Holographic aperture ladar with range compression.

Simultaneous range compression and aperture synthesis is experimentally demonstrated with a stepped linear frequency modulated waveform and holographic aperture ladar. The resultant three-dimensional (3D) data has high resolution in the aperture synthesis dimension and is recorded using a conventional low bandwidth focal plane array. Individual cross-range field segments are coherently combined using data driven registration and phase correction methods allowing range compression to be performed without the benefit of a coherent waveform.

Phase gradient algorithm method for three-dimensional holographic ladar imaging.

Three-dimensional (3D) holographic ladar uses digital holography with frequency diversity to add the ability to resolve targets in range. A key challenge is that since individual frequency samples are not recorded simultaneously, differential phase aberrations may exist between them, making it difficult to achieve range compression. We describe steps specific to this modality so that phase gradient algorithms (PGA) can be applied to 3D holographic ladar data for phase corrections across multiple temporal frequency samples.

Saturated semiconductor optical amplifier phase modulation for long range laser radar applications.

We investigate the use of a semiconductor optical amplifier operated in the saturation regime as a phase modulator for long range laser radar applications. The nature of the phase and amplitude modulation resulting from a high peak power Gaussian pulse, and the impact this has on the ideal pulse response of a laser radar system, is explored. We also present results of a proof-of-concept laboratory demonstration using phase-modulated pulses to interrogate a stationary target.

Demonstrated resolution enhancement capability of a stripmap holographic aperture ladar system.

Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL). The two processes are related in that they both seek to increase cross-range (i.e.

Experimental demonstration of a stripmap holographic aperture ladar system.

By synthesizing large effective apertures through the translation of a smaller imaging sensor and the subsequent proper phasing and correlation of detected signals in postprocessing, holographic aperture ladar (HAL) systems seek to increase the resolution of remotely imaged targets. The stripmap HAL process was demonstrated in the laboratory, for the first time to our knowledge. Our results show that the stripmap HAL transformation can precisely account for off-axis transmitter induced phase migrations.

Improving mid-frequency contrast in sparse aperture optical imaging systems based upon the Golay-9 array.

Sparse aperture imaging systems are capable of producing high resolution images while maintaining an overall light collection area that is small compared to a fully filled aperture yielding the same resolution. This is advantageous for applications where size, volume, weight and/or cost are important considerations. However, conventional sparse aperture systems pay the penalty of reduced contrast at midband spatial frequencies.

Periodic, pseudonoise waveforms for multifunction coherent ladar.

We report the use of periodic, pseudonoise waveforms in a multifunction coherent ladar system. We exploit the Doppler sensitivity of these waveforms, as well as agile processing, to enable diverse ladar functions, including high range resolution imaging, macro-Doppler imaging, synthetic aperture ladar, and range-resolved micro-Doppler imaging. We present analytic expressions and simulations demonstrating the utility of pseudonoise waveforms for each of the ladar modes.

Monte Carlo simulation of multiple photon scattering in sugar maple tree canopies.

Detecting objects hidden beneath forest canopies is a difficult task for optical remote sensing systems. Rather than relying upon the existence of gaps between leaves, as other researchers have done, our ultimate goal is to use light scattered by leaves to image through dense foliage. Herein we describe the development of a Monte Carlo model for simulating the scattering of light as it propagates through the leaves of an extended tree canopy.

Holographic aperture ladar.

Holographic aperture ladar is a variant of synthetic aperture ladar that seeks to increase cross-range scene resolution by synthesizing a large effective aperture through the motion of a smaller receiver and through the subsequent proper phasing and correlation of the detected signals in postprocessing. Unlike in conventional synthetic aperture ladar, however, holographic aperture ladar makes use of a two-dimensional translating sensor array, not simply a translating point detector. Also unlike in conventional synthetic aperture ladar, holographic aperture images will be formed in the two orthogonal cross-range dimensions parallel and perpendicular to the sensor platform's direction of motion.

Real-time, frequency-translated holographic visualization of surface acoustic wave interactions with surface-breaking defects.

A real-time, frequency-translated holographic imaging system has been developed by use of bacteriorhodopsin film. The system provides a capability for imaging surface acoustic waves and has been utilized to detect and characterize surface-breaking defects through near-field ultrasonic scattering effects. Frequency-plane filtering was used to discriminate between ultrasonic standing-wave and near-field scattering features, dramatically enhancing the holographic visualization of the defect sites.

Bidirectional scattering distribution functions of maple and cottonwood leaves.

We present our investigations into the optical scattering properties of both sugar maple (Acer saccarum) and eastern cottonwood (Populus deltoides) leaves in the near-IR wavelength regime. The bidirectional scattering distribution function (BSDF) describes the fractions of light reflected by and transmitted through a leaf for a given set of illumination and observation angles. Experiments were performed to measure the BSDF of each species at a discrete set of illumination and observation angles.

Optical sparse aperture imaging.

The resolution of a conventional diffraction-limited imaging system is proportional to its pupil diameter. A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area; the latter being desirable, in part, because of the cost of large, monolithic apertures. Performance metrics are defined and used to evaluate several sparse aperture arrays constructed from multiple, identical, circular subapertures.

Imaging diffractometer with holographic encoding enhancements for laser sensing and characterization.

What is believed to be a novel holographic optical encoding scheme has been developed to enhance the performance of laser sensors designed for the measurement of wavelength and angular trajectory. A prototype holographic imaging diffractometer has been created to reconstruct holographic cueing patterns superimposed in the focal plane of wide-angle scene imagery. Based on experimental pattern metric measurements at the focal plane, a theoretical model is used to compute the laser source wavelength and its apparent propagation direction within the sensor's field of view.

Aberration production using a high-resolution liquid-crystal spatial light modulator.

Phase-only liquid-crystal spatial light modulators provide a powerful means of wavefront control. With high resolution and diffractive (modulo 2pi) operation, they can accurately represent large-dynamic-range phase maps. As a result, they provide an excellent means of producing electrically controllable, dynamic, and repeatable aberrations.

High-speed Shack-Hartmann wavefront sensor design with commercial off-the-shelf optics.

Several trade-offs relevant to the design of a two-dimensional high-speed Shack-Hartmann wavefront sensor are presented. Also outlined are some simple preliminary experiments that can be used to establish critical design specifications not already known. These specifications include angular uncertainty, maximum measurable wavefront tilt, and spatial resolution.

Space-bandwidth product enhancement of a monostatic, multiaperture infrared image upconversion ladar receiver incorporating periodically poled liNbO3.

We investigate the space-bandwidth product of a ladar system incorporating an upconversion receiver. After illuminating a target with an eye-safe beam, we direct the return into a piece of periodically poled LiNbO3 where it is upconverted into the visible spectrum and detected with a CCD camera. The theoretical and experimental transfer functions are then found.