Thin-film aluminum filters degrade in space with significant reduction of their Extreme Ultraviolet (EUV) transmission. This degradation was observed on the EUV Spectrophotometer (ESP) onboard the Solar Dynamics Observatory’s EUV Variability Experiment and the Solar EUV Monitor (SEM) onboard the Solar and Heliospheric Observatory. One of the possible causes for deterioration of such filters over time is contamination of their surfaces from plumes coming from periodic firing of their satellite’s Monomethylhydrazine (MMH) – Nitrogen Tetroxide (NTO) thrusters. When adsorbed by the filters, the contaminant molecules are exposed to solar irradiance and could lead to two possible compositions. First, they could get polymerized leading to a permanent hydrocarbon layer buildup on the filter’s surface. Second, they could accelerate and increase the depth of oxidation into filter’s bulk aluminum material. To study the phenomena we experimentally replicate contamination of such filters in a simulated environment by MMH-NTO plumes. We apply, Scanning Electron Microscopy and X-Ray photoelectron spectroscopy to characterize the physical and the chemical changes on these contaminated sample filter surfaces. In addition, we present our first analysis of the effects of additional protective layer coatings based on self-assembled carbon monolayers for aluminum filters. This coverage is expected to significantly decrease their susceptibility to contamination and reduce the overall degradation of filter-based EUV instruments over their mission life.
The glow of interstellar plasma and solar wind pickup ions and solar wind emissions at 30.4 nm provide a way of exploring important physical processes in the heliosphere. Imaging the heliosphere at this wavelength with high spectral resolution will map the heliopause, probe pickup ions in the solar wind, and reveal the three-dimensional flow pattern of the solar wind, including in the regions over the sun's poles. The required high-throughput, high-resolution spectrometer for diffuse radiation should be able to measure 1 milli-Rayleigh irradiance in 10000 seconds with a 0.005-nm spectral resolution across pixels subtending a few degrees of celestial arc. The desired performance characteristics can be achieved by combining multiple entrance slits with an optimized spectrometer design. We present a concept of a space experiment to image the heliosphere at 30.4 nm and discuss the scientific rationale and required instrumentation.
The He+ ion provides a valuable tracer of solar wind dynamics and the heliospheric boundary. Mapping the heliosphere in the 30.4 nm resonance line of the He+ ion with high spectral resolution will open access to the heliopause and reveal the three-dimensional flow of the solar wind. The emission fluxes are however faint, just a few mR, which poses a serious limitation on the mapping rate at high signal-to-noise ratio. We have developed a spectrometer configuration for narrowband EUV emission that offers important advantages over previous designs: high throughput (~1cps/mR), high resolution (several thousand), no moving parts, and modest instrument size and mass. The concept combines a conventional normal-incidence Rowland mount grating and an efficient multilayer coating, with a microchannel plate detector performing two dimensional photon counting. One key innovation is the use of a large-area multi-slit at the spectrometer entrance. This multislit is a one dimensional sequence of open and opaque zones, against which pattern the accumulated spectral image can be correlated to recover the incident spectrum. The other innovation is arranging that each member of the multislit group is curved in such a way that the off-plane grating aberrations (which extend and rotate the image of each object point) do not introduce significant wavelength broadening. The curved slit arrangement yields a large well-corrected image field, and a high throughput for diffuse emission is achieved. The curved-multislit Rowland spectrometer may have a variety of other applications sensing diffuse fluxes with high spectral resolution.
In this paper, the phase-space formulation is applied to the evaluation of nonimaging optics sub-systems. Brightness (luminance) efficiency is introduced as a Figure of Merit for system performance maximization procedures that can be applied, for example, to plasma diagnostics (by utilizing coherent fiber imaging).
In this paper, we investigate the application of precision plastic optics into a communication/computer sub-system, such as a hybrid computer motherboard. We believe that using optical waveguides for next-generation computer motherboards can provide a high performance alternative for present multi-layer printed circuit motherboards. In response to this demand, we suggest our novel concept of a hybrid motherboard based on an internal-fiber-coupling (IFC) wavelength-division-multiplexing (WDM) optical backplane. The IFC/WDM backplane provides dedicated Tx/Rx connections, and applies low-cost, high-performance components, including CD LDs, GRIN plastic fibers, molding housing, and nonimaging optics connectors. Preliminary motherboard parameters are: speed 100 MHz/100 m, or 1 GHz/10 m; fiber loss approximately 0.01 dB/m; almost zero fan-out/fan-in optical power loss, and eight standard wavelength channels. The proposed hybrid computer motherboard, based on innovative optical backplane technology, should solve low-speed, low-parallelism bottlenecks in present electric computer motherboards.
Free-standing transmission gratings will be used in a new generation of space instruments for magnetosphere energetic neutral atom (ENA) imaging which requires efficient suppression of the exceptionally strong background extreme ultraviolet (EUV) and UV radiation. The first results of the experimental study of grating (period 200 nm) optical properties in the 50 - 130 nm wavelength range are presented. It is shown that grating transmission strongly depends on polarization of the incident radiation which makes gratings efficient polarizers. Possibilities of using a single grating and crossed gratings for EUV filtering are discussed.
We have developed a prototype spectrometer for space applications that require long-term stable EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer operating at a few electron volts, and followed by an electron multiplying detector, pulses due to individual electrons are counted. The overall efficiency of this process is essentially independent of gain drifts in the signal path, and the secular degradation of optical components that is often a problem in other techniques is avoided.
Recently proposed low-energy neutral atom (LENA) imaging techniques rely on collisional processes to convert LENAs into ions to separate the neutrals from the intense UV radiation background. At low energies, these collisional processes have poor conversion efficiencies and limit the angular resolution of these devices. However, if the intense UV light background can be suppressed, direct LENA detection is possible. We present results from a series of experiments designed to develop a novel filtering structure based on free-standing gold transmission gratings. If the grating period is sufficiently small, the gratings can substantially polarize UV light in the wavelength range 300 to 1500 Å. If a second grating is placed behind the first grating with its axis of polarization oriented perpendicular to that of the first, considerable attenuation of the UV radiation is achievable. The neutrals pass through the remaining open area of two gratings and are directly detected. We have obtained nominal 2000-Å-period (1000-Å bars with 1000-Å slits) gratings and measured their UV and atomic transmission characteristics. The geometric factor of a LENA imager based on this technology is comparable to that of other proposed LENA imagers, with a significantly better angular resolution.
Recently proposed low energy neutral atom (LENA) imaging techniques use a collisional process to convert the low energy neutrals into ions before detection. At low energies, collisional processes limit the angular resolution and conversion efficiencies of these devices. However, if the intense ultraviolet light background can be suppressed, direct LENA detection is possible. We present results from a series of experiments designed to develop a novel filtering structure based on free-standing transmission gratings. If the grating period is sufficiently small, free standing transmission gratings can be employed to substantially polarize ultraviolet (UV) light in the wavelength range 300 angstroms to 1500 angstroms. If a second grating is placed behind the first grating with its axis of polarization oriented at a right angle to the first's, a substantial attenuation of UV radiation is achievable. The neutrals will pass through the remaining open area of two gratings and be detected without UV background complications. We have obtained nominal 2000 angstroms period (1000 angstroms bars with 1000 angstroms slits) free standing, gold transmission gratings and measured their UV and atomic transmission characteristics. The geometric factor of a LENA imager based on this technology is comparable to that of other proposed LENA imagers.
The imaging of magnetosphere in energetic neutral atom (ENA) fluxes is recognized as a powerful experimental tool in the study of global magnetospheric processes. Intensity of ENA fluxes is typically very low. ENA's cannot be collected and concentrated by diffracting and refracting elements as it is done in optics, and therefore an imaging system on the basis of the pinhole camera should be used. There were several suggestions to use a coded-aperture technique to enhance geometrical throughput and, consequently, sensitivity of the instruments. The coded-aperture technique is reviewed and its application to the planetary magnetosphere imaging is considered. Computer simulation demonstrates advantages and limitations of the technique and promising applications are identified.
We have developed a prototype spectrometer for space applications which require long term absolute EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer operating at a few eV, and followed by an electron multiplying detector, pulses due to individual electrons are counted. The overall efficiency of this process is essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided.
We propose to perform in situ measurements of precipitating and escaping energetic neutral atoms (ENA) of energies between approximately 5 and 200 keV. The interface characteristics of this new type of instrument, named ISENA (Imaging particle Spectrometer for Energetic Neutral Atoms), are consistent with the SAC-B spacecraft specifications, so that it could be included in its scientific payload. The main technical properties of this experiment are here briefly described.
A novel, fledgling approach to the filtering of EUV radiation for laboratory and space applications is reviewed. Foils perforated by a set of parallel channels with submicron diameters serve as wavelength-dependent filters. Each channel passes photons when the wavelength is much smaller than the channel diameter. The transmission of the channel drops dramatically, however, when the wavelength becomes comparable to or larger than the channel diameter. The relevant theoretical considerations as well as available experimental data are presented. Several different ways to manufacture such kind of filters are outlined, including nuclear track filters, anodized metal films, and microchannel plate technology. Advantages and disadvantages of each technique are discussed. The history of the work in the field as well as prospects for the future are presented.
A new approach to study the composition of microchannel plate sensitive surface by secondary ion mass spectrometry is described. The time-of-flight technique is implemented in an unconventional way which permits using the continuous probing beam and concurrent multichannel mass identification. This makes the technique relatively simple, and the low doses and low probing beam intensities provide the opportunity to perform nondestructive analysis of thin layers and fragile films.