Recently, pulsed lasers with ultrashort pulse durations have become ubiquitous in a variety of applications, including medical procedures such as laser eye surgery. These sources are capable of generating extremely high peak powers that can cause laser-induced tissue breakdown upon exposure. However, current laser safety standards do not provide exposure limits for wavelengths longer than 1400 nm and pulse durations shorter than 1 ns due to a lack of biological data. Instead, the recommendation is to limit the peak irradiance to the maximum permissible exposure (MPE) limits applicable to 1 ns pulse durations. We applied femtosecond laser pulses of varying energies at 1540 nm and 2000 nm to corneas of anesthetized rabbits. We used slit lamp biomicroscopy and optical coherence tomography to examine the exposure sites and determine the presence or absence of visible lesions 1 h and 24 h post-exposure. The dose-response data correlating the presence or absence of any alteration of the corneal surface to the pulse energy 1 h post-exposure was evaluated using probit analysis to extract the median effective dose (ED50) corresponding to the cornea damage threshold. We compared our results to the MPE limits applicable to 1 ns pulse durations and determined that the current safety standard procedures are not adequate to evaluate small diameter single pulse femtosecond exposures at 1540 nm and 2000 nm. The results of this study contribute to the knowledge base used for setting laser safety standards in the near infrared range for ocular exposure to ultrashort pulses.
In October 2018, NATO SET-249 performed a common trial at WTD 52, Oberjettenberg, Germany, to study laser dazzle effects in an airborne scenario. The facility is equipped with a cable car and is ideal for slanted path experiments from the base station to the cable car where the sensors were mounted. NATO SET-249’s background is laser threat evaluation and the evaluation of the impact of laser eye dazzle on the visual performance of humans. This work gives an overview on the various measurements performed here: 1. Assessment of dazzle effects originating from light scattering at an aircraft canopy by comparing the images of two cameras: one outside and one inside the canopy. The general findings showed that the canopy, which had been used previously on an aircraft, substantially affected the dazzle pattern in the camera within the canopy as compared to the camera outside. 2. Sensor dazzling: Laser dazzling of complementary metal-oxide-semiconductor (CMOS) cameras in the visible domain and, in addition, laser dazzling of a camera equipped with a fisheye lens, which is commonly present in micro-unmanned aerial vehicles, is demonstrated. The dazzled area in the camera field of view (FoV) grows with increasing laser irradiance, and dazzling is effective at irradiance levels around a few μW/cm². 3. An overview on realistic handheld laser engagement scenarios to test the capabilities of a DSTL-developed Laser Event Recorder (LER) is provided. This technology is able to detect continuous wave (CW) and pulsed lasers, and extract their wavelengths, irradiances, Pulse Repetition Frequency (PRF) and directionality. Applications for this LER include collecting information on aircraft laser exposure events, giving information to assess if engagements are eye safe. 4. Measurements performed on various Fraunhofer IOSB developed sensor systems hardened against laser dazzle: The hardening measure of these systems is based either on the use of spatial light modulators or on the implementation of the principle of complementary wavelength bands. The field trial offered the possibility to generate data of the hardened systems under real life conditions.
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