Optical Aeronomy Calibration Optical Aeronomy Calibration FacilityFacility

CEDAR WORKSHOP JUNE, 2007

Jeff Baumgardner, Center for Space Physics

Boston University

Detector CalibrationDetector Calibration

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

Interference Filter Interference Filter CharacterizationCharacterization

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

Standard Light SourceStandard Light Source

• ““Standard” LampStandard” Lamp

• FIGURE 1(a)FIGURE 1(a)

Typical Brightness CurveTypical Brightness Curve

Standard DetectorStandard Detector

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

Standard Detector Standard Detector SchematicSchematic

Standard Detector Standard Detector SchematicSchematic

Standard Detector Standard Detector CharacteristicsCharacteristics

• Grating:Grating: 50mm square, 600 l/mm, blaze= 5deg.50mm square, 600 l/mm, blaze= 5deg.• Slit:Slit: 24mm x 0.150mm24mm x 0.150mm• Collimator:Collimator: 60 mm dia. 400mm fl achromat60 mm dia. 400mm fl achromat• Camera lens:Camera lens: 25mm fl, F/0.85 Fujinon25mm fl, F/0.85 Fujinon• CCD:CCD: 752 x 580 pixels; 6.3mm h x 4.76mm v752 x 580 pixels; 6.3mm h x 4.76mm v• Peak q.e.: Peak q.e.: 70%@ 540nm 70%@ 540nm • Dark currentDark current :: 0.02e/sec0.02e/sec• Read noise: Read noise: 10 e rms; gain: 0.77 [DN/e-] 16 bit10 e rms; gain: 0.77 [DN/e-] 16 bit• Dispersion:Dispersion: 4.5 [A/pixel]4.5 [A/pixel]• Resolution:Resolution: ~10 A HPFW~10 A HPFW• Predicted responsivity:Predicted responsivity: ~50 [DN-Angstrom/R-Sec]@ 540nm ~50 [DN-Angstrom/R-Sec]@ 540nm

(assuming 50% grating efficiency and full vertical binning)(assuming 50% grating efficiency and full vertical binning)

Interference Filter Interference Filter CharacterizationCharacterization

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

New Facility in Room 503New Facility in Room 503

New Facility in Room New Facility in Room 503503

Filter Testing in New FacilityFilter Testing in New Facility

Spectrogram Spectrogram

• Portion of solar spectrum without Portion of solar spectrum without filter in placefilter in place

Without filter

With Filter

Typical Filter CurveTypical Filter Curve

New Facility cont.New Facility cont.

New Facility cont.New Facility cont.