M. Philipp

Phase locking of a 1.5 Terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver

We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.

Crossing and anticrossing of energies and widths for unbound levels

Abstract The crossing and anticrossing properties of the energies and widths of two unbound levels under the influence of a symmetrical complex interaction are investigated. It is found that a sufficiently large variation of the difference of the “unperturbed” energies or of the widths leads always to a crossing of either the energies or the widths of the “perturbed” system. A particularly interesting result is that for a real off diagonal interaction there is a joint crossing of the “unperturbed” energies and of either the “perturbed” energies or the “perturbed” widths.

Resonances of a superconducting microwave cavity: A test of the Breit-Wigner formula over a large dynamic range

Abstract Resonance data spanning a dynamic range of six decades from a superconducting two-dimensional stadium microwave cavity are investigated. The data set is described by various multi-resonance formulae. A good description spanning the full dynamic range of the data with an overall accuracy of about 10% is obtained. This is presumably the first test of the Breit-Wigner formula over such a large dynamic range

Precision test of the Breit-Wigner formula on resonances in a superconducting microwave cavity

Abstract Resonance data spanning a dynamic range of six decades from a superconducting microwave cavity in the form of a two-dimensional stadium billiard are described by a multilevel formula. The fitting procedure results in relative errors of about 0.3% in the close vicinity of strongly excited resonances. As compared to a previous experiment the technique for measuring the resonances has been improved distinctly.

GREAT: the German first light heterodyne instrument for SOFIA

GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a first generation SOFIA dual channel heterodyne PI-instrument for high resolution spectroscopy. The system is developed by a consortium of German research institutes. The receiver will allow simultaneous observations in two out of the following three far-infrared frequency bands: a 1.4-1.9 THz channel for e.g. the fine-structure line of ionized carbon [CII] at 158μm; a 2.4-2.7 THz channel for e.g. the 112μm transition of HD; and a 4.7 THz channel for the 63 μm fine-structure line of neutral atomic oxygen. Hot electron bolometers (HEB) mixers provide state of the art sensitivity. A spectral resolving power of up to 108 is achieved with chirp transform spectrometers, and a total bandwidth of 4 GHz at 1 MHz resolution is reached with wide band acousto-optical spectrometers. The modular concept of GREAT allows to observe with any combination of two out of the three channels aboard SOFIA. A more complete frequency coverage of the THz regime by adding additional GREAT channels is possible in the future. The adaptation of new LO-, mixer- or backend-techniques is easily possible. We describe details of the receiver and the results of first performance tests of the system at 1.9 THz.

Cryogenic design of KOSMA's SOFIA terahertz array receiver (STAR)

We present the opto-mechanical layout of KOSMAs (Kolner Observatorium fur SubMillimeter Astronomie) submillimeter and terahertz heterodyne array receiver STAR (SOFIA Terahertz Array Receiver) which is derived from SMART (Sub-Millimeter Array Receiver for Two frequencies). To reduce the alignment effort, SMART, for the first time, uses an integrated optics concept with no adjustable optical components inside the receiver dewar. For STAR this successful design concept will be extended and adapted for 1.9 THz and for use aboard SOFIA (Stratospheric Observatory For Infrared Astronomy). The design of STARs cryostat and cryogenic optics is described. Emphasis is laid on the required accuracy for 4x4 spatially multiplexed Terahertz heterodyne receivers. The proposed design of the local oscillator, a frequency-tripled BWO (Backward Wave Oscillator), is outlined. The presentation comprises the scheme for multiplexing the local oscillator, dense arrangement of mixer elements in a cryogenic focal plane and manufacturing techniques of integrated optics units for reduction of optical adjustment efforts in astronomical submillimeter and terahertz receivers.

High spin states in147Tb

The level scheme of147Tb has been extended to 116 levels and 198 transitions in two experiments with the OSIRIS Compton suppressed detector array at the HMI Berlin with the reactions122Sn(31P, 6n)147Tb at 160 MeV and120Sn(31P, 4n)147Tb at 152 MeV. Evidence for a new high spin isomer atE=7664.1 keV with a life-time of the order of 2 ns has been found.

High spin states in148Tb

The level scheme of148Tb has been extended to an excitation energyEx=14.0 MeV and a spinI≈ 38ħ in two experiments with the OSIRIS Comptom suppressed detector array at the HMI Berlin using the reactions122Sn(31P,5n)148Tb at 160 MeV and120Sn(31P,3n)148Tb at 152 MeV.

High spin states in145Gd

The data from two experiments with heavy ion induced reactions at the OSIRIS Compton suppressed Ge detector array has been analyzed to study high spin states in145Gd. The level scheme of145Gd has been extended up to an excitation energy of 12 MeV and an estimated spin of 25 ħ. No evidence for high spin isomers was found.