ACOUSTO-OPTIC SPECTROSCOPY IN PLANETARY MISSIONS O. Korablev, Yu. Kalinnikov, A. Kiselev, D. Belyaev, A. Stepanov, I.I. Vinogradov, A. Fedorova, A.V. Grigoriev
Space Research Institute (IKI) VNIIFTRI (Inst. of Phys.-Chem. and Radiophys. Measurements) Physical Faculty of Moscow University
J.L. Bertaux, E. Dimarellis, J.P. Dubois, E. Villard, D. Nevejans, E. Neefs, J.P. Bibring, M. Berthe
Service d’Aeronomie du CNRS Belgian Institute for Space Aeronomy 1 Institut d’Astrophysique Spatiale AOTF = Acousto-Optic Tunable Filter
A birefringent crystal: for example TeO2 (0.4-5.2 µm) Effectiveness 60-70% Maximal possible resolving power 1500-2000 (best resolution in wavenumbers ~3.5 cm-1) Aperture < 1 cm2, < 5-6º Spectral range х2 and more* RF ~ 10-200 MHz RF power : 0.3 W-3W Time to tune ~30 µs.
2 Why AOTF in planetary missions?
very light, compact, and robust device with no moving parts
easily controlled by changing RF
fast and random tune
RF=OFF Æ no diffracted light Î easy modulation of signal to reject stray light
possibility to filter images
3 MARS EXPRESS PAYLOAD
ASPERA
SPICAM
PFS MARSIS
OMEGA HRSC
4 Mars Express: SPICAM
SPICAM – versatile atmospheric spectrometer PI Jean Loup Bertaux, SA Verrieres le Buisson Near-IR AOTF Electronic Cooperation: France, Belgium (mechanics), channel block Russia (IR channel), USA
UV channel
Main characteristics of SPICAM
UV Near-IR Sun UV channel 40x40 Spectral range, nm 118-320 1000-1700 Nadir Spectral resolution, 0.9 0.5-1.2 nm M Pa ra bo lo c mirro r Slit Angular resolution,
Grating mrad 0.2x1 17.5 CCD nadir 0.2 1.5 Image optcal fiber intensifier occultations
IR channel FOV di aph ragm Mass 4.9 kg li ght tra p Nadir
IR detector Ø30 Data volume 30 Mbit/orbit Telescope AOTF M 5 SPICAM Light / MEX
UV: 110-310 nm spherical IR: 1-1.7 µm grating AOTF imaging spectrometer +Z (nadir) spectrometer Two pixels with slit mechanism
6 7 IR channel of SPICAM : First Acousto Optic Tuneable Filter (AOTF) flown in civil space Mass inferior to 1 kg (700 g, DC/DC and Solar entry not included) Spectral resolution specified as 3.5 cm-1 (λ/∆λ~1800)
Capable of measuring H2O in Mars atmosphere similar to MAWD
8 9 Wavelengths calibration and resolving power
λ=a(1+αT)/f +b(1+βT) 1 accuracy ~0.1 nm α, β~10-5 K-1 1529.5 nm 1128.7 nm
1130 nm Æ λ/∆λ=2200 0.5 1500 nm Æ λ/∆λ=1750 Resolving power at least
1800 in the H2O region at
1.38 µm 0 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Sinc2δλ Æ tails 10 Noise Equivalent Brightness and S/N
Detector 1 -1 sr -1 m µ -2
S/N NEB, W m ~50 ~70 ~120 ~100
Wavelength, nm 11 MARS with SPICAM in Nadir
1.4 SPICAM relative albedo model with Earth O3/200 1.2 model with Earth O3
1.0
0.8 UV 0.6 MEX/ Relative albedo 0.4 SPICAM SPICAM – Ultra-Violet IR 0.2 observations, orbit 8, 9 jan. 2004 0.0 200 220 240 260 280 300 320 w avelength (nm)
Absorption by gas CO2 Water vapour band τv vertical optical θ1 thickness of absorption, varies strongly with wavelength SPICAM – near Infra-red observations, orbit 8, 9 jan. 2004 Scattering by surface with albedo A
12 Modes of operation
IR channel = 2 detectors (≠ polarization) Spectra acquisition in 1, 2 or 3 “windows” + dots set (starting frequency, points, step) max points = 3984, max acquisition time = 24s) normally points = 664-1328, acquisition time = 2-4s
three windows
+ dots set dots 3 2 1 single window: “full spectrum”
13 Calibrated SPICAM IR data 25 Channel 0 Channel 1
20
15
10 Orbit 30 H O Radiance, W/m2/ster/micron 2 Ls 335.7 CO2 Lon 61 Lat −46 LT 13:35 SZA 41
CO2 5
1000 1100 1200 1300 1400 1500 1600 1700 14 wavelength, nm 1 The oxygen O2a ∆g emission line O a1∆ at 1.27 µm is produced by UV 2 g dissociation of ozone
15 1 The oxygen O2a ∆g emission line O a1∆ at 1.27 µm is produced by UV 2 g dissociation of ozone 20 spectra averaged
solar line
16 Seasonal map of O2 emission by SPICAM
17 Seasonal map of Ozone by SPICAM
18 H2O seasonal distribution on MARS SPICAM vs TES
SPICAM MY27
TES MY26
Scale 0 to 50 pr. µm 19 H2O seasonal distribution on MARS SPICAM vs TES
SPICAM MY27
TES MY26
Scale 0 to 50 pr. µm 20 THE SPICAV-SOIR INSTRUMENT
21 VEX PAYLOAD
VEX Payload : 7 instruments MAG : magnetometer VIRTIS : imaging spectrometer PFS : Fourier spectrometer VMC : monitoring camera VERA : radio science ASPERA : space plasma SPICAV : UV/IR spectrometer 22 SPICAV/SOIR
SPICAV-UV Spare of SPICAM-UV Made in France SPICAV-IR (AOTF) Modified from SPICAM-IR Made in Russia SOIR (with AOTF) Completely new instrument built in two years High spectral resolution: echelle grating+AOTF Built in Belgium with Russian AOTF DPU: electronic block
23 SOIR AOTF
SPICAV-IR AOTF
24 SOIR : SPECTROMETER SCHEME (1)
Spectrometer part Front end optics (5) spectrometer slit (1) AOTF entrance optic Æ entrance aperture of spectro Æreduces Ø incoming light beam (6) collimating lens Æto match acceptance aperture of AOTF Æ collimates to parallel beam (2) diaphragm (7) echelle grating Æ confines FOV Æ disperses light Æ to avoid parasitic light effects (3) AOTF Detector part Æorder sorting filter (8) camera lens (4) AOTF exit optics Æ images spectrum to detector Æ images beam on spectrometer slit (9) detector 25 Echelle-spectrometer The principle of separation of diffraction orders
λ divide wavelength domain λ n+1 in small parts
observe sequentially or at λn random echelle : higher resolution λ6 and dispersion order n+2 echelle : orders overlap λ5 Æ order sorting λ4
AOTF bandpass order n+1
λ3 λ2 ∆λ order n
λ1 λ0 Diffraction Detector pixels angle
26 SOIR : OPTICAL DESIGN (3)
0.010 choice of design parameters 0.005 Æ guarantees quasi-continuous 1800.000 176 172 168 coverage in mid IR Æallows a wavelength to be -0.005 -0.010 associated to every pixel Diffraction angle+1.09960 rad 2.50 2.55 2.60 2.65 2.70 Wavelength, um Figure red lines represent grating diffraction 0.010 angles (orders 101 till 194) 0.005 0.000124 120 numbers are diffraction order number -0.005
-0.010 Diffraction angle+1.09960 rad black traces are overlapping parts 3.60 3.65 3.70 3.75 Wavelength, um
blue intervals correspond to AOTF 0.010 -1 bandpass (20 cm ) resulting in 0.005 (nearly perfect) order sorting 0.000112 108 104
-0.005 full vertical scale gives the angular -0.010 width of a 320 pixel detector Diffraction angle+1.09960 rad 4.00 4.05 4.10 4.15 4.20 4.25 4.30 Wavelength, um 27 SOIR Solar Occultation InfraRed
430,0 295,6 99, 9
3 ° e 6 G as bl /mm 4g ng 37,3 ati Gr
63,1° mirror 70, 0 60,2°
350 E lliptical 12,00 f= Detector 256 pix 42x800um 220,00 S2 M5 M3 50x800 um R 350 f=26 Ligh t trap
f= 2 6 D et. Electronics M4 LR 5 0 x 5 0 u m M2 S1
Pa 60x1000 um rabolic mirror rabolic f=175 To the Sun M1 25x25
Figure 3. Layout of the high-resolut ion solar occult at ion spect romet er. M1 (off-axis parab. f=175) – ent rance telescope; S1 – field diaphragm; AOTF; M2, M3, M4 (f=26) – AOTF collimat or; light trap; LR det ect or; S2 – HR spect romet er slit ; M5 (off-ax. parab., f=350) – HR spect romet er collimat or; G – HR spectrometer grating; HR detector. 28 SOIR : SPECTROMETER SCHEME (2)
compacting exercise
(3) AOTF (7) echelle grating
(9) folded detector (8) folding mirror optics (10) detector assembly placed upright (6) collimating and camera lens merged into one off-axis parabolic mirror 29 SPICAV ON VEX
SOIR : 2.2 - 4.3 µm R=25000
UV : 110 - 310 nm
IR : 0.7 - 1.7 µm
shutter
30 SOIR/VEX summary
Features
resolving power R=25000 in spectral range 2.35- 4.2 µm relatively compact design (~5 kg)
no moving parts (except cryocooler)
Spectral range with “methane on Mars” potential Limitations
Solar occultation operations
Only a small portion of spectrum at a time
31 SOIR : AOTF
Working principle • interaction light beam and acoustic wave Æ small wavelength domain transmitted • acoustic RF wave injected via transducer (001-direction) • transmitted wavelength = electronically tunable • non-polarized light beam in Æ 2 diffracted beams out with different polarization Æ small angle between diffracted and undiffracted • inclined output facet Æ correction for angular shift caused by Bragg diffraction and polarization rotation Æ refolding of diffracted beam collinear with incoming beam32 SOIR : AOTF
IN OUT
RF IN
33 SOIR: in-flight calibration of AOTF bandwidth (orbit 142) AOTF functions at different wavenumbers and different points of acoustic field
View from the top
34 HDO detection by SOIR solar occultation
35 VENUS H2O and HDO at 3 orbits, 75° N at terminator (solar occultation)
Bulk atmosphere 36 SPICAV AOTF
Serious modification from MARS EXPRESS version Extended spectral range (0.7-1.7 µm)
2 actuators on the AOTF
New detectors (Si-InGaAs sandwich detectors)
Increased sensitivity
New registration electronics
37 SPICAV AOTF: QM
38 AOTFs operating in flight
Parameter SPICAM-IR SPICAV-IR SOIR (direct (direct (selection of filtration) filtration) orders) Spectral 1-1.65µm 0.7-1.05µm 2.2-4.4 µm range 1.05-1.65µm
Spectral 0.5-1.2 nm 0.4-1.6 nm ~20 nm resolution 3.5 cm-1 5-8 cm-1 22 cm-1
RF power ~3 W ~3 W <1W
39 AOTF in preparation
MICROMEGA for EXOMARS 2013 operational temperature range –150°С …+40°С storage temperature range –200°С … +40°С Spectral range 0.8-4 µm (new version 0.8-2.6 µm) Spectral resolution 10-15 nm SOIR-Terre A high-resolution spectrometer for the Earth atmosphere: monitoring of green-house gases (CO2, CH4 with O2 reference) Spectral range 0.7-1.7 µm Spectral resolution ~35 nm
40 MICROMEGA AOTF illumination system
ÇIVA-M/I optical concept (J-P.Bibring et al.)
output
Light source F=20,00 diaphragm 2. 5 mm Blac k c oating Working Plane (light trap) 0.5-3mm from lamp acceptance Total internal reflected angle ~ 10° “0” order beam
Acoustic wave F=20,00 absorber 41