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     

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     

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.     

Ablation studies using a diode-pumped Nd : YVO4 micro-laser

We report an investigation of ablating several materials using a nanosecond pulse duration Nd:YVO₄ micro-laser operating at wavelengths of 1064 and 532 nm and high pulse-repetition rate (20 kHz). Probe beam deflection, ballistic pendulum measurements and scanning electron microscopy are used to characterise the interaction. It is shown that good-quality micro-scale features can be produced in polyimide, gold foils and silicon targets by ablation using this laser. PACS 42.55.Xi; 52.38.Mf; 87.80.Mj     

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.     

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.     

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     

Size and Interface Control of Novel Nanocrystalline Materials Using Pulsed Laser Deposition

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline materials with an accurate grain size and interface control. Using this method, the grain size in the case of Cu thin films was controlled by introducing a few monolayers of insoluble elements having high surface energy such as W, which increases interfacial energy and provides more nucleation sites. The grain size is determined by the thickness of Cu layer and the substrate temperature at which it transforms into islands (nanocrystalline grains) of fairly uniform size which we desgnate as self-assembling approach. Using this approach, the grain size was reduced from 160nm (Cu or Si (100) substrate) to 70–80nm for a simple W layer (Cu/W/Si (100)) to 4nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness of these films was evaluated using a nanoindentation technique, a significant increase in hardness from 2.0GPa for coarse-grained 180nm to 12.5GPa for 7nm films was observed. However, there is decrease in hardness below 7nm for copper nanocrystals. The increase in hardness with the decrease in grain size can be rationalized by Hall–Petch model. However, the decrease in slope and eventually the decrease in hardness below a certain grain size can be explained by a new model based upon grain-boundary deformation (sliding). We also used a similar materials processing approach to produce quantum dots in semiconductor heterostructures consisting of Ge and ZnO dots or nanocrystals in AlN or Al₂O₃ matrix. The latter composites exhibit novel optoelectronic properties with quantum confinement of phonons, electrons, holes and excitons. Similarly, we incorporated metal nanocrystals in ceramics to produce improved mechanical and optical properties.     

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.     

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.     

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     

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2:N2O. II. Silicon and oxygen bonding states

The early oxidation stages of hydrogen-terminated single-crystalline (100) silicon have been studied by X-ray photoemission spectroscopy, following the evolution of the Si2p and O1s signals after exposure to N₂:N₂O ambient at 850 °C for different durations. Evidence is given that the usual analysis of the film in terms of the Si2p peak leads to inconsistencies, related to the presence in the film of non-siloxanic bridges, as oxygen-rich defects (like hydroxyl terminations or peroxo bridges) or oxygen-deficient defects (like amino bridges). Information on the film structure is obtained by combining the analysis of the Si2p peak with that of the O1s peak. PACS 82.65.+r; 68.35.Fx; 68.35.Dv; 79.60.Jv     

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     

Efficient high-repetition-rate fs-laser based X-ray source

The generation of [_Fe]K line radiation has been studied on a compact, ultrashort, laser based hard X-ray source, particularly suited for high-repetition-rate laser systems (1 to >10 kHz). Sub-millijoule, 25 fs Ti:sapphire laser pulses are applied to generate hard X-ray radiation on a commercially available ferric audio cassette tape target. Spectroscopic investigations reveal strong iron K emission in addition to a weak bremsstrahlung continuum. Under single exposure and single pulse conditions the X-ray yield is low. Energy conversion efficiencies of about _K=2×10^-7 are observed. Prepulse and multiple shot exposure techniques, both successfully used with high energy/low repetition rate systems, are investigated for these low energy/high repetition rate conditions. Depending on the applied pulse energy and intensity, the X-ray yield can be enhanced by more than three orders of magnitude. Photon fluxes exceeding 2×10⁹Kphotons/s are generated with the presented tape target yielding conversion efficiencies of nearly _K=10^-5. PACS 42.65.-k; 52.38.Ph; 52.50.Jm     

The Formation of Porous Membranes by Filtration of Aerosol Nanoparticles

Flame-generated aerosol particles of Al₂O₃ were deposited by gas filtration on two types of porous and ceramic tubes of -Al₂O₃ with mean pore diameters of 450 and 2700nm, respectively. The particles were aggregates with average mobility diameters in the range of 30–100nm and primary particle diameters of 4–8nm. The particles are characterized by differential mobility analysis, transmission electron microscopy, and by their specific surface area. The deposited membranes are characterized by gas permeability measurements, scanning electron microscopy, and by their pore size distribution from nitrogen capillary condensation. The particles form a distinct, homogeneous membrane layer with a porosity of 90% on top of the substrate surface and only penetrate slightly into the substrate structure. The mean pore sizes of the deposited membranes determined by nitrogen condensation agree approximately with those determined by gas permeation and the specific surface area. The mean pore diameter varies in the range of 30–70nm. The gas permeability of the deposited membranes is related to the specific surface area but influenced by the high porosity. The mean pore size and the permeability of the membranes are almost independent of the substrate structure.The development of a membrane with uniform properties is preceded by a short initial period in which the deposited particles, with an equivalent membrane thickness of roughly 2m, have a significantly lower permeability than the ultimately developed uniform membrane layer. This effect is particularly significant for the aerosol particles with the lowest mean size, probably due to particles deposited in the pore mouths of the substrate.The particles and the deposited membranes are X-ray amorphous but retain their specific surface area on heating to even high temperatures. When the membranes are heated to 1473K for 10h, X-ray diffraction shows a mixture of - and -alumina, accompanied by a partial disintegration of the membrane and a considerable loss of surface area.     

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.     

ИЗЛУЧЕНИЕ ЧЕРЕНКОВА ПРОСТРАНСТВЕННОГО З АРЯДА В ВОЛНОВОДАХ И В НЕОГР АНИЧЕННОЙ СРЕДЕ

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Unusual Behavior of Nanocrystalline Strontium Oxide Toward Hydrogen Sulfide

The thermodynamically favored reaction of solid strontium oxide with gaseous hydrogen sulfide is kinetically enhanced to a large degree by the use of higher surface area nanocrystalline SrO in the form of brush-like collections of metal oxide fibers. An unusual feature is that the reaction SrO + H₂S SrS + H₂O proceeds stoichiometrically at room temperature, but at higher temperatures the reaction efficiency goes down, apparently due to rapid temperature induced crystal growth of the nanocrystalline SrO. The samples studied vary in crystallite size from 20 to 27nm, while average particle size (nanocrystal aggregates) varies in the following order; aerogel prepared SrO (100nm) 相似文献   

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     

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