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

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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

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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)

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Fit: Gauss

Gauss = 1,3 MHz

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un

ts

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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:

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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

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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

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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