Comparison between a FEL amplifier and oscillator

Previous experiments with the Raman FEL, situated at the Twente University, showed that the output was influenced by the rather strong increase of the current density with time. The field emission diode has been modified to produce a more constant current pulse to simplify the analysis of the measurements. This resulted in a lower current density of the electron beam. With this new diode two set-ups are studied. In the first set-up the laser is still configured as an amplifier whereas in the second set-up the laser configuration is changed into an oscillator using a Bragg reflector with a space-variable corrugation height. For both set-ups we measured the frequency spectrum for specific values of undulator and guide magnetic fields. The relative performance of the amplifier and the oscillator configuration will be presented

The effect of a Bragg reflector on the spectral stability of the Twente Raman free electron laser

The spectral distribution of the Twente Raman FEL has been studied as a function of the interaction length for an amplifier configuration. A stable spectrum was found for the minimum required interaction length necessary for the RF signal to be detected. Large variations in total emitted energy are observed however. With increasing interaction length the spectral distribution not only evolves but deviations are also observed, i.e. for some shots distributions are found which do not conform to the average distribution. For even longer interaction lengths the spectra can be grouped in a few different patterns. The influence of the feedback on the spectral distribution has been studied by changing the configuration to an oscillator using a Bragg reflector. For all settings investigated, the oscillator showed a more stable spectrum, i.e., less spread in total emitted energy as well as less spread in spectral distribution. For some settings operation on a single frequency in the Ka band was observed

Transverse Optical Mode Patterns for an RF Excited Ar-He-Xe Laser

Transverse optical modes for an RF excited Ar-He-Xe laser are studied both experimentally and theoretically. A diffraction model for a waveguide with a nonsaturable gain and refractive index gradients placed between two plane mirrors is formulated. The effects of gain and diffraction index gradients and of diffraction in free space are evaluated for typical experimental conditions. A direct comparison between theoretical mode patterns and experimentally measured ones at distances of 17 and 114 cm from the output mirror demonstrated a satisfactory agreement for various laser wavelengths and gas mixture composition

On the use of positive test strategies when diagnosing mental disorders

Background: Despite the adverse impact diagnostic errors can have, clinical interviewing and decision-making in psychiatric practice have received relatively little empirical attention. When diagnosing patients, clinicians tend to fall back on a specific (heuristic) rule of thumb, the positive test strategy, a confirmatory approach that increases the risk of confirmation bias. Method and results: A group of 83 clinical psychologists and psychiatrists was asked to give their diagnostic hypotheses about two vignettes. We found them to self-generate significantly (i.e., p < .01; d = 1.57) more confirming than disconfirming questions to test their initial diagnostic impressions, with supervisors considering significantly more differential diagnoses than the less experienced post-grads/residents. When offered a list of 100 potentially relevant diagnostic queries, the supervisors selected fewer confirming and proportionally more disconfirming themes. Conclusions: Our results demonstrate that irrespective of clinical experience mental-health clinicians indeed tend to use a confirmatory thinking style that contrasts with the stricter principle of falsification. More field-based research on this topic is needed, as well as studies probing whether a systematized diagnostic approach is feasible in psychiatric practice and increases diagnostic accuracy and patient satisfaction

Formation and quenching mechanisms of the electron beam pumped (XeRb)+ ionic excimer in different buffer gases

The ionic excimer molecule XeRb+ is formed in an electron beam excited gas mixture of Xe, Rb, and a buffer gas. The formation and quenching mechanisms of ionic excimers are investigated by measuring the XeRb+fluorescence as a function of the gas composition and gas pressure. The formation of XeRb+ is achieved by a three‐body association reaction between Xe+, Rb, and a buffer gas atom. For the buffer gases He, Ne, or Ar the values of the important formationrate constants are determined from the observed fluorescence signal decay

Continuous wave near‐infrared atomic Xe laser excited by a radio frequency discharge in a slab geometry

Near‐infrared atomic Xe laser lines have been generated from an Ar:He:Xe laser gas mixture excited by a radio frequency (rf) discharge in a slab geometry. A maximum continuous wave (cw) output power of 1.5 W (270 W/l) was obtained at an rf frequency of 125 MHz from a gas mixture containing Ar:He:Xe (50:49:1) at a total gas pressure of 90 Torr

Vrije-Elektronen-Laser werk aan de Universiteit van Twente in samenwerking met het Nederlands Centrum voor Laser Research

In de vakgroep Quantum Elektronica van de Faculteit Technische Natuurkunde aan de Universiteit Twente zijn momenteel drie Vrije-Elektronen-Laser projecten operationeel. De projecten worden uitgevoerd in nauwe samenwerking met het Nederlands Centrum voor Laser Research. Het FEL-onderzoek binnen de vakgroep richt zich met name op de fysische aspecten van het FEL-mechanisme en de technologische ontwikkeling van componenten voor een effectieve produktie van straling. Ook wordt veel aandacht besteed aan de ontwikkeling van diagnostiek, zowel voor de elektronenbundel als voor de optische bundel. Veel componenten zijn in huis ontwikkeld en gebouwd. Op deze wijze wordt getracht FEL’s aantrekkelijk te maken voor industriële toepassingen. Dit laatste aspect krijgt met name veel aandacht in de samenwerking met het NCLR. Hieronder volgt een korte beschrijving van de verschillende projecten