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Wide-bandgap GaN optically-controlled switches have the potential for driving down the cost and size and improving the efficiency and capabilities of high voltage pulsed-power applications. Key to these applications is the understanding of the high-field photo-conductive properties of this material to determine if it will operate in a high-gain and/or sub-bandgap triggering mode, such as has been observed in GaAs. Photoconductive semiconductor switches (PCSS) were fabricated and tested from GaN wafers from Kyma Technologies and Ammono. With relatively low voltages applied the switch, linear photoconductive currents are measured in response to exposure to laser pulses of sub-bandgap wavelength (532 nm). Above a threshold voltage applied to the PCSS, persistent conductivity is measured that lasts well beyond the duration of the laser pulse and discharges the charged transmission line in the system. The sustaining field for this switching mode is approximately 3kV/cm. Another known distinguishing characteristic of high-gain switching is the formation of filamentary current channels that can be imaged due to the emission of recombination radiation from the plasma within the filaments. These filaments have been also observed in the GaN switches. High-gain switching has been initiated in GaN devices with as little as 2.5 μJ laser energy. This persistent photoconductivity is a distinguishing characteristic of what is known as "lock-on" effect most notably known in GaAs-based photoconductive switches, and is the basis for highly-efficient photoconductive switching requiring relatively little laser energy.

The development and testing of fiber-optically controlled trigger generators (TGs) based on high gain photoconductive semiconductor switches (PCSSs), constructed from high resistivity GaAs, are described in this paper. The TGs are optimized to trigger the high voltage switches (HVSs) in pulsed power systems, where they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total system output. Future pulsed power systems are even more dependent on triggering, as they consist of many more HVS and, in some cases, produce shaped pulses by independent timing of the HVS. The goal of the PCSS TG is to improve timing precision and replace high voltage trigger cables or line-of-sight optics with fiber-optic trigger control. The PCSS trigger has independent EMP-free timing control via 200-mum-diameter optical fibers. This design is simpler than other TG because optical isolation allows PCSS triggers to be remotely located near the HVS at any voltage. PCSS can improve the performance of prime power HVS, diverters, and diagnostics by supplying trigger pulses with subnanosecond jitter and rise time that are more precise and easily adjusted than the conventional TG. For pulse-charged HVS, the PCSS TG can generally derive their trigger energy from the stray fields of the HVS. High gain PCSS capabilities for producing pulsed power TG have been demonstrated previously (not all simultaneously): 220 kV, 8 kA, 350-ps rise time, 100-ns pulsewidth, 50-ps rms jitter, and 10-kHz repetition rate. Furthermore, PCSS has previously triggered a 300-kV trigatron with 100-ps rms jitter.

We report an electrically pumped vertical-external-cavity surface-emitting laser (VECSEL) that is designed for wafer-scale fabrication. Single-mode continuous-wave operation is demonstrated at a wavelength of 970 nm. The device structure incorporates a curved micromirror output coupler that is produced using a micromolding process. In addition to outlining the VECSEL fabrication process, we quantify its spatial and spectral modal characteristics.

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.

High current switching is the most critical challenge remaining for photoconductive semiconductor switch (PCSS) applications in Pulsed Power. Many authors have described the advantageous properties of high gain PCSS such as, low optical trigger energy and inductance, sub-nanosecond risetime and jitter, optical isolation and control, pulsed or DC charging, and long device lifetime, provided the current per filament is limited to 20–30A for short pulse (10–20ns) applications [1,2]. Low energy optical triggering, long device lifetime, and current filaments are related features of high gain PCSS that make high current switching a challenge. Since the location and number of current filaments can be controlled with parallel “lines” of optical pulses across the insulating gap, the problem of high current, multi-filament PCSS switching is essentially the problem of producing a reliable, efficient, multi-line, optical delivery system [3].

Advanced optically-activated solid-state electrical switch development at Sandia has demonstrated multi-kA/kV switching and the path for scalability to even higher current/power. Realization of this potential requires development of new optical sources/switches based on key Sandia photonic device technologies: vertical-cavity surface-emitting lasers (VCSELs) and photoconductive semiconductor switch (PCSS) devices. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher is to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators. Commercial mechanically-stacked edge-emitting lasers have been used to trigger multiple filaments, but they are difficult to scale and manufacture with the required uniformity. In VCSEL arrays, adjacent lasers utilize identical semiconductor material and are lithographically patterned to the required dimensions. We have demonstrated multiple-line filament triggering using VCSEL arrays to approximate line generation. These arrays of uncoupled circular-aperture VCSELs have fill factors ranging from 2% to 30%. Using these arrays, we have developed a better understanding of the illumination requirements for stable triggering of multiple-filament PCSS devices. Photoconductive semiconductor switch (PCSS) devices offer advantages of high voltage operation (multi-kV), optical isolation, triggering with laser pulses that cannot occur accidentally in nature, low cost, high speed, small size, and radiation hardness. PCSS devices are candidates for an assortment of potential applications that require multi-kA switching of current. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher is to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators. Commercial mechanically-stacked edge-emitting lasers have been demonstrated to trigger multiple filaments, but they are difficult to scale and manufacture with the required uniformity. As a promising alternative to multiple discrete edge-emitting lasers, a single wafer of vertical-cavity surface-emitting lasers (VCSELs) can be lithographically patterned to achieve the desired layout of parallel line-shaped emitters, in which adjacent lasers utilize identical semiconductor material and thereby achieve a degree of intrinsic optical uniformity. Under this LDRD project, we have fabricated arrays of uncoupled circular-aperture VCSELs to approximate a line-shaped illumination pattern, achieving optical fill factors ranging from 2% to 30%. We have applied these VCSEL arrays to demonstrate single and dual parallel line-filament triggering of PCSS devices. Moreover, we have developed a better understanding of the illumination requirements for stable triggering of multiple-filament PCSS devices using VCSEL arrays. We have found that reliable triggering of multiple filaments requires matching of the turn-on time of adjacent VCSEL line-shaped-arrays to within approximately 1 ns. Additionally, we discovered that reliable triggering of PCSS devices at low voltages requires more optical power than we obtained with our first generation of VCSEL arrays. A second generation of higher-power VCSEL arrays was designed and fabricated at the end of this LDRD project, and testing with PCSS devices is currently underway (as of September 2008).

This paper describes technologies developed at Sandia National Laboratories to create a compact, robust, and affordable photonic proximity sensor for munitions fuzing. The proximity fuze employs high-power vertical-cavity surface-emitting laser (VCSEL) arrays, resonant-cavity photodetectors (RCPDs), and refractive micro-optics that are integrated within a microsensor whose volume is approximately 0.01 cm 3 . Successful development and integration of these custom photonic components should enable a g-hard photonic proximity fuze that replaces costly assemblies of discrete lasers, photodetectors, and bulk optics. Additional applications of this technology include void sensing, ladar and short-range 3-D imaging.

This paper describes results from a 3 year project to develop fiber-optically controlled trigger generators (TG) from high gain photoconductive semiconductor switches (PCSSs) for high voltage switches (HVSs) in pulsed power applications. Triggers for HVSs are critical components for reliable, efficient pulsed power systems because they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total output. Proposed pulse power systems are even more dependent on triggering as they consist of many triggered HVSs and produce shaped-pulses by independent timing of the HVSs.

We are developing advanced optically-activated solid-state switch technology for Firing Sets. Advanced switch development at Sandia has demonstrated multi-kA/kV switching and the path for scalability to even higher current/power, resulting in good prospects for sprytron replacement and other even higher current pulsed power switching applications. Realization of this potential requires development of new optical sources/switches based on key Sandia photonic device technologies: vertical-cavity surface-emitting lasers (VCSELs) and photoconductive semiconductor switch (PCSS) devices. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher has been to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators [Mar, A., et al., 2001]. This was limited by commercial mechanically-stacked edge-emitting lasers, which are difficult to scale and manufacture with the required uniformity. In VCSEL arrays, adjacent lasers utilize identical semiconductor material and are lithographically patterned to the required aspect ratio. However, we have demonstrated that good optical uniformity in rectangular-aperture (e.g. 5-by-500 mum) VCSELs is difficult to achieve due to the lack of optical confinement in the long dimension. We have demonstrated line filament triggering using 1-D VCSEL arrays to approximate line generation. These arrays of uncoupled circular-aperture VCSELs have fill factors ranging from 2% to 50%. Using these arrays, we are developing a better understanding of the illumination requirements for stable triggering of multiple-filament PCSS devices. In particular, we are examining the dependence of filament formation versus the illumination fill factor and spatial brightness along the length of the filament. Ultimately, we will apply effective index techniques, pioneered at Sandia for leaky-mode VCSELs, to create a lateral photonic lattice that selects a single transverse mode with high brightness and uniformity for even higher fill factors and illumination unformity [Zhou, D., et al., 2000]. These sources will be developed and tested with complementary PCSS designs employing interdigitated multifilament contacts for high-power switching.

Pulsed power systems are continually being designed to increase performance and flexibility in order to meet new needs. Drivers for fusion, equation of state research and radiography are just a few of the scientific areas driving accelerated pulsed power development. Improved system timing and jitter requirements, along with pulse shaping capabilities through independent timing of individual switches, are placing higher demands upon high voltage (HV) switch performance, triggering system performance and cost. Conventional trigger systems require high voltage trigger cables or line-of-sight optics that complicate design, demand space, require extensive maintenance, and significantly impact system cost. With electrical triggers, large diameter, high voltage transmission line cables must be fed through high field regions. With optical triggers, line-of-sight optics must focus high energy laser beams to the interior of the switches with clean, rigidly-mounted, shock-withstanding optics. This paper reports on progress in the development of fiber optically triggered photoconductive semiconductor switches (PCSS) for triggering high voltage pulsed power switches with improved precision. This technology can eliminate the need for large-diameter trigger cables and line-of-sight optics. It also has the potential of significantly reducing the cost of trigger generation systems. It has the potential to improve the performance of prime power switches, diverters, and diagnostics because of the low-jitter sub-nanosecond rise times. Test results will be presented that demonstrate sub-nanosecond jitter from a PCSS, less than 1.

The first monolithic photonic integrated circuit for all-optical generation of millimeter (mm)-wave electrical signals is reported. The design integrates a mode-locked semiconductor ring diode laser, an optical amplifier, and a high-speed photodetector into a single optical integrated circuit. Signal generation is demonstrated at frequencies of 30, 60, and 90 GHz.

Firing systems typically incorporate isolation-based architectures that are established by the safety themes of particular weapon systems. Robust electrical diversion barriers are implemented to isolate energy from detonation-critical components until the event of intended use of the system. An optical trigger assembly is being developed to enhance the safety of new firing systems. It couples a fast trigger signal through an exclusion region barrier without compromising the integrity of the barrier in abnormal environment situations. A laser diode generates an optical pulse that is coupled through a sapphire stub to a photoconductive semiconductor switch (PCSS). The PCSS drives a vacuum switch tube to complete the triggering chain in the firing system. A general discussion and comparison of triggering technology options, and the design characteristics and performance parameters of the specific optical trigger point design are presented in this paper.

This paper describes the photonic component development taking place at Sandia National Laboratories, ARDEC and the Army Research Laboratory in support of an effort to develop a robust, compact, and affordable photonic proximity sensor for munitions fuzing applications. Successful implementation of this sensor will provide a new capability for direct fire applications. The technologies under investigation for the optical fuze design covered in this paper are vertical-cavity surface-emitting lasers (VCSELs), vertical-external-cavity surface-emitting lasers (VECSELs), integrated resonant-cavity photodetectors (RCPDs), and refractive micro-optics. The culmination of this work will be low cost, robust, fully integrated, g-hardened components suitable for proximity fuzing applications. The use of advanced photonic components will enable replacement of costly assemblies that employ discrete lasers, photodetectors, and bulk optics. The integrated devices will be mass produced and impart huge savings for a variety of Army applications. The specific application under investigation is for gun-fired munitions. Nevertheless, numerous civilian uses exist for this proximity sensor in automotive, robotics and aerospace applications. This technology is also applicable to robotic ladar and short-range 3-D imaging.

Vertical-external-cavity surface-emitting lasers (VECSELs) combine high optical power and good beam quality in a device with surface-normal output. In this paper, we describe the design and operating characteristics of an electrically-pumped VECSEL that employs a wafer-scale fabrication process and operates at 850 nm. A curved micromirror output coupler is heterogeneously integrated with AlGaAs-based semiconductor material to form a compact and robust device. The structure relies on flip-chip bonding the processed epitaxial material to an aluminum nitride mount; this heatsink both dissipates thermal energy and permits high frequency modulation using coplanar traces that lead to the VECSEL mesa. Backside emission is employed, and laser operation at 850 nm is made possible by removing the entire GaAs substrate through selective wet etching. While substrate removal eliminates absorptive losses, it simultaneously compromises laser performance by increasing series resistance and degrading the spatial uniformity of current injection. Several aspects of the VECSEL design help to mitigate these issues, including the use of a novel current-spreading n type distributed Bragg reflector (DBR). Additionally, VECSEL performance is improved through the use of a p-type DBR that is modified for low thermal resistance.

Optically activated high voltage switches are commonly used in pulsed power systems for reliable low jitter, multichannel and multiswitch (low inductance) applications. In addition to low jitter switching, optical activation provides a high degree of electrical isolation between the triggering and switching power systems simplifying pulsed power design. The disadvantages of optical triggering for large-gap gas switches are the optical energy, line-of-sight optics, and system maintenance required to obtain reliable operation. This paper describes two technologies which can reduce or eliminate these disadvantages and provide more flexible optically activated switches for pulsed power systems. One approach is to reduce the optical trigger energy requirement for gas gap switches. Shorter optical pulses require less energy to initiate a plasma discharge. An experiment is being assembled to trigger a 50-100 kV gas gap switch with 120 fs wide optical pulses. Lower trigger energy has also been demonstrated by the introduction of metallic aerosols into a gas gap W. Frey (1997). The apparatus will be added to this experiment to reproduce these results and determine the optical energy and power density requirements over a range of wavelengths and pulse widths. The status of this experiment will be discussed. A second approach uses solid state switching in two configurations: (1) as the main switch and (2) as a trigger. High-gain photoconductive semiconductor switches (PCSS) are practical for some direct pulsed power switching applications. We have demonstrated switching up to 220 kV and 8 kA. Higher power optically activated switching can be obtained by combining solid state and gas gap switching technologies. Multimegavolt (MMV) switches can be triggered with fiber-optically triggered, remotely located PCSS. By placing the compact PCSS trigger extremely close to the trigger point, reliable, low-jitter, high power switching is achieved with low energy fiber-optic trigger systems that can easily be controlled and adjusted from a remote control center. Power for the trigger system can be derived from the electrical fields near the trigger, so all electrical cables to the trigger system are eliminated and replaced with 100 micron diameter fibers that trigger and monitor the operation of the system. Results from experiments with PCSS triggered gas gap switches and the design for a PCSS triggered multimegavolt switch will be reported. PCSS switching properties including new picosecond pulse results and fabrication procedures for improved longevity will also be described. A 120 fs wide 780 nm laser pulse was used to radiate THz bandwidth pulses with a GaAs PCSS operating in the linear mode. New approaches for PCSS contact fabrication are being developed and tested to simplify the growth procedure, increase the current per filament capability, and improve device longevity. Progress continues to make PCSS a more useful component for pulsed power applications.

Summary form only given. Record (14.5 W) peak powers and pulse energies of 490 pJ from a gain-switched flared waveguide quantum-well laser are presented in this paper. Because of their compactness, reliability, efficiency, and relatively low cost, semiconductor lasers are attractive sources of picosecond optical pulses of high peak power. The flared waveguide expands the optical mode from a narrow region which gives a single lateral optical mode, to a wider multimode region for higher power. Flared laser amplifiers have previously been used for mode-locking, Q- and gain-switching of diode lasers. Flared structures have also been utilized for post-amplification to achieve high peak power. Gain-switching offers a considerable advantage in terms of simplicity over mode-locking, in that no resonant cavity is required to be synchronous with the electrical drive, while the external amplifier approach requires additional alignments. High single-mode peak powers have also been obtained from bulk single-heterostructure lasers with ion implanted saturable absorbers. In this work, we gain-switch a flared waveguide laser with a reverse-biased saturable absorber section to obtain high peak powers and pulse energies from a single laser diode without post-amplification. Numerical simulations based on a microscopic laser model verify the effectiveness of the saturable absorber in the generation of high peak power, single-pulse output. Insight obtained from the model suggests that the quantum-confined Stark effect is primarily responsible for saturable absorber operation.

High gain GaAs photoconductive semiconductor switches (PCSS) are being used in a variety of electrical and optical short pulse applications. The highest power application, which we are developing, is a compact, repetitive, short pulse linear induction accelerator. The array of PCSS, which drive the accelerator, will switch 75 kA and 250 kV in 30 ns long pulses at 50 Hz. The accelerator will produce a 700 kV, 7kA electron beam for industrial and military applications. In the low power regime, these switches are being used to switch 400 A and 5 kV to drive laser diode arrays which produce 100 ps optical pulses. These short optical pulses are for military and commercial applications in optical and electrical range sensing, 3D laser radar, and high speed imaging. Both types of these applications demand a better understanding of the switch properties to increase switch lifetime, reduce jitter, optimize optical triggering, and improve overall switch performance. These applications and experiments on the fundamental behavior of high gain GaAs switches is discussed. Open shutter, infra-red images and time-resolved Schlieren images of the current filaments, which form during high gain switching, are presented. Results from optical triggering experiments to produce multiple, diffuse filaments for high current repetitive switching are described.

We present performance and modeling results for a new class of semiconductor laser that can potentially produce much more short pulse energy than conventional (injection-pumped) semiconductor lasers. High energy operation is possible because this new laser is not limited in volume or aspect ratio by the depth of a p-n junction. These lasers are created from current filaments in semi-insulating GaAs where low-field avalanche carrier generation produces a high-density, charge-neutral plasma channel having the required carrier density distribution for lasing. We have tested current filament semiconductor lasers (CFSL) that have produced 75 nJ of 890 nm light in 1.5 ns (50 W peak), approximately ten times more energy than conventional lasers. Current filaments as long as 3.4 cm and several hundred microns in diameter have been observed in our high-gain GaAs photoconductive switches. The smallest dimension of these filaments can be more than 100 times the carrier diffusion length in GaAs. It is this large active volume that enables the observed high laser output energy. This paper reports spectral narrowing, lasing thresholds, beam divergence, temporal narrowing, and energies for several configurations of CFSL. We also discuss results from models developed to simulate the unusual gain phenomena and mechanism for obtaining transparency within the electron-hole plasma of the current filament.

This paper reports on a recent comparison made between the Air Force Research Laboratory (AFRL) gallium arsenide, optically-triggered switch test configuration and the Sandia National Laboratories (SNL) gallium arsenide, optically-triggered switch test configuration. The purpose of these measurements was to compare the temporal switch jitter times. It is found that the optical trigger laser characteristics are dominant in determining the PCSS jitter.

We have developed high power vertical cavity surface emitting lasers (VCSELS) for multimode or single mode operation. We have characterized new cavity designs for individual lasers and 2-dimensional VCSEL arrays to maximize output power. Using broad area high power VCSELS under pulsed excitation, we have demonstrated the triggering of a photoconductive semiconductor switch (PCSS) with a VCSEL. We also have developed designs for high output power in a single mode. The first approach is to engineer the oxide aperture profile to influence the optical confinement and thus modal properties. A second approach focuses on "leaky-mode" concepts using lateral modification of the cavity resonance to provide the lateral refractive index difference. To this end, we have developed a regrowth process to fabricate single-mode VCSELS. The overall objective of this work was to develop high-power single-mode or multimode sources appropriate for many applications leveraging the many inherent advantages of VCSELS.

Generation of millimeter-wave electronic signals and power is required for high-frequency communication links, RADAR, remote sensing and other applications. However, in the 30 to 300 GHz mm-wave regime, signal sources are bulky and inefficient. All-optical generation of mm-wave signals promises to improve efficiency to as much as 30 to 50 percent with output power as high as 100 mW. All of this may be achieved while taking advantage of the benefits of monolithic integration to reduce the overall size to that of a single semiconductor chip only a fraction of a square centimeter in size. This report summarizes the development of the first monolithically integrated all-optical mm-wave signal generator ever built. The design integrates a mode-locked semiconductor ring diode laser with an optical amplifier and high-speed photodetector into a single optical integrated circuit. Frequency generation is demonstrated at 30, 60 and 90 Ghz.

Mode-locked semiconductor lasers have drawn considerable attention as compact, reliable, and relatively inexpensive sources of short optical pulses. Advances in the design of such lasers have resulted in vast improvements in pulsewidth and noise performance, at a very wide range of repetition rates. An attractive application for these lasers would be to serve as alternatives for large benchtop laser systems such as dye lasers and solid-state lasers. However, mode-locked semiconductor lasers have not yet approached the performance of such systems in terms of output power. Different techniques for overcoming the problem of low output power from mode-locked semiconductor lasers will be discussed. Flared and arrayed lasers have been used successfully to increase the pulse saturation energy limit by increasing the gain cross section. Further improvements have been achieved by use of the MOPA configuration, which utilizes a flared semiconductor amplifier s amplify pulses to energies of 120 pJ and peak powers of nearly 30W.

High-speed studies of packaged, submilliampere threshold, oxide-confined vertical cavity surface emitting lasers show modulation bandwidths > 16 GHz. Very high modulation current efficiency factors occur at low bias but decrease as the modulation bandwidth and frequency of the relative intensity noise peak saturate at higher currents.

Selectively oxidised vertical-cavity lasers which exhibit self-pulsating lasing at currents as low as 470 nA are reported. Characteristics including linearly polarised emission, narrow linewidths and coherent near- and far-field diffraction indicate that these devices operate as lasers at DC currents 1 mA.

We propose a novel technique to accurately measure submi-cron linewidths on photomasks and wafers. We do this by translating a phase-shifting mask across the surface containing the line whose width we wish to measure. With a Fourier-transform lens, we detect the intensity of the zero-order spatial component of the light coming from the surface as a function of the mask position. We show that the detected intensity curve varies dramatically and exhibits sharp changes in direction corresponding to the boundaries of the line. From this informa-tion the linewidth is readily apparent. We present a theoretical analysis and several computer simulations, showing that the technique is relatively independent of variations in the optical reflectance and in the height between the patterned feature and any substrate. Unlike other optical imaging methods for measur-ing linewidths, a high-resolution microscope and precise calibration are not needed. Using a laser, lateral resolution of 0.1 μm , well beyond the limit predicted by the Rayleigh criterion, is theoretically achievable. Preliminary experimental results agree well with the theoretical prediction.

We propose a new technique for robotic positioning and calibration which utilizes holographic imaging and interferometry to avoid the disadvantages associated with conventional techniques. This technique allows both gross and fine positioning of robotic devices in space and is useful in situations where it is necessary to repeatably position a moving device to a specific location. Gross positioning is accomplished by matching the robotic device to a holographic virtual image, using a computer vision system to overlap key features of the robotic device on their holographically imaged counterparts. The use of holographic images is an advantage because the robot cannot obscure them from view or collide with them. Fine positioning is achieved to better than one-micron accuracy by utilizing the interference fringes that result when the robotic device and the holographic image are aligned to within about 50 microns of each other. Elimination of the fringes indicates exact coincidence between the robot and its holographic counterpart. A computer vision system was utilized to automate the entire positioning procedure. Theory, algorithms, and experimental implementation are described.