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This pdf file contains the front matter associated with SPIE Proceedings Volume 7795, including Title Page, Copyright information, Table of Contents, and Conference Committee listing.
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Laser ignition of energetic materials is an attractive technology for replacement of low energy electro-explosive devices
which pose a safety hazard. The development of this technology has historically been based on go/no-go threshold
testing using off-the-shelf laser diodes and solid state lasers. Here we seek to build a more fundamental understanding of
the laser ignition process by analyzing the interactions and response of the energetic material to the incident laser beam.
We begin with a radiative heat transfer model of the laser-beam-assisted heating of a homogeneous energetic material
with given optical properties. An analytical solution of the 2-flux model equations is developed and this expression for
the volumetric absorption of laser energy in an absorbing and isotropically scattering medium is coupled to the
conservation of energy equation. Two limiting cases-minimum power and minimum energy thresholds for ignition - are discussed, and the minimum energy threshold is calculated directly from the energy equation in the limit of zero
dissipative losses. The effects of power density and beam shape are of particular interest and two common
configurations are analyzed. Although the applicability of thermal models is limited by large uncertainties in the optical
properties of energetic materials, the analysis provides a qualitative understanding of the ignition process and a
correlation between ignition thresholds and the various material properties and design parameters.
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The Indian Head Division, Naval
Surface Warfare Center (IHD NSWC) CAD
Engineering Division is conducting a program to
evaluate the laser and energetic components
which comprise the Canopy Fracturing Initiation
System (CFIS). This system is currently
installed on the T-6A Texan II or JPATS (Joint
Primary Aircraft Training System) aircraft. The
T-6A Texan II 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 laser configurations (Internal, External,
and Seat Motion) which generate a pulse that is
distributed through a fiber optic energy
transmission system. This pulse, in turn, initiates
one of the system's explosive components, a
detonator (specifically, the CCU-158/A Laser
Initiated Detonator). This detonator transfers the
signal to the remaining energetic components
that, in turn, function to weaken their 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 SPIE papers (2008 - Conference 7070
and 2009 - Conference 7434, respectively) and
presents the initial functional test results for the
CFIS Laser Detonator. These functional test
results provide the technical support to justify
the useful lifetime of this energetic component
while being installed in the T-6A Texan II
aircraft under operational conditions.
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Nanoporous silicon, commonly recognized for its photoluminescent properties, has gained attention as a new energetic
material capable of energy density more than twice that of TNT. The addition of an oxidizer solution to inert nanoporous
silicon results in an exothermic reaction when heat, friction, or focused light is supplied to the system. The energetic
material can be integrated alongside microelectronics and micro-electro-mechanical systems (MEMS) for on-chip
applications. This integration capability, along with the potential for large energetic yield, makes nanoporous energetic
silicon a viable material for developing novel MEMS Safing and Arming (S&A) technologies. While ignition of
nanoporous energetic silicon has been demonstrated for the purpose of propagation velocity measurements using a YAG
laser, in this paper we show optical ignition for potential integration of the energetic with a miniaturized S&A device.
Ignition is demonstrated using a 514nm laser at 37.7mW and a power density of 2.7kW/cm2 at a stand-off distance of
23cm. Raman spectroscopy verifies that significant stress in porous silicon is produced by a laser operating near the
power density observed to ignite porous silicon. Lastly, we integrate the nanoporous energetic silicon with a MEMS
S&A, and demonstrate transfer to a firetrain consisting of one primary and one secondary explosive using a thermal
initiator to ignite the nanoporous energetic silicon.
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Laser initiation of the various explosive materials requires a wide variety of energy densities. With funding from
DARPA, Alfalight has developed a Surface-Emitting Distributed Feedback (SE-DFB) lasers. The technology allows a
single laser diode to replace many of today's more complex solid state lasers in LIO applications. The highest-recorded
continuous output power from a single emitter - 73 watts - is detailed along with peak pulsed powers exceeding 300
watts. Other beneficial properties such as wafer-level processing, surface output coupling and on-chip beam-shaping are
among the attributes of this type of laser.
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We present an analysis of a reliability assessment tailored specifically to fuzes based on laser diode assemblies. Fuzes
are required to deliver high energy in a single short pulse (micro- to milliseconds) after prolonged storage (tens of years)
in thermally non-stabilized environments. The temperature variation could easily exceed 100 degrees, and the transition
from one extreme to the other could be slow or rapid, depending on a particular application. The operating requirements
for diode laser fuzes are dramatically different from the majority of other diode laser applications and thus a reliability
assurance program for laser fuzes should reflect these differences in usage. In this paper we demonstrate that it is
possible to build accelerated aging conditions based on thermal cycling. As parameters in the accelerated thermal aging,
we used the total temperature difference between the lowest and the highest points in the cycle, and the average rate of
temperature change between the extreme points. This accelerated aging technique based on thermal cycling can predict
the performance deterioration over time after storage in thermally non-stabilized environments. The basis of this
approach can be extended to the analysis of reliability in environments with high vibration and radiation levels.
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There are a number of attractive micro optical elements or combinations of elements that are
currently used or could be employed in optically initiated ordnance systems. When taking a
broad-spectrum examination of optically initiated devices, the required key parameters become
obviously straightforward for micro optics. Plainly stated, micro optics need to be simple,
inexpensive, reliable, robust and compatible within their operational environment. This
presentation focuses on the variety of optical elements and components available in the market
place today that could be used to realize micro-optical beam shaping and delivery systems for
optically initiated devices. A number of micro optical elements will be presented with specific
bulk, planar optical and thin film optical devices, such as diffractive optics, micro prisms,
axicons, waveguides, micro lenses, beam splitters and gratings. Further descriptions will be
presented on the subject of coupling light from a laser beam into a multimode optical fiber. The
use of micro optics for collimation of the laser source and conditioning of the laser beam to
achieve the highest efficiency and matching the optical fiber NA will be explained. An emphasis
on making these optical assemblies compact and rugged will be highlighted.
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Direct Optical Initiation (DOI), uses a moderate energy Q-switched Nd:YAG laser to shock initiate secondary
explosives, via either a flyer plate or exploding metal foil. DOI offers significant performance and safety advantages over
conventional electrical initiation. Optical fibers are used to transport the optical energy from the laser to the explosive
device.
Energy densities in the region of 35 J cm-2 are required for initiation, significantly above the damage threshold of typical
optical fibers. Laser-induced damage is typically caused by laser absorption at the input face due to imperfections in the
surface polishing. To successfully transmit energy densities for DOI, a high quality fiber end face finish is required.
Fiber assemblies were prepared by C Technologies Inc, NJ, USA, with Innovaquartz FG365UEC optical fiber, using a
variety of polishing methods, with both steel and zirconia ferrules. The quality of the fiber end faces was assessed using
non-contact optical profilometry. The damage threshold for each polishing method was then determined using a Q-switched
Nd:YAG laser and the optimal polishing method determined for each ferrule material. Significant performance
differences between zirconia and steel ferrules were observed, and a physical cause of this difference is proposed.
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Planar polymer waveguides provide opportunities for small form factor distribution of laser light
for communication, energy transfer and triggering devices used in the field of optically initiated
arming, safing, fusing and firing. The two primary methods or classes of polymer waveguide
technology use photolithographic processes both mask and maskless techniques. A waveguide is
a device that controls the propagation of an electromagnetic wave so that the wave is forced to
follow a path defined by the physical structure of the guide. Fabrication takes the form of both a
ridge technology (ridge or trench formed by an embossing or etching method) and the second
fabrication technique and the subject of this paper is termed Diffusion Technology [1]. This
method includes the formation of a high refractive index waveguide by monomer diffusion into
the light-exposed guide forming region with no mechanical or chemical etching contact. An
essential process feature here is the photomask-defined light exposure of a mobile monomer
waveguide forming region in a polymer matrix that converts the monomer to a polymer. The
process of continued monomer diffusion into the surrounding guide imaged region increases the
density. The addition of other laminated monomer/polymer diffusing layers with the typical
three-plus layer configuration is completely photopolymerized after diffusion is complete. The
essential steps include a light induced imaging reaction, a total polymerization light fixing for the
entire film, and final cure, all using pre-coated dry materials without waveguide side wall
contact. Light and molecular diffusion determine the guide walls [1]. This paper will provide
testing results and information on the state of polymer waveguides, the methods of fabrication
and the general conditions that these waveguides can operate under. The use of polymer
waveguides for connectivity has sufficiently advanced, is practical and available for
consideration in near term application development with the field of arming, safing, fusing and
firing or laser/optically initiated ordnance.
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The optical pulse generation system of SG-III laser facility is presented. The optical time division
multiplexing (OTDM) technique, high speed electro-optic modulation technique, pulse
single-selected based on polarization independently acousto-optic modulation technique and pulse
polarization stabilization technique applied in low repetition rate mode are successfully employed in
the system. And also the phase modulation unit is at the last stage of the system, which could avoid
FM-AM effect induced in fiber system. The test experiment results showed that the demonstrated
specification is better than the designed to a certain degree.
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Large-aperture plasma Pockels cell is one of important components for inertial confinement fusion laser facility. We
demonstrate a single-pulse driven PPC with 350mm×350mm aperture. It is different to the PPC of NIF and LMJ for its
simple operation to perform Pockels effect. With optimized operation parameters, the PPC meets the optical switching
requirement of SGII update laser facility. Only driven by one high voltage pulser, the simplified PPC system would be
provided with less associated diagnostics, less the maintenance, and higher reliability.
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