Synchronization of chaos generated in two Nd:YVO(4) microchip lasers is experimentally demonstrated with master-slave coupling schemes. For synchronization of chaos, precise locking of the sustained relaxation-oscillation frequency is required, as is optical frequency locking. One needs to match both the pump-modulation parameters for chaos generation and the laser parameters of the two lasers to generate perfectly synchronized chaotic spectra in the master-slave type I coupling scheme.

We experimentally demonstrate a chaotic on-off keying method for secure communications by using chaos synchronization in two microchip lasers. The output of the microchip laser in the transmitter is externally modulated with an acousto-optic modulator at ~4 MHz . One encodes a digital message in the chaotic carrier by turning the modulation on and off at 100 kHz. Because the accuracy of synchronization for the slave laser in the receiver tends to be degraded in the presence of external modulation in the injection laser signal, one can distinguish two binary states. The digital message can be recovered as an envelope of the chaotic oscillation when the difference between the two laser outputs of the transmitter and the receiver is calculated.

The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-inch diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4-and 6-inch, c-axis single-crystal sapphires from full-diameter seeds.

Synchronization of chaotic oscillations generated in two Nd:YVO(4) microchip lasers is experimentally and numerically demonstrated with master-slave coupling schemes. The synchronization performance under some parameter mismatch between the two lasers is quantitatively characterized. Synchronization is always achieved when the lasing frequency of the slave laser is matched to that of the master laser through injection locking. Accurate synchronization of chaos at an average intensity error of less than 2% is attained and maintained for tens of hours. The modulation parameters of the two lasers do not need to be matched for synchronization when the injection power is at a sufficiently high level, because chaos synchronization is based on its injection-locking performance. For accurate synchronization in multimode lasers, the power distribution among longitudinal modes needs to be matched.

A new technique is proposed in the traditional vertical Bridgman growth of sapphire crystals, in which thin-neck formation follows the initial seeding. Low-angle grain boundaries generated at the periphery of the seeding interface were eliminated at the thin neck, and c-axis sapphire crystals with main bodies free from low-angle grain boundaries were grown.

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Morphologies of metallic inclusions observed in sapphire crystals grown by the vertical Bridgman (VB) technique using a tungsten (W) crucible were investigated. Square-or hexagonal-shaped inclusions 2 -5 m in size were observed in sapphire crystals around the interface between the seed and the grown crystal. It was found that such inclusions consisted of W metal used for the crucible. The morphology of some of the inclusions reflects a rhombic dodecahedron which is based on the cubic structure of W and is surrounded by {110} faces. It is probable that inclusions form in the sapphire melt during the crystal growth process, and then sink in the melt to the growth interface due to the high density of W.

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