SPIE Proceedings [SPIE XXXVI Symposium on Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments (Wilga 2015) - Wilga, Poland (Monday 25 May 2015)] Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2015 - Review and present status of preparation of thin layer lead photocathodes for e - injectors of superconducting RF linacs