The dependence of quantum efficiency of alkali halide photocathodes on the radiation incidence angle

Proc SPIE 10/1999;

ABSTRACT We studied variation of quantum efficiencies of CsI, KBr and KI-evaporated reflective planar photocathodes with the angle of radiation incidence (±55 degrees) in the spectral range of 25-115 nm. The photocurrent increases with the photon incidence angle for short wavelengths (by as much as ~60% at 55 o for 25-30 nm illumination), while it changes only ~5% at wavelengths ~90-115 nm. The theoretical calculations of the photocathode angular response based on the absorption length of the photons and the escape length of the photoelectrons are in a relatively good agreement with the measured data. A detailed study of the detection efficiency angular variation for the microchannel plates with CsI, KI and KBr photocathodes in the spectral range of 25-191 nm is also presented. Heat annealing of the planar photocathodes did not result in any significant variation in their angular response.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The Io plasma torus is composed mainly of sulfur and oxygen ions and their compounds such as SO2+ derived from Io's volcanic activities, together with a background of electrons. In addition to those basic components, several in-situ observations have shown that a few percent of the electrons there have been excited to be as much as 100 times hotter than the background electrons. These hot electrons have a significant impact on the energy balance in the Jovian inner magnetosphere. However, their generation process has not yet been elucidated. One difficulty is that the available data all comes from in-situ observations, which cannot explore the temporal and spatial distributions explicitly. Therefore remote sensing, which could take a direct picture of the plasma dynamics is necessary. In order to clear up the hot electron problem, the Earth-orbiting EUV spectroscope, EXCEED will be launched in 2013. It is dedicated and optimized for observing the terrestrial planets. Because of its large effective area and the simplicity of the scientific target, better temporal resolution and more complete coverage for Io plasma torus observation is expected. In this paper, the optical design and specifications of EXCEED are introduced. Furthermore, based on a feasibility study using the spectral diagnosis method, it is shown that EXCEED can determine the Io plasma torus parameters such as the electron density, temperatures, hot electron fraction and so on. The possibility of clearing up the hot electron problem through the EXCEED observations is also discussed.
    Planetary and Space Science 03/2012; 62(1):104–110. · 2.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A vacuum ultraviolet (VUV) spectrometer of a five-channel spectral system is designed for ITER main plasma impurity measurement. To develop and verify the system design, a two-channel prototype system is fabricated with No. 3 (14.4-31.8 nm) and No. 4 (29.0-60.0 nm) among the five channels. The optical system consists of a collimating mirror to collect the light from source to slit, two holographic diffraction gratings with toroidal geometry, and two different electronic detectors. For the test of the prototype system, a hollow cathode lamp is used as a light source. To find the appropriate detector for ITER VUV system, two kinds of detectors of the back-illuminated charge-coupled device and the microchannel plate electron multiplier are tested, and their performance has been investigated.
    The Review of scientific instruments 10/2010; 81(10):10E508. · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Microchannel plate (MCP) detectors have been widely used as two-dimensional photon counting devices on numerous space EUV (extreme ultraviolet) missions. Although there are other choices for EUV photon detectors, the characteristic features of MCP detectors such as their light weight, low dark current, and high spatial resolution make them more desirable for space applications than any other detector. In addition, it is known that the photocathode can be tailored to increase the quantum detection efficiency (QDE) especially for longer UV wavelengths (100-150 nm). There are many types of photocathode materials available, typically alkali halides. In this study, we report on the EUV (50-150 nm) QDE evaluations for MCPs that were coated with Au, MgF(2), CsI, and KBr. We confirmed that CsI and KBr show 2-100 times higher QDEs than the bare photocathode MCPs, while Au and MgF(2) show reduced QDEs. In addition, the optimal geometrical parameters for the CsI deposition were also studied experimentally. The best CsI thickness was found to be 150 nm, and it should be deposited on the inner wall of the channels only where the EUV photons initially impinge. We will also discuss the techniques and procedures for reducing the degradation of the photocathode while it is being prepared on the ground before being deployed in space, as adopted by JAXA's EXCEED mission which will be launched in 2013.
    The Review of scientific instruments 08/2012; 83(8):083117. · 1.52 Impact Factor

Full-text (2 Sources)

Available from
Jul 31, 2014