Irradiance data were collected over a 1km horizontal terrestrial path using several different sized receiving apertures.
The data were collected under moderate-to-strong turbulence conditions. The receiver system consisted of a 154mm
(6") refracting telescope outfitted with several removable apertures. The path was instrumented with three 3-axis
anemometers and three scintillometers, two of which were capable of measuring the inner scale of turbulence in addition
to Cn2. Histograms were formed with the data and compared to the Log-Normal and Gamma-Gamma PDF models. As
expected, neither PDF model was applicable under all conditions of aperture averaging. Hypotheses are made as to why
the models were unable to completely capture the effects of aperture averaging on received irradiance data.
We present the first high spatial resolution, passively-illuminated polarimetric images of boosting rocket exhaust
plumes. The images shown here show significant linear and circular polarization, and the ability to resolve
the polarization signals into images allows us to make some preliminary arguments as to their origins. Our
observations are consistent with polarization caused by Rayleigh and Mie scattering (linear) and interaction
with plume plasma-generated magnetic fields (circular). We also present nearly simultaneous, two-color, narrowband
(633 ± 5 and 750 ± 5 nm) exhaust plume images, where significant structural differences are observed in
the plumes despite a relative small difference in the two wavelengths.
We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning range which is
used as the master oscillator in a master oscillator power amplifier (MOPA) thulium fiber laser system. Due to thermal
instability in the grating used for tuning, the MO could produce a power up to 4.5 W, beyond which the oscillator
became unstable. Injecting the seed laser into a bidirectionally pumped large mode area (LMA) Tm fiber amplifier, a
stable, tunable, narrow linewidth high beam quality amplified signal of >100 W was achieved. In the absence of stable
and sufficiently high power from the seed laser, the amplifier could not be tested to its full potential. The amplifier was
also, converted into an oscillator to investigate its power handling capability. An excellent beam quality and ~200 W of
power were achieved by running the power amplifier as an oscillator. Operation stability of the oscillator was measured
to be more than one hour with a minimum power fluctuation of 0.5%. Currently efforts are underway to increase the seed
laser power to ~10 W, large enough to reduce ASE and mitigate feedback to the master oscillator to demonstrate a 200
W, tunable (150 nm) and narrow linewidth (0.15 nm) MOPA system.
The MOPA system will be one of a number of new state-of-the-art high power lasers to be located at the
Innovative Science & Technology Experimentation Facility, creating a unique laser range facility for next generation
studies and tests across a broad range of sciences and technologies.
We report on a set of measurements made in December 2005 by researchers from the University of Central Florida, SPAWAR's Innovative Science and Technology Experiment Facility (ISTEF), Harris Corporation, NASA Kennedy Space Center, and Northrop Grumman. The experiments were conducted on the Shuttle Landing Facility (SLF) at Kennedy Space Center (KSC) over terrestrial paths of 1, 2, and 5 km. The purpose of the experiments was to determine the atmospheric-induced beam spreading and beam wander at various ranges. Two lasers were used in the experiments. Both were a pulsed 1.06 μm laser; however, one was single-mode and the other was multi-mode. Beam profiles were recorded near the target position. Simultaneous measurements of Cn2, wind speed and direction, humidity, visibility, temperature, and surface temperature profiles were all recorded.
The purpose of active imaging system is to provide discrimination at long ranges independently from the surrounding illumination by using and controlling its own light source. Parameters such as the Doppler shift for coherent devices, the range, or the intensity of the light back scattered by objects have already been used to encode images. However, another parameter characterizing the electromagnetic field can help to discriminate the target: its polarization. In this paper we demonstrate that images resulting from the analysis of the polarization of light can offer better contrasts than classical images encoded by the intensity of light back-scattered. The emitting part of the imaging polarimeter built at CREOL (Polarization State Generator) is a doubled YAG pulsed laser with external polarization controllers. At the receiving part, the Polarization State Analyzer separates the incoming light so as to provide two crossed polarized images of the target.These images are acquired simultaneously by two high-resolution progressive scan digital cameras controlled by a computer. Afterwards, the computer processes the acquired data and displays two new images encoded by polarization parameters (depolarization ratio for example). In several examples and experiments, the influence of the geometry of the target (roughness, shape) on the incident state of polarization will be discussed.
The detection and processing of laser communication signals are drastically affected by the fading induced onto these signals by atmospheric turbulence. One method of reducing this fading is to use an array of detectors in which each of the detector outputs are added together coherently. This requires measuring the phase difference between each of the receivers and co-phasing each of the detector outputs. This paper presents experimental verification at the Innovative Science and Technology Experimentation Facility over an outdoor range of a 1.06 micron eight element coherent receiver used to mitigate the effects of fading. The system is composed of a 60 mw Nd:Yag laser used as the transmitter and a 27 MHz AO modulator used to frequency shift the transmitted beam. The receiver is composed of eight 1 cm lenses launching the eight received optical signals into eight signal mode optical fibers. Phase compensation between each of the eight receivers is accomplished using single mode fibers wrapped around PZT cylinders that are controlled by phase compensating electronics. The carrier-to-noise (CNR) ratio was measured on a single channel and was then compared with the CNR obtained from the coherent sum of the eight channels. The improvement of the CNR for the coherent sum as compared to a single channel was then compared against theoretical predictions.
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