It is well know that the elevated satellite operating temperature causes the unused catalyst material in the Room Temperature Vulcanized materials (RTV) to volatize, which can then re-deposit or condense onto other spacecraft surfaces. In the presence of sunlight, this Volatile Condensable Material (VCM) can photo-chemically deposit onto optically-sensitive spacecraft surfaces and significantly alter their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended performance loss of the spacecraft. This has been studied in vacuum environments simulating geosynchronous orbits, but never to our knowledge in atomic oxygen environments simulating low earth orbit. In this work we present an initial study of the effect of an atomic oxygen environment on the optical properties of previously photofixed material as well the effect of an atomic oxygen environment on the photofixing process. We will employ spectroscopic ellipsometry to characterize films deposited from the outgassing of DC93500, RTV566, SCV2590, CV2568 and SCV2590-2.
We describe the evolution of laser damage spots on bulk nickel generated by multipulse femtosecond laser irradiation
with a 100 μm x 100 μm square flat-top beam profile as a function of the laser fluence and the number of pulses incident
on the target. This large-area irradiation simulates conditions associated with the interaction of femtosecond laser pulses
on a remote target. The larger area laser damage sites are characterized either by a series of self-organized surface
structures with micro- and nanoscale features or a deep circular pit rather than a crater that mirrors the beam profile.
Furthermore, the ablation rate of the deepest feature sharply increases above a laser fluence of 2 J/cm2; this increase is
associated with the creation of a deep circular ablation pit generated during ablation with the first few pulses on the
sample that continuously grows upon multipulse irradiation due to the focusing of incident laser energy into the pit by
the sloped pit surfaces.
In this paper, we present a temperature-insensitive refractive index sensor based on π-phase-shifted Bragg gratings fabricated on side-hole fibers processed by wet chemical etching technique. The reflection spectrum of the π-phase shifted gratings on etched side-hole fiber features two notches with large spectral separation, which was used for refractive index (RI) detection in our application. The relative spectral notch separation exhibited a RI sensitivity of −278.5 pm/RIU (RIU: RI unit). Theoretical simulation obtained the temperature sensitivity of −0.00241 pm/°C, and experimental results also showed little sensitivity to temperature of our RI sensor.
DC-93-500, SCV-2590 and SCV-2590-2 silicone/siloxane based co-polymers serve as adhesive components of
satellites and other spacecraft. It is well known that out gassing of these materials is a major source of
contamination. For the past several years we have been optically characterizing the condensates and their photofixed
films via in-situ ellipsometry and quartz crystal microbalance (QCM) measurements. We have identified several
common outgassed components in each of these materials via FTIR, including polydimethylsiloxane (PDMS), and
Tetra-n-propylsilicate (NPS). We have studied the optical properties of the photofixed films produced at various
wavelengths of incident light , as well as when mixtures of these films are employed as the outgassing source via
variable angle spectroscopy ellipsometry. We can relate the photofixed material optical properties to the bulk liquids
and to the films produced by the outgassssing of the actual co-polymers mentioned above. This work may lead to
the evaluation of the optical properties of the photofixed effluents of actual adhesives by evaluating a few basic
components
Room Temperature Vulcanized (RTV) materials, such as silicone adhesives, are commonly used to bond components of
communication satellites and other types of spacecraft. The elevated satellite operating temperature causes the unused
catalyst material in the RTV to volatize, which can then re-deposit or condense onto other spacecraft surfaces. This
Volatile Condensable Material (VCM) can condense onto optically-sensitive spacecraft surfaces and significantly alter
their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended
performance loss of the spacecraft. Knowledge of the optical impact of VCM's is therefore a major concern of spacecraft
designers and spacecraft-contamination engineers. In view of this we have employed in-situ spectroscopic ellipsometry
to monitor in real time the optical constants of the condensed effluent of RTV-566, SCV-2590-2 and SCV-2590 as
function of condensation temperature from 120 K to 180 K. The film is condensed directly on to a QCM crystal. Thus
the QCM generated deposition trajectory and thickness can be correlated to the optical trajectory and thickness, yielding
the film density. We will present the optical constants, n and k, as a function the condensation temperature.
Room Temperature Vulcanized (RTV) materials, such as silicone adhesives, are commonly used to bond components of
communication satellites and other types of spacecraft. The elevated satellite operating temperature causes the unused
catalyst material in the RTV to volatize, which can then re-deposit or condense onto other spacecraft surfaces. In the
presence of sunlight, this Volatile Condensable Material (VCM) can photo-chemically deposit onto optically-sensitive
spacecraft surfaces and significantly alter their original, beginning-of-life (BOL) optical properties, such as solar
absorptance and emittance, causing unintended performance loss of the spacecraft. Knowledge of the optical impact of
photo-chemically-deposited VCM's is therefore a major concern of spacecraft designers and spacecraft-contamination
engineers. In view of this we have employed in-situ spectroscopic ellipsometry to monitor in real time the optical
constants of the condensed effluent of RTV CV-566 as well as its photofixed effluent. This technique is sensitive to nm
thick layers and can be used to extract n and k as a function of wavelength. We will present the optical constants, n and
k, for both condensed unexposed and the photofixed film.
Realizable artificial medium with negative permittivity,
permeability and refractive index are fabricated by
introducing inclusions significantly smaller than the
wavelengths of excitation into an archival host medium.
Negative refractive index media normally posses a small
degree of chirality associated with the split-rings. However
in order to enhance the chirality of the artificial media, the
split rings can be replaced by spirals.
Recent work has shown that well controlled chiral media
can be fabricated using available semiconductor techniques
that have been modified to produce these structures.
Specifically the glancing angle deposition technique
(GLAD) has been shown to be well suited to producing
these types of chiral structures.
Novel devices made from metamaterials that also possess
chirality are considered. When chiral properties are
included in a negative refractive index slab, with n = -1,
two rays are refracted in the slab. The distance between the
two corresponding focal lines is determined by the
magnitude of the chiral parameter. Thus this negative
refractive index lens can also be used to measure the chiral
parameter. At the focal lines small cross polarized
components also exist.
Based on the complete model expansion of the field at the
chiral-chiral (or free space-chiral) interface it is shown that
line sources also excite several species of lateral waves that
are associated with total internal reflection. Since the
refractive index is assumed to be negative, rays incident
upon the chiral slab at the critical angles for total internal
reflection, θ1 and θ2, are refracted parallel to the interface
in the backward direction, resulting in θR1 and θL1 equal to -90°. Thus the image and the source are on the same
side of the negative refractive index chiral slab and the
device behaves like a reflector.
Inclusions embedded in conventional positive refractive index materials are used to fabricate artificial materials, with negative permittivity, permeability and negative refractive index (NRI). We consider electromagnetic wave propagation in NRI materials with chiral properties that are not negligible. To this end we initially derive explicit expressions for reflection and transmission matrices for a chiral slab. The diagonal terms of the linearly polarized reflection coefficient matrix are the familiar Fresnel reflection coefficients, and the off-diagonal, cross-polarized reflection coefficients are proportional to the chiral parameter and the product of the vertically and horizontally polarized transmission coefficients of the non-chiral host medium. The-full wave modal expansion of the fields include evanescent and propagating radiation fields, several types of lateral waves associated with the phenomena of total internal "backward" reflection as well as several different surface waves (plasmons). Using NRI materials with chiral properties it is possible to fabricate rectangular slabs that perform as lenses associated with two focal lines at the opposite side of the source. Furthermore, the backward propagating lateral waves could be used to make the chiral metamaterials perform like reflectors.
The in situ measurement capabilities and advantages of recently developed spectroscopic ellipsometry (SE) instrumentation, which covers wide spectral ranges (190-1700 nm, or 0.73-6.5 eV) and is based on rotating-compensator technology, are described. A technique which can quantitatively correct for window birefringence is presented. Current in situ SE deposition monitoring and control applications in the compound semiconductor, display, and optical coatings industries are also presented.
This paper details our experimental progress towards the synthesis of self-assembled nanostructures that may exhibit collective computational activity. Self assembled two dimensional networks of heterostructured quantum dots, linked by resistive and capacitive connections, can function as Boolean logic circuits, associative memory, image processors, and combinatorial optimizers. Computational or signal processing activity is elicited from simple charge interactions between the dots which act as non-linear resistors. Such circuits could be massively parallel, fault-tolerant, ultrafast, ultradense and dissipate very little power.
Low earth orbit exposes space materials simultaneously to atomic oxygen and ultraviolet light. Numerous materials were sputtered, e-beam evaporated, and CVD deposited. Experiments with these samples aboard the NASA (USA) 1992 and 1993 space flights STS-46 and STS-51 are discussed, and comparisons made with laboratory studies in an oxygen plasma environment. Multiple samples of thin films of Al, diamondlike carbon, diamond, silicon nitride, silicon carbide, and solar concentrator multilayer stacks were prepared. These were characterized both before and after flight by spectroscopic ellipsometry, spectrophotometry, interferometry, Auger spectroscopy, Raman spectroscopy, and atomic force microscopy.
Pulsed laser deposition is a technique commonly used to deposit high quality thin films of high temperature superconductors. This paper discusses the results obtained when this technique is applied to the deposition of Tl-Ca-Ba-Cu-O thin films using a frequency doubled Nd:YAG laser operating at 532 nm and an excimer laser operating at 248 nm. Films with onset temperatures of 125 K and zero resistance temperatures of 110 K deposited on (100) oriented MgO from a composite Tl2Ca2Ba2Cu3Ox target were obtained at both wavelengths upon appropriate post deposition annealing. Films deposited at 532 nm exhibit a rough surface, while those deposited at 248 nm are smooth and homogeneous. Upon annealing, films deposited at both wavelengths are single phase Tl2Ca2Ba2Cu3Ox.
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