We present a method for obtaining a passive Q-switched Nd : YAG / Cr4 + : YAG laser with tunable pulse width. The output pulse width is tuned based on the delay time between the pumping pulse and trigger pulse. An auxiliary laser with a narrow pulse is used to trigger the laser pulse generation at different delay times during the pumping pulse duration. It is found that the output pulse width can be continuously adjusted from 1415 to 562 ps with an output peak power ranging from 44 to 240 kW at a fixed pumping power. The beam quality factor M2 is kept <1.5 with changing of the pulse width.
For the uniformity calibration of a detecting device, a tunable range output of femto-joule to nano-joule pulse with flat top profile beam is required. In this paper, a technique of producing the wide tunable range output of pulse energy with flat top profile is presented.