Dark Energy and Large Synoptic Survey Telescope Precision Calibration Apparatus: Calibrating the Throughput and Response of Astronomical Instrumentation Department of Energy Site Visit August 21, 2009 Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Peter Doherty Harvard University Laboratory for Particle Physics and Cosmology

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 2DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Precision Calibration: Introduction We improve upon traditional celestial calibration sources by: Measuring a source with a known spectrum, namely, a narrowband tunable laser Compare the system response (telescope throughput) to a known detector (NIST-calibrated photodiode) In a related (but separate) effort, continuously monitoring the atmosphere during acquisition of astronomical data Measurement of a source is a sum of integrals:

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 3DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Current and Future Efforts: Calibrating the Telescope and Detector: Pan-STARRS Calibration Screen LSST Calibration Screen Portable Calibration System Monitoring Atmospheric Throughput: Real time water vapor monitor system (Leibler) Tunable-Lidar monitoring of atmospheric extinction (with UNM/GTRI) Precision Calibration: Current and Future

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 4DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Precision Calibration: Calibration Procedure Wavelength Calibration Procedure Illuminate full telescope aperture with monochromatic light Take a calibration “flat” while monitoring input light with calibrated photodiode Normalize flat to flux seen by photodiode Move to the next wavelength and repeat, until entire visible spectrum is spanned Construct wavelength-dependent response for each pixel in the telescope’s CCD camera End result: Measurement of relative system throughput, including telescope mirrors, corrector optics, filters, and detector

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 5DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Pan-STARRS Calibration Screen: Overview Accomplished: Installation of the world’s most advanced telescope instrument calibration system in the Pan-STARRS dome at Haleakala Hawaii Features: Rear projection screen mounted inside telescope dome Multiple fixed and tunable light sources: Quartz tungsten halogen white light NIST SIRCUS Laser (680 to 1100 nm) Supercontinuumlaser and monochromator (450 to 1100 nm) NIST calibrated photodiode for flux calibration Digital Micro-mirror Device for image projection Integrated into telescope control system

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 6DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Pan-STARRS Calibration Screen: Diagram

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 7DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Pan-STARRS Calibration Screen: Assembly

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 8DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Pan-STARRS Calibration Screen: Photograph

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 9DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Pan-STARRS Calibration Screen: Installed

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 10DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty System Enhancements 2009/2010: Installation of Ekspla Tunable laser for wavelength coverage from 350 nm to 1100 nm with a single source Improved Photodiode measurement and control system for more precise flux measurements Closing the loop with the CCD/DMD image flattener Further integration of instrument into telescope system software Incorporating calibration data into the Pan-STARRS Image Processing Pipeline Pan-STARRS Calibration Screen: Future Plans

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 11DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty LSST Calibration Screen: Overview Similar in concept to Pan-STARRS calibration screen, but much different in scale: Similarities: Ekspla (or similar) tunable laser source with wavelength coverage from 350 nm to 1100 nm NIST calibrated photodiode(s) for flux measurements Differences: Cannot use single DMD projector: not enough focal length, and a large central obscuration Much larger! Pan-STARRS = 1.8 meters, LSST = 8.5 meters Multiple small projectors?

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 12DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Comparison of Pan-STARRS Mirror Size to LSST Mirror Size LSST Calibration Screen: LSST vs. Pan-STARRS

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 13DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Filling the LSST Aperture with “Small” Projectors LSST Calibration Screen: Filling the Aperture 12 Projectors - 1.7m Diameter48 Projectors m Diameter

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 14DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty LSST Calibration Screen: Small Projector Concept: A fiber fed parabolic reflector Parabolic Mirror Optical Fiber Diffuse emitter and parabolic collimator. Light from a fiber is collimated and illuminates a diffuser. The size of the diffuse emitter determines the range of angles into which light is emitted. Uniform surface brightness on the emitter ensures uniform intensity into all angles. Diffuser Lens LPPC is currently constructing a prototype in our optics lab

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 15DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty LSST Calibration Screen: “Leaky” Fiber Panel Concept: A flat screen built of glowing optical fiber Optical Fiber Mirror Collimator Diffuser A prototype screen assembled in LPPC Lab Would a spiral work better?

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 16DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Portable Calibration System: Overview A transportable light source and photon flux measurement system for calibrating throughput of astronomical telescopes and instrumentation Makes use of existing observatory dome screen Flexible I/O and triggering modes to support a wide variety of operating modes allowing integration with diverse telescope systems In 2009/2010 LPPC will design and construct the Integrating Photodiode Amplifier. Other parts are COTS.

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 17DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Atmospheric Water Vapor: Overview Variation in aerosols and water vapor are the main sources of temporal variation in atmospheric transmission, and the airmass dependence of extinction varies with wavelength. To investigate these two effects (aerosols and water vapor) we are engaged in two lines of research: 1.Monitoring water vapor in the atmosphere via differential imaging 2.Measuring atmospheric aerosol content via lidar backscatter We are engaged in experiments of both types.

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 18DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Calibration: Undergraduate Projects Atmospheric Water Vapor via Differential Imaging Concept: Monitor bright stars simultaneously in two pass-bands: 940nm (on absorption line) and 880nm (off absorption line). 1.Monitor cloud density and correlate with simultaneous imaging through the CTIO 4m Blanco telescope 2.Distribution of water vapor and its variability spatially and temporally as well as airmass dependence. Two undergraduates travelled to CTIO in Chile with Dr. Stubbs in early July and are working to reduce their data and determine the results.

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 19DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Monitoring Atmospheric Extinction “Light from distant galaxies travels towards Earth-based telescopes for millions of years, and in the last millisecond of its trip about 20 percent of that valuable light, which carries information about the very structure of the universe, is lost as it traverses our atmosphere. For centuries, astronomers have looked through the atmosphere with their telescopes, but have seldom looked at the atmosphere in an effort to precisely correct for this lost light.” -John McGraw, Professor of Physics and Astronomy, University of New Mexico UNM/GTRI Astronomical Lidar for Extinction (ALE) ALE has been developed by the University of New Mexico and the Georgia Institute of Technology Research Institute Measures backscatter from the stratosphere to monitor minute-to-minute changes in extinction due to aerosols Current system uses a fixed, 537 nm source Harvard/LPPC will collaborate with ALE creators in testing the system using a tunable laser source with wavelength coverage from 410 to >1100 nm

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology 20DOE Site Visit 8/21/ Dark Energy and LSST– Precision Calibration Apparatus-Doherty Precision Calibration Apparatus: Credits Harvard University/LPPC: Christopher Stubbs, Professor of Physics and Astronomy Peter Doherty, Senior Instrumentation Engineer Steve Sansone, Scientific Instrument Builder Gautham Narayan, Graduate Student Claire Cramer, Post-Doctoral Research Scientist Camille Leibler, Undergraduate Student Kenneth Gottlieb, Undergraduate Student National Institute of Standards and Technology Keith Lykke, Physicist, Laser Applications Group Steven Brown, Physicist, Laser Applications Group John Woodward, Physicist, Laser Applications Group Allan Smith, Physicist, Laser Applications Group University of Hawaii, Institute for Astronomy John Tonry, Astronomer Jeffrey Morgan, Pan-STARRS Sr. Telescope Supervising Engineer Robert Calder, PS1 Operations Manager Large Synoptic Survey Telescope Kirk Gilmore, LSST Camera System Scientist, SLAC David L. Burke, Kavli Institute for Particle Astrophysics and Cosmology, SLAC Laser Applications Group