We demonstrate a low-voltage and fast laser Q-switching by using an electro-optic periodically poled lithium niobate (EO PPLN) crystal. The half-wave voltage measured from the EO PPLN crystal was 0.36 V x d (microm)/L (cm), where d is the electrode separation and L is the electrode length. When a 13-mm-long EO PPLN was used as a laser Q switch at 7-kHz switching rate, we measured an approximately 12-ns pulse width and approximately 0.74-kW laser pulses at 1064-nm wavelength from a diode-pumped Nd:YVO4 laser with continuous 1.2-W pump power at 809-nm wavelength.

The effect of metal alloying on mechanical properties including hardness and fracture toughness were investigated in three alloys, Ti~0 .33 Al 0.50 (Me)~0 .17 N (Me = Cr, Nb and V), and compared to Ti 0.50 Al 0.50 N, in the as-deposited state and after annealing. All studied alloys display similar as-deposited hardness while the hardness evolution during annealing is found to be connected to phase transformations, related to the alloy's thermal stability. The most

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This paper presents an integration of molecular simulation with computational mass transfer to predict the photocurrent-voltage ͑I-V͒ performance of photoelectrochemical solar cells. It aims at developing a general simulator for ionic-liquid-type photoelectrochemical cells, excluding the prediction of the incident photon-to-current efficiency and the injection efficiency parts. The charge transport in the electrolyte, typically iodide/tri-iodide ionic liquid, is mainly in the molecular diffusion mechanism, which partly limits the solar cell performance. The molecular dynamics technique is employed to assess the ionic conductivity and diffusion coefficient of the charge transfer. The ionic conductivity is compared with a published experimental result carried out by an impedance test. The corresponding diffusion coefficient is then inputted to a computational mass transfer code, and the depletion of redox charges at the electrode can be calculated. The electrochemical performance of the solar cell is predicted and shown in reasonable agreement with experimental I-V results.Photoelectrochemical cells, especially dye-sensitized solar cells ͑DSSCs͒, are potentially the future of photovoltaic cells because of their prevailingly lower cost than all the other types of solar cells. 1 Although the current efficiency is only acceptable ͑2-11%͒, 2-5 DSSCs are thin, light, flexible, and mainly abundant from a raw material aspect. The basic configuration of a DSSC consists of an electrode ͑anode͒ and an opposite counter electrode ͑cathode͒ with an electrolyte between them, as shown in Fig. 1. The electrode is a glass substrate made of transparent conducting oxide, which is coated by a 10-20 m film of nanocrystalline TiO 2 particles ͑10-30 nm diameters͒ that is covered by a monolayer of dye molecules. Pores of the nanocrystalline TiO 2 film are filled with an ionic liquid containing a redox couple ͑e.g., I − /I 3 − ͒ in a nonaqueous solution, such as liquid ammoniates. The counter electrode is placed in the opposite side, and the whole cell has to be well sealed. Under the photoexcitation condition, the dyes absorb photons and inject electrons into the TiO 2 conduction band. The electrons travel through the nanocrystalline TiO 2 film and are collected at the anode. After passing through the external circuit and delivering power to the external load, the electrons re-enter the cell at the cathode. The tri-iodide ions nearby are reduced to iodide ions, which then diffuse to the porous TiO 2 film via the electrolyte, to reduce the photooxidized dyes back to the original state. The best reported efficiency of this kind of solar cells in research laboratories is about 10.6%, stated by Grätzel. 6 This still needs more verification and further improvement for commercialization. This paper starts by studying the fundamental nanoscopic transport phenomena in the ionic liquid electrolyte between the anode and the cathode. This is because the slowest mechanism and the major potential loss of this kind of photoelectrochemical solar cells m...

We report the first demonstration to our knowledge of 220-ps visible laser generation from passively Q-switched-laser pumped periodically poled lithium niobate (PPLN) in a single-pass, cascaded frequency-conversion process. The monolithic PPLN consists of a 1-cm section for frequency doubling the 1064-nm Nd:YAG pump laser to a 532-nm laser and a subsequent 4-cm section for generating the visible laser in a 532-nm-pumped optical parametric generation (OPG) process. In generating the 622.3-nm OPG signal wavelength we measured a 3.0-microJ/pulse pump threshold at the 1064-nm wavelength, 16% overall efficiency, and 35% slope efficiency at two times threshold. At 10(-6) pump duty cycle and 20-mW average power in the visible, photorefractive damage was not observed at the phase-matching temperature of 40.3 degrees C.

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The phase evolution of cubic (c), solid solution TixCr~0.37Al1-0.37-xN alloys with x=0.03 and 0.16, and the kinetics of the hexagonal (h)-AlN formation are studied via in situ wide angle xray scattering experiments during high temperature (1000-1150 °C) annealing. Spinodal decomposition was observed in Ti0.16Cr0.36Al0.48N while Ti0.03Cr0.38Al0.59N decomposes through nucleation and growth of h-AlN, c-TiN and c-CrAlN. h-AlN is formed from c-CrAlN domains in both cases and the formation rate of h-AlN depends on the stability of the c-CrAlN domains. In Ti0.16Cr0.36Al0.48N, the c-CrAlN domains are stabilized by crystallographic coherency with the surrounding c-TiCrN in a microstructure originating from spinodal decomposition. This results in lower formation rates of h-AlN for this composition. These differences are reflected in higher activation energy for h-AlN formation in Ti0.16Cr0.36Al0.48N compared to Ti0.03Cr0.38Al0.59N. It also points out different stabilities of the intermediate phase c-CrAlN during phase decomposition of TiCrAlN alloys. Additional contributions to the low activation energy for formation of h-AlN in Ti0.03Cr0.38Al0.59N stems from precipitation at grain boundaries.

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