Abstract: A passband-adjustable photo-detector for inverse photoemission spectroscopy, in which an electron beam from an electron gun is applied onto a sample and a light reflected therefrom is converged, so as to effect photo-detection, wherein said photo-detector comprises a photo-electron multiplier, a LiF monocrystal window and a CaF.sub.2 monocrystal window individually deposited with a KCl thin film in the front of a photo-electron multiplier in the photo-detector, wherein said windows means are provided for arbitrarily setting the temperature from the vicinity of liquid nitrogen temperature to the order of 150.degree. C., a photo-electron multiplier having a first dinode deposited a KCl thin film on a surface thereof said photo-electron multiplier, and an output of the photo electron multiplier is connected with a pulse counter circuit through an amplifier, so as to measure anyone selected from the group consisting of light absorption property, window transmissibility and sensitivity as a bandpass filter.

Abstract: A narrow band high sensitivity photo-detector for inverse photoemission spectroscopy, in which an electron beam from an electron gun is applied onto a sample and a light reflected therefrom is converged into a photo-electron detector, so as to effect photo-electron detection in a photo-electron multiplier, wherein said photo-electron detector comprises a CaF.sub.2 monocrystal window provided with a KCl thin film in the front of said photo-electron detector, a first dynode deposited with a KCl thin film on a surface thereof, wherein an output of the photo-electron multiplier is applied with a pulse counter circuit through an amplifier, so as to measure light absorption properties, window transmissibility and detection sensitivity as a band pass filter.