This PDF file contains the front matter associated with SPIE Proceedings Volume 9491 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

A great deal of research has been performed on developing room temperature mid wave infrared (MWIR) and long wave infrared (LWIR) detectors to replace very costly mercury cadmium telluride based detectors. Among the more studied materials for high operating temperature detectors, PbSe and PbSe-type heavy metal selenides have been grown in the bulk, thin film and nano crystal morphologies. To better understand the effects of the substrate on the properties of these thin films, we have deposited lead selenide by physical vapor transport (PVT) method on highresistivity Si substrates and studied the characteristics of the film. Growth on silicon and glass substrates showed different morphologies compared to pure lead selenide material. It was seen that materials grown on a glass substrate possessed different morphology after annealing. FTIR was used to calculate bandgap information comparison with undoped PbSe. We will describe the details of the growth method, effect of substrate on nucleation and morphology of the pure and lead selenide material and band gap comparisons between substrates.

Radiation-hardened electronics used in space, nuclear energy and radiation medicine applications require robust dielectric materials to be used as passivation layers and gate insulators. Thus, there is a need to understand the response of these materials under radiation exposure (e.g., gamma, neutron and proton) to develop radiation-tolerant and reliable electronic systems. In addition, as the size of transistors continues to scale down there is a need to have physically thicker dielectric layers with similar capacitance values to ultra-thin SiO₂. High permittivity (high-k) dielectrics lend themselves well to this task as they have capacitance values similar to ultra-thin SiO₂ while not facing issues of high leakage current and power dissipation as ultra-thin SiO₂. Atomic layer deposition (ALD) of thin films has gained interest in the development of radiation-hardened electronics as this process results in high quality (continuous and pinhole-free) and conformal gate dielectric thin films with precise thickness control to the angstrom level. Here, we examine the impact of gamma-irradiation on plasma-enhanced ALD dielectric layers using metal-oxide semiconductor (MOS) capacitors. In this work, three ALD gate dielectric films: Al₂O₃, HfO₂ and SiO₂ (between 22 and 24 nm thick) are utilized. The capacitance-voltage (C-V) response of plasma-enhanced ALD-based MOS capacitors upon gamma irradiation (Co-60) up to 533 krad without any shielding is observed. It is shown that ALD grown HfO₂ films are resistant to gamma irradiation based on the negligible shift in flat band voltage and hysteresis characteristics. Additionally, ALD grown Al₂O₃ films exhibited minimal generation of mobile traps but generation of trapped charges was observed. Furthermore, the flat band and hysteresis of ALD grown SiO₂ films showed development of both trapped and mobile charges which may suggest that this material lends itself to radiation dosimetry applications. These initial findings support the use of plasma-enhanced ALD grown films in the development of radiation-hardened electronics and sensors.

Ultraviolet (UV) photodetectors are used for applications such as flame detection, space navigation, biomedical and environmental monitoring. Robust operation within large ranges of temperatures, radiation, salinity and/or corrosive chemicals require sensor materials with the ability to withstand and function reliably within these extreme harsh environments. For example, spacecraft can utilize a sun sensor (light-based sensor) to assist with determination of orientation and may be exposed to both ionizing radiation and extreme temperature swings during operation. Gallium nitride (GaN), a wide bandgap semiconductor material, has material properties enabling visible-blindness, tunable cutoff wavelength selection based on ternary alloy mole fraction, high current density, thermal/chemical stability and high radiation tolerance due to the strength of the chemical bond. Graphene, with outstanding electrical, optical and mechanical properties and a flat absorption spectrum from 300 to 2,500 nm, has potential use as a transparent conductor for GaN-based metal-semiconductor-metal (MSM) photodetectors. Here, graphene-enhanced MSM UV photodetectors are fabricated with transparent and conductive graphene interdigitated electrodes on thin film GaN-on-sapphire substrates serving as back-to-back Schottky contacts. We report on the irradiation response of graphene/GaN-based MSM UV photodetectors up to 750 krad total ionizing dose (TID) then tested under dark and UV light (365 nm) conditions. In addition, based on current-voltage measurements from 75 krad to 750 krad TID, calculated photodetector responsivity values change slightly by 25% and 11% at -5 V and -2 V, respectively. These initial findings suggest that graphene/GaN MSM UV photodetectors could potentially be engineered to reliably operate within radiation environments.

Monitoring polluting gases such as CO and NO_x emitted from gas turbines in power plants and aircraft is important, in order to both reduce the effects of such gases on the environment as well as to optimize the performance of the respective power system. Fuel cost savings as well as a reduced environmental impact can be realized if air traffic utilized next generation jet turbines with an emission/performance control sensing system. These monitoring systems must be sensitive and selective to gases as well as be reliable and stable under harsh environmental conditions where the operation temperatures are in excess of 500 °C within a highly reactive environment. In this work, plasmonics based chemical sensors with nanocomposites of a combination of gold nano particles and Yttria Stabilized Zirconia (YSZ) has enabled the sensitive (PPM) and stable detection (100s of hrs.) of H₂, NO₂ and CO at temperatures of 500 °C. Selectivity remains a challenging parameter to optimize and a layer by layer sputter deposition approach has been recently demonstrated to modify the resulting sensing properties through a change in the morphology of the deposited films. It is expected that further enhancements would be realized through control of the shape and geometry of the catalytically active Au nanoparticles. This level of control has been realized through the use of electron beam lithography to fabricate nanocomposite arrays. Sensing results towards the detection of H2 will be highlighted with specific concerns related to optimization of these nanorod arrays detailed.

Need exists for untethered transmission of electrical power and data to remote devices and sensors. Several wireless solutions, based on radiation and non-radiation are in existence. Here the focus is on the use of photonic power which is an optimized optical to electrical conversion solution, used for both wireless and guided transportation. High photonic conversion efficiencies of 50% and greater have been demonstrated for wavelength matched laser diodes and photovoltaic cells. However, these existing solutions do not meet the needs of rapid energy transfer to remote devices, such as munition shells prior to launch. We report on the design and fabrication of a 16-cell array of densely packed photonic power converters that can power a munition shell immediately prior to launch. A laser beam delivers power and data to the PPC array. Thermal simulation, using FEA shows that the each of the cells can be operated at an equivalent irradiance of 1000x suns, giving an energy transfer rate of 17.5 J.s^-1 for the array. Thus, two 10 F super-capacitors, typically used in munitions, can be charged is under 5 seconds. Further, using the measured capacitance of 2.4 nF for the array, data can be transported to the munition on the laser power beam, at a rate exceeding 5 Mbps.

Fiber optic distributed temperature sensing based on Raman scattering of light in optical fibers has become a very attractive solution for distributed temperature sensing (DTS) applications. The Raman scattered signal is independent of strain within the fiber, enabling simple packaging solutions for fiber optic temperature sensors while simultaneously improving accuracy and robustness of temperature measurements due to the lack of strain-induced errors in these measurements. Furthermore, the Raman scattered signal increases in magnitude at higher fiber temperatures, resulting in an improved SNR for high temperature measurements. Most Raman DTS instruments and fiber sensors are designed for operation up to approximately 300˚C. We will present our work in demonstrating high temperature calibration of a Raman DTS system using both Ge doped and pure silica core multi-mode optical fiber. We will demonstrate the tradeoffs involved in using each type of fiber for high temperature measurements. In addition, we will describe the challenges of measuring large temperature ranges (0 – 600˚C) with a single DTS interrogator and will demonstrate the need to customize the interrogator electronics and detector response in order to achieve reliable and repeatable high temperature measurements across a wide temperature range.

The development of a harsh environment ammonia slip sensor based on tunable diode laser absorption spectroscopy is presented. A hybrid optical sensor design, through combination of wavelength modulation spectroscopy (WMS) and alignment control, is proposed as an approach towards reliable in-situ measurements in misalignment prone harsh environments. 1531.59 nm, 1553.4 nm and 1555.56 nm are suggested as possible absorption lines for trace ammonia measurement (<1ppm at 10m path length at 500K) in gas turbine exhaust conditions. Design and performance of the alignment control system are presented in detail. Effect of misalignment related measurement degradation is investigated and significant improvement in measurement fidelity is demonstrated through the use of the hybrid optical sensor design.

Distributed Acoustic Sensing (DAS) is a highly promising technology to efficiently monitor assets for energy production and transportation, both off- and on-shore, such as boreholes, pipelines and risers. The aim of the hereby-presented measurements is to evaluate the sensitivity of the different optical fiber cables to acoustic signals in sand and water, independently from the DAS read-out unit type and manufacturer. Acoustic sensing cables specifically designed by BRUGG Cables are characterized and compared to standard telecommunication cables. The spectral response of each cable was quantified using an all-fiber Mach-Zehnder interferometer. The response was also measured with calibrated microphones in order to convert the measurements into absolute physical units (Pascal). The measurement campaign is part of an investigation program for a reliable DAS system, which comprises the sensing cable (including installation procedure), the interrogator unit and suitable software.

Advances in opto-electronics and associated signal processing have enabled the development of Distributed Acoustic and Temperature Sensors. Unlike systems relying on discrete optical sensors a distributed system does not rely upon manufactured sensors but utilises passive custom optical fibre cables resistant to harsh environments, including high temperature applications (600°C). The principle of distributed sensing is well known from the distributed temperature sensor (DTS) which uses the interaction of the source light with thermal vibrations (Raman scattering) to determine the temperature at all points along the fibre. Distributed Acoustic Sensing (DAS) uses a novel digital optical detection technique to precisely capture the true full acoustic field (amplitude, frequency and phase) over a wide dynamic range at every point simultaneously. A number of signal processing techniques have been developed to process a large array of acoustic signals to quantify the coherent temporal and spatial characteristics of the acoustic waves. Predominantly these systems have been developed for the oil and gas industry to assist reservoir engineers in optimising the well lifetime. Nowadays these systems find a wide variety of applications as integrity monitoring tools in process vessels, storage tanks and piping systems offering the operator tools to schedule maintenance programs and maximize service life.

The Planetary Atmospheres Minor Species Sensor (PAMSS) is an intracavity laser absorption spectrometer that uses a mid-infrared quantum cascade laser in an open external cavity for sensing ultra-trace gases with parts-per-billion sensitivity. PAMSS was flown on a balloon by Near Space Corporation from Madras OR to 30 km on 17 July 2014. Based on lessons learned, it was modified and was flown a second time to 32 km by World View Enterprises from Pinal AirPark AZ on 8 March 2015. Successes included continuous operation and survival of software, electronics, optics, and optical alignment during extreme conditions and a rough landing. Operation of PAMSS in the relevant environment of near space has significantly elevated its Technical Readiness Level for trace-gas sensing with potential for planetary and atmospheric science in harsh environments.

Fiber optic cables have been successfully deployed in ocean floors for decades to enable trans-oceanic telecommunication. The impact of strain and moisture on optical fibers has been thoroughly studied in the past 30 years. Cable designs have been developed to minimize strain on the fibers and prevent water uptake. As a result, the failure rates of optical fibers in subsea telecommunication cables due to moisture and strain are negligible. However, the relatively recent use of fiber optic cables to monitor temperature, acoustics, and especially strain on subsea equipment adds new reliability challenges that need to be mitigated. This paper provides a brief overview of the design for reliability considerations of fiber optic cables for subsea asset condition monitoring (SACM). In particular, experimental results on fibers immersed in water under varying accelerated conditions of static stress and temperature are discussed. Based on the data, an assessment of the survivability of optical fibers in the subsea monitoring environment is presented.

Monitoring the levels of polluting gases such as CO and NO_x from high temperature (500°C and higher) combustion environments requires materials with high thermal stability and resilience that can withstand harsh oxidizing and reducing environments. Au nanorods (AuNRs) have shown potential in plasmonic gas sensing due to their catalytic activity, high oxidation stability, and absorbance sensitivity to changes in the surrounding environment. By using electron beam lithography, AuNR geometries can be patterned with tight control of the rod dimensions and spacings, allowing tunability of their optical properties. Methods such as NR encapsulation within an yttria-stabilized zirconia overcoat layer with subsequent annealing procedures will be shown to improve temperature stability within a simulated harsh environment. Since light sources and spectrometers are typically required to obtain optical measurements, integration is a major barrier for harsh environment sensing. Plasmonic sensing results will be presented where thermal energy is harvested by the AuNRs, which replaces the need for an external incident light source. Results from gas sensing experiments that utilize thermal energy harvesting are in good agreement with experiments which use an external incident light source. Principal component analysis results demonstrate that by selecting the most “active” wavelengths in a plasmonic band, the wavelength space can be reduced from hundreds of monitored wavelengths to just four, without loss of information about selectivity of the AuNRs. By combining thermal stability, the thermal energy harvesting capability, and the selectivity in gas detection (achieved through multivariate analysis), integration of plasmonic sensors into combustion environments can be greatly simplified.

A new design for the miniaturization of an existing oxygen sensor is proposed based on the application of silicon microfabrication technologies to a cm sized O₂ sensor demonstrated by Argonne National Laboratory and The Ohio State University which seals a metal/metal oxide within the structure to provide an integrated oxygen reference. The structural and processing changes suggested will result in a novel MEMS-based device meeting the semiconductor industry standards for cost efficiency and mass production. The MEMS design requires thin film depositions to create a YSZ membrane, palladium oxide reference and platinum electrodes. Pt electrodes are studied under operational conditions ensuring film conductivity over prolonged usage. SEM imaging confirms void formation after extended tests, consistent with the literature. Furthermore, hydrophilic bonding of pairs of silicon die samples containing the YSZ membrane and palladium oxide is discussed in order to create hermetic sealed cavities for oxygen reference. The introduction of tensile Si₃N₄ films to the backside of the silicon die generates bowing of the chips, compromising bond quality. This effect is controlled through the application of pressure during the initial bonding stages. In addition, KOH etching of the bonded die samples is discussed, and a YSZ membrane that survives the etching step is characterized by Raman spectroscopy.

Electronic systems comprising of subassemblies, distributed across different physical media, require seamless communication between processors and sensors embedded in the disparate volumes. For example, smart munitions systems embed sensors and other key control electronics, throughout the structure, in vastly different physical media. In addition to the obvious space constraints, these structures are subjected to high G forces during launch. Thus, communications through wire harnesses becomes cumbersome, make assembly process and testing difficult, and challenging to make survive high G firing. Here we focus on an approach that takes advantage of the partial optical transparency of epoxy material commonly used in potting electronic components in munitions, as well as the wave guiding that is possible through the body of the munitions wall which is made from composite materials. Experimental results show that a wireless optical link, connecting various parts of the distributed system, is possible at near IR frequencies. Data can be rapidly parsed between a processor, sensors and actuators. We present experimental data for a commercial epoxy system, which is used to embed a number of IrDA devices inside the cone of 120 mm mortar shell. IrDA devices using the FIR data rates establish point-to-point communication through various media, representative of the environment inside the 120 mm mortar cone.