Godehard Wüstefeld

Bunch length measurements at BESSY

In the range from 2 ps to 40 ps the rms bunch length and the bunch shapes have been measured with a streak camera as a function of the beam current. Short bunches were produced by reducing the momentum compaction factor of the storage ring lattice. An attempt is made to distinguish between vacuum chamber and radiation impedance effects.

Coherent emission of synchrotron radiation and longitudinal instabilities

At BESSY bursts of coherent synchrotron radiation around 20 cm/sup -1/ have been observed above a certain threshold current. The repetition rate of these bursts depends on the beam current and the thresholds vary strongly with the bunch length. Observed thresholds are in agreement with the theory of beam instability and microbunching due to coherent synchrotron radiation (CSR).

Status of the IR and THz beamlines at the Metrology Light Source

The low-energy electron storage ring Metrology Light Source (MLS), a dedicated synchrotron radiation source, is in user operation since April 2008 at operating energies ranging from 105 MeV up to 630 MeV. It provides coherent THz radiation when it is operated in a low alpha mode with short electron bunches. At the MLS, two bending magnet beamlines optimized for the MIR and the THz spectral range are operational. We report the status of these two beamlines and present first results of the IR and THz measurements at the MLS.

IR and THz Beamlines at the Metrology Light Source of the PTB

The low‐energy electron storage ring Metrology Light Source (MLS), a dedicated synchrotron radiation source, is in user operation since April 2008. As a special option it provides coherent synchrotron radiation (CSR) in the THz range when it is operated in a low‐α mode with short electron bunches. At the MLS three beamlines dedicated to the use of IR and THz radiation were designed, built and commissioned.

Long wavelength response of unstressed and stressed Ge:Ga detectors

Photoconductivity spectra of unstressed and stressed Ge:Ga detectors were measured. The experiments were performed with a polarizing step scan Fourier transform spectrometer using the synchrotron facility BESSY, which was operated in a dedicated mode with a low momentum compaction factor. By this way powerful and coherent synchrotron radiation below 50 cm-1 was generated. We observed a significant response of unstressed and stressed Ge:Ga detectors below 50 cm-1 and 25 cm-1, respectively. This response can be attributed to transitions between bound excited states or from bound excited states to the valence band. The results indicate that in germanium detectors a fraction of the recombining holes is captured into bound excited states.

Field transients of coherent terahertz synchrotron radiation accessed via time-resolving and correlation techniques

Decaying oscillations of the electric field in repetitive pulses of coherent synchrotron radiation in the terahertz frequency range was evaluated by means of time-resolving and correlation techniques. Comparative analysis of real-time voltage transients of the electrical response and interferograms, which were obtained with an ultrafast zero-bias Schottky diode detector and a Martin-Puplett interferometer, delivers close values of the pulse duration. Consistent results were obtained via the correlation technique with a pair of Golay Cell detectors and a pair of resonant polarisation-sensitive superconducting detectors integrated on one chip. The duration of terahertz synchrotron pulses does not closely correlate with the duration of single-cycle electric field expected for the varying size of electron bunches. We largely attribute the difference to the charge density oscillations in electron bunches and to the low-frequency spectral cut-off imposed by both the synchrotron beamline and the coupling optics of our detectors.

Coherent synchrotron radiation experiments at BESSY II

Coherent synchrotron radiation (CSR) in the steady state and bursting mode is generated. The emitted radiation is analysed in the time and frequency domain. A step mode Fourier transform (FT) spectrometer is applied to analyse bursting CSR.

First measurements at the new dedicated THz beamline at the MLS

The Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute, is operating the low-energy electron storage ring Metrology Light Source (MLS) in Berlin-Adlershof in close cooperation with the Helmholtz-Zentrum Berlin (HZB). The MLS is designed and prepared for a low-α machine optics mode based on a sextupole and octupole correction scheme, for the production of coherent synchrotron radiation in the far-IR and THz region. We present first results obtained from the new dedicated THz beamline at MLS.

Status of the THz activities at the MLS

We report the status of the MLS as a source of powerful, stable, and pulsed THz radiation. Additionally we show results from the commissioning of the experimental stations and first measurements in the THz spectral range.

Status of the Metrology Light Source

The Physikalisch‐Technische Bundesanstalt (PTB), the German national metrology institute, has set up the low‐energy electron storage ring Metrology Light Source (MLS) in close cooperation with the Helmholtz‐Zentrum Berlin (HZB, formerly BESSY). This new storage ring has been in regular user operation since April 2008 and is dedicated to synchrotron‐radiation‐based metrology and technological developments in the far‐IR/THz, IR, UV, VUV and EUV spectral range. The MLS has a double‐bend‐achromate lattice structure, injection is from a 105 MeV racetrack microtron. The electron energy can be ramped to any value from 105 MeV up to 630 MeV and the electron beam current covers the range from one stored electron (1 pA) up to 200 mA. The MLS is the first electron storage ring optimized for the generation of coherent synchrotron radiation, based on an electron bunch shortening mode. In this mode, MLS delivers coherent radiation in the far‐IR/THz spectral range with enhanced intensity as compared to the normal mode o...