Method of measuring the time for forming refractive index grating of a

Abstract

A laser beam with a wavelength .lambda. emitted from a laser beam source is split into first and second pump beams and a probe beam. The first and second pump beams are incident on light incident surfaces of a photo-nonlinear medium from opposing directions on the same optical path. The probe beam is incident on the light incident surface forming an angle with the first pump beam to generate interference fringes in the normal direction of the light incident surface and to form a refractive index grating. A phase conjugate wave is emitted in the reverse direction to an incident optical path of the probe beam by means of irradiating the second pump beam on the refractive index grating. A direct -current electric field is applied on a pair of external electrodes to be coincident to the wave vector of the interference fringes, where by providing a frequency modulation to the first pump beam using a piezoelectric oscillator, a moving speed 'v' of the interference fringes is determined when light intensity of the phase conjugate wave is maximized. A forming time .tau. of the refractive index grating can thus be obtained. An accurate and rapid measurement can generally be obtained for the forming time of the refractive index grating of the photononlinear medium formed of photorefractive crystal including a cubic system such as BSO.