The F-35 Lightning II has a powerful combat laser designator operating at a wavelength and energy levels that are damaging to the human eye at a pulse level. Due to the faceted design of the Electro Optical Targeting System housing, unwanted Stray Laser Energy beams are emitted in uncontrolled directions. These beams are powerful enough to damage the human eye. Care must therefore be taken to ensure that observers on the ground are not unintentionally blinded. Using a general procedure where the hazard distance is determined by the length of the strongest Stray Laser Energy beam in any direction impedes the ability of the Royal Norwegian Air Force to train in Norway due to the size of the firing ranges and the limits to the maneuvering envelope. We have developed a Monte Carlo based model to determine the hazard "footprint" on the ground for typical flight patterns. The model incorporates several stochastic variables to catch the variations of an execution. The model also incorporates terrain data to evaluate if a beam will hit the actual terrain around a specified target. By running enough instances of the model, it is possible to generate an estimate for the probability of being hit by a beam for ground observers. Analysis has been performed for the unaided eye, binoculars of size 7x50mm and binoculars of size 20x120mm. By evaluating the risk level in accordance with guidelines provided by the The Norwegian Radiation and Nuclear Safety Authority, we have expanded the possibility for training using the combat laser in Norway.
We present a high energy infrared laser source where a Tm:fiber laser is used to pump a high-energy 2-μm cryogenically
cooled Ho:YLF laser. We have achieved 550 mJ of output energy at 2.05 μm, and through non-linear conversion in
ZnGeP2 generated 200 mJ in the 3-5-μm range. Using a numerical simulation tool we have also investigated a setup
which should generate more than 70 mJ in the 8-12-μm range. The conversion stage uses a master-oscillator-power-amplifier
architecture to enable high conversion efficiency and good beam quality.
In this paper we report on a high energy, low repetition rate 2-micron-laser, with high conversion efficiency in terms of
output energy per pump power. The laser consists of a Ho3+-doped LiYF4 (YLF) crystal cooled to cryogenic
temperatures in an unstable resonator, pumped by a thulium fiber laser. The cooling to 77 K makes Ho:YLF a quasi four
level laser system, which greatly enhances the extraction efficiency. We achieved 356 mJ in Q-switched operation at 1
Hz PRF when pumping the laser with 58 W for 36 ms. The high beam quality from the fiber laser and the use of an
unstable resonator with a graded reflectivity mirror (GRM) resulted in a high quality laser beam with a M2-value of 1.3.
There has been considerable progress on development of technological solutions for high power and high energy mid-IR
generation for directed optical countermeasure applications using optical parametric generators. Here we give a summary
of what we believe are the important considerations to be made in the design of such sources based on our research over
the last years and the general progress in the field. We also give a short review on our latest results in this area, and some
thoughts on possibilities for further progress.
μWe report on a high-power semi-ruggedized laser source, which can deliver radiation in all infrared transmission bands
from 2 to 10 μm. In the source a 70 W Tm-doped fiber laser pumps a Q-switched Ho:YAG laser, which produces 37 W
of output power at 2.1 μm. The Ho-laser pumps two ZnGeP2 OPOs. The first generates a combined power of 14 W at
3.9 μm and 4.5 μm, and the second generates watt-level outputs at 2.8 μm and 8 μm. The OPOs have a novel V-shaped
3-mirror ring resonator design, which gives high efficiency and beam quality.
Nonlinear optical conversion of high-energy 1.064 μm pulses from a Q-switched Nd:YAG laser to the mid-infrared
is demonstrated. The experimental setup is based on a two-stage master-oscillator/power-amplifier (MOPA)
design with a KTiOPO4 based MOPA in the first stage and a KTiOAsO4/ZnGeP2 based MOPA in the second
stage. The setup can be tuned to provide output at wavelengths within the transparency range of ZnGeP2. We
obtain more than 8 mJ at 8 μm, and up to 33 mJ in the 3-5 μm wavelength region. The measured beam quality
factors are in the range M2 =2-4 for both wavelength regions.
Nonlinear optical conversion of 1.064 μm pulses from a Q-switched Nd:YAG laser to the mid-infrared is demonstrated
experimentally. The setup is based on a two-stage master-oscillator/power-amplifier (MOPA) design
with a KTiOPO4 based MOPA in the first stage and a KTiOAsO4/ZnGeP2 based MOPA in the second stage.
We obtain more than 8 mJ at 8 μm with a beam quality factor M2 ≈ 3.6.
A high power, efficient, and tunable laser source in the 8-10 µm wavelength range, based on a ZnGeP2 (ZGP) optical
parametric oscillator (OPO) pumped by a hybrid 2-micron-laser, is demonstrated. Tuning to 9.8 μm was achieved, and
with 8.9 W of 2.1 µm pump power we obtained 0.95 W at 8 μm with an M2 value of 2.7 from an OPO with two walk-off
compensating crystals. More than 40% quantum efficiency was achieved.
We present an efficient, high-power mid-infrared laser source using a Thulium fiber laser as pump source. The CW fiber laser pumps a Q-switched Ho:YAG laser which in turn pumps a ZnGeP2-based OPO. We have built a semi-ruggedized version of the laser for countermeasure field trials, and using a 15 W fiber laser we obtained 5.2 W output power in the 3-5 μm band. We also present work on scaling up the power by using a 65 W fiber laser as the pump. Simulations and initial experiments suggest that the scaled-up version could produce more than 25 W in the mid-IR.
We present a simple design for efficient generation of high average power in the 3-5 μm wavelength range. Using a 15 W thulium-doped fibre laser to pump a Q-switched 2.1 μm Ho:YAG laser, we obtain 9.2 W average output power with excellent beam quality. The 2.1 μm output is used to pump a ZnGeP2-based OPO, resulting in 4.6 W average output power in the 3.6-5.2 μm range with beam quality M2 < 1.4.