PURPOSE: To set a characteristic with ease only by changing a rise-up speed of a voltage by a method wherein a pulse is chipped out with use of a photo switch with a simple apparatus consisting of a Pockels cell, a polarizer, a photoswitch, etc.

CONSTITUTION: When a giant pulse is generated from Q-switching laser oscillator 1, it penetrates a Pockels cell 2 with vertical deflection sustained, and is reflected at a polarizer 3, attenuated by a fixed amount with an attenuator 6 and then leads to a photoswitch 7. When an attenuating amount is decided in such a way that the switch 7 will conduct when a gaint pulse output level goes down to slightly lower than the miximum value, a high voltage 8 is applied to the cell 2. This voltage is determined to provide a giant pulse with the generation of a phase difference of one wavelength and kept until the pulse returns to zero. Then giant pulse is led to the polarizer 3 after 180° turning the plane of polarization with cell 2 while the voltage 8 is changing, and only its horizontal component of polarization is passed, thereby producing a large-output laser with a very small width.