rich bio tissues. Additionally, an experimental setup in deionized water and 10% PAA gel was made to verify the results of the simulation for early micro-cavitation formation for 10% Polyacrylamide (PAA) gel in deionized water.

A numerical analysis capable of describing the early stage of a thermal microcavitation process in a water-rich biotissue without avalanche breakdown was developed. The analysis successfully reproduced the laser-induced heating, vapor bubble formation, bubble expansion, and shockwave propagation inside a water-rich biotissue during a thermal microcavitation process. Based on the analysis, it was determined that the evolution of the temperature, pressure, and laser-induced shockwave is dependent on the incident laser energy and laser pulse width. On the other hand, the early stage dynamics of the microcavitation process showed little dependence on the elastic modulus of the biotissue for the laser and tissue conditions studied.

Melanosome microcavitation is the threshold-level retinal pigment epithelium (RPE) damage mechanism for nanosecond (ns) pulse exposures in the visible and near-infrared (NIR). Thresholds for microcavitation of isolated bovine RPE melanosomes were determined as a function of temperature (20 to 85°C) using single ns laser pulses at 532 and 1064 nm. Melanosomes were irradiated using a 1064-nm Q-switched Nd:YAG (doubled for 532-nm irradiation). For comparison to melanosome data, a similar temperature (20 to 65°C) dependence study was also performed for 532 nm, ns pulse exposures of black polystyrene microbeads. Results indicated a decrease in the microcavitation average radiant exposure threshold with increasing sample temperature for both 532- and 1064-nm single pulse exposures of melanosomes and microbeads. Threshold data and extrapolated nucleation temperatures were used to estimate melanosome absorption coefficients in the visible and NIR, and microbead absorption coefficients in the visible, indicating that melanin is a better absorber of visible light than black polystyrene. The NIR melanosome absorption coefficients ranged from 3713 cm−1 at 800 nm to 222 cm−1 at 1319 nm. These data represent the first temperature-dependent melanosome microcavitation study in the NIR and provide additional information for understanding melanosome microcavitation threshold dependence on wavelength and ambient temperature.

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.

Thresholds for microcavitation of isolated bovine retinal melanosomes were determined as a function of temperature using single nanosecond laser pulses at 532 nm and 1064 nm. Melanosomes were irradiated using a 1064-nm Qswitched Nd:YAG (doubled for 532-nm irradiation). Time-resolved microscopy was accomplished by varying the delay between the irradiation beam and an illumination beam allowing stroboscopic imaging of microcavitation events. Results indicated a decrease in microcavitation fluence threshold with increasing sample temperature for both 532-nm and 1064-nm single pulse exposures. The nucleation temperature at both wavelengths was extrapolated through the linear relationship between the temperature increases and the decrease in fluence threshold. In addition, absorption coefficients of melanosomes for visible and near-infrared wavelengths were estimated using the calculated nucleation temperatures.

Random Raman laser emission is demonstrated to be an excellent source of narrow-band, high intensity, short duration light for speckle-free imaging. Spatial coherence measurement and strobe photography of cavitation bubbles are presented.

Recent changes in the maximum permissible exposure limits (MPE) for near-infrared (NIR) laser exposures are analysed in light of nonlinear optical phenomena. We have evaluated the thresholds for supercontinuum generation for ultrashort laser exposures in the NIR and compared these with the MPE’s. Because of the strong increase in ocular absorption in the 1.2 to 1.4 micrometer range, evaluation of this phenomenon is necessary because any shift in laser energy in the eye to shorter wavelengths could lead to unforeseen increases in hazards for the retina. Trends will be discussed regarding proposed changes to the safe exposure limits in the NIR regime.

Thresholds for microcavitation of isolated bovine and porcine melanosomes were determined using single nanosecond (ns) laser pulses in the NIR (1000 – 1319 nm) wavelength regime. Average fluence thresholds for microcavitation increased non-linearly with increasing wavelength. Average fluence thresholds were also measured for 10-ns pulses at 532 nm, and found to be comparable to visible ns pulse values published in previous reports. Fluence thresholds were used to calculate melanosome absorption coefficients, which decreased with increasing wavelength. This trend was found to be comparable to the decrease in retinal pigmented epithelial (RPE) layer absorption coefficients reported over the same wavelength region. Estimated corneal total intraocular energy (TIE) values were determined and compared to the current and proposed maximum permissible exposure (MPE) safe exposure levels. Results from this study support the proposed changes to the MPE levels.

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.

In the field of laser bioeffects, the type of cellular damage induced depends on the laser wavelength and exposure duration. In the nanosecond (ns) to microsecond (μs) regime, melanin microcavitation is known to be the damage mechanism responsible for retinal threshold lesions. This process has been studied for visible and near-infrared (NIR) wavelengths out to 1.06 micrometer (μm), for ns to ps laser exposures. We expanded this investigation regime by exposing melanin granules to nanosecond pulses in the 1.06 to 1.4-μm range to look at the trend in microcavitation threshold. We used strobe microphotography to determine when microcavitation bubbles were created with varying wavelength and pulse energy. These trends are discussed in light of the proposed changes to the safe exposure limits in the NIR regime.In the field of laser bioeffects, the type of cellular damage induced depends on the laser wavelength and exposure duration. In the nanosecond (ns) to microsecond (μs) regime, melanin microcavitation is known to be the damage mechanism responsible for retinal threshold lesions. This process has been studied for visible and near-infrared (NIR) wavelengths out to 1.06 micrometer (μm), for ns to ps laser exposures. We expanded this investigation regime by exposing melanin granules to nanosecond pulses in the 1.06 to 1.4-μm range to look at the trend in microcavitation threshold. We used strobe microphotography to determine when microcavitation bubbles were created with varying wavelength and pulse energy. These trends are discussed in light of the proposed changes to the safe exposure limits in the NIR regime.

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.

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 addi- tional 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

We present preliminary results that show good correlation between elemental compositions of three bioaerosol samples, as measured in the laboratory by combustion analysis and with proton-induced x-ray emission and spark-induced breakdown spectroscopy signals integrated over the entire emission time profiles. Atomic (Ca, Al, Fe, and Si) and molecular features (CN, N2 +, and OH) were observed compared to the laboratory data.