<title>Photoemissive thin film with strange property for laser pulse detection</title>

Abstract

A kind of photoemiaaive thin films which can be expoeed or stored in the atmosphere and can be used again in a vacuum system without any activation process for laser pulse detection ía presented. They are different from usual photoemiseive materials, since they do not contain alkali elements. They consist of metallic oxide thin film or other material thin film embedded with metallic ultrafine particles. A main interesting material is barium oxide thin film embedded with Ag ultrafine particles. This thin film can detect single laser pulse or laser pulses with high repetition frequencies (--1O pulses/sec.), pulse duration nsps, and energy mJ-nJ per pulse. 1.INTRODTJCTIONThere are two basic kinds of photoemissive materials for the laser pulses detection. One is the photoemissive thin films containing alkali elements,1 such as Ag-O--s, sSb, [Cs]Na2KSb. F.Gex et a! said that the Ag-O-Cs photocathode was the only photoemiseive material for detecting laser pulse duration QOps, wavelength 1.06 t m. Another is pure metallic thin films, such as Au, Ag, Cu. The sensitivity of photocathodes containing alkali elements is higher than others. But this kind of thin films can not work at higher temperature than 150t, and it also can not be exposed to the atmosphere. The photocathodes wifi be worthlese, if they are exposed to the atmosphere. This weak point causes the trouble for use, even can not be used at some situations. The pure metallic thin films can be exposed to the atmosphere and can work at high temperature, but their sensitivity of photoemission is too low, so that detecting the laser short duration pulses is very difficult except using very strong laser pulse power density.We prepare a new kind of photoemiseive thin films which can be exposed or stored in the atmosphere and can be used again in a vacuum system without any activation process for laser pulse detection. It is different from usual photoemissive materials, since it do not contain alkali elements. It consists of metaffic oxide thin film or other material thin film embedded with metallic ultrafine particles. The ultrafine particles (IJFP's) represent particles having diameters in the range of 1 to 100 nm.8 The UFP's on the substrate have special properties that are different from those properties described by either atomic physics or solid state physics.4 A main interesting material in the new kind of photoemissive thin films is barium oxide thin film embedded with Ag ultrafine particles. We call it as special Ag-Ba-C thin film. This thin film can detect single laser pulse or laser pulses with high repetition frequencies ( -1O pulses /sec.), pulse duration ns-.-ps, and energy mJ-nJ per pulse. 2.EXPERIMENTAL MEASURING SYSTEMThe system for measuring single train laser pulse is showed in Fig.1. The system is constructed by laser source, outside opticator, photoemissive thin film, streak camera, vacuum system, detection system and related electronic circuits. The photoemissive thin film is set in the streak camera after it is exposed to the atmosphere. The singl...