Generalized Transvectants-Rankin–Cohen Brackets

We introduce o(p+1q+1)-invariant bilinear differential operators on the space of tensor densities on Rⁿ generalizing the well-known bilinear sl₂-invariant differential operators in the one-dimensional case, called Transvectants or Rankin–Cohen brackets. We also consider already known linear o(p+1q+1)-invariant differential operators given by powers of the Laplacian.     

Electroless deposition of Ag on Pd-activated TiN/p-Si(100) substrate

Nano-thick Ag films were electrolessly deposited on TiN/p-Si(100) substrates. The substrates were prepared by sputtering TiN on p-Si(100) wafers. An activation process of the substrates was performed by immersing the substrates in a solution of 0.0019 moLL^-1PdCl₂+0.45 moLL^-1HF+8.7 moLL^-1aceticacid+0.036 moLL^-1 HCl so as to obtain the Pd seed layer. The general composition of the electroless Ag bath was 0.0032 moLL^-1AgNO₃+2.24 moLL^-1NH₃+0.56 moLL^-1aceticacid+0.1 moLL^-1 NH₂NH₂ at pH 10.2. The morphologies of the Pd seed layer and the Ag films were characterized by atomic force microscopy (AFM). The effect of the Pd activation on electroless Ag deposition was tested by open circuit potential with time technology (OCP-t). For comparison, the morphology of the films deposited by electrochemical deposition on the substrates was also studied by AFM. PACS 82.45.Mp; 81.15.Pq; 81.10.Dn     

Mode-locking of neodymium lasers by glasses doped with PbS nanocrystals

Nonlinear optical absorption properties of silicate glasses doped by the PbS nanocrystals were investigated by means of the picosecond pump-probe absorption spectroscopy and absorption bleaching technique. The glass samples were used as saturable absorbers for passive mode-locking of Nd:YAG and Nd:glass lasers. Application of the PbS doped glass together with the active mode-locking and laser cavity quality control enabled the stable of generation of 28 ps and 5 ps duration pulses in Nd:YAG and Nd:glass lasers respectively. PACS 42.60.Fc; 42.70.Hj; 78.47.+p     

The Q-switched Nd : YAG and Yb : YAG microchip lasers optimization and comparative analysis

The microchip lasers based on the neodymium or the ytterbium doped yttrium-aluminium garnet crystal and Q-sw itched by the Cr⁴⁺:YAG film are considered. The optimal (maximizing of energy) values of the pumping beam radius, the absorber parameters (the thickness and tetravalent chromium ion concentration), and the output mirror reflectivity are determined. The possibility of higher values of energy in the Yb:YAG laser pulse, in comparison with a more traditional Nd:YAG laser, is also substantiated. PACS 42.60.Gd     

Influence of Hydrothermal Temperature on Structures and Photovoltaic Properties of SnO2 Nanoparticles

Two SnO₂ nanoparticles were synthesized by hydrothermal method at 170°C and 180°C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180°C has more surface electronic states at 0.3eV below the conduction band than the one synthesized at 170°C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO² nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500°C for 2h, the diameter of the nanoparticle synthesized at 180°C increased to 23nm and that of the nanoparticle synthesized at 170°C increased to 32nm as calculated from X-ray diffraction pattern.     

Luminescent CdS Nanoparticles Embedded in Polyethylene Glycol (PEG 300) Matrix Thin Film

A simple method for synthesis of well dispersed cadmium sulphide (CdS) nanoparticles embedded in a polyethylene glycol matrix (PEG 300) in thin film form is presented. The molar ratio of PEG and CdS was varied within the range 70:30 to as high as 50:50. Films with controllable sizes (r 3 –8nm) of nanocrystals could be obtained by adjusting post-deposition annealing temperature (T) and time (t). The obtained films showed systematic variation in optical properties with decreasing crystal size due to quantum confinement. Transmission electron micrographs (TEM) indicated well resolved nanoparticles for films annealed at lower temperature (T = 373K) and time (t < 45 min). Photoluminescence (PL) studies indicated blue shift with decreasing particle size. The films did not degrade with aging in a humid atmosphere (relative humidity 40%) for several weeks.     

Publisher's Note

When the article 'Modification of the finite difference scheme for efficient analysis of thin lossy metal layers in optical devices' by O. Conradi, S. Helfert, and R. Pregla was first published in the Optical Waveguide special issue of Optical and Quantum Electronics (volume 30, nos. 5–6, pages 369–373) the authors' affiliation given was incorrect. The article is printed again in full with the original pagination and credit lines. A misprint in the Results section has been corrected as well: the refractive index of both silver layers is 0.14–j11.0 at a wavelength of = 1523 nm, and not 0.41–j11.0.     

Tailoring of the functional properties of sol–gel films on Pt/TiO2/SiO2/(100)Si substrates: (Pb,La)TiO3/(Pb,Ca)TiO3 multilayer heterostructures

Preferentially oriented sol–gel (Pb,Ca)TiO₃/(Pb,La)TiO₃/(Pb,Ca)TiO₃ and (Pb,La)TiO₃/(Pb,Ca)TiO₃/(Pb,La)TiO₃ multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb,La)TiO₃ (PTL) and (Pb,Ca)TiO₃ (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, 001 and 111, results in significant ferroelectric and pyroelectric properties. P_r=26 Ccm^-2 and =28.5×10^-9 Ccm^-2K^-1, and P_r=17 Ccm^-2 and =22.8×10^-9 Ccm^-2K^-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films. PACS 68.55.Jk; 77.80.-e; 77.84.Dy     

Generation of backscattered 2 ω and 3 ω/2 harmonics of femtosecond radiation from targets with different atomic numbers

Backscattered 2 and 3/2 harmonics were investigated during the interaction of femtosecond radiation (=795 nm, t=150 fs, 10-Hz pulse repetition rate) with various targets. The harmonics were generated without changing the position of the targets from shot to shot. Various characteristics of the harmonics were analyzed and their dependences on pump radiation parameters are discussed. Efficient 2 and 3/2 harmonics were achieved for low-Z targets, whereas only second-harmonic generation was observed for high-Z materials. PACS  42.65.Ky; 52.35.Mw; 52.38.-r     

Resonances in 12C and Their Breakup to the 3α Final State

The breakup of ¹²C states into three -particles is discussed in the context of the continuum three-body problem. New information from the -decay of ¹²N populating 0⁺, 1⁺, and 2⁺ states in ¹²C is presented. The breakup mechanism of the 1⁺ state at 12.71MeV is clarified, the spin of the 10.3MeV state is determined as 0⁺, and evidence for a previously unknown 2⁺ state at 14.1(2)MeV is given.     

Diode-pumped passively Q-switched Nd : YAG laser at 1123 nm

A diode-pumped Nd:YAG laser at 1123 nm is passively Q-switched by using a low doping concentration Cr⁴⁺:YAG crystal as a saturable absorber. When pumped by a 1.5-W laser diode, the laser produces pulses of 50-ns duration with a pulse energy of as much as 15 J and a peak power of 300 W at a pulse-repetition rate of 10 kHz. PACS 42.60.Gd; 42.55.Rz; 42.55.Xi     

Optimizing non-resonant frequency conversion in periodically poled media

Non-resonant frequency conversion into the blue, green, orange, and red spectral regions is reported. Fundamental light sources were continuous-wave non-planar monolithic single-mode ring Nd:YAG lasers as well as a standing-wave multi-mode Nd:YAG laser. Periodically poled KTiOPO₄ was employed as the nonlinear medium, but the considerations could also be applied to other periodically poled materials. A multi-pass scheme resulted in a normalized conversion efficiency as high as 27.2 %W^-1 for frequency doubling in the small-signal regime at 1064 nm. PACS 42.65.Ky; 42.79.Nv; 42.70.Mp     

A sensitive non-destructive method for measuring the Nd doping concentration in Nd : YAG with high spatial resolution

This paper reports on an experimental method for measuring in Nd:YAG the Nd doping concentration (C) with high sensitivity (0.01 at.%Nd) and high spatial resolution (50 m). The method is based on the measurement of the fluorescence lifetime _f of the upper Nd laser level. Additional parameters required to determine C are the intrinsic fluorescence lifetime ₀ and the quenching parameter Q. The measured values of _f, ₀ (256.47±0.14 s) and Q (4.45±0.40×10²⁰ cm^-3) allow us to calculate the Nd concentration C with an absolute accuracy of 0.1 at.%Nd. By using this method C is measured at the outer surfaces of standard laser rods and at the faces of boule slices (with diameters of up to 50 mm). The obtained results demonstrate a detection sensitivity of 0.01 at.%Nd. PACS 42.70.Hj; 81.70.Fy     

Microstructure and Chemical States of Hydroxyapatite/silk Fibroin Nanocomposites Synthesized via A Wet-mechanochemical Route

Hydroxyapaptite (HAp)/silk fibroin (SF) nanocomposites were prepared via a wet-mechanochemical route at room temperature. The results reveal that the inorganic phase in the composites is carbonate-substituted HAp containing 2.9–3.1 wt% of carbonate ions. The primary HAp crystals are rod-like in shape with a typical size of 20–30nm in length and 8–10nm in width, and lattice parameters a = 9.423, c = 6.888. The self-assembled HAp crystals along their c-axes aggregate into bundles, which are connected with SF fibrils. Consequently, a three-dimensional porous network is formed in the composite, which is beneficial to inducing new bone formation in practical implantation.     

Low-resistivity indium tantalum oxide films by magnetron sputtering

Low-resistivity Ta-doped In₂O₃ (InTaO) films from ceramic targets of In₂O₃ doped with 2, 5, and 10 wt% Ta₂O₅ were deposited on Corning glass # 1737 substrates by magnetron sputtering. The electrical and optical properties of these films were studied. The carrier type of InTaO films was found to be n-type. The resistivity, carrier density, and Hall mobility of InTaO films were in the range of 0.28–200.2×10^-4 cm, 0.2–7.4×10²⁰ cm^-3, and 3–31 cm²V^-1s^-1, respectively. A minimum resistivity of 2.8×10^-4 cm with a mobility of 31 cm²V^-1s^-1 and a high transparency of 85% in the visible were achieved for the InTaO thin films doped with 5 wt% Ta₂O₅. PACS 81.15.Cd; 81.40.Rs; 73.90.+f     

Randomizing Quantum States: Constructions and Applications

The construction of a perfectly secure private quantum channel in dimension d is known to require 2logd shared random key bits between the sender and receiver. We show that if only near-perfect security is required, the size of the key can be reduced by a factor of two. More specifically, we show that there exists a set of roughly dlogd unitary operators whose average effect on every input pure state is almost perfectly randomizing, as compared to the d² operators required to randomize perfectly. Aside from the private quantum channel, variations of this construction can be applied to many other tasks in quantum information processing. We show, for instance, that it can be used to construct LOCC data hiding schemes for bits and qubits that are much more efficient than any others known, allowing roughly logd qubits to be hidden in 2logd qubits. The method can also be used to exhibit the existence of quantum states with locked classical correlations, an arbitrarily large amplification of the correlation being accomplished by sending a negligibly small classical key. Our construction also provides the basic building block for a method of remotely preparing arbitrary d-dimensional pure quantum states using approximately logd bits of communication and logd ebits of entanglement.     

Degenerate electrical conductive and excitonic photoluminescence properties of epitaxial films of wide gap p-type layered oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=S or Se)

Electrical and photoluminescence properties were investigated for epitaxial films of layered oxychalcogenides, LnCuOCh (Ln=La, Pr, and Nd, Ch=S or Se). Epitaxial films of Mg 10 at.% doped LaCuOS_1-xSe_x are the first demonstration of degenerate conduction with high hole concentration >10²⁰ cm^-3 in wide gap p-type semiconductors. Ion substitution varied the excitonic emission energy from 3.21 eV to 2.89 eV while lanthanide and chalcogenide ion substitutions displayed the opposite tendency against cell volume. These unique properties are discussed with respect to the electronic structure originating from the layered crystal structure. PACS 72.20.-i; 73.50.-h; 78.55.Hx; 78.66.-w     

Q-switched mode-locking with Cr4+ : YAG in a diode pumped Nd : GdVO4 laser

We have demonstrated passively Q-switched mode-locking in a laser-diode-pumped Nd:GdVO₄ laser with an intracavity Cr⁴⁺:YAG saturable absorber. At a pump power of 19.4 W, the Q-switched mode-locked laser produced an average output power of 3.22 W, and the repetition rates of the Q-switched envelope and the mode-locked laser pulse were 227 kHz and 144 MHz, respectively. The duration of the mode-locked pulse was within the sub-nanosecond range. PACS 42.55.Xi; 42.60.Fc; 42.60.Gd; 42.55.Rz     

Q-switching of a diode cladding-pumped Erbium Fibrelaser at 2.7 μm

Reliable Q-switched operation of a cladding-pumped 2.7m ZBLAN fibre laser in the range of the power limit of self-destruction is shown for the first time. The laser is pumped by a multimode diode. Q-switching is achieved by two different techniques: a rotating mirror and an acousto-optical modulator. Pulse widths of 500ns with the rotating mirror and 300ns (FWHM) with the acousto-optical modulator and pulse energies in the J range are achieved.     

Heteroepitaxial growth of wide gap p-type semiconductors: LnCuOCh (Lr=La, Pr and Nd; Ch=S or Se) by reactive solid-phase epitaxy

Heteroepitaxial thin films of Cu-based oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=mixture of S and Se), were fabricated and their resulting film structures were characterized. A reactive solid-phase epitaxy method successfully yielded heteroepitaxial films on MgO(001) substrates. A high-resolution electron microscopic examination of a LaCuOS film revealed a sharp film-substrate interface. Four-axes high-resolution X-ray diffraction measurements revealed that crystalline lattices in the films are fully relaxed and that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO. Furthermore, systematic variations in the lattice constant by lanthanide or chalcogen ion substitutions were observed. PACS 81.10.Jt; 81.15.-z; 81.15.Np; 68.55.-a; 81.20.-n