Cavity dispersing measuring method and measuring apparatus thereof

Abstract

In a cavity dispersion measuring method, there are provided the steps of: dividing a light beam emitted from a laser cavity under measurement into first, second, third, and fourth light beams; propagating the first light beam and the second light beam along a first optical path and a second optical path respectively, and superimposing two light beams with each other which have passed through the first and second optical paths respectively to cause the two light beams to interfere with each other, thereby producing a first interference light beam; propagating the third light beam and the fourth light beam along a third optical path whose light path length is variable and a fourth optical path whose light path length is fixed respectively, thereby producing a second interference light beam; controlling the optical path length of the third light path in order that intensity of the second interference light beam is kept constant; adjusting the optical path length of the first optical path in correspondence with the controlled optical path length of the third optical path; measuring the first interference light to obtain a waveform of the light intensity while varying the optical path length of the second optical path in a vicinity; and Fourier-transforming the waveform of the measured light intensity to obtain phase information in a frequency domain, whereby wavelength dispersion of the laser cavity is obtained based on the phase information.