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The 336 individual grating elements making up the High-Energy Transmission Grating (HETG) will be verified and calibrated in laboratory facilities at MIT as they are fabricated. A high instrument resolving power of order E/(Delta) E approximately equals 1000 requires an overall period uniformity of better than 250 ppm. To extract the maximum astrophysical information the diffraction efficiency of the HETG will be calibrated to the 1% level (1(sigma) ). Grating element period variations are measured and mapped in the Laser Reflection facility. Collimated HeCd (3250- angstrom) or HeNe (6328-angstrom) laser light is diffracted by the samples and measured. A per-point measurement noise of below 5 ppm rms and an overall period repeatability of 40 ppm rms have been achieved. X-ray diffraction efficiency in the 0.4 to 10 keV range is calibrated in the X-ray Grating Evaluation Facility (X- GEF). The facility combines a 17 meter vacuum beam line, a multi- anode X-ray source with monitor counter, a piezo-deformed 1D Ir coated focussing optic, a single-pixel solid state detector, and a 2D imaging proportional counter. The facility operation is under computer control and test procedures, instrumentation parameters, and acquired data are managed with a database. The system uses synchrotron-calibrated reference gratings as efficiency transfer standards. Detailed characterization and modeling of the X-GEF components and test/analysis procedures are being carried out to optimize the quality of the HETG calibration.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
