Comment on "Wide-field coherent anti-Stokes Raman scattering microscopy with non-phase-matching illumination"

We comment on a Letter by Toytman et al. [Opt. Lett.32, 1941 (2007)] in which a novel setup for wide-field imaging in coherent anti-Stokes Raman scattering (CARS) microscopy is demonstrated. There the authors state that our phase-matching implementation of a wide-field CARS system [Appl. Phys. Lett.84, 816 (2004); New J. Phys.8, 36 (2006)] suffers from a strong background from the bulk medium. However, our results show quite the contrary, i.e., that our setup provides a very good signal contrast, due to an almost vanishing background level from the bulk solvent.     

Diffraction of picosecond bulk longitudinal and shear waves in micron thick films

Investigation of thin metallic film properties by means of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies. Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal to the film free surface has been demonstrated. Such measurements cannot provide complete information about properties of anisotropic films. Extreme focusing of a laser pump beam (≈0.5 μm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting longitudinal and shear wavefronts propagate at group velocity through the bulk of the film. To interpret the received signals, source directivity diagrams are calculated taking into account material anisotropy, optical penetration, and laser beam width on the sample surface. It is shown that acoustic diffraction increases with optical penetration, so competing with the increasing of directivity caused by beam width. Reflection with mode conversion at the film-substrate interface is discussed.     

GaAs photonic crystal cavity with ultrahigh Q: microwatt nonlinearity at 1.55 microm

We haves realized and measured a GaAs nanocavity in a slab photonic crystal based on the design by Kuramochi et al. [Appl. Phys. Lett. 88, 041112 (2006)]. We measure a quality factor Q=700,000, which proves that ultrahigh Q nanocavities are also feasible in GaAs. We show that owing to larger two-photon absorption in GaAs nonlinearities appear at the microwatt level and will be more functional in gallium arsenide than in silicon nanocavities.     

Terahertz electromagnetic wave transmission through random arrays of single rectangular holes and slits in thin metallic sheets

We report on the observation of terahertz transparency in random arrays of the single rectangular holes and slits with the areal coverage of only 12%. The terahertz transparency occurs at the fundamental shape resonance of the rectangular holes and confirms the theoretical predictions of earlier works of García-Vidal et al. [Phys. Rev. Lett. 95, 103901 (2005)] on single rectangular holes and of Ruan and Qiu [Phys. Rev. Lett. 96, 233901 (2006)] on random arrays of holes.     

Crossover from three-dimensional to two-dimensional geometries of Au nanostructures on thin MgO(001) films: a confirmation of theoretical predictions

In this Letter, we report a low-temperature scanning tunneling microscopy study aiming to explore the adsorption properties of Au with respect to the thickness of supported MgO films. For different MgO film thicknesses (3 ML and 8 ML), we find significant differences in the distribution of Au adsorption sites and in the Au cluster geometry, in line with recent calculations and electron paramagnetic resonance experiments. On the surface of thick MgO films or unsupported MgO, Au adsorbs on O sites [Phys. Rev. Lett. 96, 146804 (2006)], and the equilibrium cluster geometry is three-dimensional. In contrast, on thin MgO films, the calculations predicted (i) a change of the preferred Au nucleation site [Phys. Rev. Lett. 94, 226104 (2005)] and (ii) a stabilization of two-dimensional Au cluster geometries [Phys. Rev. Lett. 97, 036106 (2006)].     

Ab initio calculation of photoionization and inelastic photon scattering spectra of He below the N=2 threshold in a dc electric field

We study the Stark effect on doubly excited states of the helium atom below N=2. We present the ab initio photoionization and total inelastic photon scattering cross sections calculated with the method of complex scaling for field strengths F 相似文献   

Stabilizing graphitic thin films of wurtzite materials by epitaxial strain

Recent theory [Phys. Rev. Lett. 96, 066102 (2006)] and experiment [Phys. Rev. Lett. 99, 026102 (2007)] show that (0001) ultrathin films of wurtzite (WZ) materials surprisingly transform into a stable graphitelike structure, but the stability is limited to thicknesses of only a few atomic layers. Using first-principles calculations of both freestanding and substrate-supported thin films, we predict that the thickness range of stable graphitic films depends sensitively on strain and can be substantially extended to much thicker films by epitaxial tensile strain. Moreover, the band gap of the stable strained graphitic films can be tuned over a wide range either above or below that of the bulk WZ phase.     

Disorder-induced losses in planar photonic crystals

The phenomenological approach introduced by Benisty [Appl. Phys. Lett. 76, 532 (2000)] to model out-of-plane radiation losses in planar photonic crystals with a low vertical refractive index contrast is extended to the case of in-plane disorder. The model is experimentally validated by means of optical measurements on GaAs-based structures. For the present fabrication techniques the disorder-induced contribution is found to be negligible compared with the other loss mechanisms.     

Efficient nonlinear-optical frequency conversion in periodic media in the presence of diffraction of the pump and harmonic fields

It has been predicted by Shelton and Shen [Phys. Rev. A 5, 1867 (1972)] and observed by Kajikawa et al. [Jpn. J. Appl. Phys. Lett. 31, L679 (1992)] and Yamada et al. [Appl. Phys. B 60, 485 (1995)] that the efficiency of nonlinear-optical frequency conversion increases significantly in a nonlinear periodic medium and, accordingly, the intensity of the generated harmonic increases as the fourth power of the sample thickness, as opposed to the square law observed in homogeneous media. In this paper it is shown that the same enhancement of the efficiency of nonlinear-optical frequency conversion in a nonlinear periodic medium can be achieved using an ordinary pump wave in the form of a plane wave when both the pump wave and the harmonics are diffracted by the periodic structure of the nonlinear medium. The phenomenon is analyzed quantitatively in the example of second-harmonic generation. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 12, 793–799 (25 December 1999)     

Exact analytical solution of a nonlinear equation arising in heat transfer

This Letter shows that the nonlinear equation arising in heat transfer recently investigated in papers [D.D. Ganji, Phys. Lett. A 355 (2006) 337; S. Abbasbandy, Phys. Lett. A 360 (2006) 109; Hafez Tari, D.D. Ganji, H. Babazadeh, Phys. Lett. A 363 (2007) 213] and [M.S.H. Chowdhury, I. Hashim, Phys. Lett. A 372 (2008) 1240] is exactly solvable, analyses the equation fully and, furthermore, gives analytic exact solution in implicit form for each value of parameters of equation.     

A genuine 3N-qubit entanglement and controlled teleportation

A genuine 3N-qubit entanglement is derived based on N GHZ trios and controlled teleportation. The state is a complementarity to the genuine 2N-qubit entangled state constructed with N Bell states by Yeo-Chua for N = 2 [Phys. Rev. Lett. 96, 060502 (2006)] and by Chen-Zhu-Guo for any N [Phys. Rev. A 74, 032324 (2006)]. By means of the measures proposed in Phys. Rev. A 74, 022314 (2006), the entanglement of the constructed state is quantified and classified with the well-known GHZ, W and Chen-Zhu-Guo's 2N-qubit entangled state.     

Nonsteady condensation and evaporation waves

Recent scaling results for the ac conductivity of ionic glasses by Roling et al. [Phys. Rev. Lett. 78, 2160 (1997)] and Sidebottom [Phys. Rev. Lett. 82, 3653 (1999)] are discussed. We prove that Sidebottom's version of scaling is completely general. A new approximation to the universal ac conductivity arising in the extreme disorder limit of the symmetric hopping model, the "diffusion cluster approximation," is presented and compared to computer simulations and experiments.     

Optical gap solitons: Past,present, and future; theory and experiments

Optical gap solitons refer to nonlinear waves propagating in optical fibers whose linear refractive index has a periodic variation. Stationary gap solitons came to light first in 1987 [Chen and Mills, Phys. Rev. Lett. 58, 160 (1987)]; two years later, they re-emerge in Christodoulides and Joseph [Phys. Rev. Lett. 62, 1746 (1989)] and are first extended to a more general traveling wave form in Aceves and Wabnitz [Phys. Lett. A 141, 37 (1989)]. But it was not until seven years later, that the first experimental demonstration [Eggleton et al., Phys. Rev. Lett. 76, 1627 (1996); J. Opt. Soc. Am. B 14, 2980 (1997)] was reported. Since then, there has been an increase in the study of the dynamics and applications of such solitons. This paper is a brief survey of some of the ongoing and future research on optical gap solitons. (c) 2000 American Institute of Physics.     

The Amigó paradigm of forbidden/missing patterns: a detailed analysis

We deal here with the issue of determinism versus randomness in time series (TS), withthe goal of identifying their relative importance in a given TS. To this end we extend (i)the use of ordinal patterns based probability distribution functions associated to a TS[C. Bandt and B. Pompe, Phys. Rev. Lett. 88, 174102 (2002)] and (ii) theso-called Amigó paradigm of forbidden/missing patterns [J.M. Amigó et al., Europhys. Lett.79, 50001 (2007)], to analyze deterministic finite TS contaminated withstrong additive noises of different correlation-degree. Useful information on thedeterministic component of the original time series is obtained with the help of theso-called causal entropy-complexity plane [O.A. Rosso et al., Phys. Rev. Lett.99, 154102 (2007)].     

Divergence of Tolman's length for a droplet near the critical point

The application of "complete scaling" [Kim et al., Phys. Rev. E 67, 061506 (2003); Anisimov and Wang, Phys. Rev. Lett. 97, 025703 (2006)] to the interfacial behavior of fluids shows that Tolman's length, a curvature correction to the surface tension, diverges at the critical point of fluids much more strongly than is commonly believed. The amplitude of the divergence depends on the degree of asymmetry in fluid phase coexistence. In highly asymmetric fluids and fluid mixtures the Tolman length may become large enough to significantly affect the interfacial behavior.     

Three-dimensionally modulated graded-index diffractive elements by thermal ion exchange in glass

Thermal ion exchange was introduced recently [Appl. Phys. Lett. 66, 917 (1995)] as a method to generate graded refractive-index distributions that permit continuous one-dimensional phase modulation in diffractive optics. We apply enhanced diffusion-modeling techniques and a novel three-step optimization procedure to design, for the first time to our knowledge, efficient three-dimensional graded-index profiles with two-dimensional phase-modulation capability. A discrete, nonseparable inversion-symmetric signal pattern is demonstrated experimentally in which the uniformity error in the intensities of the seven signal spots is less than 5%.     

Comment on Radiative transfer over small distances from a heated metal

We show that there is no contradiction between the results presented by Pan [Opt. Lett. 25, 369 (2000)] and the 1/L(2) dependence of the radiative energy flux between two half-spaces separated by a small vacuum gap of width L obtained by Polder and Van Hove [Phys. Rev. B 4, 3303 (1971)] and by Loomis and Maris [Phys. Rev. B 50, 18517 (1994)].     

Quantum entanglement formation by repeated spin blockade measurements in a spin field-effect transistor structure embedded with quantum dots

We propose a method of operating a quantum state machine made of stacked quantum dots buried in adjacent to the channel of a spin field-effect transistor (FET) [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665; K. Yoh, et al., Proceedings of the 23rd International Conference on Physics of Semiconductors (ICPS) 2004; H. Ohno, K. Yoh et al., Jpn. J. Appl. Phys. 42 (2003) L87; K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134]. In this method, a spin blockade measurement extracts the quantum state of a nearest quantum dot through Coulomb blockade [K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134; K. Yoh, H. Kazama, Physica E 7 (2000) 440] of the adjacent channel conductance. Repeated quantum Zeno-like (QZ) measurements [H. Nakazato, et al., Phys. Rev. Lett. 90 (2003) 060401] of the spin blockade is shown to purify the quantum dot states within several repetitions. The growth constraints of the stacked InAs quantum dots are shown to provide an exchange interaction energy in the range of 0.01–1 meV [S. Itoh, et al., Jpn. J. Appl. Phys. 38 (1999) L917; A. Tackeuchi, et al., Jpn. J. Appl. Phys. 42 (2003) 4278]. We have verified that one can reach the fidelity of 90% by repeating the measurement twice, and that of 99.9% by repeating only eleven QZ measurements. Entangled states with two and three vertically stacked dots are achieved with the sampling frequency of the order of 100 MHz.     

Quantum Correlations in a Family of Two-Qubit Separable States

Quantum correlations in a family of two-qubit separable classical-quantum correlated states are intensively studied with four different approaches, namely, quantum discord [Phys. Rev. Lett. 88 (2002) 017901], measurement- induced disturbance (MID) [Phys. Rev. A 77 (2008) 022301], ameliorated MID [J. Phys. A: Math. Theor. 44 (2011) 352002] and quantum dissonance [Phys. Rev. Lett. 104 (2010) 080501]. Quantum correlations captured with different approaches are compared and discussed so that their three distinct features are exposed.     

Nanoscale oscillatory fracture propagation in metallic glasses

We describe the oscillatory crack propagation for small propagation velocities at the atomistic scale that was recently observed for brittle metallic glasses [G. Wang, Y.T. Wang, Y.H. Liu, M.X. Pan, D.Q. Zhao, W.H. Wang, Appl. Lett. 89 (2006) 121909; G. Wang, D.Q. Zhao, H.Y. Bai, M.X. Pan, A.L. Xia, B.S. Han, X.K. Xi, Y. Wu, W.H. Wang, Phys. Rev. Lett. 98 (2007) 235501]. Based on a simple model of crack propagation [Y. Braiman, T. Egami, Phys. Rev. E, 77 (2008) 065101(R)], we derived and analyzed expressions for the feature size, oscillation period, and maximum strain accumulated in the material.