We present a pulsed all-fiber Er/Yb-doped master oscillator power amplifier at 1.55 μm wavelength. In a simple two-stage amplifier design, the source delivers 140 μJ pulses at 25 kHz and 50 kHz pulse repetition frequency, and 100 μJ at 100 kHz, with pulse durations of ∼10 ns and beam quality of M2 = 1.3. The MOPA is suitable as a robust field source for ladar applications, and has been tested in an in-house developed scanning ladar system.
Early warning systems based on standoff detection of biological aerosols require real-time signal processing of a large
quantity of high-dimensional data, challenging the systems efficiency in terms of both computational complexity and
classification accuracy. Hence, optimal feature selection is essential in forming a stable and efficient classification
system. This involves finding optimal signal processing parameters, characteristic spectral frequencies and other data
transformations in large magnitude variable space, stating the need for an efficient and smart search algorithm.
Evolutionary algorithms are population-based optimization methods inspired by Darwinian evolutionary theory. These
methods focus on application of selection, mutation and recombination on a population of competing solutions and
optimize this set by evolving the population of solutions for each generation. We have employed genetic algorithms in
the search for optimal feature selection and signal processing parameters for classification of biological agents. The
experimental data were achieved with a spectrally resolved lidar based on ultraviolet laser induced fluorescence, and
included several releases of 5 common simulants. The genetic algorithm outperform benchmark methods involving
analytic, sequential and random methods like support vector machines, Fisher's linear discriminant and principal
component analysis, with significantly improved classification accuracy compared to the best classical method.
A new method for obtaining high beam quality from high pulse energy optical parametric oscillators (OPOs) is
demonstrated. By using different nonlinear crystals that have walk-off in orthogonal directions but are type 2 phase
matched for the same interaction, the strong beam asymmetry that is common in critically type 2 phase matched OPOs is
removed. Experimentally, this was demonstrated by adding BBO crystals to a type 2 phase matched KTA OPO, where
the beam quality improved from M2 ≈ 2 x 12 in the KTA OPO to M2 ≈ 2 x 2 from the KTA-BBO OPO.
We have performed a field trial to evaluate technologies for stand-off detection of biological aerosols, both in daytime
and at night. Several lidar (light detection and ranging) systems were tested in parallel. We present the results from three
different lidar systems; one system for detection and localization of aerosol clouds using elastic backscattering at
1.57 μm, and two systems for detection and classification of aerosol using spectral detection of ultraviolet laser-induced
fluorescence (UV LIF) excited at 355 nm. The UV lidar systems were utilizing different technologies for the spectral
detection, a photomultiplier tube (PMT) array and an intensified charge-coupled device (ICCD), respectively. During the
first week of the field trial, the lidar systems were measuring towards a semi-closed chamber at a distance of 230 m. The
chamber was built from two docked standard 20-feet containers with air curtains in the short sides to contain the aerosol
inside the chamber. Aerosol was generated inside the semi-closed chamber and monitored by reference equipments, e.g.
slit sampler and particle counters. Signatures from several biological warfare agent simulants and interferents were
measured at different aerosol concentrations. During the second week the aerosol was released in the air and the
reference equipments were located in the centre of the test site. The lidar systems were measuring towards the test site
centre at distances of either 230 m or approximately 1 km. In this paper we are presenting results and some preliminary
signal processing for discrimination between different types of simulants and interference aerosols.
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.
Nonlinear optical conversion of 500 mJ pulses from a Nd:YAG laser to the mid-infrared is demonstrated in a two-step architecture. Using a type 2 phase matched KTiOPO4-based master-oscillator/power-amplifier (MOPA) architecture for conversion to 2 μm, 140 mJ signal at 2.08 μm with M2 = 2.3 and 80 mJ idler at 2.18 μm were obtained. Using 58 mJ of the signal beam to pump a ZnGeP2-based MOPA, we have obtained 21 mJ in the 3-5 μm range with M2 ≈ 15.
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.
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