The Technology of High Resolution Terahertz Spectroscopy Frank

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

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) Mo. Me. D Frequency Tripler 2300 – 2400 GHz d) Superlattice Multiplier Spectrometer 200 - >2700 GHz

Motivation Apex 2 A Laboca Flash Condor 500 - 2100 GHz 345 GHz; 295 Pixel 780 - 890 GHz 300 -1500 GHz Herschel HIFI 480 - 1250 GHz 1410 - 1910 GHz Resolution ~ 107 Cologne THz-Spektrometer SOFIA (CASIMIR, GREAT) Herschel (HIFI) APEX (Condor), ALMA ? 0 0. 5 1 1. 5 2 2. 5 3 Frequency [THz]

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 Spectrometer Frequency Range Accuracy [GHz] [mm] [k. Hz] Dn/n Backward Wave Oscillators (BWO) 53 -1270 240 – 5700 0. 5 -10 10 -8 -10 -9 BWO + Multiplier (Schottky or SL) 240 -2700 190 -500 10 -15 10 -8 FIR Side Band + BWO 1750 -2005 150 -170 10 -30 10 -8 80 -325 900 -4000 30 3*10 -7 15 -100 THz 3 -20 1000 10 -7 Intracavity (Orotron) IR-Tunable Diode Lasers

Orotron Spectrometer (Double Resonance Setup)

Pump Beam Setup Spacek amplifier 18 -43 GHz 100 m. W output power level, connected to a new broadband electroformed horn antenna Agilent/HP 83650 A synthesizer 0. 01 to 50 GHz, 1 m. W at 40 GHz min. resolution/stepsize 10 Hz remote controled

Double Resonance Spectrum Linewidth 210 k. Hz

Condition for Double Resonance Experiments: Common Energy Level

Orotron: Two Photon Absorption L. A. Surin et al. , Phys. Rev. Lett. 86. 2002

BWO stabilized with PLL Cologne Terahertz Spectrometer Digital Lock In DATA IEEE Interface PC Voltage Controlled Oscillator FM MM-Wave Synthesizer Harmonic Mixer 78 - 118 GHz In. Sb Detector QFI/4 (2 BI) Rubidium Reference df/f 10 -11 Absorption Cell IF Amp Elliptical Mirror PLL Beamsplitter Diff. Pump Rotary Pump magn. Coils Power Supply BWO Power Supply R

Operation of BWO

BWO Characteristics BWO Beam Pattern @600 GHz

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, Su. Je. STA (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. De. Lucia) • Cologne Orotron Spectrometer (S. Schlemmer)

COSSTA Cologne Sideband Spectrometer for Terahertz Applications • BWO + FIR- gas laser Sideband Radiation Schottky-Diode BWO FIR lower sideband (filtered) 0, 2 - 0, 4 upper sideband 1, 2 - 1, 4 1, 6 • frequency range 1, 8 – 2, 0 1750 - 2100 GHz • frequency stability BWO (phase stabilized) <1 Hz • frequency stability FIR - laser (frequency stab. ) 5 k. Hz • absolute frequency determination 108 20 -100 k. Hz • output power < 1. 5 µW Sensitivity 10 -4 cm -1

COSSTA Parabolic mirror PLL Upper Sideband 1. 75 -2. 01 THz Permanent Magnet Filter BWO In. Sb. Detector Absorption Cell CO 2 - Pumplaser Si-beamsplitter Grating FIR-Ringlaser Laserbeam Polarizing Filter BWORadiation Elliptical Mirror AFC Gunn IF Harmonic Mixer 125 -385 GHz BWO phase stabilization THz-Sideband. Mixer Evacuated Optics with Mixer Harmonic Mixer 1. 626 THz ZF Stabilized FIR - Laser

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

ortho-CH 2 at 1955 GHz

Mo. Me. D Tripler 2300 – 2700 GHz • • Monolithic Membrane Diode, Mo. Me. D SEM Image courtesy F. Maiwald / P. Siegel JPL

Mo. Med Mux Spectrometer Power BWO 765 – 900 GHz 3 - 12 m. W

Mo. Med Tripler

Mo. Med Mux Spectrum

Super. Lattice Structure

Super. Lattice: Symmetric I/V Curve

Hi. Res THz Spectrometer: Superlattice Multiplier THz-SL Multiplier SL Input 80 – 118 GHz 5 -8 m. W SL Output 234 – >1060 GHz

AMC + SL Spectrometer Microwave Synthesizer Generator Unit 80 – 118 GHz 5 - 8 m. W BWO Sweeper

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

Super. Lattice Broadband Scan

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

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

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

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

Conclusions Orotron-Spectrometer, sensitivity higher than FTMW, first 2 photon absorption / double resonance spectra (80 -325 GHz) BWO in fundamental mode, Sub-Doppler capability (53 to 1. 2 THz) Schottky Frequency Tripler for Hi. Res Spectroscopy up to 2. 4 THz Introduction of Superlattice devices for broadband Hi. Res Terahertz Spectroscopy (0. 2 - 2. 7 THz) The Gap is closed!

• • • 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) Hi. Res. Humboldt Foundation and State of NRW Russian Science Foundation for Basic Research

Phase Lock Loop 1. 9 THz LO c fc f HV BS 633 GHz BWO X 3 1. 9 THz BWO j DC Bias ± 10 V DC Bias Ref 2 Ref 1 PLL 2 PLL 1 336 MHz 8 -10 V X - d. B 24 MHz Synth. Prot. GUNN T 6 -7 GHz HM 80 -90 GHz GUNN power frequency

Breadboard Construction SOFIA LO B W O Heat Sink Pump PLL protect Chopper optics Locked ! QO Harmonic Mixer GUNN Bias GREAT Heterodyne Receicer TP D 1

Orotron L. A. Surin et al. , Phys. Rev. Lett. 86. 2002

SL Spectrometer

DCN Subdoppler

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