Deuteration Level Research Articles

Ionic rearrangements and domain growth near antiferroelectric transitions: EPR study of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4

Using electron paramagnetic resonance spectroscopy we have measured the temperature dependence of ionic rearrangements and domain nucleation around the antiferroelectric transition temperature Tc of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4. CrO43− radicals, produced by γ-irradiation of K2CrO4-doped samples, were used as microscopic probes because their charge, size, and symmetry match those of the host anions. The use of high deuteration level and "monodomain" samples prepared by temperature cycling was found to be crucial in the signal assignment and line-shape analysis. The results show that as a sample approaches Tc from T > Tc, the hydrogen-bonded protons slow down anomalously, much more slowly than expected for Arrhenius behaviour. Simultaneously, the lattices develop "clusters" of antiferroelectrically ordered molecules. These clusters eventually [Formula: see text] expand to occupy the whole lattice and thus complete the lattice ordering. The probe selection and sample preparation methodology discussed and the microscopic details of the ionic rearrangements reported appear to be highly significant for further studies of these phase transitions.

High-Efficiency Frequency Doubling of Nd:YAG

The second harmonic of the Nd:YAG output wavelength (1,064 nm) can be produced with both CD*A and KD*P with efficiencies approaching 50% when the crystal indices of refraction are equal at the fundamental and second-harmonic frequencies - the so-called "phase-matching" condition. For Type I doubling processes, this condition can be satisfied by allowing the ordinary index of refraction at the fundamental wavelength to be equal to the extraordinary index at the doubled frequency. For Type II doubling, the necessary condition is that the extraordinary index at the second harmonic be the average of the extraordinary and ordinary indices at the fundamental. For CD*A, phase matching can be accomplished via the Type I process with 0m=90° by elevating the crystal temperature to ~100 deg C, depending on the deuteration level of a specific crystal. For a 21-mm-long CD*A crystal, the width of the temperature versus efficiency curve is 3.25 C FWHM. Ninety-degree phase matching allows efficient doubling with incident beam divergences an order of magnitude greater than diffraction limited and does not introduce walkoff resulting from double refraction. Data are presented showing doubling efficiency as a function of crystal length and incident average power density, including considerations of efficiency and average power saturation. Type II KD*P phase matches at room temperature with 0m=53°36'. To obtain efficient doubling in this case, the incident fundamental beam divergence must be close to diffraction-limited. The angular halfwidth of a 25-mm crystal is 1 mr FWHM for rotation about the ordinary axis. Compared to CD*A, the use of KD*P is advantageous because of its ready availability, high damage thresh-old, high saturation levels and usefulness at room temperature. Using a 3.0-J pulsed Nd:YAG laser with a repetition rate of 10 pps, 10.5 W of 532-nm power has been achieved.

Effect of deuteration on the ferroelectric transition temperature and the distribution coefficient of deuterium in K(H1−xDx)2PO4

The variation in the ferroelectric transition temperature with deuteration is described by a linear function only if the deuteration level in the crystal is considered. A least-squares fit of these data resulted in the relation Tc=121.7K + 1.07m, with m in mole% D. The effective distribution coefficient (keff) of deuterium in the system KH2PO4–KD2PO4–D2O was found to vary from 0.75 to 0.99 over the range of 25–99.8 mole% D.