GaAsP Photocathode Research Articles

2.45 GHz synchronised polarised electron injection at MAMI

A semiconductor modelocked diode laser has been used to produce picosecond spin-polarised electron bunches from strained GaAsP photocathodes and inject them into MAMI, synchronised to the 2.45 GHz accelerating field. The laser meets the operational requirements of MAMI producing stable electron beams, with a polarisation purity of 72% and a transmission efficiency of 52% at an accelerated beam current of 10.1 μA.

A high resolution multiposition Thomson scattering system for the Rijnhuizen Tokamak Project

A high resolution multiposition Thomson scattering setup to measure the electron temperature (Te) and density (ne) of a hot plasma is described. The system is operational at the Rijnhuizen Tokamak Project. Light from a high power pulsed ruby laser is scattered by the free plasma electrons and relayed to a Littrow polychromator for spectral analysis. The spectrally and spatially resolved light is detected by a GaAsP photocathode. The two-dimensional image is intensified and recorded with a charge-coupled device camera. Te in the range of 50 eV–6 keV can be measured at 115 spatial elements of 2.6 mm length along the laser beam. The observation error is <6% at ne=2×1019 m−3 and smaller for higher ne. The high resolution and accuracy enabled the observation of small scale structures in Te and ne.

Test of the new hybrid INTEVAC intensified photocell for the use in air Cherenkov telescopes

For a new large diameter (17 m ∅ mirror collector) air Cherenkov telescope project a “camera” of photosensors with high, red extended quantum efficiency is needed. A candidate is a variant of the INTEVAC intensified photocell with a GaAsP photocathode (≈45% QE). A version with an avalanche diode as secondary amplifying element with fast (ns) single electron response is under consideration. The motivation for the development and first test results are discussed.

Picosecond polarized electron bunches from a strained layer GaAsP photocathode

At the Mainz electron accelerator MAMI a facility has been set up that allows the measurement of the bunchlength, the energy spread and the averaged and phase resolved polarization of picosecond electron bunches from a source of polarized electrons for MAMI. Electron bunches of typically 10 to 30 ps duration are generated by illuminating a strained layer GaAsP photocathode with femtosecond laser pulses.

Lasertron, a Photocathode Microwave Device Switched by Laser

We study a new rf-source, LASERTRON, aiming to apply it for future very-highenergy e/sup +/e/sup -/ linear colliders. We started a research and development program to construct a LASERTRON with a peak rf-power of 50 MW by using GaAs or GaAsP photocathode as a first step to achieve GW. Design studies and preliminary experiments are described.

Surface magnetism: Recent progress and opportunities

Analytical and numerical progresses (i.e., Monte Carlo simulations) in the theory of phase transitions as well as experimental advances in the tools for surface magnetism are opening new horizons for this old field of solid state physics. Examples we shall describe involve 10 yr old predictions of magnetic surface reconstruction, their relation to the understanding of different phenomena like wetting or prewetting. Spin-resolved photoemission spectroscopy using synchrotron radiation, inverse photoemission, and electron scattering using polarized electrons from AlGaAs or GaAsP photocathodes are the primary new tools, which take advantage of the simultaneous availability of conventional preparation (e.g., UHV-epitaxy) and characterization techniques used in surface science studies. These experiments are expected to lead also to new insights in the microscopic origin of second order phase transitions in the special case of 3d metals.