This PDF file contains the front matter associated with SPIE Proceedings Volume 7070, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The Indian Head Division, Naval Surface Warfare Center (IHDIV, NSWC) CAD Engineering Division is conducting a program to evaluate the laser components which comprise the Canopy Fracturing Initiation System (CFIS) currently installed on the T-6A Texan or JPATS (Joint Primary Aircraft Training System) aircraft. The T-6A Texan is the first aircraft used by the military to train future pilots. The CFIS is an element of the pilot emergency escape system which weakens the canopy in the path of the ejection seat. The CFIS is comprised of three differing configurations (Internal, External, and Seat Motion) which generate a laser pulse that is distributed through a fiber optic energy transmission system. This pulse, in turn, initiates explosive components which weaken the respective canopies. All of the CFIS laser types are flashlamp-pumped, neodymium glass lasers which are located at various positions in the aircraft cockpit area. This paper presents the CAD Engineering Division effort to evaluate the functional performance of the three CCFIS laser signal generators after their being in fleet use for a period of time.

The ignition of the liquid gun propellant (LGP) 1846 or XM46 by 1-μm neodymium (Nd):glass laser light has been explored under conditions of confinement. Variation in ignition delay with energy and initial pressure are explored. Good repeatability, millisecond delay times, and reasonable pulse energy requirements characterize the observations.

Laser-driven flyer plates comprise of one or more thin layers forming a foil coated onto a transparent substrate. Irradiation of the foil/substrate interface with a Q-switched laser pulse produces a plasma, the expansion of which forms a flyer plate, which can reach velocities in excess of 5 km/s. These plates impart shocks in excess of 50 GPa, with duration of less than a nanosecond. This shock is sufficient to initiate secondary explosives such as Hexanitrostilbene (HNS) and Pentaerythritol Tetranitrate (PETN). Thresholds of detonators based on laser-driven flyer plates are typically measured in terms of energy. By using a Photonic Doppler Velocimeter (PDV) we measure the velocity of the flyer plate at the threshold energy. This allows calculation of the shock pressure and duration imparted to the explosive. By initiating HNS with a variety of flyer thicknesses, from 3 to 5 &mgr;m, we are able to evaluate Pn&tgr; in this extreme shock regime. The calculated value of n is compared to published values and discussed for similar systems. We are also able to use the James Criterion to analyze the initiation, with values of Ec and &Sgr;c being determined from experimental data, providing a predictive capability to model other configurations such as different flyer thicknesses and materials.

Remington was one of the first firearm manufacturing companies to file a patent for laser initiated firearms, in 1969. Nearly 40 years later, the development of laser initiated firearms has not become a mainstream technology in the civilian market. Requiring a battery is definitely a short coming, so it is easy to see how such a concept would be problematic. Having a firearm operate reliably and the delivery of laser energy in an efficient manner to ignite the shock-sensitive explosive primer mixtures is a tall task indeed. There has been considerable research on optical element based methods of transferring or compressing laser energy to ignite primer charges, including windows, laser chip primers and various lens shaped windows to focus the laser energy. The focusing of laser light needs to achieve igniting temperatures upwards of >400°C. Many of the patent filings covering this type of technology discuss simple approaches where a single point of light might be sufficient to perform this task. Alternatively a multi-point method might provide better performance, especially for mission critical applications, such as precision military firearms. This paper covers initial design and performance test of the laser beam shaping optics to create simultaneous multiple point ignition locations and a circumferential intense ring for igniting primer charge compounds. A simple initial test of the ring beam shaping technique was evaluated on a standard large caliber primer to determine its effectiveness on igniting the primer material. Several tests were conducted to gauge the feasibility of laser beam shaping, including optic fabrication and mounting on a cartridge, optic durability and functional ignition performance. Initial data will be presented, including testing of optically elements and empirical primer ignition / burn analysis.

The design and characterization of small, ruggedized laser-optical subsystems is required for the continued development of robust laser-optical firing systems. Typically, these subsystems must be capable of generating the needed laser optical energy, delivering that energy via fiber-optical cables while occupying a volume as small as possible. A novel beam splitting and fiber injection scheme has been proposed which utilizes two diffractive optical components. These components were utilized to reduce the volume of a previously designed system. A laser-optical prototype system was assembled and tested which utilized this beam splitting and fiber injection scheme along other modifications to the laser module and power supply. This prototype was based on earlier designs that utilized environmentally proven opto-mechanical sub-assemblies. The system was tested to characterize the laser performance, the splitter-coupler transmission efficiency, channel-to-channel energy balance and fiber interchangeability. The results obtained for this design will be compared to the performance of a prototype system based on a more traditional beam splitting and fiber injection scheme. The traditional design utilized partially reflecting mirrors for beam splitting and plano-convex lenses for fiber injection. These results will be discussed as will their ultimate impact on future designs and packaging strategies.

An industrial process was developed to grow quartz crystals for fabrication of large aperture optical components up to 150 mm in diameter with extended transmission range into the shorter UV. The material's transmission degradation was measured in range of wavelengths from 185 nm to 800 nm before and after gradual increase of irradiation up to 30 kGy dose, using an ArF laser and gamma-rays. The absorption coefficient for X-grown material increases from 0.024 cm-1 before irradiation to 0.132 cm-1 after gamma irradiation at 195 nm and from 0.018 to 0.132 at 460 nm, respectively. Absorption coefficient for Z-grown material increases from 0.025 to 0.038 at 195 nm and from 0.022 to 0.032 at 460 nm, respectively. Optical microscopy, interferometry, and Schlieren method were used for inclusion density and optical inhomogeneity evaluation. Virtually no inclusions and low optical inhomogeneity were revealed. Scanning of the samples at 800 nm and 460 nm (test wave) and plotting the extinction coefficients also confirms high optical homogeneity along growth directions.

Over the past ten years, NASA has studied the effects of harsh environments on optical fiber assemblies for communication systems, lidar systems, and science missions. The culmination of this has resulted in recent technologies that are unique and tailored to meeting difficult requirements under challenging performance constraints. This presentation will focus on the past mission applications of optical fiber assemblies, including: qualification information, lessons learned, and new technological advances that will enable the road ahead.

Fiber optic cables are increasingly being used in harsh environments where they are subjected to vibration. Understanding the degradation in performance under these conditions is essential for integration of the fibers into the given application. System constraints often require fiber optic connectors so that subsystems can be removed or assembled as needed. In the present work, various types of fiber optic connectors were monitored in-situ during vibration testing to examine the transient change in optical transmission and the steady-state variation following the event. The fiber endfaces and connectors were inspected at selected intervals throughout the testing.

Fiber optic cables are widely used in modern systems that must provide stable operation during exposure to changing environmental conditions. For example, a fiber optic cable on a satellite may have to reliably function over a temperature range of -50°C up to 125°C. While the system requirements for a particular application will dictate the exact method by which the fibers should be prepared, this work will examine multiple ruggedized fibers prepared in different fashions and subjected to thermal qualification testing. The data show that if properly conditioned the fiber cables can provide stable operation, but if done incorrectly, they will have large fluctuations in transmission.

One reason to use optical fibers to transmit data is for isolation from unintended electrical energy. Using fiber optics in an application where the fiber cable/system penetrates the aperture of a grounded enclosure serves two purposes: first, it allows for control signals to be transmitted where they are required, and second, the insulating properties of the fiber system help to electrically isolate the fiber terminations on the inside of the grounded enclosure. A fundamental question is whether fiber optic cables can allow electrical energy to pass through a grounded enclosure, with a lightning strike representing an extreme but very important case. A DC test bed capable of producing voltages up to 200 kV was used to characterize electrical properties of a variety of fiber optic cable samples. Leakage current in the samples were measured with a micro-Ammeter. In addition to the leakage current measurements, samples were also tested to DC voltage breakdown. After the fiber optic cables samples were tested with DC methods, they were tested under representative lightning conditions at the Sandia Lightning Simulator (SLS). Simulated lightning currents of 30 kA and 200 kA were selected for this test series. This paper documents measurement methods and test results for DC high voltage and simulated lightning tests performed at the Sandia Lightning Simulator on fiber optic cables. The tests performed at the SLS evaluated whether electrical energy can be conducted inside or along the surface of a fiber optic cable into a grounded enclosure under representative lightning conditions.

A variety of optical systems use high optical powers or energies, for example, power transport. These systems may be expected to operate in harsh and challenging environments, which may include ionizing radiation. In this paper, several different types of modern, commercially available optical fiber designs have been assessed for reliable operation in a transient gamma radiation environment. The fibers tested are large core multimode silica fibers optimized for the delivery of high power infrared laser light. Some of the fibers are specifically designed to operate in harsh radiation environments, and these are compared against designs of varying radiation resilience from other manufacturers. It was found that fibers were able to successfully transmit a laser pulse of up to 0.375 MW in peak power within a few hundred nanoseconds after irradiation, with less than a 10% loss in transmission.

The laser diode was first developed in 1962, since which its design and some of the initial concepts have changed vastly. Improvements in laser diode technology have assisted in the development of many modern day technologies, ranging from remote sensing instruments to highly efficient pumping of other laser systems. As technologies where laser diodes can be applied advance, it is important to understand the behaviour of the laser diode in such environments which may become more hostile or complex. This paper presents information and data from literatures published on previous investigations carried out on laser diodes under the influence of neutron, gamma or X-ray irradiation. Any behavioural trends will be observed, as will any abnormalities to provide a succinct review of the laser diodes in these environments, and allow for predictions or further investigations into this subject to be made.

Increased reliance on optical components in harsh radiation environments requires a deeper understanding of the radiation-induced behavior of common optical elements. Of particular interest is the impact of ionizing radiation on both optical transmission and absorption. The present work focuses on an examination of the optical response of singlecrystal Nd:YAG, Cr:YAG and co-doped Nd:Cr:YAG to pulses of gamma-radiation. In-situ, transient optical behavior was observed by measuring the transmittance of the materials at 1064 nm before, during and after exposure to 30-60 krad (Si) of pulsed gamma radiation. The gamma-radiation-induced response of the Cr-doped materials was seen to exhibit exceptional radiation resistance as compared to the undoped YAG and to the Nd-doped materials. Furthermore, the addition of Cr³⁺ into the Nd:YAG crystal matrix was seen to greatly improve the radiation resistance of the laser materials. Both transient and permanent effects will be discussed.

The design and packaging of laser-optical system was tested to harsh environments outside lab conditions and post mortem activities will be discussed. Previously, custom mounts and bonded optical assemblies were environmentally tested to ensure their survivability. The results verified the sub-assemblies would enable the design of a laser-optical initiation system that could be fielded for use in extreme conditions. The design package, which utilized the proven opto-mechanical sub-assemblies, was then tested to the same levels as the sub-assemblies. The test regiment encompassed the harshest environments currently utilized. Temperature tests were performed ranging from a maximum of +75 degrees C to a minimum of -55 degrees C, allowing for two hour soak at each temperature set point. Vibration tests were performed to a maximum level of 15.5 grms for forty seconds in each of three critical axes. Shock tests were performed to a maximum impulse level of 5700 G's for the sub-assemblies with a 1.1 millisecond long pulse; whereas the packaged laser system maximum level reached was 3700 G's at 1.1 millisecond long pulse. The laser-optical assembly was visually inspected and functionally tested before and after each test to verify survival. As designed, the system covers were laser welded shut for hermetic seal. The only open port was the laser output for testing and verification of laser performance. No optical cables were utilized. Therefore the visual inspection of the interior was performed post mortem. The post mortem results will be discussed as will the potential of redesigns on future packaging strategies.

Diffractive Optical Elements (DOEs) are lightweight, thin optical components with many applications in laser beam-shaping. In this paper we consider the application of DOEs for coupling of high power Nd:YAG laser light to fibre For the laser system in question intra-cavity DOEs are considered for the generation of a super-Gaussian cavity mode, while an extra-cavity element is considered for shaping the beam to produce a profile suitable for fibre coupling. The arrangement to be considered in our application involves coupling a 100mJ, 20ns pulse laser beam of 5mm diameter into 3 fibres, each with a core diameter of 400μm, positioned in an equilateral triangle formation with a centre to centre spacing of 2mm. The threshold power density for the fibres is 4.5GW/cm². 512x512 pixel DOEs with 16 phase levels have been optimized using the iterative Fourier transform algorithm (IFTA). The optimized element produces spots with a radius of 14 diffraction orders. The modeled efficiency of the element is 91.4% with a peak power of 1.26GW/cm². Experimental measurements using a low power 633nm source equate to a peak power of 2.65GW/cm² for the high power laser, well within the damage threshold.

The aim of this paper is to compare the electrical performance of an orthogonally with a coaxially laser-triggered spark gap. Each of these two gaps has its own advantages and disadvantages. At the same time, a Rogowski profile spark gap was investigated in terms of its orthogonally laser-triggered performance. It was found that the Nd:YAG laser used (1 064 nm, 800 mJ) was able to reduced the breakdown voltage of a 50 mm gap by 70% from 135 kV to about 40 kV. The position of the laser-induced plasma was found to play a significant role in the breakdown process - best results being obtained when the laser was focused in the centre of the gap. Finally, the shape of the laser-induced arc is dependant on the applied electric field. When the field is low, the arc tends to avoid the laser-induced plasma thus exhibiting a very anomalous behaviour. When the field is increased, the arc tends to attach itself to the plasma as expected.

Direct Optical Initiation (DOI) of explosives offers significant safety advantages over traditional electrical initiation of explosives, primarily by removing the electrically conducting pathway to the explosive material. A firing system typically consists of three main components: the fireset, which provides the energy to initiate the explosive; the cable, which transmits or conducts this energy; and the detonator, which uses this energy to initiate the explosive charge. Electrical firing systems used to fire secondary explosives typically use voltages of 500 volts and upwards, with currents of 500 amps and upwards. The technology to transmit such signals over the short distances required is mature and well-proven. However, an optical initiation system requires optical powers in excess of 10 MW, and the technology to deliver such powers is relatively immature. Optical fibers are used to transmit the firing energy, which require very high tolerances to ensure the beam is successfully coupled into the fiber without damage. Fiber optic tapers offer a method to relax these tolerances, and hence reduce system cost and complexity, by providing a larger area into which to couple this beam. We present here our initial results from a series of tests aimed at establishing the feasibility of using tapered optical fibers for this purpose. The transmission loss and beam profiles are reported as a function of the beam position on the input face of the optical fiber.

For well over one hundred years the science of Firearm and Tool Mark Identification has relied on the theory that unintentional random tooling marks generated during the manufacture of a firearm onto its interior surfaces are unique to each individual firearm.^[1][2] Forensic Firearm and Tool Mark Examiners have had to rely on the analysis of these randomly formed unintentional striations, or scratches and dings, transferred onto ammunition components from firearms used to commit crimes, as a way of developing clues and evidence. Such transfers take place during the cycle of fire and ejection of the cartridge from the firearm during the commission of a crime. The typical striations on the cartridge casings are caused by tooling marks that are randomly formed during the machining of interior surfaces of the manufactured firearm and by other firearm components that come in contact with the cycling ammunition. Components like the firing pin, extractor and ejector, impact the surfaces of the cartridges as they are fed, fired and ejected from the firearm. When found at a crime scene, these striae constitute ballistic evidence when effectively analyzed by a Forensic Firearm and Tool Mark Examiner. Examiners categorize these striations looking for matches to be made between the components that created the marks and the recovered firearm. Reality is that nearly 50% of firearms used in violent crimes are not recovered at a crime scene, requiring the analysis to be processed and logged into evidence files or imaged into reference image databases for future comparison whenever a firearm might be recovered. This paper will present a unique law enforcement technology, embedded into firearms for tracking the sources of illegally trafficked firearms, called Microstamping. Microstamping is a laser based micromachining process that forms microscopic "intentional structures and marks" on components within a firearm. Thus when the firearm is fired, these microstamp structures transfer an identifying tracking code onto the expended cartridge ejected from the firearm. Microstamped structures are laser micromachined alpha numeric and encoded geometric tracking numbers, linked to the serial number of the firearm. Ballistic testing data will be presented covering microstamp transfer quality, transfer rates and survivability/durability. Further information will provide an overview on how microstamping information can be utilized by law enforcement to combat illegal firearm trafficking.

Porro prism lasers are insensitive to misalignment caused by, for example, shock and temperature variation, making them useful in field applications, for example in target designation and range-finding systems. This property is a result of the property of Porro prisms that they return a reflected beam parallel to the incident beam, regardless of any tilt on the prism. These lasers are generally used in a marginally stable or unstable configuration for low divergence, but in the stable configuration some interesting kaleidoscope modes can be modelled. In previous work on Porro prism resonators we formulated an analytical method of determining which Porro angles resonate and result in petal output modes, as well as the corresponding number of petals. This work has been verified using a numerical model as well as experimentally. We have developed this work further and have investigated the losses associated with a range of Porro angles as well as the effects of these losses on the resulting modes. We conclude by summarizing the design considerations for Porro prism lasers.

We investigate the inversion dynamics in Nd:Cr:GSGG laser rods as a function of pumping frequency in order to optimize Nd:Cr:GSGG Q switched lasers for rapid time to fire applications. By frequency filtering the pump light to the Nd:Cr:GSGG rod and measuring the florescence from the rod, we determine the dynamics for different excitation processes in the laser (i.e. direct excitation of the Nd ions or indirect excitation via Cr ions). We also measure the flashlamp pulse shape using various spectral filters This combination of measurements help us understand the processes contributing and limiting the efficiency of Nd:Cr:GSGG lasers when the lasers must fire on a short time scale.

Passive phasing of fiber amplifier arrays are promising for the power scaling of high power fiber laser systems. The broadband operation of passively phased systems mitigates nonlinear effects such as Stimulated Brillouin Scattering. This leads to the possibility of scaling the individual fiber amplifiers in the passively phased arrays to multi-kilowatt power levels. In effect, a smaller number of fiber amplifiers can be used compared to other methods of fiber amplifiers combining. We report the passive phasing of 16 Yb-doped fiber amplifiers at 5W each for a total of 80W.

System temporal response in passively phased fiber amplifier arrays dictates how fast a passively phased system can correct for phase fluctuations due to thermal and mechanical effects. The system response time was measured by employing a variable-speed mechanical chopper in the feedback loop of a passively phased system then measuring the on-axis output intensity of the system as a function of time. Observed relaxation oscillations are compared to theory. The system response time was measured to be about 20 μsec. We also find that passive phasing improved the system's beam stability and extraction efficiency.

Detonators are used to convert electrical or other energy into an explosive output. This output can then be used to initiate further explosive charges. To aid in the development of explosive systems, it is important to characterize the output of detonators, in particularly the pressure produced. Recent advances over the last five years in high-speed digitizing oscilloscopes and high-bandwidth photodiodes, driven primarily by the telecommunications industry, have enabled the development of a new type of interferometer for measuring high velocities, such as those found in detonics experiments. The Photonic Doppler Velocimeter (PDV) can be visualized as a fiber-based Michelson interferometer. The light from a single-mode fiber laser at 1550 nm is passed through a circulator, which acts to separate bi-directional light. The beam is then reflected via free-space optics off the surface of interest, and then focused back into the same fiber. This reflected light is then mixed with an approximately equal amount of non-reflected light, and the resulting interference is recorded using a high-bandwidth photodiode and oscilloscope. In contrast to more traditional Velocimetry techniques such as VISAR, only a single data channel is required. We have used our PDV system to investigate the performance of optical and electrical detonators. The detonators examined are the commercially available RISI RP-80, and an AWE DOI (Direct Optical Initiation) detonator. The RP-80 is an exploding bridgewire (EBW) detonator, utilizing Pentaerythritol Tetranitrate as the initiating explosive and a RDX output pellet. The DOI detonator uses an aluminum flyer to initiate a Hexanitrostilbene (HNS) pellet. Both detonators are canned in aluminum and the velocity of the can was measured, and from this, the output pressure of the detonator has been determined. This is compared to calculated values.

The performance of a series connected photovoltaic array is limited by the photocell that is illuminated the least. This paper quantifies the effects of single-mode and multi-mode illumination and discusses the design parameters.

Hexanitrostilbene (HNS) is a widely used explosive, due in part to its high thermal stability. Degradation of HNS is known to occur through UV, chemical exposure, and heat exposure, which can lead to reduced performance of the material. Common methods of testing for HNS degradation include wet chemical and surface area testing of the material itself, and performance testing of devices that use HNS. The commonly used chemical tests, such as volatility, conductivity and contaminant trapping provide information on contaminants rather than the chemical stability of the HNS itself. Additionally, these tests are destructive in nature. As an alternative to these methods, we have been exploring the use of vibrational spectroscopy as a means of monitoring HNS degradation non-destructively. In particular, infrared (IR) spectroscopy lends itself well to non-destructive analysis. Molecular variations in the material can be identified and compared to pure samples. The utility of IR spectroscopy was evaluated using pressed pellets of HNS exposed to DETA (diethylaminetriamine). Amines are known to degrade HNS, with the proposed product being a σ-adduct. We have followed these changes as a function of time using various IR sampling techniques including photoacoustic and attenuated total reflectance (ATR).

Fiber-optic sensors for sensing electrical current are attractive due to their inherent immunity to electromagnetic interference. Several groups have shown the use of Faraday rotation in magneto-optical materials as a function of current-induced magnetic field. In this work, fiber-optic sensors based on different mechanisms such as magnetic-fielddependent polarization coherence and power scattering effects in magneto-optical materials are demonstrated. These novel sensor configurations can have advantages in that they exhibit power-independent or polarization-independent operation which can ultimately lead to fewer components and relaxed light source requirements compared to fiber-optic current sensor systems based on Faraday rotation.

Recent improvements in photovoltaic cell technologies have increased efficiency and decreased size to the point that they are much more attractive for use in optically powered and isolated electronics. Applications can include powering a small group of components for simple sensors to much more complex systems which incorporate high speed digital communication between remote locations. Although optical to electrical conversion efficiencies are approaching 50%, the remaining power is still lost as heat. Heat becomes a compound problem because too much can cause photocell efficiency to decrease producing more heat and eventually leading to thermal runaway and breakdown. Thermal management is the key to balancing the maximum amount of input power while minimizing the effect of heat on the efficiency. This paper describes an effort currently under way to develop packaging which combines passive alignment techniques with changes to photocell architecture specifically designed to improve thermal management.

This paper describes technologies developed at Sandia National Laboratories to support a joint DoD/DoE initiative 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 cm³. 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.

Liquefied natural gas (LNG) transport carriers are exposed to a risk by the repeated bump in the LNG container during the vessel traveling over the wave in ocean. The liquid inside the container, especially when it was not fully contained, make a strong bump onto the insulation panel of the tank wall. The insulation panel consists of several layers of thick polyurethane foam (PUF) to maintain the LNG below the cryogenic temperature, -162°C. Due to the repeated shock on the PUF, a crack could be developed on the tank wall causing a tremendous disaster for LNG carriers. To prevent the accidental crack on the tank, a continuous monitoring of the strain imposed on the PUF is recommended. In this work, a fiber-optic Bragg grating was imbedded inside the PUF for monitoring the strain parallel to the impact direction. The optical fiber sensor with a small diameter of 125 μm was suitable to be inserted in the PUF through a small hole drilled after the PUF was cured. In-situ monitoring of the strain producing the change of Bragg reflection wavelength, a high speed wavelength interrogation method was employed by using an arrayed waveguide grating. By dropping a heavy mass on the PUF, we measured the strain imposed on the insulation panel.