Measurement method of time jitter between pump laser pulse and RF wave by the charge change in photoinjector

In photocathode RF gun, the Schottky effect in process of photoemission and electron lognitudinal accelerating process bring forth a linear work range in which electron charge out of gun is linear proportion to laser injection phase . According to the result ,we develop a method that can be used to measure time jitter between laser pulse and RF wave. The method can attain to high precision and small error. On general photoinjector condition, the precision is almost 1.15fs，the error is almost 0.23fs.