LIDAR-based systems measure the time-of-flight of a laser source onto the scene and back to the sensor, building a wide
field of view 3D raster image, but as a scanning process, there are problems associated with motion inside the scene over
the duration of the scan. By illuminating the entire scene simultaneously using a broad laser pulse, a 2D camera
equipped with a high speed shutter can measure the time-of-flight over the entire field of view (FOV), thereby, recording
an instantaneous snap-shot of the entire scene. However, spreading the laser reduces the range. So what is required is a
programmable system that can track multiple regions of interest by varying the field of regard to (1) a single direction, (2)
the entire FOV, or (3) intermediate views of interest as required by the evolving scene environment. In this project, the
investigators intend to add this variable illumination capability to existing instantaneous ranging hardware by using a
liquid crystal spatial light modulator (SLM) beam steering system that adaptively varies the (single or multi) beam
intensity profiles and pointing directions. For autonomous satellite rendezvous, docking, and inspection, the system can
perform long-range sensing with a narrow FOV while being able to expand the FOV as the target object approaches the
sensor. To this end in a previous paper, we analyzed the performance of a commercially available TOF sensor
(3DVSystems' Zmini) in terms of the depth sensitivity versus target range and albedo. In this paper, we will analyze the
laser system specifications versus range of field-of-view when beam steering is performed by means of a Boulder
Nonlinear Systems' phase-only liquid crystal SLM. Experimental results show that the adjustable laser beam FOV
extensively compensate the reflected image grayscale from objects at long range, and prove the feasibility of expanding
range with the projection from the SLM.
A multi-beam, variable footprint, laser beam steering and shaping system is described and used with a microscope to demonstrate multi-particle laser trapping. It is built around a computer-interfaced 512x512 pixel analog phase-only spatial light modulator (SLM) and a 1 W, 1064 nm wavelength laser. Hand sketches on paper made with a digital pen are used to prescribe the footprints, velocities and trajectories of multiple, independently-controlled diffracted spots. Continuous scanning is approximated by automatically designing a sequence of phase-patterns that are run through and diffracted by the SLM. Very complex scanning sequences of dozens of independently controlled spots can be quickly designed and run. The number of beams that we can trap with is necessarily limited due to the low throughput (~23 mW) of the IR light through the microscope optics. Among the trapping experiments done with the system a triangular shaped vortex ring tends to stop single particles at the apexes of the triangle. However, collision with a second particle pushes the first particle past the apex and sets it into motion, leaving the second particle stopped until collision with a third particle. The discrete motion conditioned on collisions is suggestive of a queuing process or a Markov chain.
The advantages of laser communications including high bandwidth, resistance to jamming and secure links have made it a key technology for current and future C4ISR capabilities. Laser Communications between space/air/ground/sea-based assets may require multiple links. One advantage of this redundancy is that the signal is more likely to reach the intended receiver even if the environmental conditions are poor for laser transmission. In addition, multiple links provide simultaneous receipt of information to various assets engaged in activities that may need to be coordinated. That is, multibeam laser communication mimics the "broadcast" advantage of RF communications but with less likelihood of jamming or intercept. Liquid Crystal spatial light modulators are a versatile optical head that can be used for multispot beam steering applications. One advantage of the liquid crystal approach to multibeam laser communication is that the device is a modulator in addition to a mirror, so that one could conceivably send different signal amplitudes to different locations simultaneously. This paper discusses recent improvements to a 5 12x5 1 2 spatial light modulator that is specifically implemented as a multispot beamsteerer. This will include characterization of the device, analysis of its performance, and what improvements should be incorporated into the next generation device.