Precision Astrophysics &
Cosmology Enabled by a
Tunable Laser in Space
Dark Energy
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Precision
Cosmology
Justin Albert
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CCAPP
Univ. of Victoria
Atmospheric
Physics Jan. 12, 2007
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Supernovae are one of the powerful probes for
understanding the eventual fate of the Universe
Distances to ~6% from brightness
Redshifts from features in spectra
600 million light-years away
(Hubble Space Telescope, NASA)
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Cosmic Arithmetic
General Relativity, isotropy, and homogeneity require that
(in the relevant units)
Wgeometry + Wmatter&radiation + WL = 1
If the underlying geometry is flat (Wgeom = 0), & if Wm&r <1
then WL (“cosmological constant term”) must be non-zero.
Cosmic microwave background (CMB) measurements
demonstrate the geometry is flat, Wgeometry = 0.
Mass inventories fall short of Wmatter&radiation =1
(Wmatter ≈ 0.3, and the radiation contribution is tiny)
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 4
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Insufficient mass to halt
the expansion…
“Best Fit”
at
Wmass ~ 0.3
WL
Universe is
ACCELERATING
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WL ~ 0.7
Rate of expansion is
increasing…
WM
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 5
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The Perplexing Result
 Expansion of Universe is accelerating!
 Implies something new: “Dark Energy”
 Regions of empty space repel each other!
? “Cosmological constant”…
Einstein’s greatest blunder?
? What’s going on in the vacuum?
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CCAPP Seminar 1/12/2007
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: Tunable Laser for Precision Cosmology
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J. Albert 6
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Vacuum Energy and the Casimir Effect
 Vacuum energy is real -- we can see it:
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
Predicted in 1948
by H.B.G. Casimir
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
Since measured to
better than 5% precision

So -- since vacuum fluctuations are real, why
isn’t dark energy enormous (10120 times larger)???
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 7
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Limitations on our Knowledge of Dark Energy
 Calibration of, and
corrections to, brightness
and color measurements are
a significant source of
uncertainty in measured
cosmological parameters.
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 Unless we improve
calibration standards (for flux
as a function of color) to
< 1%, this will be a limiting
systematic uncertainty for
upcoming projects …
7.7 billion light-years away
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 8
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Understanding the Acceleration of the Universe
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Launch date ~2015
First data ~2013
First science data
this year !
… and others
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 9
SNAP Concept
Aperture
Field of
View
Resolution
Bandpass
1.8 meter
1.37 square deg
< 0.06 arcsec FWHM blur
0.35-1.7 m
SNAP Concept
All instruments/detectors on single focal plane.
 Passively cooled to 140K
 0.7 square degrees instrumented FOV
 9 fixed filters from 350nm to 1700nm
 36 CCDs. 36 HgCdTe detectors
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The Large Synoptic Survey Telescope (LSST)
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
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8.4 m aperture
Survey: 20,000 sq. degrees
9.6 sq. degree field-of-view
6 filters from 320nm to 1060nm
Site: Cerro Pachon, Chile
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: Tunable Laser for Precision Cosmology
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J. Albert 12
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The Large Synoptic Survey Telescope (LSST)
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CCAPP Seminar 1/12/2007
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: Tunable Laser for Precision Cosmology
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J. Albert 13
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Complementarity of SNAP and LSST
 The power spectrum of matter in the Universe
(analogous, e.g., to the power spectrum of the CMB)
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 Ground can survey whole sky, space can probe deeper in
selected areas.
 Space data with lower systematics and higher redshift
accuracy can calibrate ground surveys.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 14
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Pan-STARRS
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Four 1.8 m primary mirrors (start with 1)
Survey: 20000 sq. degrees
9 sq. degree field-of-view
6 filters from 320nm to 1060nm
Novel CCD technology to mimimize
atmospheric distortion (OTCCDs)
 Site: Mauna Kea (prototype on
Haleakala)
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CCAPP Seminar 1/12/2007
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: Tunable Laser for Precision Cosmology
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J. Albert 15
Systematic Uncertainties are the Key
From Kim, Linder, Miquel, & Mostek (MNRAS, 2004):

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Minimizing uncertainties on these cosmological parameters
is largely a matter of keeping systematic uncertainties at a
minimum (especially flux as a function of redshift).
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 16
The Same Applies to Weak Gravitational Lensing
From Bernstein & Jain (ApJ, 2004):

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The 3 main techniques for measuring the cosmological parameters:
using type Ia supernovae (“standard candles”: measure luminosity
and redshift), weak gravitational lensing (shapes of galaxies “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 measurement.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 17
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And Other Astronomy & Astrophysics
 Constraints on changes in fundamental constants over the lifetime of
the Universe (fine structure constant, speed of light) are obtained via
absorption spectra of the light from quasars.
From Levshakov et al. (proceedings of "Precision
Spectroscopy in Astrophysics", Portugal, Sept. 2006):
 The uncertainties are
presently dominated
by the precision of
the wavelength
calibration of the spectra.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 18
And Atmospheric Science Applications
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 The CALIPSO satellite (launched on Apr. 23 of this year) uses
an 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 provide information in a far greater
range of wavelengths.
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CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 19
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Improving Fundamental Calibration
Idea: Rockets
(ACCESS)
Not Easy
Need to get above the ATMOSPHERE
Another possibility: Balloons
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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 … ?
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 20
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Using a Tunable Laser on the Ground
 Use tunable laser to calibrate telescope optical throughput (Stubbs & Tonry):
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 21
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A Tunable Laser in Space
1) Would allow atmospheric calibration for all major groundbased 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 (e.g. SNAP).
4) Minimizes calibration transfers; precision is limited
essentially only by radiometer uncertainty (only 0.01% !!)
5) Cost could be reduced by placing on a satellite needed
anyway (e.g. GPS-III [upgrade to GPS, …).
6) Defense uses of a tunable laser in space ….
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 22
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Defense Applications …
Variable wavelength
(more difficult to detect, or to
develop contermeasures)
 Target illumination, also space communication.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 23
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Tunable laser
Opotek Vibrant LD 355 II
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 Recently purchased
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: Tunable Laser for Precision Cosmology
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J. Albert 24
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Tunable Laser Setup
Safety barrier
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 25
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Tunable Laser Setup
Radiometer
Opotek Vibrant
LD 355 II
Radiometer
Beam Sampler
Beam Sampler
CCD
Imager
Radiometer
CCD
Imager
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: Tunable Laser for Precision Cosmology
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J. Albert 26
532 nm CALIPSO satellite laser spot
in space, as observed from Earth during
satellite overpass near Granby, Quebec,
07:08:30 Nov. 23, 2006 UTC
Before
During
After
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Setup for Calibrated CALIPSO Observation
James Battat
Chris Stubbs
Yorke Brown
J.A.
2:03 am Eastern time
Dec. 17, 2006
30 m
Master
Switch
30 m
83.5 m
83.5 m
83.5 m
30 m
= calibrated photodiode (with 532 nm notch filter)
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= Panasonic FZ50 digital camera
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 28
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Toward a Space-Qualified Tunable Laser …
 The CALIPSO satellite uses an Nd:YAG
from Fibertek Inc. that clearly is
qualified.
 Such a laser could potentially be used
a pump laser for an OPO (which
then itself need to be space-
laser
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as
would
qualified).
 Eli Margalith (president, Opotek Inc.,
Carlsbad, CA) has started to work on requirements
for a space-qualified OPO. Together we’ll be
developing a space-qualified diode-pumped OPO for
laboratory tests (stability, durability, radiation
hardness) over the next years.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 29
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Diode-Pumped OPO system
300 Hz, 1.8Watt
• Click to edit Master text styles
– Second level
• Third level
– Fourth level
» Fifth level
OPOTEK Inc.
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Pumped by Brightlite by JMAR
: Tunable Laser for Precision Cosmology
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J. Albert 30
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Measuring the Flux (Radiometry)
 LASP (Laboratory for Atmospheric and Space Physics, at UC
Boulder) has produced and flown space-qualified radiometers (for
solar irradiance measurement) that achieve better than 200 ppm in
(laser) flux measurement (and better than 10 ppm/yr stability) :
 Use as a laser radiometer.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 31
Telescopes must measure flux & color of galaxies and supernovae precisely (despite the atmosphere),
so we can understand exactly how our universe is expanding. (It is actually accelerating! Why??
Nobody knows… [Acceleration in fact implies a mysterious new form of energy throughout the
universe!])
Mirror
mover
Tunable laser
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EARTH
GPS jamming
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Orbit
 20000 km MEO orbit (e.g. GPS satellites, etc.) is optimal.
 Above that, laser divergence becomes a major issue. Below
that, slew rate is too fast for ground-based telescopes to track,
and Earthshine contamination becomes significant for spacebased telescope images.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 33
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Several Relatively Convenenient Platforms
on 2012-2016 Timescale
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CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 34
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Pointing Accuracy & Telemetry
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HST gyro
 From a 20000 km orbit, 20 m on
Earth’s surface = 1 rad ≈ 0.2
arcsecond stability.
 Not technically challenging -e.g. HST obtains (obtained)
0.005 arcsecond stability, 40x
better than this requirement.
 Must track Earth’s rotation,
however Earth-observing
satellites (e.g. ALOS) typically
achieve at least 5x better
stability than this requirement.
 Data rate is low (radiometer
readout data, station keeping),
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could be used as downlink…
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 35
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Calibrated Lamp
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 As a broadband calibration crosscheck for a tunable laser, it would be
very useful to also have a simple
calibrated incandescent lamp onboard.
 A 150W “lightbulb” (radiating into 4)
would appear as a 23 magnitude “star”
when at 20000 km.
 QTH (Quartz-Tungsten-Halogen) lamps
are the NIST “gold standard” for
calibrated lamps.
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 200W QTH standard sources are widely
available. (Could be on only ~5% of
the time to avoid power consumption.)
 A low-power QTH lamp is onboard the
HST: basic space-qualification is done.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 36
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A lot to do! … for example:
1) Radiation Tests: Survivability/Degradation at 20000
km. (TRIUMF [Canada] 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) Calibrated lamp / calibrated power source radiation
hardness, …
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
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J. Albert 37
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Collaboration Started and Growing
 http://www.starcal.org
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
Qu i ck Ti m e ™ an d a
TI F F ( Un co m pr e ss ed ) d ec om p r es so r
ar e n ee de d t o s ee t h is pi ct u re .
J. Albert 38
QuickT ime ™an d a
TIFF ( Uncomp res sed) deco mpre ssor
ar e need ed to see this pictur e.
Understanding Dark Energy
 The dark energy problem is
one of the ultimate problems
in modern physics.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 What is over 2/3 of the
Universe??
 The answer might contain
a clue on how quantum
mechanics relates to gravity…
 Superb wavelength calibration is one of the
frontier experimental requirements of this goal.
CCAPP Seminar 1/12/2007
: Tunable Laser for Precision Cosmology
Qu i ck Ti m e ™ an d a
TI F F ( Un co m pr e ss ed ) d ec om p r es so r
ar e n ee de d t o s ee t h is pi ct u re .
J. Albert 39