A New Spectrometer For High Resolution Measurements of THz Transitions in Cold Carbon Clusters Martin Philipp, Michael Caris, Thomas Giesen, Stephan Schlemmer I. Physikalisches Institut University of Cologne Germany

Why Carbon? Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07  fourth most abundant element in Interstellar Medium  75% of identified molecules contain carbon  tends to form large chains Carbon:  carbon chains are nonpolar Hale-Bopp IRC (Artist view)

Lowest Bending Modes of Linear Carbon Chains Measured: C 3 Schmuttenmaer et al. (1990) Gendrisch et al. (2003) Lab: Sgr B2: Giesen et al. (2001) Calc. band origins (Botschwina 2002) Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 T=100 K Cernicharo et al. (2000)

GREAT Heterodyne Receiver Local Oscillator slots SI-Flange 1m LOs of GREAT are stand-alone THz sources! Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 MPAe Berlin 4.7 THz MPIfR Bonn 2.4 – 2.7 THz KOSMA 1.4 THz KOSMA 1.6 – 1.9 THz Dual-channel, four-band: SOFIA

frequency range (sample): GHz device bandwidth: 20% output power: mW minimum lifetime: > 500 h BWO sample (OB-80, ISTOK)multipliers for 1900 GHz ( RPG,JPL ) GHz  W 4% / 10% 15cm 2cm Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/ THz LO: Principle of Operation

X 3 1.9THz 633GHz astigmatic PLL ( to receiver optics ) heat sink synthesizer water pump fan array LO-Box boundary BWO optics two-stage magnet Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 frequency precision ~ 30 kHz power supply HV

1.9 THz Local Oscillator of GREAT 1 m optics BWO+ magnet cooling electronics Philipp et al. (2006) Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

buffer gas Nd: Yag laser 1.9 THz LO pump Supersonic Jet Spectrometer for THz Applications lnSb Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 pulse generator for valve

Laser Ablation of Graphite Rod  UV-Pulse (~10 8 Wcm -2 ) for ablation  ~10 15 ablated atoms / pulse  He-pulse (~10bar) for expansion  T ~ 20K Nd:YaG UV-pulse 266 nm vacuum Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

Beam Alignment: 10 passes through jet, vertical alignment of jet transits absorption path length ~10 cm 1 cm

First Measurements CO (16 15)  verify beam path  check timing  optimize readout used for: electronics CO measured in T~20K Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

Measured C GHz C 3 Q(10) M.Caris. M.Philipp (2006) buffer gasHe backing pressure4 bar laser energy per pulse mJ number of points76 total scanning time17 min radiation power100 nW Conditions: Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 Q (10) this work: Q (10) Gendrisch et al (153) MHz (150) MHz

Predictions for C 7 C 3 Q-branch C 3 R-branch C7C7 IR: C 7 → estimated band origin 54 ± 11 cm -1 (1.6 ± 0.3 THz) Neubauer-Guenther et al. (in press, 2007) (from calculations) tuning range of radiation source C 3 P-branch frequency [GHz] Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 C7C7 (from experiment)

Conclusion + Outlook Conclusions:  1.9 THz LO of GREAT is a compact and easy-to-use source  Q(10) transition of C 3 was verified Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 Outlook:  measuring of C 7 should be possible  13 C 3 maybe of THz radiation was a success!  Combination of the LO with the SuJeSTA spectrometer

Funding This work is supported by the Deutsche Forschungsgemeinschaft through Grant SFB 494 and by the state Nordrhein-Westfalen. Thanks to Dr. U. U. Graf Dr. F. Lewen Dr. A. Wagner-Gentner Prof. Dr. J. Stutzki D. Rabanus B. Schmidt Acknowledgments Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

GREAT Heterodyne Receiver SOFIA LO-slots Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 MPAe Berlin 4.7 THz MPIfR Bonn 2.4 – 2.7 THz KOSMA 1.4 THz KOSMA 1.6 – 1.9 THz Dual-channel, four-band:

1.9 THz Local Oscillator of GREAT optics BWO+ magnet coolingelectronics Philipp et al. (2006) Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07 1 m radiation output

BWO 'OB-80' Power Output measured using Erickson PM1 Power Meter Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

LO Power Output: Example! C3C3 C+C+ measured using Golay Cell Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

Supersonic Jet Spectrometer for THz Applications BWO gas mixture pulse generator for valve lnSb 600 GHz BWO source "Herriott"- Cell Discharge Nozzle Adiabatic Expansion of jet nozzle Used for studying of: C 3 H, CO +, Si 2 C... "SuJeSTA" pump Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07

Cluster Size of Vaporized Graphite Rod Masse / C x10 Rohlfing, Cox, Kaldor (1984) Martin PhilippA New Spectrometer For Measurements of THz Transistions in Cold Carbon Clusters06/22/07