Search

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 SOHO/CELIAS Solar EUV Monitor (SEM) has measured absolute extreme ultraviolet (EUV) solar irradiance nearly continuously over a 15 year period that includes two solar cycle minima, 22/23 (1996) and 23/24 (2008). Calibration of the SEM flight instrument and verification of the data have been maintained through measurements from a series of sounding rocket calibration underflights that have included a NIST calibrated SEM clone instrument as well as a Rare Gas Ionization Cell (RGIC) absolute detector. From the beginning of SEM data collection in 1996, the SOLERS 22 fixed reference solar spectrum has been used to calculate absolute EUV flux values from SEM raw data. Specifically, the reference spectrum provides a set of weighting factors for determining a weighted average for the wavelength dependent SEM response. The spectrum is used for calculation of the second order contamination in the first order channel signals, and for the comparison between SEM flux measurements with broader-band absolute RGIC measurements. SOHO/SEM EUV flux measurements for different levels of solar activity will be presented to show how the choice of reference spectra now available affects these SEM data. Both fixed (i.e. SOLERS 22) and non-fixed (Solar Irradiance Platform/Solar 2000 and SDO/EVE/MEGS) reference spectra have been included in this analysis.

We present a simple EUV spectrometer based on chemically inert rare gas photon ionization and energy analysis of the resulting electrons. Precise photoelectron focusing and high electron transmission efficiency from the gas ionization area to the detector are combined with an optimum luminosity angle of 90 deg in an axi-symmetric design. All together, these features will allow us to achieve higher efficiency and spectral resolution than other spectrometers of this type reported to date. The modeled (neon) spectral resolution in the spectral range of 5 - 40 nm is 0.1 - 0.035 nm, respectively. A model of the proposed photoelectron focusing system is analyzed.

We report the design and laboratory testing of a prototype dual-grating filter-free extreme ultraviolet (EUV) spectrometer that has potential as a highly stable instrument for measuring absolute solar irradiance in the X-ray through far ultraviolet spectral range. The instrument is based on the same freestanding transmission gratings and silicon photodiodes used on the successful Solar EUV Monitor (SEM) aboard SOHO and the EUV Spectrophotometer (ESP) part of the EVE instrument suite to be flown on SDO. Its two gratings, placed in series, along with a simple baffle structure provide excellent out of band "white" light rejection. Because the instrument does not use any thin film filters or reflective optics it is not susceptible to the degradation and instability associated with such optical elements. We present photometric efficiency data from laboratory tests with a Helium and Hydrogen discharge light source and measurements of "white" light rejection taken using the Mt Wilson Observatory 60' solar telescope.

The Solar Dynamics Observatory (SDO) Extreme ultraviolet Spectro-Photometer (ESP), as a part of the Extreme ultraviolet Variability Experiment (EVE) suite of instruments, was calibrated at the National Institute of Standards and Technology (NIST) on the Synchrotron Ultraviolet Radiation Facility (SURF) Beam Line 2 in February 2007. Precise ESP alignment to the SURF beam was achieved through successive scans in X, Y, Pitch and Yaw, using a comparison of the four channels of the ESP quad photodiode as a measure of alignment. The observed alignment between the ESP and the other instruments in the EVE package was found to be in very good agreement with that measured at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado during ESP/EVE integration. The radiometric calibration of the ESP photometers in the spectral range around 4.4 nm (central zeroth order), and the four first order channels centered at about 18.9, 25.4, 29.8, and 36.1 nm was performed with SURF synchrotron radiation. The co-alignment of the SURF beam and the ESP optical axis for each energy and injected current was determined based on quad diode (QD) photometer responses (photodiode count-rate data). This determined beam position was later used to obtain exact energy-wavelength-flux profiles for each of the calibration energies and to calculate the quantum efficiency of the ESP channels. The results of this calibration (quantum efficiencies) are compared to the previous ESP NIST calibration results at SURF Beam Line 9 and to SOHO/SEM efficiencies.