Some Project Info Justin Albert Univ. of Victoria & Caltech Jul. 21, 2006

: Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 2 Limitations on our Knowledge of Dark Energy  Calibration of redshift is a significant uncertainty in cosmological parameter measurement.  Unless we improve calibration standards to < 1%, this will be a limiting systematic for upcoming projects … “Dark energy” Clearly nonzero!

: Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 3 Understanding the Acceleration of the Universe  Several projects in planning as well as construction phases will take data soon to examine what the source of the dark energy might be (via measuring its properties, e.g. its equation of state, its time-dependence, spatial-dependence). A fifth force (“quintessance”)? A “plain” cosmological constant? Something else? … and others Launch date ~2013 First data ~2011 First data next year !

Systematic Uncertainties are the Key  Minimizing uncertainties on these cosmological parameters is largely a matter of keeping systematic uncertainties at a minimum (especially flux as a function of redshift). From Kim, Linder, Miquel, & Mostek (MNRAS, 2004): : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 4

The Same Applies to Weak Gravitational Lensing  There are 3 main techniques for measuring the cosmological parameters: using type Ia supernovae (“standard candles”: measure their luminosity and redshift), weak gravitational lensing (shapes of galaxies are “lensed” by foreground matter, as a function of their redshift), and “baryon oscillations” (ripples are present in the distribution of galaxies, as a function of redshift). All require superb redshift (spectrophotometric) calibration. From Bernstein & Jain (ApJ, 2004): : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 5

And Possible Atmospheric Science Applications  The CALIPSO satellite (launched on Apr. 23 of this year) uses a Nd:YAG LIDAR laser at 1064 and 532 nm to measure the properties of clouds and the atmosphere. A tunable laser (and LIDAR receiver) could potentially provide information in a far greater range of wavelengths.  Issue: A tunable laser for atmospheric studies would prefer to be as close as possible to the atmosphere (CALIPSO and its sister satellites are at 705 km) whereas SNAP and ground-based telescopes prefer a higher orbit (  km). Ways to ameleiorate? : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 6

Improving Fundamental Calibration Not Easy Need to get above the ATMOSPHERE Idea: Rockets (ACCESS) Another possibility: Balloons But even after you very carefully calibrate them, stars are VARIABLE (majority on the > 1% scale). Wouldn’t it be nice to just have a (man-made) source up there … ? : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 7

A Tunable Laser in Space 1)Would allow atmospheric calibration for all major ground- based observatories (without any worries of stellar variability). 2)A monochromatic source that covers the entire wavelength range (250 to 2500 nm) -- avoids worries about differences between stars and galaxies. 3)Would provide an always-available fundamental spectrophotometric standard source for space-based observatories (SNAP). 4)Minimizes calibration transfers; precision is limited basically only by radiometer uncertainty. 5)Cost could be reduced by placing on a satellite needed anyway (e.g. GPS-III [upgrade to GPS], TSAT, …). 6)Funding: Military is traditionally (very) interested in lasers in space… : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 8

Defense Applications …  Target illumination, as well as space communication. Variable wavelength (more difficult to detect / defend) : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 9

How can we build it?  NO. Pulse-to-pulse laser energy variations mandate measuring the energy on every pulse, rather than just sampling some pulses with the radiometer (as pointed out by Chris Stubbs)! : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 10 Tunable laser Mirror mover Radiometer Beam expander Satellite Neutral density filter shutter Tunable laser Optics mover Radiometer Beam expander Satellite Neutral density filter shutter A better idea (with thanks to Eli Margalith): Uncoated “piece of glass”  Using an uncoated “piece of glass” as a beam sampler provides a reflectance that is known from first principles (just the index of the material) and avoids issues with a coating degrading over time.  Nevertheless, still issues…

1)We would need to ensure that the “glass” reflectance is known to 1 part in 10 4 over a period of 3-5 years, as we would be depending on its stability. Surface effects on “glass” …? (Would it be better to use glass, or quartz, … fused silica, sapphire, … ?) 2)Can we ensure stability of calibration if optics are moving? (and can we move the parts with an ensured precision of less than a part in 10 4 ??) 3)How can we calibrate the beam expander (to a part in 10 4 ???)? (and ensure it remains calibrated over 3-5 years??) How can we build it? : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 11 Tunable laser Optics mover Radiometer Beam expander Satellite Neutral density filter shutter Uncoated “piece of glass” Details… I have no idea if there is answer for each of these issues …

 It would be worthwhile to have a detailed simulation for all parts of the satellite (laser, optics, radiometer) and atmosphere to better understand uncertainties.  Should interface with SNAP, LSST, … pixel level simulations.  What simulation software to base such a simulation on? ?GEANT4 (particle physics simulator)? Probably no good for this since energies of photons are much too low. ?LIGO “e2e” (end-to-end) simulation? More applicable but no atmospheric simulation, and interferometry is irrelevant. LISA simulations? ?LRSP (Laser Ranging Simulation Program, by David Tratt [NASA] et al)? Would probably need to modify for to make source laser tunable, and add simulation of radiometer, but could be a possibility…Simulation : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 12 Tunable laser Optics mover Radiometer Beam expander Satellite Neutral density filter shutter Uncoated “piece of glass”

Tunable laser  To be purchased on Sept. 1 ! … Opotek Vibrant LD 355 II : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 13

Toward a Space-Qualified Tunable Laser … : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 14  The CALIPSO satellite uses an Nd:YAG laser from Fibertek Inc. that (clearly) is space-qualified.  Such a laser could potentially be used as a pump laser for an OPO (which would then itself need to be space-qualified).  However, it would be nice to have a laser that is closer to CW rather than pulsed, as CW would be more similar to astronomical sources (galaxies, stars, supernovae) and thus provide a better calibration.  Eli Margalith says that he may be able to develop a very fast-pulsed (i.e. MHz frquencies) OPO system, which would be similar to (in fact indistinguishable from) a CW source.  Would need to diode-pumped (like the Fibertek laser -- due to lifetime issues, as well as input power, a flashlamp is unsuitable as an optical pump in space), durable, tested, and space qualified …

CALIPSO orbit request … : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 15

Collaboration Issues

Meetings, Communication : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 17  Are phone meetings good/sufficient, or should we use one of the (free) videoconferencing systems that are available (e.g. VRVS, etc.) ??  I definitely hope we can have a system of fully public communication, where nothing is hidden behind passwords and everything is open. “Transparency is the hallmark of a democracy”, …  Due to the military applications (and the possibility of military support), this might unfortunately have to change at some point in the future.  I very much hope we can maintain an open system.  How do people find the webpage? Should we try to find a server on which we can all have accounts, and place the webpage -- and perhaps a document server -- on that? And what do people think of the logo? Is it OK, or should it be changed, …?

Organization : Some Project Info Biweekly Mtg. 7/21/06 : Some Project Info J. Albert 18  It would be good to get to the point where we can have actual real elections, a self-propagating organization system, ASAP.  I have no experience in organizing a collaboration.  How shall we develop a collaboration structure, with a membership committee, decision-making bodies, etc.? (And would we be able to do that yet?)  Is anyone interested in helping to write an organizational document? Would anyone perhaps be interested in being on a committee to write a draft of such a document?  This is (clearly) important…

Backup Slides

Straight From the Pentagon !! Forwarded message Date: Mon, 22 May :00: From: Muslimov Alexander Ctr AF/A8XC To: Subject: your preprint Dr. Albert, I've just come across of your and your collaborators' preprint "Telescope Spectrophotometric and Absolute Flux Calibration..." It sounds interesting to me, and I believe you can come up with a somewhat more detailed presentation of your idea. If so, would you be interested in briefing our Directorate about your proposal at the Pentagon? Are you going to be in the DC area sometime this summer/fall? Although we don't have our own resources to fund proposals, we collaborate with the AFRL, AFOSR, DARPA and some other agencies, and could help you to find the appropriate POCs within the USAF who might be interested in your proposal. I look forward to hearing from you. Best regards, Alex Alex Muslimov, Ph.D. Staff Physicist HAF/A8XC Air Force Pentagon, Washington DC (703) AF/A8XC Mission: Explore, develop, advocate and link future concepts, capabilities, promising technologies and their program funding to continue transforming the Air Force into a more effective fighting force astro-ph/ :

(main) Space Tunable Laser Requirements 1)Wide tuning range (~ nm) 2) No Moving Parts (Including cooling; could use radiative and/or Peltier chip cooling, but no flowing coolant) 3)Low beam divergence, O(1 mrad) (Will require beam spreader for further reduction.) 4)Light into air, not optical fiber (obviously) 5)At least 100 mW power (but needn’t be high-power) 6)Radiation-hard

Slewing Rate (20000 km orbit)  Easily trackable from ground/space.

Upcoming Data from new CALIPSO Satellite…!  Launched 1 month ago (April 28)  Nd:YAG laser (532 and 1064 nm)  Will take data at Palomar later this year.

Several Relatively Convenenient Platforms on Timescale

To Do: Tunable Laser and Diode Studies 1)Radiation Tests: Survivability/Degradation at km. TRIUMF irradiation facility. 2)Characterize beam divergence. Beam expander optics. 3)Explore options for eliminating moving parts (or momentum-balance when absolutely necessary), reducing cooling power. 4)Electronics / power source requirements. 5)4  -radiating source, etc.

Tunable laser Mirror mover Radiometer EARTH Friendly country Mountain with observatory Rogue state Beam expander GPS jamming Satellite Neutral density filter shutter All beam movement controlled by (small) mirror mover -- no movement of laser or satellite itself needed. “Secret” wavelength or wavelength sequence -- much harder to detect/defend than specific (known) wavelength. Also can optimize for weather conditions if not clear sky. Opening provides additional power needed to illuminate during daytime. a space telescope