Decay Characteristic of Gallium Nitride Photocathode in a High Vacuum System

The decay characteristics of the originally-activated GaN photocathode are explored by testing the change of quantum efficiency (QE).The QE after degradation for 9 hours can still keep more than 42% of the original value, and after reactivated with cesium, the QEs are almost recovered. The restorations of both the band bending and the ideal Cs/O ratio on the surface, along with the double dipole model are proposed to explain the QE variation of the GaN photocathode. Further exploration should include the roles played by the achievement of the maximum band bending of the GaN surface when deposited with Cs and its relationship with the surface Mg doping concentration.

Decay Characteristic of Fiber Bragg Grating and Fabrication of High Temperature Resistance Grating Temperature Sensor

Thermal decay characteristic of fiber Bra gg Grating (FBG) written into hydrogen-loaded optical fiber by exposing to ultraviolet (UV) laser irradiation through a phase mask is presented and experimentally demonstrated. Results of the experiment show that the FBG has a high temperature sustainability of 600 °C with main taining 26.6% of initial reflected light power after annealing for 24 hours. High temperature resistance grating based on the hydrogen-loaded conventional FBG has been fabrication and the shift of the Bragg wavelength w ith temperature is investigated over a range from -60 °C to 700 °C. The relationship between the wavelength of the FBG and te mperature indicates its feasibility as temperature sensor for high temperature.