Stephane Nicolas

Midinfrared laser source with high power and beam quality

A simple scheme for generation of high power in the midinfrared is demonstrated. By using a 15 W thulium-doped fiber laser emitting at 1907 nm to pump a Q-switched Ho:YAG laser, we obtained 9.8 W at 2096 nm at a 20 kHz pulse repetition rate with excellent beam quality. The output of this laser was used to pump a doubly resonant zinc germanium phosphide based optical parametric oscillator, and we obtained 5.1 W average power in the 3-5 microm range with M2 approximately = 1.8.

High-pulse-energy mid-infrared laser source based on optical parametric amplification in ZnGeP2

Nonlinear optical conversion of 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 8 µm or in the 3–5 µm wavelength region. We obtain more than 8 mJ at 8 µm, and up to 33 mJ at 3–5 µm. The measured beam quality factors are in the range M2=2–4 for both wavelength regions.

Compact camera for multispectral and conventional imaging based on patterned filters.

A multispectral camera concept is presented. The concept is based on using a patterned filter in the focal plane, combined with scanning of the field of view. The filter layout has stripes of different bandpass filters extending orthogonally to the scan direction. The pattern of filter stripes is such that all bands are sampled multiple times, while minimizing the total duration of the sampling of a given scene point. As a consequence, the filter needs only a small part of the area of an image sensor. The remaining area can be used for conventional 2D imaging. A demonstrator camera has been built with six bands in the visible and near infrared, as well as a panchromatic 2D imaging capability. Image recording and reconstruction is demonstrated, but the quality of image reconstruction is expected to be a main challenge for systems based on this concept. An important advantage is that the camera can potentially be made very compact, and also low cost. It is shown that under assumptions that are not unreasonable, the proposed camera concept can be much smaller than a conventional imaging spectrometer. In principle, it can be smaller in volume by a factor on the order of several hundred while collecting the same amount of light per multispectral band. This makes the proposed camera concept very interesting for small airborne platforms and other applications requiring compact spectral imagers.

High pulse energy mid-infrared laser source

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.

High-power fiber-laser-pumped mid-infrared laser sources

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.

High-Energy Mid-IR Source Based on Two-Stage Conversion from 1.06 μm

We present a two-stage system for parametric frequency conversion of high-energy Nd:YAG laser pulses to the 3-5 μm range. The first stage, which converts from 1.06 μm to about 2.1 μm, is based on KTiOPO4 (KTP) and has a master oscillator / power amplifier (MOPA) architecture, where the oscillator is an optical parametric oscillator (OPO) and the amplifier is an optical parametric amplifier (OPA). This architecture ensures that the 2.1 μm beam quality is good enough for pumping a ZnGeP2 (ZGP)-based OPO in the second stage. With 500 mJ from the Nd:YAG laser we obtain up to 138 mJ signal and 80 mJ idler in orthogonal polarizations at 2.1 μm. Using 86 mJ of the signal to pump the ZGP-OPO we have so far obtained 28 mJ in the 3-5 μm range.

Fibre-laser-pumped mid-infrared source

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.

Laser beam propagation through turbulence and adaptive optics for beam delivery improvement

We report results from numerical simulations of laser beam propagation through atmospheric turbulence. In particular, we study the statistical variations of the fractional beam energy hitting inside an optical aperture placed at several kilometer distance. The simulations are performed for different turbulence conditions and engagement ranges, with and without the use of turbulence mitigation. Turbulence mitigation is simulated with phase conjugation. The energy fluctuations are deduced from time sequence realizations. It is shown that turbulence mitigation leads to an increase of the mean energy inside the aperture and decrease of the fluctuations even in strong turbulence conditions and long distance engagement. As an example, the results are applied to a high energy laser countermeasure system, where we determine the probability that a single laser pulse, or one of the pulses in a sequence, will provide a lethal energy inside the target aperture. Again, turbulence mitigation contributes to increase the performance of the system at long-distance and for strong turbulence conditions in terms of kill probability. We also discuss a specific case where turbulence contributes to increase the pulse energy within the target aperture. The present analysis can be used to evaluate the performance of a variety of systems, such as directed countermeasures, laser communication, and laser weapons.

Tunable high-pulse-energy mid-infrared laser source based on optical parametric amplification in ZnGeP2

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.

High-Pulse-Energy Mid-Infrared Laser Source Based on Optical Parametric Amplification in ZnGeP 2

Nonlinear optical conversion of ~500 mJ pulses from a Q-switched Nd:YAG laser to the mid-infrared is demonstrated experimentally. Using optical parametric amplification in ZnGeP2, we obtain up to 6 mJ at 8 µm.