Heterodyne Interferometry A New Start Long Baseline Interferometry in the Mid-Infrared Schloß Ringberg, Sept. 1-5, 2003 Andreas Eckart I.Physikalisches Institut der Universität zu Köln

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 Institut Universität zu Köln The group of Kostiuk et al. GSFC/NASA is running a CO 2 heterodyne spectrometer system

HeNe PCAOS IF Diplexer Scanner- mirror HeNe-Detector HgCdTe- Detector +HEMT SignalReferenceHot Telescope Cold Loads QCL Experimental Setup

The Diplexer Ring FP Diplexer tuned to LO frequency 60% transmission signal in reflection 100% reflection principle of notch filter accepts a broad range of beam modes! LO locked through diplexer-detector line: stabile performance long integration up 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 mW power (Bell Labs, Alpes Laser CH etc.)

Quantum Cascade Laser

Performance: QCL versus CO 2 -Laser Comparable noise temperatures are reached with both LOs Tsys=NEP/k 3 x quantum limit ( 1440 K)

TDL-QCL Beat-Experiment Narrow linewidths; useful for heterodyne operation MIDI ~10e-2 THIS 4e-8

Transportable Spektrometer Setup MIR-Heterodyne-Receiver Dimensions 60x60x45 cm Weight 80 kg stabilized HeNe-Laser blackbody to the telescope diplexer HeNe-Laser detector LN 2 -dewar with QCL and MCT detector

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 CO 2 -laser emission from Venus Science Applications:

Ozone against the Moon

SiO in a Sunspot

None-LTE CO 2 Emission from Venus

Ozone and CO 2 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  H 2 S 0 (1) line Second generation instrument for SOFIA (2007) II. The Future

Large Bandwidths with QWIPs Liu et al Appl.Phys.Lett. 67, 1594 QWIP: Quantum Well Photodiode

QWIP plus CO 2 -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 the telescope foci. Full delay compensation could be performed in the radio domain. In a test phase two of the ATs could be equipped with MIR heterodyne receivers for single dish measurements 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 the input ports in the beam combination laboratory. The system makes use of the VLT delay lines and can correct for differential delays at radio frequencies 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 Ats will be ready for the VLTI in the first half of AMOS, Liege

VLTI Delay Line

The telescopes are relocatable on 30 stations of the arry providing baselines between 8m and 200m VLTI with Unite and Auxiliary Telescopes

Possible Locations of a VLTI Heterodyne Backend

3) Phase Referencing The broad continuum capabilities of the VLTI could 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 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