Scientific Research and Analysis
Specializing in Optical Physics

RAN Science & Technology LLC

RAN Science & Technology, LLC, was founded in 2007 by three scientists with a combined 75 years of experience in optical physics research.  With over a decade in SBIR research, we have learned to respond rapidly and accurately to our customers' needs. 

Please look through our website and find out more about our research interests, capabilities, and experience.

©2010 RAN Science & Technology, LLC. All rights reserved.

About RAN Science & Technology, LLC

Research & Development Expertise

RAN Science & Technology, LLC boasts recognized experts in holography, holographic measurement technology, holographic optical elements, nonlinear optics, photorefractivity, nanotechnology, short- and long-range target detection and recognition, active and passive tracking, solar energy, and infrared illumination systems.  We not only have experience in research, but also in consulting with both research and production companies.  Our R&D experience has taught us to respond rapidly to our customer's needs, rapidly enough to have been awarded several government SBIR contracts.

Russell Kurtz, Ph.D., Chief Scientist

RAN's Chief Scientist is Russell Kurtz, Ph.D., who received his S.B. in electrical engineering from the Massachusetts Institute of Technology (MIT), and his Ph.D. in quantum electronics and optics from the University of Southern California (USC).

Dr. Kurtz was instrumental in early research into four‑wave mixing phase conjugation in an active gain medium, helped develop a low‑signal reception system using optical parametric amplification, and, under a grant from Allied‑Signal Corporation, developed unique laser materials.  Dr. Kurtz’s recent achievements include the development of high‑power laser arrays, improved visible‑to‑infrared scene generators, and a high‑PRF, short-pulse laser system.

His research interests include applications of solid‑state lasers, phase conjugation, nonlinear optics in liquids and liquid crystals, application of nonlinear optics to improvements in lasers, improvements to infrared sensors, nondestructive evaluation, and new laser materials. His recent work has concentrated on high‑speed infrared photodetectors, automultiscopic 3D displays, and nanomotion measurement.

Dr. Kurtz’s wide‑ranging expertise in lasers includes solid state, including unique ions, multiple wavelength lasers, and high‑power systems; chemical and gas, with experience in optimization, discard of toxic by‑products, and high‑power systems; and semiconductor.  He is highly proficient in nonlinear optics, having experience in phase conjugation, in solids (including his invention of the phase conjugate interferometer, used in nanomotion detection), liquids, gases, and plasma. Dr. Kurtz participated in early experiments demonstrating four‑wave mixing phase conjugation in an active chemical laser medium.

Working as Director of Holographic Systems at Principal Optics Corporation, Kurtz oversaw the development of the predistorted HOE. His in‑depth knowledge of displays is demonstrated by his development of automultiscopic and autostereoscopic 3D systems and high‑resolution helmet‑mounted displays.

Dr. Kurtz worked in sensors for several years, developing successful projects in radar, infrared, and visible imaging and nonimaging systems.  He also wrote some of the most useful modeling software in these areas.  His understanding of displays and sensors led to technological breakthroughs in the fields of scene projection and hardware‑in‑the‑loop testing.  Dr. Kurtz recently combined his expertise in quantum electronics, semiconductor physics, and detector arrays to invent the “quantum dust” photodetector, an inexpensive, high‑speed sensor for the telecommunications band.  He has combined all his fields of knowledge in developments in nondestructive testing and inspection.  His nonlinear optics and sensing expertise led Dr. Kurtz to identify and explain the Fast Photorefractive Effect, and apply this effect to low-signal, long-range tracking.

His patent disclosures include a Digital Integrated Shearographic Camera, an Improved Laser‑Pumped Laser Cavity, seven other inventions related to laser systems, Ultralong Range Vibrometry, the Nanodust nanoelectrical optical detector, and th Phase Conjugate Micromotion Detector.

Dr. Kurtz is a Life Member of the Association of Old Crows and SPIE, a Senior Member of IEEE (including LEOS, EMS, EMBS, and ISA), and a Member of OSA, ASNT, DEPS, LIA, and AAAS, and has published more than a dozen papers in referred journals.  Dr. Kurtz is a U.S. citizen.

More Information Available

In addition to Dr. Kurtz, RAN scientists include a well-known expert in holography and applications of holographic optical elements, a physicist with over 30 years' experience in nonlinear optics, one of the early laser pioneers, and an expert in optoelectronic circuitry.

For more information, please send us a message, either by email at or by clicking on the Contact Us tab above.

©2010 RAN Science & Technology, LLC. All rights reserved.

Scientific Analysis
at RAN Science & Technology, LLC

Validation of Science & Technology

We have experience in studying scientific and technological concepts to determine whether or not they are likely to succeed. Our many years of experience in Physics and Engineering make RAN your best choice for concept validation. We can check your concepts' potential in science (including being sure they don't violate the laws of physics), technology (and consider how easy it will be to manufacture these products), and even some market analysis (to optimize your target market and look for existing competitors). Based on our years of marketing science and technology, we can validate your concepts and, if desired, produce a report of our analysis that you can present to investors, board members, or others who need to know more about your ideas. We can write this report at whatever level of technical language you desire, so it can be presented to scientists, managers, or investors.

Optimization and Design

The scientists at RAN Science & Technology, LLC, have nearly a century of experience in science and engineering.  We can apply this experience to your projects, designing sections of the project as needed.  We have expertise and understanding in designing experiments that will easily and accurately measure exactly what you want to measure, and can also eliminate random factors that may affect your experiments.  In addition, we can review your designs and suggest how to optimize them for specific purposes (laboratory demo, productization, etc.).

Analysis for Investment

A line of business that is new to RAN, but not to our top scientists, is reviewing concepts for development.  We’ve seen many cases where a company wants investors to fund a specific project.  The investors look at it, and it looks good, so they do their due diligence on the company and the market, and find that the company’s stock price will soar after this project.  What have they forgotten?  They don’t know if the concept is feasible!  We have experience studying these concepts and projects, looking at their possibilities and some of their market potential, and determining how feasible the projects are from a technical standpoint.  Then we translate this analysis into everyday English to explain why the project is or is not likely to succeed.  (This service does not replace due diligence, it is an additional service that should be exercised if you are considering an investment in new science or technology.)

A Note On Security

If you hire RAN Science & Technology, LLC, to perform consulting or analysis for you, you should know that your information is safe.  We do not share any information between companies, and we do not use the analyzed technology in any way.  We have decades of experience guarding data.  The lead members of RAN all have either active or recent security clearances, and we are experienced in protecting government data through the International Trade in Arms Regulations (ITAR).  We have been trusted by, and executed nondisclosure agreements and proprietary information agreements with, companies such as Boeing and Northrop Grumman, and both federal and state governments.  We would be happy to execute an information protection agreement with you, and expect to do so before beginning any analysis project.

©2010 RAN Science & Technology, LLC. All rights reserved.

Research by the Scientists of RAN Science & Technology, LLC

1 rod capacityLaser Systems and Applications

  • High Power Laser Systems
  • Laser Cavity Design
  • Long Standoff Metrology







PIVconceptNonlinear Optics

  • Photorefractivity
  • Phase Conjugation
  • Frequency Shifting




holography (HOE)Holography

  • Holographic Measurements
  • Holographic Optical Elements
  • Color Shifting
  • Solar Concetration









Nondestructive Evaluation (NDE)Nondestructive Evaluation

  • IED Detection
  • Sub-surface Fault Testing
  • Hidden Objects







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©2009 RAN Science & Technology, LLC. All rights reserved.

Publications by Russell Kurtz, Ph.D.

Enhanced Surface Metrology (2012)
There is a constant search for more accurate measurement, which generally leads to higher cost, greater complexity, or devices that do not lend themselves to manufacturing environments. For example, surface metrology can be accomplished by a number of methods, ranging from rulers and visual estimation (cheap, fast, and inaccurate) up to fixed Coordinate Measurement Machines (expensive, slow, and accurate). The tradeoffs involved in selecting metrology methods generally involve these three parameters of cost (initial and operation), measurement speed, and accuracy. We present a method of adding one more tradeoff: measurement precision (perpendicular to the surface) vs. sampling resolution (along the surface). Through application of statistical sampling and curve fitting, we can improve precision by approximately the square root of the amount that we decrease resolution.
          We applied this technique to a number of known and unknown targets, using the Cognitens WLS400 by Hexagon Metrology and a custom laser interferometry measurement system. Using the enhancements described in this paper, we were able to improve the measurements significantly. Measurement of a flat reference surface, for example, was enhanced by reducing noise a factor of 11 and improving surface measurement accuracy 2× (limited by the actual surface figure). An application of this technology to a known sphere reduced noise by a factor of eight and demonstrated that the sphere was within its surface and diameter specifications. We used this statistical technique to reduce noise in an interferometry system by 15× and demonstrated that the supposedly flat surface had deviations exceeding 16% over a square region 1 cm on a side. Finally, we modeled the WLS400 to determine its probability of identifying small surface features. Based on this model, we found that statistical noise reduction can improve the minimum resolvable feature height by a factor of five without significant difficulty.

Improving the Accuracy of Surface Metrology (2011)
There is a constant search for a more accurate measurement, which generally leads to higher cost, greater complexity, or devices that do not lend themselves to manufacturing environments. We present a method of using statistical sampling to improve metrological accuracy without these undesirable effects. For metrology of flat surfaces and steps between flat surfaces, this method demonstrated precision improvement up to a factor of 55, and accuracy increase of at least a factor of 10. The corresponding precision and accuracy improvements on a spherical surface were both factors of 8. Since this accuracy improvement can be implemented in software, it does not affect the speed of measurement or the complexity of the hardware, and it can be used to improve the accuracy of a wide range of metrology systems.

Reducing Statistical Noise Improves Surface Measurement Accuracy (2011)
Applying statistical methods to commercial metrology systems enhances the accuracy of surface measurement by an order of magnitude without increasing the time required to complete the task.

Photorefractive Amplification at High Frequencies (2011)
Photorefractive optical amplification, while useful, is a slow process. Under some circumstances, however, it amplifies optical signals effectively even when one is modulated at a relatively high frequency. We determine the reasons for this capability (what we have called the “Fast Photorefractive Effect”) and analyze its enhanced bandwidth, improvements over standard photorefractivity, and limitations.

Directed Acoustic Shearography (2010)
Modern vehicles use modern materials, including multiple metallic layers, composites, and ceramics. This has led to significant improvements in quality, reliability, and lifetime, at the cost of significantly increased complexity. It is particularly difficult to test these modern materials for buried defects such as internal corrosion, glue/weld failures, and disbonds, yet these defects can lead to damage and even failure of the part. As one tool in the array of nondestructive evaluation (NDE) technologies, we report on Directed Acoustic Shearography (DAS), which combines the sensitivity of shearography with the speed of ultrasonic imaging, and adds improved depth resolution. We show that DAS is particularly useful in detecting buried defects in modern materials, how it lends itself to automation, and present early tests of DAS detecting buried defects as small as 1/32 inch in a multilayer aluminum structure.

The Fast Photorefractive Effect and Its Application to Vibrometry (2009)
We previously reported on what we describe as the “fast photorefractive effect,” photorefractive signal amplification at much greater frequencies than predicted by its grating formation speed. In this paper we explain the effect and its potential for application to vibrometry. We demonstrated photorefractive amplification in Cu:KNSBN (whose grating formation speed is <5 Hz), matching the standard model with CW illumination. We then demonstrated photorefractive amplification of vibrometric signals at frequencies up to 4 MHz. Our theory of the fast photorefractive effect indicates that the amplification bandwidth of Cu:KNSBN at 488 nm illumination could exceed 800 GHz.

Micro-Raman Spectroscopic Characterization of ZnO Quantum Dots, Nanocrystals and Nanowires (2007)
Nanostructures, such as quantum dots, nanocrystals and nanowires, made of wurtzite ZnO have recently attracted attention due to their proposed applications in optoelectronic devices. Raman spectroscopy has been widely used to study the optical phonon spectrum modification in ZnO nanostructures as compared to bulk crystals. Understanding the phonon spectrum change in wurtzite nanostructures is important because the optical phonons affect the light emission and absorption. The interpretation of the phonon peaks in the Raman spectrum from ZnO nanostructures continues to be the subject of debates. Here we present a comparative study of micro-Raman spectra from ZnO quantum dots, nanocrystals and nanowires. Several possible mechanisms for the peak position shifts, i.e., optical phonon confinement, phonon localization on defects and laser-induced heating, are discussed in details. We show that the shifts of ~2 cm-1 in non-resonant spectra are likely due to the optical phonon confinement in ZnO quantum dots with the average diameter of 4 nm. The small shifts in the non-Resonant spectra from ZnO nanowires with the diameter ~20 nm – 50 nm can be attributed to either defects or large size dispersion, which results in a substantial contribution from nanowires with smaller diameters. The large red-shifts of ~10 cm-1 in the resonant Raman spectrum from nanocrystals were proved to be due to local laser heating.

High Speed Nano-Optical Photodetector for Free Space Communication (2007)
An inexpensive, easily integrated, sensitive photoreceiver operating in the communications band with a 50-GHz bandwidth would revolutionize the free-space communication industry. While generation of 50-GHz carrier AM or FM signals is not difficult, its reception and heterodyning require specific, known technologies, generally based on silicon semiconductors. We present a 50 GHz photoreceiver that exceeds the capabilities of current devices. The proposed photoreceiver is based on a technology we call Nanodust. This new technology enables nano-optical photodetectors to be directly embedded in silicon matrices, or into CMOS reception/heterodyning circuits. Photoreceivers based on Nanodust technology can be designed to operate in any spectral region, the most important to date being the telecommunications band near 1.55 micrometers. Unlike current photodetectors that operate in this spectral region, Nanodust photodetectors can be directly integrated with standard CMOS and silicon-based circuitry. Nanodust technology lends itself well to normal-incidence signal reception, significantly increasing the reception area without compromising the bandwidth. Preliminary experiments have demonstrated a free-space responsivity of 50 A/(W/cm2), nearly an order of magnitude greater than that offered by current 50-GHz detectors. We expect to increase the Nanodust responsivity significantly in upcoming experiments.

High-Frequency Photorefractive Amplification for ATR Applications (2006)
Automatic target recognition (ATR) can be accomplished by many methods, including recognition of vibrometric signatures. In many cases, ATR is enhanced by photorefractive amplification, a two-wave mixing effect in which two input beams form a dynamic holographic grating. One of the two beams (the pump) diffracts from that grating into the other (the signal), assuming the characteristics of the signal. When the pump is much stronger than the signal, the diffracted pump becomes a highly amplified signal beam. Traditionally, however, the frequency at which this amplification can be applied is limited to <1/2πτ0, where τ0 is the decay time of the grating in the absence of a pump or signal. We demonstrate that the amplification has no such limit in the case of vibrometry, which measures frequency-modulated, rather than amplitude-modulated, signals. This is shown by constant photorefractive amplification at frequencies up to >700 kHz in Cu:KNSBN, which has τ0 > 100 ms (corresponding to a maximum amplification frequency of 1.6 Hz).

Mutual Injection Locking: A New Architecture for High-Power Solid-State Laser Arrays (2005)
Bidirectional (mutual) injection locking was demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full phase-locking is significantly lower than the requirement for traditional injection locking. The large coupling requirement limits traditional injection-locked arrays to fewer than 20 elements, while mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.

A New Approach to Wideband Scene Projection (2005)
Advances in the development of imaging sensors depend upon (among other things) the testing capabilities of research laboratories. Sensors and sensor suites need to be rigorously tested under laboratory and field conditions before being put to use. Real-time dynamic simulation of real targets is a key component of such testing, as actual full-scale tests with real targets are extremely expensive and time consuming and are not suitable for early stages of development. Dynamic projectors simulate tactical images and scenes. Several technologies exist for projecting IR and visible scenes to simulate tactical battlefield patterns – large format resistor arrays, liquid crystal light valves, Eidophor type projecting systems, and micromirror arrays, for example. These technologies are slow, or are restricted either in the modulator array size or in spectral bandwidth. In addition, many operate only in specific bandwidth regions. Physical Optics Corporation is developing an alternative to current scene projectors. This projector is designed to operate over the visible, near-IR, MWIR, and LWIR spectra simultaneously, from 300 nm to 20 µm. The resolution is 2 megapixels, and the designed frame rate is 120 Hz (40 Hz in color). To ensure high-resolution visible imagery and pixel-to-pixel apparent temperature difference of 100°C, the contrast between adjacent pixels is >100:1 in the visible to near-IR, MWIR, and LWIR. This scene projector is designed to produce a flickerless analog signal, suitable for staring and scanning arrays, and to be capable of operation in a hardware-in-the-loop test system. Tests performed on an initial prototype demonstrated contrast of 250:1 in the visible with non-optimized hardware.

Determination of the Er3+ to Ho3+ Energy Transfer Coefficient in (Er, Ho):YAG (2005)
The coefficient describing energy transfer from the first excited level of trivalent erbium to the first excited level of trivalent holmium in YAG was obtained from measurement of the relevant material parameters. The value of this coefficient is necessary for estimating the improvement in Er:YAG and/or Ho:YAG lasing when the two ions are co-doped in the same crystal. This coefficient determines the depopulation efficiency of the lower level of the erbium 3-μm transition and the sensitization of the upper level of the 2-μm transition in holmium. Our technique for measuring the energy transfer coefficient, by fluorescence decay measurements in
conjunction with computer simulations of the decay and rate equation modeling, resulted in a value of 4.33x10-19 cm3s-1, implying that the erbium to holmium energy transfer is strong enough to improve the room-temperature holmium 2-μm laser.

High Speed Nanotechnology-Based Photodetector (2005)
An inexpensive, easily integrated, 40 Gbps photoreceiver operating in the communications band would revolutionize the telecommunications industry. While generation of 40 Gbps data is not difficult, its reception and decoding require specific technologies. We present a 40 Gbps photoreceiver that exceeds the capabilities of current devices. This photoreceiver is based on a technology we call “nanodust.” This new technology enables nanoscale photodetectors to be embedded in matrices made from a different semiconductor, or directly integrated into a CMOS amplification circuit. Photoreceivers based on nanodust technology can be designed to operate in any spectral region, including the telecommunications bands near 1.31 and 1.55 micrometers. This technology also lends itself to normal-incidence detection, enabling a large detector size with its associated increase in sensitivity, even at high speeds and reception wavelengths beyond the capability of silicon.

Image Tiling for a High-Resolution Helmet-Mounted Display (2005)
Head-mounted or helmet-mounted displays (HMDs) have long proven invaluable for many military applications. Integrated with head position, orientation, and/or eye-tracking sensors, HMDs can be powerful tools for training. For such training applications as flight simulation, HMDs need to be lightweight and compact with good center-of-gravity characteristics, and must display realistic full-color imagery with eye-limited resolution and large field-of-view (FOV) so that the pilot sees a truly realistic out-the-window scene. Under bright illumination, the resolution of the eye is ~300 µr (1 arc-min), setting the minimum HMD resolution. There are several methods of achieving this resolution, including increasing the number of individual pixels on a CRT or LCD display, thereby increasing the size, weight, and complexity of the HMD; dithering the image to provide an apparent resolution increase at the cost of reduced frame rate; and tiling normal resolution subimages into a single, larger high-resolution image. Physical Optics Corporation (POC) is developing a 5120 x 4096 pixel HMD covering 1500 x 1200 mr with resolution of 300 µr by tiling 20 subimages, each of which has a resolution of 1024 x 1024 pixels, in a 5 x 4 array. We present theory and results of our preliminary development of this HMD, resulting in a 4k x 1k image tiled from 16 subimages, each with resolution 512 x 512, in an 8 x 2 array.

Development of an Automultiscopic True 3D Display (2005)
      Invited Paper
True 3D displays, whether generated by volume holography, merged stereopsis (requiring glasses), or autostereoscopic methods (stereopsis without the need for special glasses), are useful in a great number of applications, ranging from training through product visualization to computer gaming. Holography provides an excellent 3D image but cannot yet be produced in real time, merged stereopsis results in accommodation-convergence conflict (where distance cues generated by the 3D appearance of the image conflict with those obtained from the angular position of the eyes) and lacks parallax cues, and autostereoscopy produces a 3D image visible only from a small region of space. Physical Optics Corporation is developing the next step in real-time 3D displays, the automultiscopic system, which eliminates accommodation-convergence conflict, produces 3D imagery from any position around the display, and includes true image parallax. Theory of automultiscopic display systems is presented, together with results from our prototype display, which produces 3D video imagery with full parallax cues from any viewing direction.

Reflection Shearography for Non-Destructive Evaluation (2004)
Conventional nondestructive evaluation (NDE) techniques include visual inspection, eddy current scanning, ultrasonics, and fluorescent dye penetration. These techniques are limited to local evaluation, often miss small buried defects, and are useful on polished surfaces only. Advanced NDE techniques include laser ultrasonics, holographic interferometry, structural integrity monitoring, shearography, and thermography. A variation of shearography, employing reflective shearographic interferometry, has been developed. This new shearographic interferometer is presented, together with models to optimize its performance and experiments demonstrating its use in NDE.

Long-Range Phase-Conjugate Interferometry (2004)
The most accurate method of measuring distance and motion is interferometry. This method of motion measurement correlates change in distance to change in phase of an optical signal. As one mirror in the interferometer moves, the resulting phase variation is visualized as motion of interferometric fringes. While traditional optical interferometry can easily be used to measure distance variation as small as 10 nm, it is not a viable method for measuring distance to, or motion of, an object more than half the illumination coherence length distant. This typically limits interferometry to measurements of objects within <1 km of the interferometer. We present a new interferometer based on phase conjugation, which greatly increases the maximum distance between the illumination laser and the movable target. This method is as accurate as traditional interferometry, but is less sensitive to laser pointing error and operates over a longer path. Experiments demonstrated measurement accuracy <15 nm with a laser-target separation of 50x the laser coherence length.

Injection Locking Efficiency of Two Independent Lasers (2004)
Bidirectional (mutual) injection locking was demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full phase-locking limits traditional injection-locked arrays to fewer than 100 elements, while mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.

HIWIL LIDAR Imaging Sensor, 3-D Synthetic and Natural Environment, and Temporal ATR (2002)
In this paper, LIDAR imaging sensors, 3-D synthetic and natural object-centric environment, and temporal (progressive) ATR (Automatic Target Recognition), are discussed in the context of Modeling and Simulation (M&S) and Hardware-in-the loop (HWIL) testing.

Increase Your Laser System's Lifetime (1992)
When using lasers in an industrial setting, there are many sources of unbudgeted costs. Among these costs are costs of replacing lenses and reflectors damaged in use, the costs of remachining parts which were incorrectly machined due to alignment or laser quality problems, and down time for unexpected repairs. Although none of the sources of unbudgeted costs can be eliminated, many can be ameliorated by a properly implemented routine maintenance program. Such a program prevents many problems by anticipating and eliminating the causes, and reduces the damage of others by detecting blemishes before they turn into disasters. Those companies which have implemented effective routine maintenance programs have mean times between failure of their laser machining systems several times longer, and mean times to repair these systems several times shorter, than companies that have no such program.
This paper presents an example of a routine maintenance program. This program does take some time to implement, probably about five to six hours per month, but this time is likely to be less than the down time prevented by its implementation. When one also recalls the cost reduction due to avoidance of unexpected replacements and remachining, it becomes obvious that implementing a good maintenance program pays for itself in increased efficiency and reduced down time.

Spectroscopic and 3-Micron Lasing Properties of Erbium-Doped Yttrium Aluminum Garnet and the Effects of Holmium Co-Doping (1991, PhD Dissertation)
The spectroscopy and 3-µm lasing behavior of Er:YAG are studied. Er:YAG is shown to lase on two distinct lines near 2.94 µm, specifically 2.9393 and 2.9362 µm. These two laser lines operate simultaneously. Although both begin in level A2 (the second lowest energy Stark sublevel of the 4I11/2 level), the 2.9362-µm line terminates at level Y6 and the 2.9393-µm line at level Y7 (Y7 and Y6 are the highest and second highest energy Stark sublevels, respectively, of the 4I13/2 level). These wavelengths imply that the Y6 level, whose energy was previously unknown, has an energy of 6873.8 cm-1.
     The effects of adding Ho3+ ions to Er:YAG is also reported. Energy is transferred from the 4I13/2 level of Er3+ to the 5I7 level of Ho3+. As reported in this dissertation, the value of the coefficient describing this energy transfer is WEH = 9.5±1.0 x 10-20 cm3/s [a later reanalysis of the data finds a value of 4.33 x 10-19 cm3/s, 4.5x greater]. This value suggests that the Er3+-->Ho3+ energy transfer is not strong enongh to unblock the Er:YAG 3-µm transition, but is strong enough to unblock the Er:YLF 3-µm transition. The energy transfer also suggests diode-pumping Er3+ ions, which then transfer their energy to the Ho3+ ions, creating an efficient, diode-pumped 2-µm Ho3+ laser.
     Multiple wavelength lasing of (30% Er, 1.5% Ho):YAG is described. In addition to the two wavelengths seen in Er:YAG, (Er, Ho):YAG lases at 2.796 and 2.766 µm during the same pump pulse as the 2.936- and 2.939-µm lines. Both these transitions are attributed to the Er3+ ions. The 3-µm lasing is shown to have a lower gain than the lasing near 2.8 µm, but atmospheric losses at 2.8 µm are sufficient to prevent lasing at these wavelengths. The 2.8-µm lines are seen in (Er, Ho):YAG after the 3-µm lines have self-terminated due to excited-state absorption in the Ho3+.

New Laser Lines of Erbium in Yttrium Aluminum Garnet (1990)
We studied the lasing and spectroscopic properties of erbium in yttrium aluminum garnet, both a a single impurity and when codoped with neodymium or holmium. In all cases, we observed lasing at 2.936 and 2.939 µm; when erbium was codoped with holmium, we also observed lasing at 2.795 and 2.766 µm. [This is in contrast to (Er, Nd):YAlO3, which lased on only one line, 2.73 µm.] By determining the energy-level splitting implied by the four observed laser lines, and combining this with transmission spectroscopy, we were able to assign unambiguous values to the Stark sublevels of the three lowest energy levels of Er3+ in YAG at room temperature.

Multiple Wavelength Lasing of (Er, Ho): YAG (1989)
We tested a solid state laser material, YAG doped with 30% /(at.) Er3+ ions and 1.5% (at.) Ho3+ ions. The laser levels in both Er3+ and H03+ demonstrated altered lifetimes when compared to equivalently-doped Er:YAG and Ho:YAG, indicating moderate interactions between the Er3+ and Ho3+ ions. When we lased (Er, Ho):YAG, we observed output at three wavelengths: approximately 2.939, 2.936, and 2.796 µm. The first two of these lased simultaneously, while the third appeared later in the same pump pulse. This lasing blueshift may be explained by excited-state absorption (ESA) in the Ho3+ ions.

Simultaneous, Multiple Wavelength Lasing of (Ho, Nd):Y3Al5O12 (1987)
Simultaneous lasing of both Ho3+ and Nd3+ in the same crystal of yttrium aluminum garnet (YAG) is reported. The crystal was doped with 10% Ho3+ and 1% Nd3+ ions. Lasing occurred at 2.940 and 3.011 µm due to Ho3+ ion transitions and at 1.064 µm due to a Nd3+ transition. Appropriate mirrors produced simultaneous lasing at 1.064 and 1.339 µm due to Nd3+ ion transitions. The fluorescent lifetimes of both the Nd3+ 4F3/2 and the Ho3+ 5I7 states were significantly lower in the doubly doped material than in Nd:YAG and Ho:YAG. This indicates very strong ion-ion interactions in the (Ho, Nd):YAG crystal.

Simultaneous, Multiple Wavelength Lasing of (Er, Nd):Y3Al5O12 (1987)
Simultaneous lasing of both Er3+ and Nd3+ ions in yttrium aluminum garnet is reported. The crystal was doped with 15% Er3+ ions and 1% Nd3+ ions. The Er3+ ions lased at 2.94 µm and the Nd3+ ions in a broad band from 1.01 to 1.15 µm with a strong peak at 1.064 µm. Significant ion-ion interaction is suggested by the drastically altered fluorscent lifetimes and unusal lasing properties.

Operation of High Dopant Density Er: YAG (1986)
Free- running, pulsed, flashlamp- excited operation of 50% and 33% Er doped YAG lasers is reported at 2.94 µm. This laser was described by researchers in the Soviet Union as early as 1975. Since then there have been a number of further reports concerning this material all published by Soviet scientists. This paper represents, to our knowledge, the first publication outside of the Soviet Union about high dopant density Er:YAG laser operation. In addition to confirming some of the performance properties described earlier, this paper presents the unusual temporal waveforms of the Er:YAG, 2.94 µm laser. An outline is given of possible pumping and relaxation processes which may contribute to the laser's operation. Er:YAG does not lase well at 2.94 µm when the concentration of Er is the usual 1%. However, when larger concentrations are used (generally over 15%) operation at this wavelength can be quite efficient.

Spot Size Dependent Laser Materials Interactions Due to Surface Electromagnetic Waves (1986)
Measurements of the transient reflectivity change due to heating by a surface electromagnetic wave are reported. Initial results are inconclusive with regard to the existance of surface electromagnetic waves. Implications concerning the effects upon the laser-induced damage threshold are discussed.

A High Efficiency Switching Power Supply (1981, Undergraduate Thesis)
My project was to design a switching power supply which output 5 volts regulated at up to about 5 amps load current, given dc inputs of 16 to 60 volts. The circuit I was originally given, which was not working correctly, used a monolithic "switching power supply regulator" chip. I redesigned the switching power supply so that it would work. The original circuit used the switching regulator mentioned above as most of its control section; I discovered that this version of the switching power supply could not work correctly, and redesigned it so that it would. The new control section was formed of discrete components and a pulse-width modulator (PWM). The specifications forthis new design were: efficiency )96% (to prevent excessive heat losses), small size, about 7 volts unregulated output (i.e., the ripple is unimportant) with up to 5% variation for loads of 0 to 5 amps, inputs of 10.0 to 40.0 volts, and operating temperature range of -25 to +125 degrees centigrade. These specifications were eventually met.

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