Pulse duration measuring apparatus

A pulse duration measuring apparatus having a plurality of optical parts for measuring pulse duration of a pulsed laser beam, comprising:

• a laser beam entry element for receiving a pulsed laser beam;
• a polarizing beam splitter for splitting the pulsed laser beam from the laser beam entry element into a first laser beam traveling along a first optical path and a second laser beam traveling along a second optical path;
• a first mirror for reflecting the first laser beam traveling along the first optical path toward the polarizing beam splitter;
• a second mirror for reflecting the second laser beam traveling along the second optical path toward the polarizing beam splitter;
• a first quarter wavelength plate disposed between the polarizing beam splitter and the first mirror;
• a second quarter wavelength plate disposed between the polarizing beam splitter and the second mirror;
• an optical path length changing unit for moving the first mirror or the second mirror along the optical path of the first laser beam or the second laser beam to change a length of the optical path;
• a nonlinear crystal body for allowing a combined laser beam to pass therethrough, the combined laser beam including respective returning laser beams of the first and second laser beams reflected respectively by the first and second mirrors and combined by the polarizing beam splitter;
• and
• a photodetector for measuring an optical intensity of the combined laser beam that has passed through the nonlinear crystal body,
• wherein the laser beam entry element, the polarizing beam splitter, the first mirror, the second mirror, the first quarter wavelength plate, the second quarter wavelength plate, the optical path length changing unit, the nonlinear crystal body, and the photodetector are disposed on a planar surface.