The Nonlinear Properties Of Cr: KNSBN Crystal And Its Applications In Image Processing

In this experiment, the nonlinear properties and the image storage property of the volume grating written by two-wave coupling of He-Ne 632.8nm laser beam in a Cr:KNSBN crystal were studied. Based on the nonlinear properties of the crystal, optical image edge enhancement was achieved in two-wave coupling coherent system. When the incident beams were both extraordinarily polarized, some specific parameters were determined, including the gain coefficient, the diffraction efficiency of the volume grating and the response time with respect to the parameters of the writing beams, such as the signal-to-pump beam intensity ratio, the total incident intensity, the angle between two writing beams; and the nonlinear property that diffraction efficiency exhibited a loop with the variation of the fringe modulation. The experimental data showed that the effective gain and the diffraction efficiency would not change with the total incident intensity; the response time was in inverse proportion to the signal-to-pump beam intensity ratio and the total incident intensity; the diffraction efficiency was above 20% when the incident angle was from 10o to 25o; and the response time was 5.3s when the experimental parameters were selected as follows: the incident angle between the signal beam and the pump beam was 12o, the total incident intensity was 40mW/cm2, and the incident beam intensity ratio was 0.33. Then with different incident parameters under the non-simultaneous readout condition, the transmitted intensity of the signal beam and the pump beam was measured as a function of the time during the two-wave coupling process. Also, the transmitted intensity of the pump beam with the signal beam shutting was measured, which was shown that the beam fanning effect in the Cr:KNSBN crystal that was used in our experiment was inconspicuous by calculating the equivalent intensity of the fanning beam. The result was proved in the image storage experiment. At last, based on the nonlinear diffraction property of the crystal, optical image edge enhancement operation was achieved. The degree of the optical image edge enhancement depended on the signal-to-pump beam intensity ratio. When the signal-to-pump beam intensity ratio was more than 1/10, the edge enhancement image was clear, and the signal to-noise ratio was high. The experimental results will give important data for the applications of the Cr:KNSBN crystal in the fields of optical information processing.