The Technology of High Resolution

Terahertz Spectroscopy

International Symposium on

Molecular SpectroscopyJune 19 – 23, 2006

I. Physikalisches InstitutUniversität 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 200 - >2700 GHz

0 1 1.5 2.520.5 3

Frequency [THz]

Herschel (HIFI)

Apex Apex 2A 500 - 2100 GHz Laboca 345 GHz; 295 Pixel Flash 780 - 890 GHz Condor 300 -1500 GHz

Herschel HIFI 480 - 1250 GHz

1410 - 1910 GHz Resolution ~ 107

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 detectionof highly excited carbon monoxide (CO J = 13 → 12) at 1.5 THz

Cologne Terahertz High Resolution Spectrometers

Spectrometer Frequency Range Accuracy

[GHz] [m] [kHz]

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

Intracavity (Orotron)

80-325 900-4000 30 3*10-7

IR-Tunable Diode Lasers

15-100THz 3-20 1000 10-7

Orotron Spectrometer (Double Resonance Setup)

Agilent/HP 83650A synthesizer0.01 to 50GHz, 1mW at 40GHzmin. resolution/stepsize 10Hzremote controled

Spacek amplifier 18-43GHz100mW output power level,connected to a new broadbandelectroformed horn antenna

Pump Beam Setup

Double Resonance Spectrum

Linewidth 210kHz

Condition for Double Resonance Experiments: Common Energy Level

L.A. Surin et al.,PhysRevLett.86.2002

Orotron: Two Photon Absorption

BWO stabilized with PLL

Beamsplitter

BWO

Absorption Cell Rubidium Reference

MM-Wave Synthesizer

df/f 10 -11

78 - 118GHz

magn. Coils

Cologne Terahertz Spectrometer

Harmonic Mixer

Diff. Pump

Rotary Pump

Elliptical Mirror

PLL

PCDigital Lock In

IF Amp

FM

IEEE Interface

InSb DetectorQFI/4 (2BI)

DATA

Voltage Controlled Oscillator

Power

BWO Power

Supply

Supply

R

e

Magnetic FieldH

Window

Radiation Out

Filament Filament + Cathode

Slow Wave Structure

Operation of BWO

Backward Wave Oscillator OB-44U/f characteristic

Slow Wave Structure Voltage U [kV]

f [THz]

BWO Characteristics

Slow Wave Structure Voltage [V]

RF Power[mW]

Frequency[GHz]

Backward Wave Oscillator OB5-0

ISTOK, 141120 Fryazino, Moscow Region

*

*

BWO Beam Pattern @600GHz

Harmonic Mixer with Planar Diode

IF Matching Unit

HEMT Port

Z=50 Ohms

BIAS Port

Harmonic Mixer

Planar FilterParabolic Mirror

(Waveguide Input e.g. 53-178 GHz)

mm Wave Synthesizer BWO or FIR 200 - 1650 GHz

RFC

IF & DC

L

C

HMIX 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)

COSSTACologne Sideband Spectrometer for Terahertz Applications

• frequency range 1750 - 2100 GHz

• frequency stability BWO (phase stabilized) <1 Hz

• frequency stability FIR - laser (frequency stab.) 5 kHz

• absolute frequency determination 108 20-100 kHz

• output power < 1.5 µW Sensitivity 10-4 cm -1

0,2 - 0,4 1,61,2 - 1,4 1,8 – 2,0

BWO

FIR

upper sidebandlower sideband(filtered)

• BWO + FIR- gas laser Sideband Radiation Schottky-Diode

COSSTA

PermanentMagnet

PolarizingFilter

IF

Harmonic Mixer125-385GHz

BWO phase stabilization Evacuated Optics with Mixer Stabilized FIR - Laser

THz-Sideband-Mixer

BWO-

Radiation

Grating

Upper Sideband

1.75-2.01THz

Parabolicmirror

Absorption Cell InSb-Detector

Laserbeam

EllipticalMirror

Si-beamsplitter

Harmonic Mixer1.626THz

ZF

GunnAFC

FIR-Ringlaser

CO2 - PumplaserFilterBWO

PLL

CCC Lowest Bending Transitionsmeasured with COSSTA

Gendriesch et al. (2003)

ortho-CH2 at 1955 GHz

MoMeD Tripler 2300 – 2700 GHz

• Monolithic Membrane Diode, MoMeD• SEM Image courtesy F. Maiwald / P. Siegel JPL

MoMed Mux Spectrometer

Power BWO765 – 900 GHz3- 12mW

MoMed Tripler

MoMed Mux Spectrum

2333840 2333860 2333880 2333900 2333920 2333940

-200

0

200

400

2.33 THz Tripler, BWO x 3

calc.: 2333887.400(36)obs.: 2333887.446(52)Line width 6.36(16) MHz

D2O 8

2 6 - 7

3 5

Inte

nsity

[ar

b. U

nits

]

Frequency [MHz]

SuperLattice Structure

SuperLattice: Symmetric I/V Curve

HiRes THz Spectrometer:Superlattice Multiplier

THz-SLMultiplier

SL Input80 – 118GHz5-8mW

SL Output234 – >1060GHz

MicrowaveSynthesizer

GeneratorUnit

AMC + SL Spectrometer

80 – 118 GHz5 - 8 mW

BWO Sweeper

Multiplication x 3rd, x 5th, x 7th, x 9th

First Record> 1THz!

CH3OH

SuperLattice 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 (80 -325 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 (0.2 - 2.7 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

BWO1.9 THz633 GHz

- dB

DC Bias

T

GUNNfrequency

power

DC Bias

X 3

PLL 2Ref 2

PLL 1Ref 1

BWO

Prot. GUNN

HM

X

Synth.

HV ffcc

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 protectBWO

Locked !

L.A. Surin et al.,PhysRevLett.86.2002

Orotron

SL Spectrometer

DCN Subdoppler

The Methylene Radical CH2

Ozeki & Saito

Ozeki & Saito

Lovas, SuenramEvenson

Cologne 1955 GHz

943 GHz