Laser Safety Standards Research Articles

A compact optical sensor for risk assessment from high-power laser scattering

The outdoor operation of multi-kilowatt high-power lasers involves the potential hazard of exposing the human eye and skin to scattered radiation. In present laser safety standards and regulations, the effects of atmospheric off-axis scattering and the dynamic interaction between the laser beam and the target object are not adequately represented. Therefore, experimental studies are dedicated to providing quantitative information on scattered radiation for comprehensive laser safety evaluations. With this end in view, a mobile detection system has been developed that relies on the technical specifications (i.e. entrance aperture and field-of-view) of laser safety regulations. The mobile detection system is deployed at the German Aerospace Center (DLR) laser test range at Lampoldshausen. Atmospheric scattering experiments are performed by placing the calibrated detection system under specified scattering angles relative to the direction of the laser beam and determining the scattered radiation, i.e. absolute values for scattered laser power. In addition, the detection system is used for target scattering experiments. In these experiments, the sensor’s versatility is demonstrated by measuring the specularly and diffusely scattered laser radiation from metallic target objects. The dependence of the scattering power as a function of the scattering angle, distance, and laser output power is investigated during laser-matter interaction to demonstrate the capabilities of the system.

Corneal damage threshold induced by supercontinuum source: A further study.

Previous report shows that corneal spot size is an important influence factor on damage threshold induced by supercontinumm (SC) source. However, damage thresholds were determined for the spot size of only 0.37 mm due to the low output of the employed SC source at that time. The objectives of this study are to determine the lowest possible corneal damage threshold at a large corneal spot size using a more powerful SC source and provide data for the future possible refinements of laser safety standards. A series of experiments was conducted in the New Zealand white rabbit model to determine the corneal damage threshold induced by a 900-2000 nm SC source, with corneal 1/e beam diameter of about 1.2 mm. Slit-lamp biomicroscope was employed to reveal the corneal damage characteristics. By employing the action spectra determined through the analysis of current laser safety guidelines and standards, the effective damage threshold could be calculated. The determined damage threshold given in terms of the peak radiant exposure for the exposure duration of 0.14 s was 44.3 J/cm2 . At threshold level, corneal damages involved the epithelium and the shallower stroma. The safety factor between the effective damage threshold and the corresponding maximum permissible exposure (MPE) was about 45. Present corneal MPEs in the wavelength range of 700-1200 nm may be conservative and corneal damage thresholds for the infrared A wavelengths should be determined in future studies.

Demonstration of a Real-Time 14 Tb/s Multi-Aperture Transmit Single-Aperture Receive FSO System With Class 1 Eye-Safe Transmit Intensity

To achieve a link budget capable of supporting high capacity free space optical communication (FSO), a high transmit power is required. However, the transmitter can become potentially hazardous to the human eye. For a C-band transmitter to be classified as Class 1 eye-safe, the transmit intensity should be limited such that the optical power passing through a 24.5 mm diameter area is below 10 dBm. In this work we used a 9-aperture transmit, single-aperture receive FSO system to reduce the transmit intensity. Wavelength division multiplexed (WDM) signals were divided into 9 groups and transmitted through 9 apertures as separate beams. The apertures were arranged in a 3 x 3 array at a 25 mm pitch, and the transmit power from each aperture was set to 10 dBm. As a validation of the system by numerical simulation of propagation over 220 m, we showed that the additional free space loss due to pointing errors for the beams transmitted through the off-center apertures was less than 7.4 dB, and that using multiple apertures can significantly increase the transmission capacity. In the outdoor demonstration we transmitted 35 WDM 400 Gb/s dual-polarization probabilistically shaped 16-ary quadrature amplitude modulation signals over 220 m. By distributing the WDM channels across the 9 apertures to suit the transmission loss from their positions in the 3 x 3 array, we demonstrated error-free real-time transmission of a record capacity of 14 Tb/s, while satisfying the requirements of the Class 1 laser safety standard.

Simulation of laser-induced retinal thermal injuries for non-uniform irradiance profiles and the applicability of the laser safety standard

Significance: A validated biophysical computer model simulating retinal thermal damage thresholds is used to investigate elongated retinal images. The International Commission on Non-Ionizing Radiation Protection Guideline and the laser safety standard IEC 60825-1:2014 include a method for averaging non-uniform extended sources, however, there are no studies that have examined the applicability in detail. Our study represents a method that can also support future research in the field of eye safety. Aim: As there is currently no experimental data available for non-uniform irradiance profiles, the calculation procedure given in the laser safety standard is derived from symmetric retinal images. We aim to verify this calculation procedure for such profiles on the retina in the thermal hazard regime. Approach: A three-dimensional computer model, which solves the heat transfer equation and the Arrhenius equation describing the denaturation of the proteins in the retina, is used to simulate the threshold values for the retinal thermal injury. Three different non-uniform irradiance profiles, elliptical Gaussian, elliptical top-hat, and rectangular top-hat distributions, are investigated for a wavelength of 530 nm. The profiles are varied in their sizes and simulated for different single-pulse durations. By applying the laser safety standard, the maximum allowed energies are calculated and divided by the corresponding threshold values to obtain the reduction factor (RF) which is a crucial parameter. Results: Due to the thermal behavior in the retinal tissues, the Gaussian irradiance profiles yield larger threshold values than both top-hat profiles. Furthermore, the ratio between the threshold values and the maximum allowed energies are found to be the lowest for the Gaussian profiles. Conclusion: The simulated retinal thermal injury thresholds for the three investigated non-uniform irradiance profiles show larger RFs than the minimum RF found for symmetric profiles. This supports the applicability of the evaluation scheme of the laser safety standard for non-uniform retinal images.

Multiple-pulse damage thresholds of retinal explants in the ns-time regime.

The data situation of laser-induced damage measurements after multiple-pulse irradiation in the ns-time regime is limited. Since the laser safety standard is based on damage experiments, it is crucial to determine damage thresholds. For a better understanding of the underlying damage mechanism after repetitive irradiation, we generate damage thresholds for pulse sequences up to N = 20 000 with 1.8 ns-pulses using a square-core fiber and a pulsed Nd:YAG laser. Porcine retinal pigment epithelial layers were used as tissue samples, irradiated with six pulse sequences and evaluated for damage by fluorescence microscopy. The damage thresholds decreased from 31.16 µJ for N = 1 to 11.56 µJ for N = 20 000. The reduction indicates photo-chemical damage mechanisms after reaching a critical energy dose.

Porcine skin damage threshold from mid-infrared optical parametric oscillator radiation at 3.743 µm.

There is increasing use of mid-infrared optical parametric oscillator radiation operating in the wavelength range of 3-5 µm. To expand existing damage data for skin exposure to lasers in this wavelength region, the in-vivo damage threshold at the wavelength of 3.743 µm was determined in a Guizhou miniature pig model for an exposure duration of 1.0 s. The irradiance of the laser spot was nearly Gaussian-distributed and the 1/e2 beam diameter on the animal skin surface was fixed at 0.94 and 0.88 cm along horizontal and vertical directions. Damage lesion determinations were performed at 1- and 24-hour post-exposure. The probit analysis was employed to establish the ED50 values. The ED50 expressed in peak radiant exposure for the Gaussian spot was 4.04 J/cm2 at the 24-hour post-exposure. Sufficient margin existed between the damage threshold and MPE from the current laser safety standard. The obtained data may contribute to the knowledge base for refinement of laser safety standard in the wavelength range of 2.6-1000 µm.

Validation of a generalized laser safety analysis method for irregular pulse trains

The current laser safety standards do not address specifically how to account for repetitively pulsed lasers with irregular pulse trains. Variations in peak power, pulse duration, and duty cycle within a pulse train pose a number of problems when it comes to product classification or to assess the hazard of a given exposure. This study proposes to analyze irregular pulse trains by generalizing the determination of the number of pulses N used in the IEC 60825-1 or n in the ANSI Z136.1 standard. The proposed method for the determination of N applies to emission durations longer than 5 μs and was validated by generating a large number of theoretical pulse patterns and by comparing the retinal injury threshold, determined with a computer model, with the applicable emission limit. For 18 000 different pulse patterns, the ratio of the injury threshold to the emission limit was never less than 2, which is commonly considered as a sufficient safety margin. The smallest safety margin found for regular pulse patterns also equals 2. This study validates an analysis method for irregular pulse trains that can be included in the standards by simple generalization of the determination of the parameter N.

Porcine skin damage thresholds and histological damage characteristics from 1319-nm laser radiation.

.There is an increasing use of near-infrared lasers in biomedical applications operating in the spectrum between 1300 and 1400 nm. To corroborate and expand the existing safety data for skin exposure to lasers in this wavelength region, the in-vivo damage thresholds were determined in Guizhou miniature pigs for 1319-nm laser radiation. Exposure durations of 0.4, 1.0, and 3.0 s and beam diameters of 0.98 and 1.96 cm were employed. Damage lesion determinations were performed at 1- and 24 h post exposure. The Bliss probit analysis was employed to establish the damage thresholds. Histopathological studies of skin damage were performed at 48 h after irradiation to reveal the damage characteristics. The skin damage thresholds at 1 h post exposure, given in peak radiant exposure, were 35.5, 36.1, and at exposure durations of 0.4, 1.0, and 3.0 s with the spot diameter of 0.98 cm, and at exposure duration of 3.0 s with the spot diameter of 1.96 cm. At 24 h post exposure, the increased slightly. Histologically, the thermal damage characteristics at the near-threshold level included gathering of the nuclear chromatin and cell vacuolation in the epidermis and deposition of blood cells in the capillary vessels. However, at the apparently above-threshold level, the damage characteristics included obvious stretching of the nuclear chromatin in the epidermis, closing of the capillary lumen, structural change of collagen fibers, and coagulative necrosis of the hair follicle cells. The damage induced by this laser could go deep into the fatty tissue. The obtained results may contribute to the knowledge base for the damage mechanisms and expand the database for the refinement of laser safety standards in the wavelength range of 1300 to 1400 nm.

Filamentation in Atmospheric Air with Tunable 1100\u20132400\u2009nm Near-Infrared Femtosecond Laser Source

Intense femtosecond pulse filamentation in open-air has been utilized for long distance optical communication and remote sensing, but it results in nonlinear-effect driven eye hazards which are not addressed by current eye safety standards. A systematic study of filamentation in atmospheric air was performed using a tunable 100 fs near-infrared laser (1100 nm–2400 nm). While undergoing filamentation, each source wavelength was spectrally broadened resulting in supercontinuum and third harmonic generation in the visible and near-IR spectrum. We record the spectra at the center and fringes of the supercontinuum as it is imaged onto a planar surface. In a full beam collection regime, we report the energy of the sub-1000 nm light generation for source wavelengths from 1100 nm to 1600 nm and compare the energy density to the maximum permissible exposure values under the ANSI Z136.1 laser safety standard.

Retinal safety evaluation of two-photon laser scanning in rats

Safe use of retinal imaging with two-photon excitation in human eyes is crucial, as the effects of ultrashort pulsed lasers on the retina are relatively unknown. At the time of the study, the laser safety standards were inadequate due to the lack of biological data. This article addresses the feasibility of two-photon retinal imaging with respect to laser safety. In this study, rat retinas were evaluated at various laser exposure levels and with different laser parameters to determine the effects of laser-induced optical damage. The results were experimentally verified using confocal reflectance imaging, two-photon fluorescein angiography, immunohistochemistry, and correlated to the IEC 60825-1 laser safety standard.

Determination of a laser eye dazzle safety framework

A simple safety framework for laser eye dazzle, based on a complex model developed from human subject experiments, is proposed to address the urgent need for guidance within international laser safety standards. Maximum Dazzle Exposure (MDE) safety limits are derived that set the laser irradiance at the eye above which an object cannot be visually detected. A newly defined concept of dazzle level accounts for the extent of visual obscuration, and different ambient light levels are accommodated by determining safety limits for night, dusk/dawn, and day conditions. The resulting table of MDE values allows dazzle effects to be quantified in simple safety calculations across a wide range of scenarios. This safety framework is intended to empower the laser safety community to understand and quantify the impacts of laser eye dazzle, specify protection measures for those at risk, and assure the safety and effectiveness of laser dazzle devices.

Quantitative Evaluation of a Time-Dependent Eye Hazard Posed by Laser Pointers.

A novel test methodology was developed for quantitative evaluation of critical radiant power characteristics as a function of time for diode pumped solid state (DPSS) laser pointers. It is based on a simultaneous measurement of time-dependent radiant power characteristics of multi-wavelength spectral components emitted by DPSS laser pointers. The authors tested green DPSS laser pointers, which emit three spectral components at the fundamental near-infrared (1064-nm), pumping near-infrared (808-nm), and second-harmonic green (532-nm) wavelengths. The obtained experimental results are employed for performing eye hazard evaluation according to U.S. and International laser safety standards. All tested green laser pointers demonstrated significant variability of radiant power as a function of time and wavelength. Thus, the severity of the potential eye hazard from DPSS laser pointers for a given exposure time depends on when a person was exposed after the pointer was turned on. Most laser pointers emitted radiation in excess of their classification limits, including unwanted infrared radiation that is not necessary for their intended use as laser pointers.

Optoacoustic Dermoscopy of the Human Skin: Tuning Excitation Energy for Optimal Detection Bandwidth With Fast and Deep Imaging <italic>in vivo</italic>

Optoacoustic (photoacoustic) dermoscopy offers two principal advantages over conventional optical imaging applied in dermatology. First, it yields high-resolution cross-sectional images of the skin at depths not accessible to other non-invasive optical imaging methods. Second, by resolving absorption spectra at multiple wavelengths, it enables label-free 3D visualization of morphological and functional features. However, the relation of pulse energy to generated bandwidth and imaging depth remains poorly defined. In this paper, we apply computer models to investigate the optoacoustic frequency response generated by simulated skin. We relate our simulation results to experimental measurements of the detection bandwidth as a function of optical excitation energy in phantoms and human skin. Using raster-scan optoacoustic mesoscopy, we further compare the performance of two broadband ultrasonic detectors (a bandwidth of 20-180 and 10-90MHz) in acquiring optoacoustic readouts. Based on the findings of this paper, we propose energy ranges required for skin imaging with considerations of laser safety standards.

Investigation of interaction femtosecond laser pulses with skin and eyes mathematical model

We present a mathematical model of linear and nonlinear processes that takes place under the action of femtosecond laser radiation on the cutaneous covering. The study is carried out and the analytical solution of the set of equations describing the dynamics of the electron and atomic subsystems and investigated the processes of linear and nonlinear interaction of femtosecond laser pulses in the vitreous of the human eye, revealed the dependence of the pulse duration on the retina of the duration of the input pulse and found the value of the radiation power density, in which there is a self-focusing is obtained. The results of the work can be used to determine the maximum acceptable energy, generated by femtosecond laser systems, and to develop Russian laser safety standards for femtosecond laser systems.

Effects of femtosecond laser radiation on the skin

A mathematical model of linear and nonlinear processes is presented occurring under the influence of femtosecond laser radiation on the skin. There was held an analysis and the numerical solution of an equation system describing the dynamics of the electron and phonon subsystems were received. The results can be used to determine the maximum permissible levels of energy generated by femtosecond laser systems and the establishment of Russian laser safety standards for femtosecond laser systems.

Retinal thermal damage threshold dependence on exposure duration for the transitional near-infrared laser radiation at 1319 nm.

The retinal damage effects induced by transitional near-infrared (NIR) lasers have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. In this paper, the in-vivo retinal damage ED50 thresholds were determined in chinchilla grey rabbits for 1319 nm laser radiation for exposure durations from 0.1 s to 10 s. The incident corneal irradiance diameter was fixed at 5 mm. The ED50 thresholds given in terms of the total intraocular energy (TIE) for exposure durations of 0.1, 1 and 10 s were 1.36, 6.33 and 28.6 J respectively. The ED50 thresholds were correlated by a power law equation, ED50 = 6.31t0.66 [J] where t is time [s], with correlation coefficient R = 0.9999. There exists a sufficient safety margin (factor of 28~60) between the human ED50 thresholds derived from the rabbit and the maximum permissible exposure (MPE) values in the current laser safety standards.

Corneal thermal damage threshold dependence on the exposure duration for near-infrared laser radiation at 1319 nm.

The corneal damage effects induced by 1319-nm transitional near-infrared laser have been inves- tigated for years. However, the damage threshold dependence on exposure duration has not been revealed. The in vivo corneal damage thresholds (ED50s) were determined in New Zealand rabbits for 1319-nm laser radiation for exposure durations from 75 ms to 10 s. An additional corneal ED50 was determined at 1338 nm for a 5-ms exposure. The incident corneal irradiance diameter was fixed at 2 mm for all exposure conditions to avoid the influence of spot size on threshold. The ED50s given in terms of the corneal radiant exposure for exposure dura- tions of 5 ms, 75 ms, 0.35 s, 2 s, and 10 s were 39.4, 51.5, 87.2, 156.3, and 311.1 J∕cm 2 , respectively. The 39.4 J∕cm 2 was derived from the ED50 for 1338 nm (27.0 J∕cm 2 ). The ED50s for exposure durations of 75 ms to 10 s were correlated by a power law equation, ED50 ¼ 128.9t 0.36 in J∕cm 2 , where t was the input in the unit of second, with correlation coefficient (R) of 0.997. Enough safe margins existed between the ED50s and the maxi- mum permitted exposures from current laser safety standard. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Mathematical model оf laser radiation femtosecond interaction with human skin

We present a mathematical model of linear and nonlinear processes that occur under the action of femtosecond laser radiation on the cutaneous covering. The analysis is carried out and the analytical solution of the set of equations describing the dynamics of the electron and atomic subsystems is obtained. The results of the work can be used to determine the maximum acceptable energy, generated by femtosecond laser systems, and to develop Russian laser safety standards for femtosecond laser systems.

Selecting laser eye protectors – a helping hand

Abstract The European laser safety standards EN 207, EN 208, and EN 12254 each contain an annex B, which serves as a guidance for the selection of products. These annexes are informative only and are therefore not binding. As there are a variety of hazard scenarios, it is not recommended to change these annexes to a normative status, through which they would become mandatory. Instead, it is recommended to allow users to apply their own skills and know-how in selecting appropriate products, justifying where and why they deviate from the guidance in the standards. This paper explains the background on which the guidance for selection in the annexes of the standards is based and shows physically meaningful leeway.

Research of linear and nonlinear processes at femtosecond laser radiation propagation in the medium simulating the human eye vitreous

The paper deals with mathematical model of linear and nonlinear processes occurring at the propagation of femtosecond laser pulses in the vitreous of the human eye. Methods of computing modeling are applied for the nonlinear spectral equation solution describing the dynamics of a two-dimensional TE-polarized radiation in a homogeneous isotropic medium with cubic fast-response nonlinearity without the u retina when passing through the vitreous body of the eye. Dependence between the pulse duration on the retina has been revealed and the duration of the input pulse and the values of power density at which there is self-focusing have been found. It is shown that the main mechanism of radiation damage with the use of titanium-sapphire laser is photoionization. The results coincide with those obtained by the other scientists, and are usable for creation Russian laser safety standards for femtosecond laser systems.sage of slowly varying envelope approximation. Environments close to the optical media parameters of the eye were used for the simulation. The model of femtosecond radiation propagation takes into account the process dynamics for dispersion broadening of pulses in time and the occurence of the self-focusing near the