A photocathode includes a first layer having a first energy band gap for providing absorption of light of wavelengths shorter than or equal to a first wavelength, a second layer having a second energy band gap for providing transmission of light of wavelengths longer than the first wavelength, and a third layer having a third energy band gap for providing absorption of light of wavelengths between the first wavelength and a second wavelength. The first wavelength is shorter than the second wavelength. The first, second and third layers are positioned in sequence between input and output sides of the photocathode.