This PDF file contains the front matter associated with SPIE Proceedings Volume 7434, including the Title Page, Copyright information, Table of Contents, 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 builds on the previous 2008 SPIE paper (Conference 7070) and presents further CAD Engineering Division test results and analysis which were utilized to evaluate the functional performance of the three CFIS laser signal generators after their being installed fleet applications over a period of time.

Laser-driven flyer plates offer a convenient, laboratory-based method for generating extremely high pressure shocks, in excess of 30 GPa, in a variety of materials. They comprise of one or more thin layers forming a foil, coated onto a transparent substrate. By irradiating the interface between foil and substrate with a moderate-energy, short-duration laser pulse, it is possible to form a flyer plate, which can reach velocities in excess of 5 km/s. These flyer plates have several applications, from micrometeorite simulation to initiation of secondary explosives. The flyer plates considered here have up to four layers: an absorption layer, to absorb the laser energy; an ablation layer, to form a plasma; an insulating layer; and a final, thicker layer that forms the final flyer plates. By careful selection of both layer material and thickness, it is possible to increase the maximum velocity achieved for a given laser pulse energy by increasing the proportion of laser energy coupled into flyer kinetic energy. Photonic Doppler Velocimetry (PDV) is used to measure the flyer velocity.

With the maturing of high-power diode laser technology, studies of laser-assisted ignition of a variety of substances are becoming an increasingly popular research topic. Its range of applications is wide - from fusing in the defense, construction and exploration industries to ignition in future combustion engines. Recent advances in InP-based technology have expanded the wavelength range that can be covered by multi-watt GaAs- and InP-based diode lasers to about 0.8 to 2 μm. With such a wide range, the wattage is no longer the sole defining factor for efficient ignition. Ignition-related studies should include the interaction of radiation of various wavelengths with matter and the reliability of devices based on different material systems. In this paper, we focus on the reliability of pulsed laser diodes for use in ignition applications. We discuss the existing data on the catastrophic optical damage (COD) of the mirrors of the GaAsbased laser diodes and come up with a non-destructive test method to predict the COD level of a particular device. This allows pre-characterization of the devices intended for fusing to eliminate failures during single-pulse operation in the field. We also tested InP-based devices and demonstrated that the maximum power is not limited by COD. Currently, devices with >10W output power are available from both GaAs- and InP-based devices, which dramatically expands the potential use of laser diodes in ignition systems.

The design, assembly and characterization of the latest generation of a small, ruggedized laser-optical firing system will be discussed. This work builds upon earlier results in an effort to continue the development of robust fiber-coupled laseroptical firing systems.^[1][2] This newest prototype strives to improve on earlier designs, while continuing to utilize many of the environmentally proven opto-mechanical sub-assemblies.^[2][3] One area of improvement involves the implementation of a second optical safing and arming component. Several additional design improvements were also incorporated to address shortcomings uncovered during environmental testing.^[4][5] These tests and the subsequent failure analysis were performed at the laser sub-system level. Four identical prototypes were assembled and characterized. The performance of the units were evaluated by comparing a number of parameters including laser output energy, slope efficiency, beam divergence, spatial intensity profile, fiber injection and splitter-coupler transmission efficiency. Other factors evaluated were the ease of alignment, repeatability of the alignment process and the fabrication of the fiberoptical cables. The experimentally obtained results will be compared and contrasted to the performance of earlier prototypes.

Hexanitrostilbene (HNS) is a secondary explosive widely used in a variety of commercial and military applications, due in part to its high heat resistivity. Degradation of HNS is known to occur through exposure to a variety of sources including heat, UV radiation, and certain chemical compounds, all of which may lead to reduced performance. Detecting the degradation of HNS within a device, however, has required destructive analyses of the entire device while probing the HNS in only an indirect fashion. Specifically, the common methods of investigating this degradation include wet chemical, surface area and performance testing of the devices incorporating HNS rather than a direct interrogation of the material itself. For example, chemical tests frequently utilized, such as volatility, conductivity, and contaminant trapping, provide information on contaminants present in the system rather than the chemical stability of the HNS. To instead probe the material directly, we have pursued the use of optical methods, in particular infrared (IR) spectroscopy, in order to assess changes within the HNS itself. In addition, by successfully implementing miniature silicon (Si) waveguides fabricated at Sandia National Laboratories to facilitate this spectroscopic approach, we have demonstrated that HNS degradation monitoring may take place in a non-destructive, in-situ fashion. Furthermore, as these waveguides may be manufactured in a variety of configurations, this direct, non-destructive, approach holds promise for incorporation into a variety of devices.

Laser initiation of explosive material requires consistent achievement of specific optical power densities and extremely high reliability under a wide variety of harsh environmental conditions. Ensuring successful and timely detonation drives laser diode-based systems towards testing algorithms that far exceed the standard Telcordia GR-468 qualifications. As diode technology advances, options for increased power density and alternate system configurations expand. An understanding of the basis of diode laser reliability in this application will be provided, along with key optical system metrics for a variety of current and future LIO systems.

High power laser systems have a number of uses in a variety of scientific and defense applications, for example laser induced breakdown spectroscopy (LIBS) or laser-triggered switches. In general, high power optical fibers are used to deliver the laser energy from the source to the target in preference to free space beams. In certain cases, such as nuclear reactors, these optical systems are expected to operate in ionizing radiation environments. In this paper, a variety of modern, currently available commercial off-the-shelf (COTS) optical fiber designs have been assessed for successful operation in the transient gamma radiation environment produced by the HERMES III accelerator at Sandia National Laboratories, USA. The performance of these fibers was evaluated for high (~1 MW) and low (<1 W) optical power transmission during high dose rate, high total dose gamma irradiation. A significant reduction in low optical power transmission to 32% of maximum was observed for low OH- content fibers, and 35% of maximum for high OH- fibers. The high OH- fibers were observed to recover to 80% transmission within 1 μs and 100% transmission within 1 ms. High optical power transmission losses followed generally similar trends to the low optical power transmission losses, though evidence for an optical power dependent recovery was observed. For 10-20 mJ, 15 ns laser pulses, around 46% was transmitted coincident with the radiation pulse, recovering to 70% transmission within 40 ns of the radiation pulse. All fibers were observed to completely recover within a few minutes for high optical powers. High optical power densities in excess of 1 GW/cm² were successfully transmitted during the period of highest loss without any observed damage to the optical fibers.

The optical response of single-crystal Nd:YAG and Cr³⁺:YAG to ionizing radiation has been previously studied using intense pulses of gamma-rays at the HERMES III facility at Sandia National Laboratory, where samples' transmission at 1064 nm was observed during exposure to gamma radiation. A further study of similar samples when exposed to 10-ns UV laser pulses reveals nearly identical dynamics, with both tests producing similar transient and permanent response in the medium. This strongly suggests that the material response to UV radiation can be used to gauge its gamma-radiation hardness, therefore yielding a material testing technique that is much simpler and less costly than gamma-radiation tests.

Fibers doped with rare-earth constituents such as Yb³⁺ and Er³⁺, as well as fibers co-doped with these species, form an essential part of many optical systems requiring amplification. This study consists of two separate investigations examining the effects of gamma-radiation-induced photodarkening on the behavior of rare-earth doped fibers. In one part of this study, a suite of previously irradiated rare-earth doped fibers was heated to an elevated temperature of 300°C and the transmittance monitored over an 8-hour period. Transmittance recoveries of ~10 - 20% were found for Er 3⁺- doped fiber, while recoveries of ~5 - 15% and ~20% were found for Yb³⁺- and Yb³⁺/Er³⁺ co-doped fibers, respectively. In the other part of this study, an Yb³⁺-doped fiber was actively pumped by a laser diode during a gamma-radiation exposure to simulate the operation of an optical amplifier in a radiation environment. The response of the amplified signal was observed and monitored over time. A significant decrease in amplifier output was observed to result from the gamma-radiation exposure.

Q-switches for laser ignition applications must meet a unique set of requirements. The inherent challenges to providing extremely reliable, compact, practical, and cost effective devices are daunting. The capabilities and limitations of various passive and active technologies will be explored and compared against generic laser driven ignition requirements. Emphasis will be placed on providing practical limits of operation to guide systems design. These include alignment sensitivity, voltage/power requirements, laser induced damage, the effects of extreme temperature, shock and vibration, mechanical mounting strain, and piezoelectric driven ringing. An example of a new Q-switch suitable for mid-IR lasers, which may improve ignition, will be described.

Over the years law enforcement has become increasingly complex, driving a need for a better level of organization of knowledge within policing. The use of COMPSTAT or other Geospatial Information Systems (GIS) for crime mapping and analysis has provided opportunities for careful analysis of crime trends. By identifying hotspots within communities, data collected and entered into these systems can be analyzed to determine how, when and where law enforcement assets can be deployed efficiently. This paper will introduce in detail, a powerful new law enforcement and forensic investigative technology called Intentional Firearm Microstamping (IFM). Once embedded and deployed into firearms, IFM will provide data for identifying and tracking the sources of illegally trafficked firearms within the borders of the United States and across the border with Mexico. Intentional Firearm Microstamping is a micro code technology that leverages a laser based micromachining process to form optimally located, microscopic "intentional structures and marks" on components within a firearm. Thus when the firearm is fired, these IFM structures transfer an identifying tracking code onto the expended cartridge that is ejected from the firearm. Intentional Firearm Microstamped structures are laser micromachined alpha numeric and encoded geometric tracking numbers, linked to the serial number of the firearm. IFM codes can be extracted quickly and used without the need to recover the firearm. Furthermore, through the process of extraction, IFM codes can be quantitatively verified to a higher level of certainty as compared to traditional forensic matching techniques. IFM provides critical intelligence capable of identifying straw purchasers, trafficking routes and networks across state borders and can be used on firearms illegally exported across international borders. This paper will outline IFM applications for supporting intelligence led policing initiatives, IFM implementation strategies, describe the how IFM overcomes the firearms stochastic properties and explain the code extraction technologies that can be used by forensic investigators and discuss the applications where the extracted data will benefit geospatial information systems for forensic intelligence benefit.

Strain-balanced, InP-based quantum cascade laser structures, designed for light emission at 4.6 μm using a new non-resonant extraction design approach, were grown by molecular beam epitaxy. Removal of the restrictive two-phonon resonance condition, currently used in most structure designs, allows simultaneous optimization of several structure parameters influencing laser performance. Following the growth, the structure was processed to yield buried heterostructure lasers. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of 5 mm by 11.6 μ;m. Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and 0.86 kA/cm². Fully packaged, air-cooled lasers with the same active region/waveguide design and increased laser core doping delivered approximately 2.2 W in collimated beam. The high performance and level of device integration make these quantum cascade lasers the primary choice for various defense applications, including directional infrared countermeasures, infrared beacons/target designators and free space optical communications.

Early detection of explosive substances is the first and most difficult step in defeating explosive devices. Many currently available methods suffer from fundamental failure modes limiting their realworld suitability. Infrared spectroscopy is ideal for reliable identification of explosives since it probes the chemical composition of molecules. Quantum cascade lasers rapidly became the light source of choice of IR spectroscopy due to their wavelength agility, relatively high output power, and small size and weight. Our compact, rapid, and rugged multi-explosives sensor based on external grating cavity QCLs simultaneously detects TNT, TATP, and acetone while being immune to ammonium nitrate interference. The instrument features low false alarm rate, and low probability of false negatives. Receiver operation characteristics curves are presented.