The invention provides a light detector, comprising a light sensor, a first electrode and a second electrode which are connected with the light sensor, and a first electrode lead and a second electrode lead; the ends of the first electrode lead and the second electrode lead are respectively connected with the first electrode and the second electrode and the other ends thereof are used as output terminals; light response material of the light sensor is strontium lanthanum aluminate single wafer, strontium lanthanum aluminate mono-crystalline film or strontium lanthanum aluminate polycrystalline film; the mono-crystalline film or the polycrystalline film is prepared on a substrate. The light detector of the invention can quickly respond to a laser pulse of ns pulse width under the ultraviolet band, with the width of generated voltage pulse of less than 2 ns and full width of pulse of only a plurality of ns.