A detailed model of the diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on Kogelnik's theory of coupled waves is presented. The model describes transmitting gratings with arbitrary orientation in a plane-parallel plate taking into ac- count spectral width and angular divergence of laser beams along with material dispersion of a photosensitive medium. The model results are compared with experimental data for high-efficiency Bragg gratings in a photothermorefractive PTR glass. © 2006 Society of Photo-Optical Instrumenta- why our modeling is illustrated for those variations of grat- ing parameters that are typical for PTR VBGs: the refrac- tive index is in the range of 1.5 at wavelengths ranging from 0.4 to 2.7 m, refractive index modulation is up to 1000 ppm 10 3 , and grating thickness is from 0.2 to 20 mm. The goal of this work is to reduce Kogelnik's theory to practical formulas that enable practical modeling and de- sign of diffractive optical elements based on VBGs. This part of modeling considers diffraction of plane monochro- matic, divergent, and polychromatic laser beams on uni- form sinusoidal lossless transmitting volume gratings and compares the model with experimental results in PTR Bragg gratings. Further parts will describe modeling of re- flecting volume gratings holographic mirrors as well as the application of both transmitting and reflecting grating for spectral beam combining for different types of lasers.

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Modeling of phase volume diffractive gratings, part 1: transmitting sinusoidal uniform gratings

In this letter we demonstrate continuous-wave blue and green diffuse laser light generation from a Nd3+-doped Sr0.6Ba0.4(NbO3)2 crystal located in an end-pumped laser cavity and operating at the 4F3/2→4I11/2 laser channel. The diffuse nature of the visible radiation is attributed to numerous ferroelectric cylindrical domains, which appear in the as-grown crystal. Green radiation is obtained by self-frequency doubling of the infrared radiation, whereas tunable blue radiation is generated by self-frequency sum mixing of infrared and pump radiations. The variety of visible colors is due to the spread in the domain sizes. Finally, we report on the spectral and spatial distribution of this visible radiation.

Diffuse multiself-frequency conversion processes in the blue and green by quasicylindrical ferroelectric domains in Nd3+:Sr0.6Ba0.4(NbO3)2 laser crystal

A simple method to trap and manipulate metallic micro/nano-particles on the surface of photorefractive crystals is proposed. After inducing inhomogeneous charge density and space-charge fields in photorefractive crystals by non-uniform illumination, both uncharged and charged metallic particles can be trapped on the illuminated surface due to dielectrophoretic force and electrophoretic force, respectively. A transition from dielectrophoresis to electrophoresis is observed when manipulating nano-silver particles with high surface space-charge field. Our results show that this method is simple and effective to form surface microstructures of metallic particles.

Optical trapping and manipulation of metallic micro/nanoparticles via photorefractive crystals

Continuous-wave red, green, and blue coherent light has been simultaneously generated by quasiphase matching in a strontium barium niobate crystal used as an intracavity frequency converter of a Nd:YVO4 laser operating at 1.34 μm. The broad distribution of ferroelectric domain sizes (1–8 μm) provides the possibility of different simultaneous frequency conversion processes without requiring angle or temperature tuning. Blue and red colors were generated by second-harmonic generation of pump (0.88 μm) and infrared (1.34 μm) laser radiation, respectively. Green light was produced by sum frequency mixing of pump and laser radiations.

Simultaneous generation of coherent light in the three fundamental colors by quasicylindrical ferroelectric domains in Sr0.6Ba0.4(NbO3)2

A first spectroscopic characterization of Yb3+ ions in Sr0.6Ba0.4(NbO3)2 nonlinear crystal is presented. From low temperature emission and absorption spectra the energy level diagram of Yb3+ ions in this crystal has been built up. The ground state splitting has been found to be as high as 940 cm−1 allowing for potential quasi-four-level laser operation. In order to assess the ability of this system as a tunable solid state laser the main parameters of relevance in laser dynamics have been obtained and compared to those reported for other Yb3+ doped lasers. Optical microscopy has been used to study the ferroelectric domains appearing in the as-grown crystals. A relatively broad distribution of domain sizes (around 3 μm) will, in principle, allow for broadband noncritical second-harmonic generation of fundamental radiation by quasiphase matching. The obtained results make this crystal a promising candidate for tunable laser generation in the visible domain.

Evaluation of ytterbium doped strontium barium niobate as a potential tunable laser crystal in the visible

We investigate the diffraction properties of vector synthetic gratings, which consist of two volume index gratings with different grating wave vectors, using coupled-wave analysis. These index gratings can be obtained in photorefractive materials or in Bragg cells with two driving acoustic waves. We consider the case of pseudo phase matching in which a Bragg mismatch exists in the scattering from the individual index gratings while a Bragg condition is satisfied for the scattering from the vector sum of the two index gratings. Analytic expressions for the diffraction efficiency as well as the amplitude of the three waves involved are obtained. The results are presented and discussed.

Diffraction properties of vector synthetic volume index gratings

We propose and demonstrate a novel method for recording second-harmonic volume index gratings in photorefractive crystals. The fundamental component of the index grating is eliminated by means of a ?-phase shifted double-exposure process that uses the Mach–Zehnder interferometric technique. Experimental results for K0.5Na0.50.2Sr0.75Ba0.250.9Nb2O6 crystals are presented and discussed.

Recording of second-harmonic index gratings in photorefractive (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals.

Electrical domain fixing in Cu- and Mn-doped (K05Na05)02(Sr075Ba025)09Nb2O6 (KNSBN) crystals is presented The relation between the applied field and the revealed grating in single and multidomain crystals is investigated In multidomain Mn-doped KNSBN, a revealing efficiency of over 233% is obtained The mechanism of domain fixing in single and multidomain crystal is discussed

Electrical domain fixing of photorefractive index gratings in (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystals

In this article, we studied the photorefractive properties of Cu-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals with different doping levels. The properties include two-wave mixing and self-pumped phase conjugation, absorption properties, and the growth conditions as well. We also studied the effect of the dimensions on the photorefractive properties. The mechanism of Cu-doped KNSBN and the influence of the different sites occupied by Cu+ on photorefractive properties are also discussed. All the experimental results showed that doping levels have much effect on the photorefractive properties. The crystal with a higher doping level has a higher effective charge carrier density, a larger coupling coefficient, and a faster response rate, which is suitable for fast optical information processing. Dimension has much influence on the photorefractive properties. The thinner crystal with the same doping level has a larger coupling gain coefficient, and a shorter response time.

Photorefractive properties of cu-doped (k0.5na0.5)0.2(sr0.75ba0.25)0.9nb2o6 crystals with different doping levels and different dimensions

We report the photorefractive properties of a new kind of Cu-doped KNSBN crystal in which a small fraction of oxygen (O) atoms are replaced with fluorine (F) atoms. The replacement of oxygen with fluorine in Cu:KNSBN crystals leads to a much shorter response time of 30 ms at an incident intensity of 5 W/cm2. We also discuss the effect of electron–hole competition on the coupling constant.

Jianhua Zhao

Papers

Diffraction properties of vector synthetic volume index gratings

Recording of second-harmonic index gratings in photorefractive (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals.

Electrical domain fixing of photorefractive index gratings in (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystals

Photorefractive properties of cu-doped (k0.5na0.5)0.2(sr0.75ba0.25)0.9nb2o6 crystals with different doping levels and different dimensions

Photorefractive properties of Cu-doped KNSBN crystal with fluorine replacing oxygen.