Published By National Aeronautics and Space Administration
Issued over 9 years ago
Summary
Description
<p> The optical design of RAISE is based on a new class of UV/EUV imaging spectrometers that use&nbsp; only two reflections to provide quasi-stigmatic performance simultaneously over multiple wavelengths&nbsp; and spatial fields. Figure 5 summarizes the RAISE instrument design, showing photographs of each of&nbsp; the components or subsystems. The design uses an off-axis parabolic telescope mirror to form a real&nbsp; image of the sun on the spectrometer entrance aperture. A slit then selects a portion of the solar image,&nbsp; passing its light onto a near-normal incidence toroidal grating, which re-images the spectrally dispersed&nbsp; radiation onto two array detectors. Two full spectral passbands over the same one-dimensional spatial&nbsp; field are recorded simultaneously with no scanning of the detectors or grating. The two different spectral&nbsp; bands (1st-order 1205-1243&Aring; and 1526-1564&Aring;) are imaged onto two intensified Active Pixel Sensor&nbsp; (APS) detectors whose focal planes are individually adjusted for optimized performance. The telescope&nbsp; and grating are coated with B4C to enhance short wavelength (2nd order) reflectance (Fig. 6), enabling the&nbsp; instrument to record the brightest lines between 602-622&Aring; and 761-780&Aring; at the same time. Table 1&nbsp; summarizes the main optical parameters for RAISE. &nbsp;&nbsp;</p> <p> <strong>TVLS Grating. </strong>The single toroidal variable line space (TVLS) grating has a toroidal surface&nbsp; (Sagittal Radius = 640.5 mm, Tangential Radius = 635.3 mm), with varied line space (VLS) rulings of the&nbsp; type developed originally for spherical substrates by Kita, Harada, and collaborators (1983, 1995). By&nbsp; combining this VLS concept with toroidal surfaces, RAISE is the first to exploit this new class of&nbsp; spectrometers, as described by Thomas (2003). For RAISE, the grating is placed 400 mm behind the slit,&nbsp; with focus at a distance of approximately 1700 mm, for a spectrometer magnification of 4.25. By&nbsp; operating at high magnification, the RAISE spectrometer most effectively utilizes the full length and&nbsp; width available in the sounding rocket payload. The first RAISE grating, mechanically ruled by Bach&nbsp; Research, Inc., was delivered in August 2007 and tested for figure, ruling density and total grating&nbsp; efficiency.&nbsp;</p> <p> <strong>Intensified APS Cameras</strong>. The RAISE Intensified APS camera systems are 1k x 1k CMOS Active&nbsp; Pixel Sensors using miniature digital camera electronics and fed by an MCP intensifier. APS cameras&nbsp; were chosen for RAISE (rather than CCDs) because of their extremely fast readout, direct digital output,&nbsp; low mass, low power, deep full well and high radiation tolerance. The RAISE cameras were developed at&nbsp; DLR (Germany) using a Cypress/Filfactory Star 1000 APS and include a 12-bit external ADC and USB&nbsp; 2.0 interface. We will operate the cameras at 5-10 frames/sec readout, making dark current negligible&nbsp; compared to the incoming signal. The complete camera electronics including its controller is integrated&nbsp; on only one printed circuit board, and uses a rigid-flex 3D-interconnection between the boards to form a&nbsp; lightweight, compact sensor head. Flight detectors were delivered by DLR in August 2008.&nbsp;</p> <p> <strong><em>RAISE Chromospheric Slit Jaw Camera (SJC)&nbsp; </em></strong>To co-align the RAISE spectra with observations from SDO, HINODE, and IRIS, and to collect&nbsp; chromospheric disk images in C IV and the continuum between 1500-1700 &Aring;, the solar image at the&nbsp; telescope focal plane (spectrograph entrance slit plane) is re-imaged onto a SJC mounted on the bottom&nbsp; side of the optical bench. The slit plane is tilted 5 degrees to reflect incident light onto a pair of flat relay&nbsp; mirrors that fold the light down through the optical bench to a re-imaging system mounted to the bottom&nbsp; side of the optical bench, through a 200 &Aring; wide interference filter centered at 1600 &Aring;, and then onto an&nbsp; intensified APS camera identical to those discussed above. The SJC re-images the 4&#39; x 16&#39; region of the&nbsp; slit plane onto the camera with 4.25:1 magnification (matching the magnification of the spectrograph) for&nbsp; an image plate scale of 1.0&quot;/pixel.&nbsp; The primary purpose of the RAISE Slit Jaw Camera (SJC) is to provide co-alignment context images&nbsp; for the spectroscopic observations with those from other ground and space-based platforms. The&nbsp; relatively broad passband (1600 &plusmn; 100&Aring;) SJC image consists of largely chromospheric continuum and a&nbsp; large contribution (20% of the signal in the quiet-Sun) from the C IV line at 1550&Aring; and provide &ldquo;cool&nbsp; loop&rdquo; and evolving supergranular context for the spectral observations discussed above. The SJC&nbsp; observations will also enable us to actively study the connection, if any, of broad-frequency spectrum&nbsp; oscillations in the chromosphere, how they dynamically interact with the magnetic fields that thread the&nbsp; line of sight of the spectrograph slit and how they connect to the spectroscopic signals in the upper&nbsp; chromosphere, transition region and low corona (e.g., McIntosh &amp; Poland 2004).&nbsp;</p>