Characterization of SIM on SIRCUS

Transcription

Characterization of
SIM on SIRCUS
Joseph P. Rice
NIST
Gaithersburg, MD
Solar Spectral Irradiance Intercomparison Workshop
19 September 2006
Characterization Team
• LASP
– Jerry Harder, Erik Richard, and Nate Miller
• NIST
– Keith Lykke, Steve Brown, Robert Bousquet,
and Joe O’Connell
19 September 2006
Outline
• Description of the SIRCUS Facility
• SIM Instrument Characterization
• SIM ESR Responsivity
19 September 2006
SIRCUS Facility
Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources
Tunable Laser
Reference
Radiometer
Intensity
Stabilizer
Chopper
or
Shutter
Radiometer
under Test
Linear Encoder
Spectrum
Analyser
Wavemeter
Exit
Port
Computer
Integrating
Sphere
Optical
fiber
Speckleremoval
System
Monitor Detector
(output to stabilizer)
19 September 2006
SIRCUS Lasers & Powers
-5
10
10000
Ti:Sapphire
-6
10
Dye
PPLN
idler
100
2
Tripled
Ti:Sapphire
-7
10
KTP
OPO
CTA
OPO
Doubled
Ti:Sapphire
-8
10
10
irradiance at 1 m from sphere(W/cm )
output power (mW)
1000
PPLN
signal
Doubled
Dye
Quadrupled
Ti:Sapphire
-9
10
1
200
400
600
800 1000
3000
5000
Wavelength (nm)
19 September 2006
SIM Optical Properties Overview
IR
Vis2
Vis1
ESR
‘
Fery
Prism
35 mm
Sun
UV
400 mm
o
R=435.3 mm
Concave
To ESR
5
Value
0.25-34
800-30
f/16
f/115
25 × 18
400
7 × 0.3
70
5
0.3-2.2
.3
Optical Characteristics
Resolution (nm)
Resolving Power
Spectrometer f/#
Solar f/#
Prism Aperture (mm)
Effective Focal Length (mm)
Slit Sizes (mm)
Scan Range in Focal Plane (mm)
Optical Aberrations at Exit Slit (μm)
Diffraction Correction (%)
34
Focal Plane
From
Entrance
Slit
Suprasil 300
R=445.4 mm
Aluminized
Convex
19 September 2006
Two possible methods for
instrument function characterization
1. Fix prism, scan laser
=>Direct Method
2. Fix laser, scan prism
=>Indirect Method
19 September 2006
Wavelengths used for instrument function scans
(vertical scale for red curve only (solar spectrum)
19 September 2006
Indirect Method
λo = 458 nm
λo = 1600 nm
19 September 2006
Direct vs. Indirect Method
(first cut)
Fix prism @ CCD Pixel(λ =646)
Scan laser
Fix laser @ λ =646 nm
Scan prism angle
19 September 2006
Summary of SIM Characterization
• Good set of measurements to compare with
theoretical predictions
– from 458 nm to 1650 nm
• Like to
–
–
–
–
–
Repeat IR measurements
Extend spectral coverage to UV and IR
Make spectral scans at other wavelengths
Make good baseline scattering measurements
Consider polarization?
200
700
1200
1700
2200
Wavelength [nm]
19 September 2006
The ESR Problem:
SIM disagrees with SOLSPEC
19 September 2006
SIM ESR Responsivity: Setup
Keep track of laser spot size
and incident direction
Need to measure
Incident Power
Window Transmittance
to get
Power on the ESR
19 September 2006
SIM ESR Setup Pictures
19 September 2006
SIM ESR Results: Vertical Mapping
ESR Normalized Signal
Bolometer ~ 1.5 mm x 12 mm => laser alignment critical
Micrometer Position [mm]
19 September 2006
SIM ESR Setup
Beam Profiler Results
850 nm
19 September 2006
Beam Profiler
Y linewidth, 1 % measured values
850.0
800.0
Beam Width [um]
750.0
700.0
650.0
600.0
550.0
500.0
450.0
400
600
800
1000
1200
1400
1600
1800
Wavelength [nm]
19 September 2006
Incident Power
• Measured with integrating sphere receiver
with Si and InGaAs photodiodes
• Calibrated directly against a cryogenic
radiometer
19 September 2006
Window Transmittance Measurements
• Measured in place, without moving chamber
19 September 2006
Preliminary ESR Efficiency Results
Beam was recentered prior to
measurements
(center shifted
~200 um)
Beam was not recentered after Ti:S
measurements
•
•
•
Centering laser beam on bolometer critical (mapping); must be done with every
laser change
Brewster window improvements needed, transmittance should be measured
prior to comparison w/ detector to save time with instrument
Greater point density, extended coverage on both sides would be useful
19 September 2006
Summary and Future Work
• Good characterization of the SIM slit scatter function
• Promising measurements of the ESR responsivity
• Worthwhile repeating the measurements
– SIM:
• Extend slit scatter function measurements into the UV & IR
• Look more closely at baseline scatter level
– ESR:
• Extend the spectral coverage to UV & IR
• Establish the uncertainty in the measurements
• Timing for those measurements:
– TBD, but currently planned for December-January
19 September 2006
Backup Slides
19 September 2006
SIM Measurement Equation
Ideally,
Eλ ( λ s ) =
PD (λs )
A Δλ
(Wm −2 nm −1 )
19 September 2006
SIM “Brassboard” Layout
Linear CCD Encoder
Entrance Slit
Exit Slits
Prism Assembly
19 September 2006
SIM Fery prism assembly
19 September 2006
SIM focal plane assembly
19 September 2006
Entrance slit (view from back of focal plane)
19 September 2006
Direct determination of relative responsivity function
(Fix prism at λo and scan laser wavelength)
The spectral response of SIM set at λo to a laser source scanned over all
wavelengths λ’ where there is a nonzero response (Δλ range) is
S(Δλ , λo ) =
∫λ Eλ (λ ) ⋅ R
E
( λo , λ ) ⋅ d λ
Δ
Or,
S(Δλ , λo ) = κ ⋅ ∫ Eλ (λ ) ⋅ r(λo , λ ) ⋅ d λ
Δλ
where r(λo,λ) is the relative responsivity function and
κ is a constant with respect to wavelength
If the laser line is sufficiently narrow, r(λo,λ) can be assumed constant over Δλline , then
'
S(Δλline
, λo ) = κ ⋅ r(λo , λ ' ) ⋅
∫
Eλ ( λ ) ⋅ d λ
'
Δλline
The output signal is proportional to the relative responsivity function for the wavelength
setting of the prism, λo, and evaluated at the wavelength of the laser, λ’
By varying the laser wavelength, λ’, continuously over the range Δλ (with the laser irradiance
constant), results in a determination of the relative responsivity function for prism wavelength
setting λo.
19 September 2006
Indirect determination of relative responsivity function
(Fix a narrow laser at λo and scan the prism)
Again,
S(Δλ , λo ) = κ ⋅ ∫ Eλ (λ ) ⋅ r(λo , λ ) ⋅ d λ
Δλ
However, since the laser wavelength is fixed, the detector responsivity is
constant and must be explicitly accounted for in the determination of r(λo,λ)
over all wavelengths
r(λo , λ ) = z(λo − λ ) ⋅ r f (λ )
Slit-scattering function
Responsivity factor
If laser is fixed at λo and narrow
S(Δλ , λo ) = κ ⋅ Eλ (λo ) ⋅ r f (λo ) ∫ z(λo − λ ) ⋅ d λ
Δλ
The major limitation of the indirect method is the validity of the λo-λ dependence in z(λo-λ)
It has been assumed that the dispersion of the instrument is constant over the wavelength interval Δλ (as well as the optical aberrations,
scattering and diffraction are the same)
While generally okay for a high spectral resolution grating spectrometer, not the case for a low-res. prism spectrometer
One would hope that the slit-scattering function z(λo-λ) would be stationary and symmetric, namely depend
only on | λo-λ | However, the variable instrument dispersion introduces an additional dependence on the
width of the instrument function. Additionally, in the wings, λo-λ dependence is no longer symmetric and
shows a significant dependence on λ
19 September 2006
Two laser peaks observed in IR
Quick note on why two peaks…
λs = 1459 nm
Two wavelengths appear here because
of the optical parametric process used
to generate the longer wavelength colors
λi = 1570 nm
Ti:sapphire pump laser ( λp = 756 nm)
is parametrically “down-converted” into
a signal and idler wavelength the OPO crystal
ωi
ωp
ωs
in
out
19 September 2006

Characterization of SIM on SIRCUS

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