Saturation Energy Density Research Articles

Resolving nanograin morphology and sub-grain nanodomains via scanning probe acoustic microscopy in high energy density BaTiO3 ferroelectric films

Energy storage property of a dielectric is closely tied with its nanostructure. In this study, we aim to achieve a deep understanding of this relationship in high energy density ferroelectric ceramic films, by probing into the nanograin and sub-grain nanostructures in polycrystalline BaTiO3 films integrated on Si. Through scanning probe acoustic microscopy analyses, it is revealed that the BaTiO3 films directly grown on Pt/Ti/Si mostly consist of large discontinuous columnar nanograins, while those grown on LaNiO3-buffered Pt/Ti/Si substrates have a dominant microstructure of continuous columnar nanograins. Furthermore, ultrafine ferroelastic domains of ∼ 10 nm wide are revealed inside the grains of the buffered BaTiO3 films, while those unbuffered films show about ∼50% increase in the domain width. The dielectric properties of the BaTiO3 films are well correlated with their characteristic nanostructures. Under an increasing electric field, the LaNiO3-buffered films display a slower decline in its dielectric constant and a later saturation of its electric polarization, leading to an improved energy storage performance. Device-level charge-discharge tests have verified not only the delayed polarization saturation and high energy density of the LaNiO3-buffered BaTiO3 film capacitors, but also a high power density in the same order as those of the ferroelectric ceramics.

Galactic Dynamos

Spiral galaxies, including the Milky Way, have large-scale magnetic fields with significant energy densities. The dominant theory attributes these magnetic fields to a large-scale dynamo. We review the current status of dynamo theory and discuss various numerical simulations designed either to explain particular aspects of the problem or to reproduce galactic magnetic fields globally. Our main conclusions can be summarized as follows: ▪Idealized direct numerical simulations produce mean magnetic fields, whose saturation energy density tends to decline with increasing magnetic Reynolds number. This is still an unsolved problem.▪Large-scale galactic magnetic fields of microgauss strengths can probably be explained only if helical magnetic fields of small or moderate length scales can be rapidly ejected or destroyed.▪Small-scale dynamos are important throughout a galaxy's life and probably provide strong seed fields at early stages.▪The circumgalactic medium (CGM) may play an important role in driving dynamo action at small and large length scales. These interactions between the galactic disk and the CGM may provide important insights into our understanding of galactic dynamos. We expect future research in galactic dynamos to focus on the cosmological history of galaxies and the interaction with the CGM as means of replacing the idealized boundary conditions used in earlier work.

Short-pulse KrF amplifier using spatially tunable x-ray preionization.

The small saturation energy density of excimers requires amplifiers of large cross sections for amplification of short pulses of already medium power. Homogeneous excitation of large volumes of fluorine-based gas mixtures by discharge pumping is a critical interplay of the properties of both pumping and preionization, generally necessitating an intense spatially and temporally controlled x-ray preionization. In the present realization, the stringent intensity requirements of preionization are fulfilled by reducing the pulse duration of the x-ray flash to ∼16 ns and by positioning the x-ray source in the near vicinity of the active volume. It is proven both theoretically and experimentally that by proper choice of the positions of two cylindrical x-ray guns, the spatial distribution of preionization can be tuned to (and around) the optimum distribution. In this way, the spatial distribution of the discharge can also be controlled, giving a practical method to compensate for eventual inhomogenities of the E-field of excitation and to tune the discharge to the desired geometry. In this paper, design considerations and experimental realization of a KrF excimer amplifier of ∼5 × 4 cm2 cross section and a spatially tunable x-ray preionization are presented.

Effect of Ag nanoparticles on the amplifying parameters of a dye laser amplifier

The paper presents the experimental results on the influence of Ag nanoparticles on the small-signal gain and saturation energy density of an oscillator-amplifier dye laser transversely pumped by a second harmonic Nd: YAG laser. Our measurements indicated that the measured g0 and Es parameters depend on concentration of Ag in Rhodamine 6 G solution. We have observed that the valves of amplifying parameters (g0, Es) can be controlled by adding various amounts of silver nanoparticles to the solution of Rhodamine 6 G dye in a dye laser.

Brightness Temperature of Radio Zebras and Wave Energy Densities in Their Sources

We estimated the brightness temperature of radio zebras (zebra pattern -- ZP), considering that ZPs are generated in loops having an exponential density profile in their cross-section. We took into account that when in plasma there is a source emitting in all directions, then in the escape process from the plasma the emission obtains a directional character nearly perpendicular to the constant-density profile. Owing to the high directivity of the plasma emission the region from which the emission escapes can be very small. We estimated the brightness temperature of three observed ZPs for two values of the density scale height (1 and 0.21 Mm) and two values of the loop width (1 and 2 arcsec). In all cases high brightness temperatures were obtained. For the higher value of the density scale height, the brightness temperature was estimated as 1.1 $\times$ 10$^{15}$ - 1.3 $\times$ 10$^{17}$ K, and for the lower value as 4.7 $\times$ 10$^{13}$ - 5.6 $\times$ 10$^{15}$ K. We also computed the saturation energy density of the upper-hybrid waves (which according to the double plasma resonance model are generated in the zebra source) using a 3D particle-in-cell model with the loss-cone type of distribution of hot electrons. We found that this saturated energy is proportional to the ratio of hot electron and background plasma densities. Thus, comparing the growth rate and collisional damping of the upper-hybrid waves, we estimated minimal densities of hot electrons as well as the minimal value of the saturation energy density of the upper-hybrid waves. Finally, we compared the computed energy density of the upper-hybrid waves with the energy density of the electromagnetic waves in the zebra source and thus estimated the efficiency of the wave transformation.

Poly methyl methacrylate films containing metallophthalocyanines in the presence of CdTe quantum dots: Non-linear optical behaviour and triplet state lifetimes

Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in poly (methyl methacrylate) polymer in the absence and presence of quantum dots (QDs) in an effort to create the most optimal optical limiting material. The QDs employed were CdTe–TGA (TGA=thioglylcolic acid). Triplet lifetimes generally increased as the value of the ratio of absorption cross sections of the excited state to that of the ground state (k) decreased on addition of CdTe–TGA to the phthalocyanines. The saturation energy density (Fsat) values were generally smaller in the films when compared to the solutions. Fsat, Ilim, Im[χ(3)]/α and γ all gave values which were of optimal range (i.e. the Im[χ(3)]/α and γ values were high enough to ensure adequate optical limiting but not too high to make the compounds behave like optical filters. Also, the Fsat and Ilim values were small enough to mean that the optical limiting process started at an intensity which was not too high) for complex 10 containing Zn central metal and tetrasubstituted with amino groups.

Optical limiting properties of trimeric metallo-phthalocyanines/polymer composite films

The nonlinear absorption and optical limiting properties of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M=Zn for compound ZnPc and Cu for compound CuPc) doped polyvinyl chloride (PVC) thin film in the nanosecond regime were investigated by using the open-aperture Z-scan technique. The measurements were performed using 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective nonlinear absorption coefficient β eff , the linear absorption coefficient α 0 and the saturation density or energy density F sat values were determined. The results show that MPc/PVC composite displays much larger nonlinear absorption coefficient and lower saturable fluence for optical limiting when compared to the same Pc molecules in solution. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.

The effect of higher partial waves ( [formula omitted]) on the nuclear matter binding energy and saturation density

The available phenomenological nucleon–nucleon ( NN) potentials usually fit the experimental phase shifts up to a maximum partial wave (energy). In this work we intend to use the lowest order constrained variational (LOCV) method to calculate the binding energy and the saturation density of nuclear matter (NM) up to the different maximum partial waves ( J max ), and investigate their effects on the saturation properties of NM. The NN potentials such as the Reid86, the Δ – Reid 68 , the Reid93 and the Av 18 interactions are used to calculate the saturation energy–density curve of NM with different J max . It is shown that the higher partial waves have sizable effect on the properties of NM, and it is not possible to ignore them simply. Finally, the contribution of various channel energies in terms of J max are presented and discussed, and once again concluded that the inclusion of channel dependence of correlation functions are more important than to parameterize them to reduce the amount of computational procedure or to take into account the many-body cluster terms.

Synthesis, Characterization, Electrochemical, and Optic Limiting Properties of Novel CoII, CuII, and Double‐Decker LuIII Phthalocyanines

AbstractThe synthesis, spectroscopic, electrochemical, and optical properties of tetrasubstituted CoII, CuII, and double‐decker LuIII phthalocyanines are reported. The new compounds were characterized by elemental analysis, IR and UV/Vis spectroscopy, and MALDI TOF mass spectrometry. Their electrochemistry was studied by cyclic voltammetry and Osteryoung square‐wave voltammetry in nonaqueous medium. Nonlinear absorption and optical limiting performance of peripheral‐substituted (C30H28N30)4Co (5), (C30H28N30)4Cu (6), and [(C30H28N30)4]2Lu (7) were investigated by the Z‐scan technique. Whereas 6 and 7 showed good nonlinear absorption, 5 did not. Optical limiting parameters of the ratio of the excited state to the ground state absorption cross sections κ, the effective nonlinear absorption coefficient βeff, the linear absorption coefficient α0, limiting threshold Fth, and the saturation density or energy density Fsat values were determined for 6 and 7. The results indicated that both compounds exhibited good optical limiting performances. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Nitrogen lasers: Optical devices of variable gain coefficient

A N 2-laser system, consists of an oscillator and an amplifier of different electrode lengths, ranged from 5 to 31 cm, operating under the optimized gas pressures conditions and 14 kV input voltage, was used to measure small signal gain, g 0, and saturation energy density, E s. It was found that g 0-parameter follows a profile of the type m + n/ l AMP, where l AMP is the effective electrode length of the laser amplifier, and ( m, n) are some constants. So, by reducing the active length a gain value as high as ∼1.2 cm −1 for l AMP = 5 cm was obtained. The proposed function, with a rather good approximation, can be used to explain almost all the reported g 0-values of laser systems with moderate current densities. For explaining more details of the reported gain coefficients, the g 0 l AMP-parameter was introduced, where it was realized that with a good approximation a Gaussian profile is a suitable function for explaining the reported g 0 l AMP-products. Furthermore, we found that at a constant input voltage the saturation energy density and output energy density, E out, regardless of the type of N 2-lasers and their operational conditions, are linearly correlated. Based on this observation, and by operating the system at different input voltages, the functional dependence of the measured E s/ E out-values with respect to the operational voltages is introduced. Details of our present observations, along with the previously reported g 0, and E s-measurements are presented graphically, or tabulated. The results are giving some interesting features of TE/TEA N 2-lasers for lasers g 0 , E s predictions which are valuable for laser designs and also for further theoretical investigations.

Trimeric metallo-phthalocyanines with good performances for nanosecond optical limiting in solution

Optical limiting (OL) performances of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M = Zn for compound ZnPc and Cu for compound CuPc) were investigated by using the Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective non-linear absorption coefficient β eff, the linear absorption coefficient α 0, limiting threshold F th and the saturation density or energy density F sat values were determined for the investigated compounds. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.

Optical limiting properties of axially substituted indium phthalocyanines in the solid PMMA composite films

The protection of sensitive optical equipment has been the focus of much attention in recent times. Of great important is the protection of the human eye from potentially harmful intense beams. The optical limiting properties of axially substituted indium phthalocyanines in solutions and in the solid poly(methylmethacrylate) (PMMA) composite films were investigated for these purposes. Embedding the phthalocyanine as inclusion in PMMA host significantly improved the linear absorption coefficient and effective third order susceptibility and considerably reduced the saturation energy density of parent compound at 532 nm as a result of the higher concentration of absorbing molecules in the PMMA than in solution.

GARPUN-MTW: A hybrid Ti:Sapphire/KrF laser facility for simultaneous amplification of subpicosecond/nanosecond pulses relevant to fast-ignition ICF concept

The first stage of the petawatt excimer laser project started at the P.N. Lebedev Physical Institute, implements a development of multiterawatt hybrid GARPUN-MTW laser facility for generation of ultra-high intensity subpicosecond ultraviolet (UV) laser pulses. Under this project, a multi-stage e-beam-pumped 100-J, 100-ns GARPUN KrF laser was upgraded with a femtosecond Ti:Sapphire front-end, to produce combined subpicosecond/nanosecond laser pulses with variable time delay. Attractive possibility to amplify simultaneously short and long pulses in the same large-scale KrF amplifiers is analyzed with regard to the fast-ignition, inertial confinement fusion problem. Detailed description of hybrid laser system is presented with synchronized KrF and Ti:Sapphire master oscillators. Based on gain and absorption measurements at GARPUN amplifier and numerical simulations with a quasi-stationary code, we are predicting that 1.6 J can be obtained in a short pulse at hybrid GARPUN-MTW Ti:Sapphire/KrF laser facility, combined with several tens of joules in nanosecond pulse. Amplified spontaneous emission, which is responsible for the pre-pulse formation on a target, was also investigated: its acceptable level can be provided by properly choosing staged gain or loading the amplifiers by quasi-steady laser radiation. Fluorescence and transient absorption spectra of Ar/Kr/F2 mixtures conventionally used in KrF amplifiers were recorded to find out the possibility for femtosecond pulse amplification at the broadband Kr2F (42Γ → 1,2 2Γ) transition, which benefits in 100 times higher saturation energy density than for KrF (B → X) transition.

Gain and saturation energy characteristics in transversely excited N2 lasers

Measurements for laser parameters (i.e., small signal gain, g0, and saturation energy density, Es) have been carried out in a transversely excited N2 laser with a variable electrode gap separation, using an arrangement based on an oscillator-amplifier laser system. Our measurements indicate that the measured g0 and Es parameters depend on the electrode gap separation, and thereby the relevant characteristic curves showing this dependency, and consequently the g0 and Es dependencies on the E∕p value or electron temperature in the laser amplifier are introduced. It was also found experimentally that in the present system with the corona preionization, the product of the optimum N2 gas pressure and the gap separation is a constant value of 54Torrcm, where it is valid only for a system operating in a rather small range of electrode gap separation where the laser output power is maximized. Therefore, we show that the pd product is playing an important role for optimized performances of transversely excited N2 lasers. At last, the g0 and Es measurements across the amplifier discharge width have shown that the g0 parameter is not uniformly distributed within the discharge electrode gap separation, while the Es parameter has a minimum at the gap center with a symmetrical distribution of the output energy density.

Polarization-dependent gain and saturation energy density in a TE N2-laser amplifier

The polarization-dependent gain, g0, and saturation energy density, Es, in a TE N2-laser amplifier were measured, using an oscillator–amplifier laser system for different amplifier electrode gap separations, dAMP, of 7, 9 and 4mm and gas pressure of p=77, 60, and 165Torr, respectively. It was realized that for the amplifier with the gap separation of 7 and 9mm, where the pdAMP-value has its optimum-value of 54Torrcm, the gain-coefficient for the input beam with the polarization parallel to the discharge electrodes (P-polarized beam) is slightly higher than the case when the beam polarization is perpendicular to the discharge electrodes (S-polarized beam). In this case, the depolarization ratio for dAMP=7mm is the range of ∼0.998 to ∼0.962 as the input voltage increases from 12 to 15.5kV, having a minimum of 0.937 around 14kV. For the Es-parameter, the reversed order is true. Also, it was found that the saturation energy densities for three states of polarization are linearly related to the output energy densities, having different slopes of 0.11, 0.14, and 0.17 for R (randomly), P- and S-polarization, respectively. The present measurement supports qualitatively the prediction of polarization–inhomogeneity model for the stimulated emission cross-section, showing that randomly oriented dipoles exhibit slightly larger gain on the direction of the electric field.

Photophysical and nonlinear optical properties of μ-oxo-bridged indium and gallium phthalocyanines

The photophysical and nonlinear optical properties of a μ-oxo-bridged phthalocyanine heterodimer, i.e., [ tBu 4PcGa-O-InPc tBu 4] ( 5), where gallium is located in one macrocycle and indium is on the other macrocycle and the two metal atoms are connected through oxygen, have been described. Its photophysical properties are compared with the dimers: [ tBu 4PcGa] 2O ( 3) and [ tBu 4PcIn] 2O ( 4). The very small shifts of Q- and B-bands for all μ-oxo Pc dimers 3– 5 relative to the starting materials tBu 4PcGaCl ( 1) and tBu 4PcInCl ( 2) is indicative of a very weak interaction between two phthalocyanine rings in the ground state. The deactivation processes of the excited singlet state of 5 occur independently for tBu 4PcGa-O-moiety and tBu 4PcIn-O-moiety. Dimerization in the manner of 5 has no advantages over 3 and 4 from the point of view of optical limiting as it does not increase the ratio of the excited to ground state absorption cross-sections nor does it reduce the saturation energy density.

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N2 laser system, both operating with corona preionizers, the laser parameters (small-signal gain g 0 and saturation energy density E s) have been measured at different N2 gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N2 laser gain values in the literature, we found that the g 0-N2-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N2 laser system, both operating with corona preionizers, the laser parameters (small-signal gain g 0 and saturation energy density E s) have been measured at different N2 gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N2 laser gain values in the literature, we found that the g 0-N2-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.

Axially Modified Gallium Phthalocyanines and Naphthalocyanines for Optical Limiting

AbstractFor Abstract see ChemInform Abstract in Full Text.

Yield of photo-adduct formation of LOV domains from Chlamydomonas reinhardtii by picosecond laser excitation

The photo-excitation of flavin mononucleotide (FMN) in the wild-type light, oxygen and voltage sensitive (LOV) domains of the blue-light photoreceptors phototropin causes the formation of an intermediate flavin-C(4a)-cysteinyl adduct. The adduct formation due to picosecond laser pulse exaction (wavelength 400 nm) is studied on wild-type LOV1 and LOV2 domains of the phototropin phot from Chlamydomonas reinhardtii. The efficiency of adduct formation is probed by detection of the fluorescence signals caused by time-separated picosecond excitation pulses since FMN is fluorescent and the formed adduct is non-fluorescent. Quantum yields of adduct formation of ϕ Ad ≈ 0.06 are determined for excitation with intense single-pulses of energy densities, w L, comparable to or larger than the saturation energy density, w sat , S 0 , of ground-state population depletion. Under repetitive picosecond pulse excitation conditions the efficiency of adduct formation rises with decreasing picosecond pulse energy density and approaches for w L < 0.001 w sat , S 0 the continuous blue-light exposure quantum yields of adduct formation in the range from ϕ Ad = 0.5–0.9. Picosecond laser pulse induced energy deposition in the LOV domains causing protein conformational changes is discussed as main origin of the intensity dependent reduction of the efficiency of adduct-formation.