1. Optical Aeronomy Calibration Facility CEDAR WORKSHOP JUNE, 2007 Jeff Baumgardner, Center for Space Physics Boston University

2. Detector Calibration First, a system of calibrated light sources and standard detectors will be developed, that will be shipped to the various aeronomy observatories. At the observatories, these instruments will be used to check the brightness of any local “standard” light sources and to provide a measure of the responsivities of the optical detectors used at the observatory. These calibrated instruments will be robust enough to survive the shipping process with no measurable effect on their output or responsivity. First, a system of calibrated light sources and standard detectors will be developed, that will be shipped to the various aeronomy observatories. At the observatories, these instruments will be used to check the brightness of any local “standard” light sources and to provide a measure of the responsivities of the optical detectors used at the observatory. These calibrated instruments will be robust enough to survive the shipping process with no measurable effect on their output or responsivity.

3. Interference Filter Characterization The second area of concern is that of the characterization of interference filters. All-sky imagers, narrow field imagers, tilting filter photometers, and Fabry-Perot spectrometers all use interference filters. The information usually provided with these filters from the manufacturer is not always precise enough to predict how a filter will perform in a given system. At Boston University, we have been using a high resolution spectrograph built for the solar teaching laboratory, to measure these filters. Because of its increased use for teaching, this facility is now rarely available for our use, and the sun is not always shinning. We proposed to obtain a similar instrument equipped with a xenon lamp for the sole purpose of measuring filters. Once this facility is completed, researchers could bring or ship their filters to the facility to be measured. The second area of concern is that of the characterization of interference filters. All-sky imagers, narrow field imagers, tilting filter photometers, and Fabry-Perot spectrometers all use interference filters. The information usually provided with these filters from the manufacturer is not always precise enough to predict how a filter will perform in a given system. At Boston University, we have been using a high resolution spectrograph built for the solar teaching laboratory, to measure these filters. Because of its increased use for teaching, this facility is now rarely available for our use, and the sun is not always shinning. We proposed to obtain a similar instrument equipped with a xenon lamp for the sole purpose of measuring filters. Once this facility is completed, researchers could bring or ship their filters to the facility to be measured.

4. Standard Light Source “Standard” Lamp “Standard” Lamp FIGURE 1(a) FIGURE 1(a)

5. Typical Brightness Curve

6. Standard Detector The notion of a standard detector is not new…after all, the light meters in cameras are just that. The question is, can a standard detector be made that is stable to the 1% level over long periods of time? Periodic measurements of the responsivities of multiple instruments at the Boston University station at the McDonald Observatory and Millstone Hill Observatory have suggested that the detectors may be more stable than the tungsten filament “standard” lamp used to calibrate them. The difficulty in getting the required permits and licenses prevents a C-14 source from being used at these “remote” observatories. The notion of a standard detector is not new…after all, the light meters in cameras are just that. The question is, can a standard detector be made that is stable to the 1% level over long periods of time? Periodic measurements of the responsivities of multiple instruments at the Boston University station at the McDonald Observatory and Millstone Hill Observatory have suggested that the detectors may be more stable than the tungsten filament “standard” lamp used to calibrate them. The difficulty in getting the required permits and licenses prevents a C-14 source from being used at these “remote” observatories.

7. Standard Detector Schematic

8. Standard Detector Schematic Standard Detector Schematic

9. Standard Detector Characteristics Grating:50mm square, 600 l/mm, blaze= 5deg. Grating:50mm square, 600 l/mm, blaze= 5deg. Slit:24mm x 0.150mm Slit:24mm x 0.150mm Collimator:60 mm dia. 400mm fl achromat Collimator:60 mm dia. 400mm fl achromat Camera lens:25mm fl, F/0.85 Fujinon Camera lens:25mm fl, F/0.85 Fujinon CCD:752 x 580 pixels; 6.3mm h x 4.76mm v CCD:752 x 580 pixels; 6.3mm h x 4.76mm v Peak q.e.: 70%@ 540nm Peak q.e.: 70%@ 540nm Dark current:0.02e/sec Dark current:0.02e/sec Read noise: 10 e rms; gain: 0.77 [DN/e-] 16 bit Read noise: 10 e rms; gain: 0.77 [DN/e-] 16 bit Dispersion:4.5 [A/pixel] Dispersion:4.5 [A/pixel] Resolution:~10 A HPFW Resolution:~10 A HPFW Predicted responsivity:~50 [DN-Angstrom/R-Sec]@ 540nm (assuming 50% grating efficiency and full vertical binning) Predicted responsivity:~50 [DN-Angstrom/R-Sec]@ 540nm (assuming 50% grating efficiency and full vertical binning)

10. Interference Filter Characterization Interference filters are used in many instruments in aeronomical research. The transmission curves supplied with the filters are not specific enough (i.e., they typically do not take into account the specific optical configuration of the instrument in which it is to be used), to predict the transmission of the filter to a particular emission line to a precision better than 10% or so. The curves supplied by the manufacturer are usually made by illuminating the filter with a collimated bundle of rays over a region smaller than the clear aperture of the filter. To obtain the average filter curve, a weighted average is made from individual measurements taken at various radii from the center of the filter. Interference filters are used in many instruments in aeronomical research. The transmission curves supplied with the filters are not specific enough (i.e., they typically do not take into account the specific optical configuration of the instrument in which it is to be used), to predict the transmission of the filter to a particular emission line to a precision better than 10% or so. The curves supplied by the manufacturer are usually made by illuminating the filter with a collimated bundle of rays over a region smaller than the clear aperture of the filter. To obtain the average filter curve, a weighted average is made from individual measurements taken at various radii from the center of the filter.

11. New Facility in Room 503

12. New Facility in Room 503 New Facility in Room 503

13. Filter Testing in New Facility

14. Spectrogram Portion of solar spectrum without filter in place Portion of solar spectrum without filter in place Without filter With Filter

15. Typical Filter Curve

16. New Facility cont.