SDI''s Global Protection Against Limited Strikes program has undertaken the development of both solid-state laser and CO2 laser-based ladars. CO2 ladar development is intensively concerned with the reduction of system volumes and weights for orbital deployment, as can be seen in the development milestones of the LOWKATER space-traceable ladar system, Laser Imager Component Development, and a compact, multiple-CO2-laser ladar configuration for interceptor applications

A coherent pulse-burst 1.06 (mu) ladar transmitter is described. The output consists of a 1.6 J, 800 microsecond(s) burst of 550 ps pulses occurring at a 50 MHz repetition rate. The burst repetition rate is 10 Hz. The optical frequency stability before coherent processing at the receiver is +/- 100 kHz. The transmitter consists of a CW-pumped mode-locked Nd:YAG oscillator followed by a pulsed double-pass amplifier, and is used as part of a calibrated range-Doppler imaging target signature measurement system

The properties of a pseudodeep hologram are studied. This new term refers here to an inclined thin hologram on which a one-dimensional line object is recorded by a sagittal system of beams. In this case the reconstructed image is read out only within the line corresponding to the object. It is shown that, similar to deep 3-D hologram, the pseudodeep hologram has high angular and spectral selectivity. A simple graphic method for the construction of the images restored by the pseudodeep hologram is presented. A reference-free hologram has been recorded with the help of such a system. When reading out such a hologram for a part of the object recorded on it, the associative image of the object as a whole was reconstructed. The possibilities of using the pseudodeep hologram was performing different operations are considered, including heteroassociative readout of information by the keys associated with it, recognition of pages of information by the keys associated with it, recognition of pages of information when illuminating the hologram by the objective wave, and multiple recording of information in the same region of the photographic material. In conclusion, the associative memory scheme in which the information pages are recorded on separate stripes of the pseudodeep hologram with the use of different reference sources as the keys associated with these pages has been considered. The retrieval of the pages is performed by illuminating the entire surface of the hologram with one of the reference sources

The LIDAR In-space Technology Experiment (LITE) is scheduled for flight in mid-1994 on the Space Shuttle Atlantis (STS-65) as its primary payload. The purpose of this experiment to gather data based on the atmospheric backscatter from the earth''s upper and lower atmospheres from the three-color neodymium:YAG-based lidar. The heart of this experiment is the Laser Transmitter Module (LTM). Designed and built by TITAN/SPECTRON, the LTM is a dual redundant flashlamp-pumped Nd:YAG laser that emits three wavelengths at 1064, 532, and 355 nm. This paper describes the systems approach used to develop, test, and build the world''s first high-powered laser system for use in space

Since 1986, the USAF Wright Laboratories, at Eglin Air Force Base has conducted a series of related test programs and technology development activities with the purpose of determining the feasibility of using diode-laser radar systems as sensors for autonomous targeting guided weapons. Schwartz Electro-Optics, working under a USAF contract to develop a diode-laser radar for submunition applications, has developed a real-time (30 Hz frame rate) imaging diode-laser radar system which employs a proprietary algorithm for target recognition and classification. In captive flight testing using a remotely piloted vehicle (RPV), the system has been used to detect, classify, and determine aim-points of targets (tanks, trucks) in a high-clutter environment; false-color range and gray-scale reflectance imagery were displayed in real-time. The testing yielded excellent target acquisition performance. The 42,000 frames of range and reflectance data which were obtained during the testing are being used for further development of the target recognition and classification algorithm. This paper reviews the imaging diode-laser radar development and the captive flight testprogram

This paper presents an imaging scheme for high-resolution 3D characterization of potential targets. The phenomenology exploited is the linear electrooptic effect to produce pixel registered range maps and images. The technique requires illumination using a pulsed laser source. The return signal from the target region is modulated using an electrooptic shuttering device which temporally varies the polarization of the return illumination in a controlled manner. The degree of return signal polarization modulation is proportional to the time of arrival. A dual camera data acquisition system senses the two polarization states as a function of time. The sensed illumination at one camera is ratioed to the other camera illumination. The ratio value is a unique number specific to the relative range of the return for that pixel or pixel region. A critical advantage of this technique is self-normalization since ratioing the pixel intensities discounts the illumination. Simulated imagery is generated using predicted photon statistics based on the characteristics of the experimental set-up. Experimental data is currently being analyzed to determine sensor scheme performance and potential areas of improvement

The problems of obtaining and processing information in pulsed laser rangefinders in order to determine ranging object characteristic feature selection and identification under permanent echo conditions are considered, including the influence of target spatial length, radiation beam nonuniformity, and random rangefinder target guidance error. Automatic target selection algorithms and circuits are also considered. The principle of target signal selection and identification based on reflected pulse data is proposed.

An account is given of the experimental apparatus and test results of an investigation aimed at the quantification of wavelength-dependent effects on laser radar performance of various atmospheric conditions. Attention is also given to the differences between eye-safe, 2-micron-laser-based ladar system performance and that of the conventional 10.6-micron CO2-laser-based ladars that have been used to date. Attention is given to the results obtained for atmospheric turbulence and path extinction; marked differences emerge between 2-micron and 10.6-micron systems in the case of aerosols and water absorption.

Operation of a coherent 1.06 micron all solid state lidar system made from all commercially available components has been accomplished. The system uses fiber optics for coherently mixing the signal energy with the local oscillator and it has a sub kHz frequency sensitivity making it ideal for examining the effects on system performance of the optical fiber amplifiers that are currently under development. The coherent 1.06 micron system uses a Nd:YAG stable ring laser as the source. This source is protected from reflections further along the optical train by an optical isolator. The local oscillator energy is pulled off from the main beam with a polarization beam splitter cube and frequency-shifted by 200 MHz with an acoustooptic modulator. The transmit/receive switch utilizes a polarization beam splitter-polarization rotator combination. The signal and local oscillator energies are focused into separate polarization preserving single mode fibers and coherently mixed with a variable evanescent wave coupler. Detection is achieved with a room temperature InGaAs pigtailed PiN diode. The output of the detector is processed with an RF electronic spectrum analyzer.

A miniature laser with a total volume less than 15 cu cm and weight less than 100 g has been designed, fabricated, and assembled. The laser uses a composite rod consisting of Nd:Cr:GSGG material rod cladded with an Er:Cr:YSGG tube. The laser provides output at 1 and 3 micron wavelengths. The size and weight reduction is obtained by chemical pumping which eliminates the prime power and the power supply. The laser is used as an illuminator in a direct detection radar.

A beam-scanning binary logic (BSBL) and its implementation using a beam-scanning laser diode (BSLD) are proposed. The BSBL is categorized as spatial coding information processing, which operates with spatially coded light signals. A basic BSBL unit consists of two photodetectors, two amplifiers, a light source, and a beam scanner. A unit with three output photodetectors can execute eight types of binary two-inputs/one-output optical logic operations with small modifications: FALSE, AND, XOR, OR, NOR, XNOR, NAND, and TRUE.

The refractive index of an optical glass sample in the form of a wedge is measured by comparison with that of a reference liquid. This holographic technique can also be applied to the measurement of the refractive index of the immersion liquid, if the refractive index of the glass wedge is known. The accuracy of the method with respect to index matching, glass wedge preparation, and fringe position measurement on the interferogram is discussed.

The relationship between diffraction efficiency of a reflection hologram and the thickness and absorption coefficient of a recording medium was studied. The diffraction efficiency of a reflection hologram was found to increase monotonically with a decrease in the absorption coefficient (alpha) of the recording medium, but varies nonmonotonically with an increase of the thickness T of the recording medium. Maximum diffraction efficiency was obtained with T and (alpha) satisfied the relationship T equals 1/(alpha) . Finally, we suggest a method to improve the quality of reflection holograms.

A low cost, handheld lidar or laser range finder (LRF) system based on a GaAs laser diode was developed for automotive speed detection and law enforcement. The innovative lidar incorporates a head up display (HUD) to provide both an aiming reticle and data display of range and/or velocity. The design of this eyesafe lidar system is based on shared aperture optics, a pulsed high power Gallium Arsenide laser diode and a proprietary 'telephoto' HUD that allows the use of off the shelf displays. An embedded processor continuously computes range and velocity using a special algorithm optimized for the system.

We show that global and local characteristic features of thermal images undergo considerable diurnal changes. In particular, the standard deviation of the gray-level distribution of thermal images increases with the intensity of the solar flux and the diversity of the microtopography, while the spatial correlation length decreases under the same conditions.

A range sensor based on a laser diode has been developed. The laser diode transmitter and avalanche photodiode receiver are housed adjacently. The laser current monitor generates a 'start' pulse while the receiver generates a 'stop' pulse. The two pulses are input to a Schmitt trigger, monostable multivibrator, inverter and D flip-flop. The flip-flop output pulse train starts and stops a binary counter. The counter output is latched and displayed, giving the range in meters. The paper presents the results of the experiment, giving the flip-flop output pulse width versus the range to a mirror reflecting back the laser diode pulse.

The essential features and performance characteristics of a narrowband isotopic CO2 laser amplifier system are described. Sealed-off operation with over 30 dB net power gain, negligible frequency chirp and up to 70 microsec pulse duration, 300 mJ pulse energy, and 10 Hz pulse repetition rate have been achieved.

ISAR is a form of range-Doppler imaging in which object motion is used to form an image. An account is presently given of the use of laser radar to conduct ambiguity function-like (AFL) and subaperture AFL (SAFL) imaging with all-digital processing. Attention is given to waveform resolution and ambiguities, SAFL image samples, the application of correlation-mixing 'stretch processing', and a plausible design for a heterodyne receiver and generic waveform processor for all-digital stretch processing.

The concept of two magnetically tunable electro-optic (EO) modulators is described. A single-sideband in which the E-O crystal is surrounded by a hollow square tube of ferrite is axially magnetized in a square waveguide. The other is a double sideband device in a rectangular waveguide with the E-O crystal sandwiched between two ferrite slabs oppositely magnetized transverse to the waveguide. Each is tuned by a variable magnetic field in order to match the phase velocities of the varying microwave frequency and the optical velocity of the laser beam. Perturbation theory yields tuning curves of frequency versus magnetic field over a relatively broadband.

A tunable electro-optic single sideband modulator having a configuration consisting of a CdTe crystal surrounded by a ferrite placed inside a microwave waveguide can be used as a laser local oscillator to track the target translational Doppler frequency in a CO2 laser radar return. Results on measurements to determine the phase velocity matched bandwidth for the above composite modulator configuration are reported.

An account is given of a scaled functional testbed laser for space-qualified coherent-detection lidar applications which employs a CO2 laser. This laser has undergone modification and characterization for inherent performance capabilities as a model of coherent detection. While characterization results show good overall performance that is in agreement with theoretical predictions, frequency-stability and pulse-length limitations severely limit the laser''s use in coherent detection

The Hughes Imaging Laser Radar sensor gathers separate range and intensity data channels at 2 megabytes/s/channel. Commercially available SIMD parallel processors provide the horsepower to process this data in real time. In this paper we discuss a fairly generic hardware/software architecture to process this data using an APx-128 SIMD processor for each channel and a 386-based host that provides control of an image display and the recording of features. The expandability and affordability of this approach makes our design applicable to a wide variety of similar problems.

The use of surface-emitting distributed-feedback diode laser arrays in conjunction with microoptics lens arrays to assemble a 10 W power-class laser source exhibiting submilliradian beam divergence is demonstrated. Such a diode laser promises to serve as a low cost, compact, efficient illumination source for imaging laser radar applications. Attention is given to the configuration of the collimating array and the comparative performance of the diode laser array and Fabry-Perot lasers.

Hughes Danbury Optical Systems (HDOS) has developed and flight tested a unique GaAs laser radar which produces high resolution 3-D imagery of the terrain beneath the aircraft. This line scanner is described along with the design parameters used to develop the current model. Improvements planned for the sensor include the addition of an IR channel which would be used to provide passive imagery for target cueing. This would have the effect of reducing the system processing requirements while simultaneously increasing the probability of detection (POD) and reducing the false alarm performance.

The kinetic-cooling effect of a CO2-N2-He gas mixture on the cell placed within a laser cavity is here used as the basis of a scheme for chirp-compensation in an injection-locked TEA CO2 laser. The cooling of the gas is a result of its irradiation by the laser pulse. A kinetics model has been developed in order to determine both temperature and refractive index on the basis of detailed vibrational relaxation kinetics

An examination is conducted of the feasibility of using a Doppler lidar (DL) to detect artificially generated vortices, such as those due to aircraft drag-due-to-lift, and clearly distinguish them from natural gusts and turbulence on the basis of the C(V)-squared constant's magnitude. Both experimental and theoretical results are presented for DL performance; the intersection of the probing DL beam with the aircraft vortex generated a satisfactory Doppler signal whose S/N decreased with increasing distance to the passing aircraft.

A Nd:YAG Raman lidar system is here used to derive the temperature profile of sea water with varying depth by extracting it from the Raman spectrum. The study was conducted both in the laboratory and in situ; the temperature accuracy thus achieved is 0.4 C rms, and the depth-resolution is +/- 1.5 m. Attention is given to the theory of subsurface water temperature detection and the configuration of the detector hardware employed

This paper describes a coherent CO2 laser system. The master laser is stabilized over its tuning range by NH2D Stark cell and the local laser is offset frequency-locked by an electric loop. Error signal produced by NH2D Stark cell is analyzed and the phase fluctuation of the heterodyne signal due to noises is discussed. A 23Hz Allan variance for the beating signal between laser beams has been achieved at 1 s gate time.

An analysis of the theoretical basis for the lidar range equation is here used to characterize the primary factors implicated in the achievement of maximum lidar range. Attention is given to system parameters, the influence of the characteristics of the target object and of the atmospheric medium, and the lidar system's sui generis effects on maximum range.

Sensor simulation codes such as SPARTA''s optical sensor simulation (SENSORSIM) and the Defense Laser-Target Signatures (DELTAS) Code require a high fidelity computer model capable of simulating any type of detection system that might be employed in an optical sensor system. Detection system models for these codes must additionally satisfy sometimes conflicting needs of a diverse user community. Although current detection models in these codes are accurate and easy to use they are limited in the types of detection systems that they can simulate and lack the flexibility to incorporate new detection schemes that are still under development or that may be developed in the future. The authors are developing a comprehensive model of optical detection systems that can be integrated into signature simulation codes such as SENSORSIM and DELTAS. This model uses a radically different approach to simulate the performance of all existing and future detection systems. The model features a hierarchical structure that directly corresponds to the design of a detection system. The first (top) level of this hierarchy represents the overall detection system as an assembly of individual components the components are represented by the second level. Elements of some components such as image intensifier tubes may be represented by a third level. At the lowest level of the hierarchy which may vary from component to component a sequence of mathematical operations describes the behavior of each component or The model simulates a single instance of each random event using a cascaded noise model that is consistent with the philosophy of the SENSORSIM and DELTAS codes. Each detection system is defined by standard text files that follow an intuitive and efficient syntax corresponding to the hierarchy of the detection system model. This input structure allows components to be defined once and incorporated in many detection systems minimizing the library maintenance burden and also facilitates validation of detection system specifications. The specification files can also be transferred between computer systems electronically without special protocols or special conversion of embedded numerical data that would be required for binary files.

This paper describes a performance metric for the evaluation of active coherent imaging systems. This metric can be determined for any system using analytical considerations or measured using standard targets. It has implications for comparison of different imaging systems, optimization of imaging systems, and identification of areas in which significant improvements in particular systems can be realized. The imaging system performance metric described here is suitable for analysis of unconventional imaging systems in which the image is sensed by an array of discrete detectors or in which the image is produced by manipulation of arrays of data. The implications of this formula for determination of photon-efficient and optimized systems are discussed. An important result of this paper will be to show that the efficient use of photons is only part of the story. An efficient system must still be optimized to make best use of the imaging hardware.

In this paper SPARTA reports on the design and field testing of a flexible low-cost diode-based ladar system. It serves as a data collection and research tool that can image extended targets to ranges exceeding 1.0 km and wirelike targets to ranges of 250 m. Range imagery is presented and discussed that illustrates the application to helicopter obstacle avoidance, geophysical mapping, and surveillance.

The detection statistics of avalanche photodiode detectors when used in laser radar systems are examined. In the laser radar systems considered here, a diffuse hard target is illuminated by a transmitted laser beam and the photons subtended by the receiving aperture and focused onto the detector obey negative-binomial statistics. The specific negative-binomial distribution is determined by the coherence length of the laser and the angular subtense of the target. These received photons are converted into photoelectrons and amplified by the avalanche photodiode which is an imperfect device. Dark current, amplifier, and background-produced noise electrons must be exceeded by the avalanche photodiode output electron pulse for a detection to occur. The required mean number of signal photons from a given negative-binomial target as a function of probability of detection and probability of false alarm is calculated. For perfect photon counters, the probability of detection at high discrete false alarm probabilities is also calculated. It is shown that for probabilities of detection of 0.9, three to five times more laser power may be required than for the generally assumed Poisson signal photons case. At probabilities of detection of 0.3, corresponding to multipulse waveforms, the statistics are independent of the target photon distribution.

Coherent ladar detection which is virtually free of oscillator instabilities (random phasing effects) may be obtained through the use of two local oscillator frequencies and subsequent four-wave mixing for heterodyne square-law detection. Such a stabilized four-wave system will allow for more compact, lighter, simpler, and shorter-wavelength coherent ladars.

Vibration signatures from the Low Power Atmospheric Compensation (LACE) satellite were obtained using a ground-based coherent CO2 laser radar facility. Analysis of pulsed CW laser radar measurements of the satellite indicates the presence of complex time-varying vibration modes. These data represent the first observations of satellite vibration modes from a ground-based laser radar.