Kryno K Geissler

Enhancement of laser-induced electron emission from ferroelectrics by surface charge refreshment

Abstract The emission from ferroelectric material is dominated by surface electrons, which screen a large part of the spontaneous polarization. The surface charge compensation of the polarization can be modified by various methods in certain limits and, hence, also the efficiency of the electron emission. An increase of the emitted charge by laser irradiation of more than two orders of magnitude was measured after switching the polarization of polycrystalline lead-lanthanum-zirconium-titanate ceramics (PLZT). An enhancement of electron emission is also observed by pre-illumination with laser light in absence of an extraction voltage compared to regular illumination under a dc extraction field. The laser-induced emission is shown to be dependent on the ferroelectric state and on the full absorption of the laser light in the material.

Intense laser‐induced electron emission from prepoled lead‐lanthanum‐zirconium‐titanate ceramics

A sample of lead‐lanthanum‐zirconium‐titanate (PLZT 9/65/35) has been exposed to 6‐ns‐long laser pulses of 266 nm wavelength. The maximum output pulse energy of the laser beam was 300 μJ, the output power density on the sample 5×105 W/cm2, and the beam diameter 3 mm. By applying a moderate extraction voltage of several kilovolts, intense electron beam pulses are emitted from the free sample surface. Their time structure corresponds to the time structure of the laser pulse. Electron beam current intensities of up to 0.1 A and 2 A/cm2 and total charges of 1 nC (corresponding to 20 nC/cm2 ) were measured with a simple Faraday cup. In the range where the parameters of laser intensity and of extraction voltage could be varied their influence on the emitted electron beam current amplitude was determined.

Intense laser-induced self-emission of electrons from ferroelectrics

Abstract We report on laser-induced electron emission (LIEE) from ferroelectrics (FE) at 266, 355 and 532 nm wavelength without any extraction voltage. Emitted charges of up to 4 nC/cm 2 with kinetic energies of up to 10 KeV, currents exceeding 100 mA, and emitted current densities of several A/cm 2 were observed with PLZT ceramics at laser pulse energies of 1 to 2 mJ (10 6 W/cm 2 ) and a pulse width of 5 ns FWHM. The driving electric field is generated by the switching of the spontaneous FE polarization P s in a thin surface layer at the time scale of 1 ns. The extraction-field-free emission can be maintained at a constant level, when the polarization switching of the FE cathode is regularly repeated. Reliable long-term LIEE operation of FE cathodes, emitting nC electron charges, has been demonstrated.

FEMTOSECOND LASER-INDUCED ELECTRON EMISSION FROM FERROELECTRICS

Abstract The efficiency of laser-induced electron emission from ferroelectric (FE) cathodes has been measured by illumination with a Ti:sapphire laser at a pulse length of 140 fs and is compared to earlier measurements at 40 ps and 5 ns pulse lengths. Two modes of emission are observed: (i) a “normal steady-state” emission in the presence of a constant extraction field and (ii) a transient mode after a polarization switching of the FE cathode by a high-voltage pulse. The latter mode leads to “self-emission” of high electron currents with kinetic electron energies of several kilovolts. The physical interpretation and the potential applications of laser-induced electron emission from FE cathodes are briefly pointed out.

Self-emission and enhancement of laser-induced emission of electrons from ferroelectrics

Abstract We report on laser-induced electron emission (LIEE) from ferroelectrics (FE) at 266, 355 and 532 nm wavelength. The self-emission of charges up to 20 nC/cm2 with kinetic energies up to several keV was observed with PLZT ceramics at laser-pulse energy densities of 13 mJ/cm2 and a pulse width of 5 ns FWHM after high-voltage-induced polarization switching. The driving electric field is generated by the laser-induced change of the spontaneous polarization in a time scale of 1 ns. The dependence of the emission on the laser-pulse energy density is shown and the relation between the enhancement of LIEE and the laser-induced self-emission is discussed.

Scintillation light from liquid argon and its use in a new hybrid detector

Abstract Scintillation light, produced by 200 MeV/ c pions in a liquid argon bubble chamber/calorimeter was measured. Results from the test device show that this signal could be used in future large bubble chambers to trigger the flash on the occurrence of an interesting event. Furthermore, this signal give rough information about total track lengths, hence energy contained in massive electromagnetic and hadronic showers, and could complement measurements obtained by charge collection.

The HOLMES project

Abstract HOLMES is a working prototype of a scanning and measuring machine for in-line holograms of HOBC heavy liquid bubble chamber events.

Generation of short laser pulses

Abstract Progress in the technology of ultrashort pulse generation during the last years is outlined. After a short reminder of the basic active/passive mode locking processes and the combined pulse forming action of passive mode locking and gain saturation in the colliding-pulse mode locking arrangement (CPM), the recently developed coupled cavity/additive pulse mode locking (CCM/APM) configurations are reviewed. The Kerr lens mode locking (KLM) process constitutes an important advance towards simplicity and reliability. Its lack of a self-starting property has been of concern, but can finally be overcome by custom-built semiconductor nonlinear absorbers. Reduction of the thermal load of the active materials, higher output efficiencies and much enhanced beam quality result from the use of laser diodes to pump solid state lasers. Synchronisation of the process of picosecond laser pulse generation with an external signal with subpicosecond phase jitter is an important subject. As an illustration the CERN synchro laser system in use at the CLIC test facility for the generation of short electron bunches is presented. Possibilities for future improvements in this system as a consequence of recent technological advances are indicated.