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Heterodyne InterferometryHeterodyne InterferometryA New Start A New Start
Long Baseline Interferometry in the Mid-InfraredLong Baseline Interferometry in the Mid-InfraredSchloß Ringberg, Sept. 1-5, 2003Schloß Ringberg, Sept. 1-5, 2003
Andreas EckartAndreas Eckart I.Physikalisches Institut der Universität zu Köln I.Physikalisches Institut der Universität zu Köln
400 500 600 700 800 900 1000 1100 12000,70
0,75
0,80
0,85
0,90
0,95
1,00
1,05
Dec 1st, 2002
CO2 Emission from Venus 9.2 m-laser-band
R(36) @ 1087.94465 cm-1
Doppler-Shift 1102 MHzIntegration time 6000 sT
sys 5000 K
Resolution 20 MHz
T* [K
]
i.f. [MHz]
Outline
I. The Cologne MIR Heterodyne Spectrometer THIS
II. Future Developements in MIR Heterodyne Detection
III. Future Perspectives for Heterodyne VLTI
I. THIS
Cologne Tuneable Heterodyne Infrared Spectrometer
Daniel Wirtz / Guido Sonnabend /Volker Vetterle / Rudolf Schieder
I. Physikalisches InstitutUniversität zu Köln
The group of Kostiuk et al. GSFC/NASA is running a CO2 heterodyne spectrometer system
HeNe
PC AOS IF
DiplexerScanner-mirror
HeNe-Detector
HgCdTe-Detector+HEMT Signal Reference Hot
Telescope
Cold
Loads
QCL
Experimental Setup
The Diplexer
Ring FP Diplexertuned to LO frequency60% transmissionsignal in reflection100% reflectionprinciple of notch filteraccepts a broad range ofbeam modes!
LO locked throughdiplexer-detector line:stabile performancelong integrationup to 8 hours.
HgCdTe Detector / MCT
Array capability of system!
QCL: Quantum Cascade Laser
MIR-Heterodyne-Receiver
•Semicinductor (AlGaAs,GaAs) device based on tunneling and quantum confinement, tunable via temperature and diode current•cascade of up to 40 light emitting cells•FIR-NIR 20 - 100 mW power (Bell Labs, Alpes Laser CH etc.)
Quantum Cascade Laser
400 600 800 1000 1200 1400 16004000
5000
6000
7000
8000
9000
10000
11000
12000
13000
MCT300 mV2 mA
detector: bias:photo-current:
CO2- vs. QC-laser
QC-laser CO
2-laser
Sys
tem
Tem
pe
ratu
re [
K]
i.f. [MHz]
Performance: QCL versus CO2-Laser
Comparable noise temperatures are reached with both LOs
Tsys=NEP/k
3 x quantumlimit ( 1440 K)
1145 1150 1155 1160 1165 1170 1175
10
20
30
40
50
Fit: Gauss
Gauss = 1,3 MHz
co
un
ts
i.f. [MHz]
TDL-QCL Beat-Experiment
Narrow linewidths; useful for heterodyne operation
MIDI ~10e-2THIS 4e-8
Transportable Spektrometer Setup
MIR-Heterodyne-Receiver
•Dimensions 60x60x45 cm•Weight 80 kg
stabilizedHeNe-Laser blackbody
to the telescope
diplexer
HeNe-Laser detectorLN2-dewar
with QCLand MCTdetector
THIS: Present Technical Specifictions
MIR-Heterodyne-Receiver
•wavelength range: 3-30 microns (requires change of LO, diplexer or detector) •spectroscopic resolution: up to 1 MHz
•bandwidth 1.4 GHz
• atmospheric measurements
• molecules in sunspots
• CO2-laser emission from Venus
Science Applications:
400 600 800 1000 1200 14000,035
0,040
0,045
0,050
0,055
0,060
integration time:1600s
systemtemperature: 7000K
resolution: 1 MHz
6 K
8 K
stratospheric
ozone-absorption seen against
the moon at 1088,8cm-1
T* [
K]
re
l. In
t.
intermediate frequency [MHz]
Ozone against the Moon
400 600 800 1000 1200 1400 16000,77
0,78
0,79
0,80
0,81
0,82
0,83
0,84
Combined Gauss fit Gauss fit Peak 1 Gauss fit Peak 2 Data binned to 5 MHz resolution
2
1
28SiO [5-4 P56] @ 1088.64 cm-1
second feature not assigned
Peak Molecule Center Width------------------------------------------------1 SiO 819,16 332,572 n.a. 1190,7 240,48------------------------------------------------
rel.
Inte
nsi
ty
i.f.[MHz]
SiO in a Sunspot
400 500 600 700 800 900 1000 1100 12000,70
0,75
0,80
0,85
0,90
0,95
1,00
1,05
Dec 1st, 2002
CO2 Emission from Venus 9.2 m-laser-band
R(36) @ 1087.94465 cm-1
Doppler-Shift 1102 MHzIntegration time 6000 sT
sys 5000 K
Resolution 20 MHz
T* [
K]
i.f. [MHz]
None-LTE CO2 Emission from Venus
• Ozone and CO2 observations on Mars/Venus
• Titan‘s atmosphere resolvable with large telescopes
• Other molecules in planetary atmospheres / bright IR-sources (IRC+10216, CRL 618)
• Bandwidth enhancement- next generation AOS (3-4 GHz)- QWIP (and HEB) detectors ?
• 17µm development H2 S0(1) line
• Second generation instrument for SOFIA (2007)
II. The Future
Large Bandwidths
with QWIPs
Liu et al. 1995Appl.Phys.Lett. 67, 1594
QWIP: Quantum Well Photodiode
600 700 800 900 1000 1100 1200 1300 14000
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
QWIP (100 periods) with an area of 120µm2 U
Bias=8V
PCO
2-Laser
=6mW
IPhoto
=1,2 mA
Sys
tem
Te
mp
era
ture
[K
]
i.f. [MHz]
QWIP plus CO2-LASER
QWIP: Quantum Well Photodiode
III. Prospects for Heterodyne VLTI
1) Receivers at the telescopes
2) Receivers in the VLTI Lab
3) Phase referencing operation
Possible Heterodyne Observing Modes using the the VLTI
1) VLTI Heterodyne Operation at the UTs or ATs
Use one receiver per telescope at each of thetelescope foci.
Full delay compensation could be performed in the radio domain.
In a test phase two of the ATs could be equippedwith MIR heterodyne receivers for single dishmeasurements and for interferometric measurements.
Problem: LO reference has to be provided across the array to phase lock the receivers (LASER-line)
2) Heterodyne Operation in the VLTI Laboratory
Use one receiver per telescope at each of theinput ports in the beam combination laboratory.
The system makes use of the VLT delay lines and can correct for differential delays at radiofrequencies in the ‘usual way‘.
Advantages: 1) LO can be distributed locally (low power LO distribution?!)[2) Could use available delay compensation system]
VLTI Auxiliary Telescopes
The first 2 of 4 Atswill be ready for the VLTI in the first half of 2004.
AMOS, Liege
VLTI Delay Line
The telescopes are relocatable on 30 stationsof the arry providing baselines between8m and 200m
VLTI with Unite and Auxiliary Telescopes
Possible Locations of a VLTI Heterodyne Backend
3) Phase Referencing
The broad continuum capabilities of the VLTIcould be used to phase the interferometer and at the same time to integrate on a faint sources in the vicinity of a bright continuum source.
Advantages: 1) LO can be distributed locally (low power LO distribution?!) 2) System makes use of available delay compensation system 3) highest sensitivity plus large sky coverage
Finito: On axis NIR fringe tracker ESO/OA di Torino First Lab-fringes in Garching 2003 First Paranal fringes planned end of 2003
PRIMA: separation to reference star - 1 arcmin field of view - 2 arcsec reference star brightness 12-13 UTs/ 9-10 ATs
Phase Referencing
Sky Coverage
Summary
I. The Cologne MIR Heterodyne Spectrometer THIS
Tunable system operational
II. Future Developements in MIR Heterodyne Detection
Sensitive broad band operation over several GHz bandwidth
III. Future Perspectives for Heterodyne VLTI
Promissing operation modes could be installed
END