Experimental research on modulation degree of refractive index in the SCLP/E_7/C_(60) polymer using a fiber Fabry-Perot Interferometer

Modulation degree of refractive index is an important parameter for information storage in photorefractive materials. Using the relationship between the refractive index and the wavelengths of laser and the order of interference, we introduce a new method to measure the modulation degree of refractive index in photorefractive materials through detecting the shift of the interference fringe in a fiber Fabry-Perot interferometer with a CCD. The measurement precision is also analyzed. With this method, the modulation degree of refractive index in our prepared SCLP/E7/C 60 photorefractive polymer is measured for different external voltages and the external voltage corresponding to the maximal modulation degree of refractive index is reported. The dynamic change of refractive index in the SCLP/E7/C 60 is also studied, which will be helpful to understand the reaction mechanism of photochemistry in the material.

Study of the near-field modulation property of microwaviness on a KH_2PO_4 crystal surface

The KH2PO4 crystal is a key component in optical systems of inertial confinement fusion （ICF）. The microwaviness on a KH2PO4 crystal surface is strongly related to its damage threshold which is a key parameter for application. To study the laser induced damage mechanism caused by microwaviness, in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method. Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal; in a common range of microwaviness amplitude, the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm; 1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal; the light intensity modulation is just around the microwaviness in the form of an evanescent wave, not inside the crystal when the microwaviness period is below 0.712μm; light intensity modulation degree has two extreme points in microwaviness periods of 1.064μm and 1.6μm, remains unchanged between periods of 3μm and 150μm, and descends above the period of 150μm to 920μm.

Study on incident laser modulation using surface micro-defects on KH_2PO_4 crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.

The influence of smoothing by spectral dispersion on the beam characteristics in the near field

The influences of SSD on the beam characteristics in the near held are investigated. Results snow that it the SSD parameters are increased, the laser intensity modulation increases while fluence modulation decreases, which is attributed to the temporal and spatial variation of the SSD pulse phase. The variations of intensity and fluence modulations with the SSD parameters are given. The simulation results are presented along with a method for choosing appropriate SSD parameters according to the variations and the requirements of applications.