The Technology of High Resolution Terahertz Spectroscopy International Symposium on Molecular Spectroscopy June 19 – 23, 2006 I. Physikalisches Institut Universität zu Köln Frank Lewen

The Terahertz Gap a) Orotron 80 – 325 GHz and fundamental Backward Wave Oscillator (BWO) 53 – 1200 GHz b) Laser Sideband Spectrometer 1750 – 2005 GHz c) MoMeD Frequency Tripler 2300 – 2400 GHz d) Superlattice Multiplier Spectrometer >2700 GHz

Frequency [THz] Herschel (HIFI) Apex Apex 2A GHz Laboca345 GHz; 295 Pixel Flash GHz Condor GHz Herschel HIFI GHz GHz Resolution ~ 10 7 APEX (Condor), ALMA SOFIA (CASIMIR, GREAT) Cologne THz-Spektrometer ? Motivation

New High Resolution Instrumentation for Astrophysics APEX (Atacama Pathfinder EXperiment) in the Chilean Andes with CONDOR, the CO N+ Deuterium Observation Receiver developed in Cologne Star formation in the Orion Nebula. First Apex/CONDOR detection of highly excited carbon monoxide (CO J = 13 → 12) at 1.5 THz

Cologne Terahertz High Resolution Spectrometers SpectrometerFrequency RangeAccuracy [GHz] [  m] [kHz]  Backward Wave Oscillators (BWO) – BWO + Multiplier (Schottky or SL) FIR Side Band + BWO Intracavity (Orotron) *10 -7 IR-Tunable Diode Lasers THz

Orotron Spectrometer (D ouble R esonance Setup)

Agilent/HP 83650A synthesizer 0.01 to 50GHz, 1mW at 40GHz min. resolution/stepsize 10Hz remote controled Spacek amplifier 18-43GHz 100mW output power level, connected to a new broadband electroformed horn antenna Pump Beam Setup

Double Resonance Spectrum Linewidth 210kHz

Condition for D ouble R esonance Experiments: Common Energy Level

L.A. Surin et al., PhysRevLett Orotron: Two Photon Absorption

BWO stabilized with PLL Beamsplitter BWO Absorption Cell Rubidium Reference MM-Wave Synthesizer df/f GHz magn. Coils Cologne Terahertz Spectrometer Harmonic Mixer Diff. Pump Rotary Pump Elliptical Mirror PLL PC Digital Lock In IF Amp FM IEEE Interface InSb Detector QFI/4 (2BI) DATA Voltage Controlled Oscillator Power BWO Power Supply R

Operation of BWO

BWO Characteristics BWO Beam

Harmonic Mixer with Planar Diode Colaboration with D. Paveljev, State Univ. of N. Novgorod

High Resolution Spectroscopy: Present Status of selected Systems High Resolution Spectrometers with Phase Lock Loop Electronics Zürich ETH 380 GHz High Resolution Submm-wave source, for high Rydberg states measurements (F. Merkt) New Prague mm- and submm-wave spectrometer based on a µW synthesizer with efficent multiplier stages (S. Urban) Cologne THz BWO Spectrometer (G. Winnewisser) The new Cologne Supersonic Jet Spectrometer for Terahertz Applications, SuJeSTA (T. Giesen) AIST BWO Spectrometer Tsukuba/Tokio (K.M.T. Yamada) University of Waterloo BWO Spectrometer (T. Amano) RAD Spectrometer, N. Novgorod (A. Krupnov) Free running devices Ohio FASSST Spectrometer (F.C. DeLucia) Cologne Orotron Spectrometer (S. Schlemmer)

COSSTA Cologne Sideband Spectrometer for Terahertz Applications frequency range GHz frequency stability BWO (phase stabilized) <1 Hz frequency stability FIR - laser (frequency stab.) 5 kHz absolute frequency determination  10 8  kHz output power < 1.5 µW Sensitivity  cm -1 0,2 - 0,41,61,2 - 1,41,8 – 2,0 BWO FIR upper sideband lower sideband (filtered) BWO + FIR- gas laser  Sideband Radiation Schottky-Diode

COSSTA Permanent Magnet Polarizing Filter IF Harmonic Mixer GHz BWO phase stabilization Evacuated Optics with Mixer Stabilized FIR - Laser THz-Sideband- Mixer BWO - Radiation Grating Upper Sideband THz Parabolic mirror Absorption Cell InSb- Detector Laserbeam Elliptical Mirror Si-beamsplitter Harmonic Mixer 1.626THz ZF Gunn AFC FIR-Ringlaser CO 2 - Pumplaser Filter BWO PLL

CCC Lowest Bending Transitions measured with COSSTA Gendriesch et al. (2003)

ortho-CH 2 at 1955 GHz

MoMeD Tripler 2300 – 2700 GHz Monolithic Membrane Diode, MoMeD SEM Image courtesy F. Maiwald / P. Siegel JPL

MoMed Mux Spectrometer Power BWO 765 – 900 GHz 3- 12mW

MoMed Tripler

MoMed Mux Spectrum

S uper L attice Structure

S uper L attice : Symmetric I/V Curve

HiRes THz Spectrometer: Superlattice Multiplier THz-SL Multiplier SL Input 80 – 118GHz 5-8mW SL Output 234 – >1060GHz

Microwave Synthesizer Generator Unit AMC + SL Spectrometer 80 – 118 GHz mW BWO Sweeper

Multiplication x 3 rd, x 5 th, x 7 th, x 9 th First Record > 1THz! CH 3 OH

S uper L attice Broadband Scan

HiRes THz Spectrometer: Superlattice Multiplier C. Endres et al. in prep.

HiRes THz Spectrometer: Superlattice Multiplier C. Endres et al. in prep.

HiRes THz Spectrometer: Superlattice Multiplier C. Endres et al. in prep.

HiRes THz Spectrometer: Superlattice Multiplier C. Endres et al. in prep.

Conclusions The Gap is closed! Orotron-Spectrometer, sensitivity higher than FTMW, first 2 photon absorption / double resonance spectra ( GHz) BWO in fundamental mode, Sub-Doppler capability (53 to 1.2 THz) Schottky Frequency Tripler for HiRes Spectroscopy up to 2.4 THz Introduction of Superlattice devices for broadband HiRes Terahertz Spectroscopy ( THz)

Acknowledgement Sandra Brünken, Christian Endres, Holger Spahn, Leonid Surin, Dimitri Fourzikov, Holger S.P. Müller, Frank Maiwald (JPL), Hideta Habara, Hiroyuki Ozeki, Martin Philip, Bernd Vowinkel and G. Winnewisser Thomas Giesen and Michael Caris (Chain Molecules) D.G. Paveliev, K. Renk (Superlattice) Gen. Dir. A.N. Korolev and A.A. Negirev (both ISTOK, BWOs) Deutsche Forschungsgemeinschaft Grant SFB 494 Grant GI 319/1-1 within the Laboratoire Européen Associé ( LEA) HiRes. Humboldt Foundation and State of NRW Russian Science Foundation for Basic Research Acknowledgement

BWO 1.9 THz633 GHz - dB DC Bias T GUNN frequency power DC Bias X 3 PLL 2 Ref 2 PLL 1 Ref 1 BWO  Prot. GUNN HM X Synth. HV f fc c 336 MHz 24 MHz 6-7GHz 80-90GHz 8-10 V ±10 V BS Phase Lock Loop 1.9THz LO

Breadboard Construction SOFIA LO GREAT Heterodyne Receicer TP D1 Heat Sink Bias GUNN QO Harmonic Mixer Pump Chopper optics PLL protect BWOBWO Locked !

L.A. Surin et al., PhysRevLett Orotron

SL Spectrometer

DCN Subdoppler

The Methylene Radical CH 2 Ozeki & Saito Lovas, Suenram Evenson Cologne 1955 GHz 943 GHz