Grigory Adamovsky

National Aeronautics and Space Administration

This paper discusses extraction of images and sensing information from targets located in harsh planetary environments. Various configurations of sensing systems with imaging fiber optic conduits are presented and discussed, including some experimental data. Prototypes are designed and their performance is demonstrated with a focus on potential app...

We have conducted experiments to demonstrate an efficient generation of plasma discharges by focused nanosecond pulsed laser beams in air and provided recommendations on the design of optical systems to implement such plasma generation. We have also demonstrated generation of the secondary plasma discharge using the unused energy from the primary o...

A High Temperature Fiber Optic Sensor (HTFOS) has been developed at NASA Glenn Research Center for aircraft engine applications. After fabrication and preliminary in-house performance evaluation, the HTFOS was tested in an engine environment at NASA Armstrong Flight Research Center. The engine tests enabled the performance of the HTFOS in real engi...

The use of high-temperature materials in current and future applications, including silicone materials for handling hot foods and metal alloys for developing high-speed aircraft and spacecraft systems, has generated a growing interest in high-temperature technologies. High Temperature Materials and Mechanisms explores a broad range of issues relate...

The paper reviews potential applications of functional Near-Infrared Spectroscopy (fNIRS), a well-known medical diagnostic technique, to monitoring the cognitive state of pilots with a focus on identifying ways to adopt this technique to airborne environments. We also discuss various fNIRS techniques and the direction of technology maturation of as...

This paper reviews the effects of varying gravitational levels on functional Near-Infrared Spectroscopy (fNIRS) headgear. fNIRS systems quantify neural activations in the cortex by measuring hemoglobin concentration changes via optical intensity. Such activation measurement allows for the detection of cognitive state, which can be important for emo...

An underwater dielectric barrier discharge (DBD) plasma jet excited by a repetitively pulsed nanosecond pulsed power modulator was used to study plasma-induced decolorization of a 1.4 × 10-4 M solution of methylene blue (MB). Past plasma decolorization studies have focused on spectrophotometry as the main diagnostic to assess decomposition. Because...

Whispering gallery modes in microspheres are excited by light delivered to them via optical fibers imbedded in a half-block coupler. The corresponding light intensity resonances in microspheres and coupling of two low-order linearly polarized modes in the fibers, LP01 and LP11, into the microspheres are observed. The LP01 and LP11 modes are deliver...

Fiber Bragg gratings (FBGs) embedded in conventional fibers may serve as temperature sensors over a wide temperature range and withstand temperatures around 1200 K. A variety of linearly polarized (LP) modes for the wavelengths between 400 and 700 nm may be sustained in fibers with and without FBGs. The composition of the LP modes and their competi...

A DBD plasma jet excited by a repetitively pulsed ns pulse power modulator was used to decolorize a 1.4 × 10-4 M solution Methylene Blue (MB). Time-resolved decomposition of the MB in solution was assessed using spectrophotometry and high-pressure liquid chromatography (HPLC). Spectrophotometry results were found to be in agreement with chromatogra...

Plasma production or plasma injection in liquid water affords one the opportunity to nonthermally inject advanced oxidation processes into water for the purpose of purification or chemical processing. Such technology could potentially revolutionize the treatment of drinking water, as well as current methods of chemical processing through the elimin...

Direct experimental measurements of the thermo-optic and the thermal expansion coefficients for fixed temperature intervals (20-200°C, 200-500°C, 500-660°C, 660-780°C) in fused silica fiber containing fiber Bragg gratings (FBGs) were conducted. The diffraction efficiency of a FBG fluctuated with temperature between 2.01×10-4 and 0.17×10-4 while the...

A 15- by 15-cm supersonic wind tunnel application of a one-dimensional laser beam scanning approach to shock sensing is presented. The measurement system design allowed easy switching between a focused beam and a laser sheet mode for comparison purposes. The scanning results were compared to images from the tunnel Schlieren imaging system. The test...

Develop Advanced Sensor Technology and rotordynamic structural diagnostics to address existing Aviation Safety Propulsion Health Management needs as well as proactively begin to address anticipated safety issues for new technologies.

In this paper techniques used to manufacture thermally stable fiber Bragg gratings capable to operate at extreme temperatures for long durations of time are analyzed. Results on packaging and long durability tests performed on sensor units comprised of chemical composition grating or CCG-type fiber Bragg gratings are also reported. The tests includ...

Two sets of resonances in glass microspheres attached to a standard communication grade single mode optical fiber have been observed. It has been found that the strength of the resonances depends strongly on the polarization of the coupled light. Furthermore, the position of the resonances in the wavelength domain depends on the polarization of lig...

This paper discusses fiber optic sensors designed and constructed to withstand extreme temperatures of aircraft engine. The paper describes development and performance evaluation of fiber optic Bragg grating based sensors. It also describes the design and presents test results of packaged sensors subjected to temperatures up to 1000 °C for prolonge...

The development of a sensitive oxygen sensor suitable for deployment in the ullage of an aircraft fuel tank is discussed here. Instead of using plain optical fibers, fibers with a long period grating are utilized to produce lightweight optical sensors that strongly couple the core guided light into the cladding and vice versa. The detection princip...

Measurement tools for high speed air flow are sought both in industry and academia. Particular interest is shown in air flows that exhibit aerodynamic shocks. Shocks are accompanied by sudden changes in density, pressure, and temperature. Optical detection and characterization of such shocks can be difficult because the medium is normally transpare...

This paper reviews recent developments in morphology-dependent-resonance based sensors for aerospace applications. The sensor concept is based on the detection of small shifts of optical resonances (also called the whispering gallery modes) of dielectric spheres caused by external effects. Recent developments in morphology-dependent-resonance-based...

The paper describes phenomena observed as a result of laser pencil beam interactions with abrupt interfaces including aerodynamic shocks. Based on these phenomena, a novel flow visualization technique based on a laser scanning pencil beam is introduced. The technique reveals properties of light interaction with interfaces including aerodynamic shoc...

The development of sensor networks for cooperative target tracking is discussed. Simple measurements from individual sensors are fed to an algorithm that estimates the path of a target and generates an optimized intercept path for the UAV. Sensor networks are also being implemented for space-based systems. Researchers at JPL are using onboard auton...

New light-driven actuators based on films of polymer polyvinylidene fluoride are described. The actuators employ the photomechanical bending of the polymer film caused by low power (10mW and less) laser radiation. The photomechanical effect combines various physical mechanisms, such as anisotropic thermal expansion, converse piezoelectric mechanism...

New light-driven actuators based on films of polymer polyvinylidene fluoride are described. The actuators employ the photomechanical bending of the polymer film caused by low power (10 mW and less) laser radiation. The photomechanical effect combines various physical mechanisms, such as anisotropic thermal expansion, converse piezoelectric mechanis...

We describe new light-driven actuators based on films of polymer polyvinylidene fluoride, known as PVDF. The actuators employ the photomechanic bending of the polymer film caused by low-power (10 mW and less) laser radiation. The photomechanic effect combines various physical mechanisms, such as thermal expansion, the converse piezoelectric mechani...

New light-driven actuators based on films of polymer polyvinylidene fluoride are described. The actuators employ the photomechanical bending of the polymer film caused by low power (10 mW and less) laser radiation. The photomechanical effect combines various physical mechanisms, such as anisotropic thermal expansion, converse piezoelectric mechanis...

Significant developments in integrated sensors, novel applications of visible and infrared (IR) cameras, and advances in applied nanotechnology is seen this year. NASA Glenn has tested a new generation sensitive aircraft fire detector with multisensor approach using microelectromechanical systems that can reduce the rate of false alarm to zero. NAS...

Fiber Bragg gratings (FBG) have become preferred sensory structures in fiber optic sensing system. High sensitivity, embedability, and multiplexing capabilities make FBGs superior to other sensor configurations. The main feature of FBGs is that they respond in the wavelength domain with the wavelength of the returned signal as the indicator of the...

The development of integrated fiber optic sensors for use in aerospace health monitoring systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor's capabilities, limitations, and performance under extrem...

Experiment on single-mode Faraday waves having two, thee, and four wavelengths across a rectangular cylinder of high aspect ratio is the subject of discussion. Previous experiments recently done by Henderson & Miles (1989) and by Lei Jiang et. a1 (1996) focused on Faraday waves with one and two wavelengths across rectangular cylinders. In this expe...

The development of a sensitive oxygen sensor suitable for deployment in the ullage of an aircraft fuel tank is discussed here. Instead of using plain optical fibers, a long period grating is utilized for achieving a light weight optical sensor that strongly couples the core guided light into the cladding and vice versa. The detection principle is b...

Photothermal bending of strips of polyvinylidene fluoride was initiated by a laser beam with a power of a few milliwatts. A bending strip generated a force of 10−4 N that propelled a 1 g oscillating wheel of a mechanical clock. The frequency of photomechanical resonance at pulsed illumination was inversely proportional to the length of the strip. T...

We describe new light-driven actuator based on films of the polymer polyvinylidene fluoride known as PVDF. The actuator employs the photomechanic effect of bending of the polymer film caused by low power (10 mW and less) laser radiation. The photomechanic effect combines various physical mechanisms, such as thermal expansion, converse piezoelectric...

The development of integrated fiber optic sensors for smart propulsion systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor s limits and how it responds under various environmental conditions. The se...

A thin, hollow, monocone antenna above a ground plane was constructed and studied. The antenna was used to roughly model the convergent region of a rocket exhaust nozzle. The input impedances and currents on the aluminum antenna were measured. The monocone field expansions were found for the exterior and interior regions of the antenna. Mode matchi...

This research effort was a feasibility study of the concept of an all-optical micro motor with a rotor driven by a traveling wave. The wave was a result of a photo induced surface deformation of a photosensitive material produced by a traveling holographic grating. Two phases modulated coherent optical beams were used to generate the grating in two...

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant waveleng...

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant waveleng...

In this paper the sensitivity of embedded fiber optic sensors to changes in modal characteristics of plates is discussed. In order to determine the feasibility of embedded fiber Bragg gratings for the detection of modal shapes and modal frequencies, a comparison of holographically imaged modes and the detected dynamic strain from embedded fiber opt...

We describe an optical fiber splicing process based on the phenomenon of optical beam self-trapping in photocurable organic materials with light induced increase of the refractive index. The ends of two optical fiber cables to be spliced are immersed in a photocurable material with a gap maintained between them. The terminal ends of individual fibe...

We report a novel single-arm double-mode double-order waveguide interferometer being used as a chemical sensor for detection f toxic industrial materials such as ammonia in air. The sensor is based on thin films of polymers poly(methyl methacrylate) and polyimide doped with indicator dyes bromocresol purple and bromothymol blue. These dye- doped po...

An all-optical micromotor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo-induced surface deformation of a photosensitive materi...

Fiber optic Bragg gratings have been used for years to measure quasi-static phenomena. In aircraft engine applications there is a need to measure dynamic signals such as variable pressures. In order to monitor these pressures a detection system with broad dynamic range is needed. This paper describes an interferometric demodulator that was develope...

Surface gratings associated with holographic volume gratings in photorefractive crystals of iron-doped lithium niobate have been studied using diffraction of a reflected probe beam and high-resolution phase-shifted interferometric profilometry. Both techniques show that the surface gratings exist in the form of periodical corrugations of the same p...

We studied forward-scattered laser light that is produced when the light strikes an abrupt interface (air bubble in water) and when it passes unimpeded through diffused water layers caused by temperature gradients. Measured intensities of the scattered light indicated patterns that are due to both geometrical and physical optics. Distribution of in...

A sensor is described for which interference measurements of the phase delay between two propagating modes of different orders in a slab thin-film waveguide are used as the sensing technique. The basic building block of the sensor is a polymer film doped with an indicator dye such as Bromocresol Purple. The modes of two orders such as TM0 and TM1 a...

The need to make manufacturing, operation, and support of airborne vehicles safer and more efficient forces engineers and scientists to look for lighter, cheaper, more reliable technologies. Light weight, immunity to EMI, fire safety, high bandwidth, and high signal fidelity have already made photonics in general and fiber optics in particular an e...

Generating a moving holographic grating in a slab os photorefractive crystal can turn it into a smart optical material making up an optically driven actuator. Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect. The charge distribution is periodical...

Generating a moving holographic grating in a slab os photorefractive crystal can turn it into a smart optical material making up an optically driven actuator. Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect. The charge distribution is periodical...

We report on a single-arm double-mode waveguide interferometer being used as a chemical sensor for detection of presence of ammonia and other pollutants in ambient air. The sensor is based on thin films of polymers such as poly(methyl methacrylate) and polymide doped with various indicator dyes such as bromocresol purple. These dye-doped polymer ma...

Single-arm dual-mode optical waveguide interferometer utilizes interference between two modes of different order. Sensing effect results from the change in propagation conditions of the modes caused by the environment. The waveguide is made as an open asymmetric structure containing a dye-doped polymer film onto a quartz substrate. It is more sensi...

We report a simple evanescent field fiber optic electric field sensor constructed by coating the exposed fiber optic core with a polymer-dispersed liquid crystal (PDLC). It is well known that the effective refractive index of the liquid-crystal polymers has a large dependence on the direction and the magnitude of an applied electric field. This dep...

We demonstrate theoretically and experimentally that an initially Gaussian red light beam sent through a (pi) -step phase mask and launched into a thin film of polymer poly(methyl methacrylate) doped with laser dye 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H- pyran known as DCM evolves into a spatial structure similar to a dark spati...

Fiber optic sensors have the potential to be used in the very hostile environments necessary for advanced aerospace platforms. This paper reviews some of the key issues associated with the implementation of distributed fiber optic sensors in harsh environments and outlines baseline system designs.

We describe a simple yet efficient technique of delineation of various polymer MEMS structures using computer driven liquid jet dispenser. A syringe-type dispenser with a replaceable needle is filled with a polymer solution and mounted on a vertical translation stage. The substrate is mounted on two-coordinate horizontal translation stage. Addition...

To compete globally in the next millennium, designers of new transportation vehicles will have to be innovative. Keen competition will reward innovative concepts that are developed and proven first. In order to improve reliability of aerospace platforms and reduce operating cots, new technologies must be exploited to produce autonomous systems, bas...

Single arm dual mode optical waveguide interferometer utilizes interference between two modes of different order. Sensing effect results from the change in traveling conditions of the modes caused by the environment. The waveguide is made as an open asymmetric structure containing a dye-doped high temperature polyimide film onto a silica substrate....

Single arm dual mode optical waveguide interferometer utilizes interference between two modes of different order. Sensing effect results from the change in traveling conditions of the modes caused by the environment. The waveguide is made as an open asymmetric structure containing a dye-doped high temperature polyimide film onto a silica substrate....

Various optical technologies can be implemented in chemical sensing. Sensitive, rugged, and compact systems will be more likely built using interferometric waveguide sensors. Currently existing sensors comprise dual-arm systems with external reference arm, dual-arm devices with internal reference arm such as integrated Mach-Zehnder interferometer,...

Traditional optical methods that include interferometry, Schlieren, and shadowgraphy have been used successfully for visualization and evaluation of various media. Aerodynamics and hydrodynamics are major fields where these methods have been applied. However, these methods have such major drawbacks as a relatively low power density and suppression...

Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in wave propagation through shocks in supersonic flows. Resu...

We present the results on fabrication of plastic integrated optical elements using molding, liquid jet delineation, and UV irradiation. Coupling gratings with a period of 620 mm-1 and a diffraction efficiency of 3.3 percent were molded in a preheated poly(methyl methacrylate) planar waveguide using master saw shaped grating. An experimental device...

We report on the formation of a graded-index waveguide in a photocrosslinkable fluorinated polyimide upon its photodarkening with the spectral line 313 nm of a mercury arc lamp at exposures exceeding 5 J/cm2. Photodarkening prevents the UV radiation from penetration deep into the polymer and finally sets the region with increased refractive index n...

Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in the atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in the wave propagation through shocks generated in supe...

We present the results of study of thin film optical waveguides based on photocrosslinkable polyimide with glass transition temperature approaching 400 degrees C. The birefringence of the waveguides can possibly be reduced by eliminating the effect of gravity on the conditions of the film fabrication. We propose fabrication technique that allows us...

Scattering of coherent light as it propagates parallel to a shock wave, formed in front of a bluff cylindrical body placed in a supersonic stream, is studied experimentally and numerically. Two incident optical fields are considered. First, a large diameter collimated beam is allowed to pass through the shock containing flow. The light intensity di...

While the classical methods of shadowgraph and schlieren do yield a shadow in the neighborhood of a shock, they often suffer from low power densities and the need for relatively long distances. Scanning methods may help in solving these problems. The paper describes various scanning techniques, presents experimental data obtained by mechanical scan...

The NASA Lewis Research Center conducted a workshop on fiber optic technology on October 18-20, 1994. The workshop objective was to discuss the future direction of fiber optics and optical sensor research, especially in the aerospace arena. The workshop was separated into four sections: (1) a Systems Section which dealt specifically with top level...

In this paper we present a simplified one-dimensional theory for predicting locations of normal shocks in a converging diverging nozzle. The theory assumes that the flow is quasi one-dimensional and the flow is accelerated in the throat area. Optical aspects of the model consider propagation of electromagnetic fields transverse to the shock front....

We present a simplified 1D theory for detecting locations of normal shocks in a converging- diverging nozzle. The theory assumes that the flow is quasi 2D and the flow is accelerated in the throat area. Optical aspects of the model consider propagation of electromagnetic fields transverse to the shock front. The theory consists of an inverse proble...