Supersymmetry-driven segmented tapered laser for stabilized single transverse and longitudinal mode engineering

Previous works on photorefractive self-organizing laser cavities were about lasers that oscillate, prior the self-organization process occurs, on a set of axial modes sharing the same transverse structure. We have now demonstrated that the insertion of a photorefractive crystal can also create a dynamic spatial filter. In a well-designed extended cavity broad-area laser diode, such a filter can affect the transverse modal structure to force a laser, initially oscillating on several transverse modes, to oscillate on a single transverse and longitudinal mode. A large increase of the single-mode operating range of the laser has been observed.

The nonlocal theoretical model developed to observe current-driven low-frequency electrostatic modes in a collisional magnetized strongly coupled dusty plasma, in the strongly coupled kinetic regime ωτ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ≫ 1 (i.e., wave frequency is much larger than the dust particle relaxation time) led to a new set of equations for dispersion relation, frequency, and the growth rate. The theoretical investigations on a cylindrical magnetized strongly coupled dusty plasma led to a current driven ion dust hybrid like longitudinal dust wave propagating nearly along radial direction and a peculiar transverse shear dust wave mode along axial direction. Dispersion properties of both longitudinal dust acoustic modes and transverse shear modes are modified in the presence of ion and dust currents and the effective perpendicular wave number provided by finite geometry of strongly coupled magnetized dusty plasma. The magnetic field has a destabilizing effect on the growth of longitudinal wave modes, while the dependence of transverse modes on the strength of magnetic field is not prominent. Transverse shear modes are characterized as the short wavelength modes with a long wavelength cutoffs. A comparison of nonlocal effects with local effects shows that in bounded magnetized strongly coupled dusty plasmas, the longitudinal wave modes need a large magnetic field and weak collisional regime to support the excitation of dust wave modes, whereas the transverse modes are a consequence of viscous and collisional damping.

A longitudinally laser diode (LD)-pumped Nd:YAP microchip master oscillator power amplifier (MOPA) system operating at 1.08 μm was demonstrated. The system consisted of a longitudinally LD-pumped monolithic Nd:YAP microchip master laser and a two-stage disc amplifier. The cavity length of the master oscillator was 500 μm. The short cavity length lead to a large frequency separation between the resonator modes and hence single longitudinal mode operation was achieved. Pumped by a high-brightness LD an output power of 155 mW in both single longitudinal and transverse mode was generated. To scale to a high power, the output power from the master oscillator was amplified by amplifier discs. The amplified output power was 1.43 W. The central wavelength of the laser system was tuned by changing the cavity length and refractive index via temperature. Using a shorter master oscillator (L = 310 μm) a continuous output wavelength tuning over the gain profile of 0.9 nm was realized. To our knowledge this is the first study of a MOPA system based on an LD-pumped microchip Nd:YAP laser.

Laser shock induced lateral compression has been demonstrated to controllably flatten cylindrical silver nanowires. Nanowires with circular cross-sections of diameter 70 nm are significantly shaped laterally, which transformed them to metallic ribbons of huge width of 290 nm and of thickness down to 13 nm, amounting the aspect ratio to as high as 22, at a laser intensity of 0.30 GW cm(-2). Above the laser intensity of 0.30 GW cm(-2) though, nanowires are observed to be ruptured. Lateral deformations of nanowires are achieved without altering longitudinal dimensions. Selected area electron diffraction patterns on the laterally deformed nanowires reveal that the flattening gives rise to twinning under high strain rate deformation without actually degrading crystallinity. As the 1D nanowire turns into a 2D metallic nanoribbon, new plasmonic modes and their combinations emerge. The transverse plasmon mode does not shift substantially, whereas longitudinal modes and their combinations are greatly influenced by lateral deformation. Apart from the transverse mode, which is dominant in a 1D nanowire and diminishes heavily when lateral deformation occurs, there is a presence of several longitudinal plasmonic modes and their combinations for metallic nanoribbons, which are revealed by experimental extinction spectra and also supported by finite-difference time-domain (FDTD) simulation. Such plasmonic tuning of silver nanowires across the visible range demonstrates the capability of a laser shock induced lateral compression technique for various emerging plasmonic applications. The laser shock compression technique has the advantages of flexibility, selectivity and tunability while retaining crystallinity of metallic nanowires, all of which enable it to be a potential candidate for plasmonic tuning of nanogeometries.

In this paper, we demonstrate a scheme to tailor both longitudinal and transverse modes inside a laser cavity and constitute an eye-safe single longitudinal mode Er:Y3Al5O12 (Er:YAG) vector laser. A q-plate is employed as a spin-orbital conversion element to modulate the transverse mode and obtain cylindrical vector beams. An optical isolator is employed as a non-reciprocal element for the ring cavity to enforce unidirectional operation and achieve single longitudinal oscillation. The characteristics of power, transverse intensity, and polarization spectrum of the output beams are observed. The observed typical single longitudinal mode and highly matched special polarizations prove the successful tailoring of both longitudinal and transverse modes.

We report a detailed theoretical investigation about the influence of the nanorod length and incident polarization on the far-field and near-field optical properties of Al nanorod using the discrete dipole approximation. The results show that Al nanorod has great tunability in the UV-Vis-NIR region and much stronger near-field intensity at UV and NIR wavelengths. The band position of transverse mode (TM) for the nanorod has a little blueshifted as the length increases, while that of the longitudinal mode (LM) is linearly redshifted with the size. In addition, we investigate how the incident polarization affects the extinction position and efficiency of the TM and LM. Finally, the near-field distribution dependences of the nanorod length for the TM and the LM have been analyzed. It is shown that much enhanced near-field always occur in the lateral surface of the nanorod for TM and the tip of the nanorod for the LM, respectively. The maximum local field enhancement factor of the TM is found to be about two times higher than that of the LM, which is due to close the region of interband transitions at about nm. These results would be of great potential application in localized surface plasmon resonance sensor and UV-plasmonic device.

The authors have realized a film bulk acoustic wave resonator (FBAR) using a thin LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film deposited by a chemical vapor deposition (CVD) for the first time. As a result, a 2.9GHz FBAR, which is higher than 2.1GHz of the BAW using a LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single crystal thin plate, with an impedance ratio of 40dB at a resonant (fr) and an antiresonant (fa) frequencies was realized. The LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film has a mixture of the polarity. As a result of a scanning non-linear dielectric microscope (SNDM) measurement, -c domains and +c domains occupy 82% and 18%, respectively. A quality factor is small because it is considered that the film has the mixed polarity, the thickness is not flat and the structure of electrode is not optimum. A transverse mode was not excited on the fabricated FABR According to a calculation, the transverse wave mode is observed when the thickness of electrodes is thin. On the other hand, the transverse wave mode isn't observed when the thickness of electrodes is thick. The main responses of longitudinal mode wave are not different by the thicknesses of electrodes. Therefore it is found that the transverse wave mode can be suppressed by selecting the thickness of electrodes. Further, the effect that LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film is twinned crystalline epitaxial one is evaluated by calculation. The transverse wave mode is excited even if the film is twinned epitaxial one. It is important to deposit another oriented LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film with larger coupling factor to realize a wider band resonator.

Based on the coupled mode theory by using the reversely recursive transmission matrix method, the switching characteristics of the λ/4 phase-shifted fiber grating and the influence of introducing chirp on the switching characteristics have been numerically studied when the reflection of the transmission facet is taken into consideration. The results show: for coherent superposition reflection strengthening, it can reduce the threshold switching energy of the λ/4 phase-shifted grating, but the switching contrast will decline; with the introduction of negative chirp in λ/4 phase-shifted grating, the switching contrast will be greatly improved, but the threshold switching energy will increase; with the introduction of positive chirp in λ/4 phase-shifted grating, the switching threshold can be further reduced, but the switching contrast will decline; and the hysteresis loop width will be influenced obviously by the introducing chirp.

We study the Casimir effect due to a massive vector field in a system of two\nparallel plates made of real materials, in an arbitrary magnetodielectric\nbackground. The plane waves satisfying the Proca equations are classified into\ntransverse modes and longitudinal modes which have different dispersion\nrelations. Transverse modes are further divided into type I and type II\ncorresponding to TE and TM modes in the massless case. For general\nmagnetodielectric media, we argue that the correct boundary conditions are the\ncontinuities of $\\mathbf{H}_{\\parallel}, \\phi, \\mathbf{A}$ and $\\pa_xA_x$,\nwhere $x$ is the direction normal to the plates. Whereas there are type I\ntransverse modes that satisfy all the boundary conditions, it is impossible to\nfind type II transverse modes or longitudinal modes that satisfy all the\nboundary conditions. To circumvent this problem, type II transverse modes and\nlongitudinal modes have to be considered together. We call the contribution to\nthe Casimir energy from type I transverse modes as TE contribution, and the\ncontribution from the superposition of type II transverse modes and\nlongitudinal modes as TM contribution. Their massless limits give respectively\nthe TE and TM contributions to the Casimir energy of a massless vector field.\nThe limit where the plates become perfectly conducting is discussed in detail.\nFor the special case where the background has unity refractive index, it is\nshown that the TM contribution to the Casimir energy can be written as a sum of\ncontributions from two different types of modes, corresponding to type 2\ndiscrete modes and type 3 continuum modes discussed by Barton and Dombey\n\\cite{1}. For general background, this splitting does not work. The limit where\nboth plates become infinitely permeable and the limit where one plate becomes\nperfectly conducting and one plate becomes infinitely permeable are also\ninvestigated.\n

The dynamics of a surface-emitting laser (SEL) with cw optical injection are studied. The molecular-beam-epitaxy grown SEL has an active region consisting of 0.72-μm bulk GaAs and two high-reflectivity mirrors with 22 and 27 periods of 62.5-nm AlGaAs (x = 0.143)/73.3-nm AlAs, respectively. Lasing occurs in a single longitudinal and transverse mode at 886 nm when pumped by an 830-nm edge-emitting diode laser. A tunable dye laser generates the injection signal. At a detuning of 3 GHz, the lasing frequency is pulled toward the injection until complete locking is achieved at an injection level of 5 μW. Asymmetric relaxation-oscillation side-bands spaced about 6 GHz from the injection frequency are observed at higher injection powers, the low-frequency band being stronger. When the injected power is increased further to 0.2 mW, a new lower-frequency sideband appears and is pushed away by as much as 30 GHz as the injection power is increased to 5 mW. Preliminary calculations show that the observed complex phenomena can only be understood by including both the gain saturation and nonlinear index change in the theoretical modelling.

Measurements were made of the resolution of holograms formed with a Q-switched ruby laser operating in a single longitudinal and transverse mode. Diffraction limited, 4 μ detail was observed in the reconstructed real image as viewed in CW He–Ne illumination.

A new laser structure, the plano-convex waveguide (PCW) laser is described. A thickness-varied waveguide layer used for transverse mode stabilization was formed adjacent to the planar active layer. The laser structure was fabricated by a single-step liquid phase epitaxial growth on a grooved substrate. With pulsed injection, stable fundamental transverse mode operation was observed up to 3.5 times threshold current, where power output was 36 mW/facet. At zero dc bias, single longitudinal mode was attained after 10 ns of the leading edge of the optical pulse. Far-field beam divergences of about 10° and 50° were obtained in directions parallel and perpendicular to the junction plane, respectively.

In this paper we deal with the macroscopic electromagnetic response of a finite size dispersive dielectric object, in unbounded space, in the framework of quantum electrodynamics using the Heisenberg picture. We apply a Hopfield type scheme to account for the dispersion and dissipation of the matter. We provide a general expression of the polarization density field operator as functions of the initial conditions of the matter field operators and of the electromagnetic field operators. It is a linear functional whose kernel is a linear expression of the impulse response of the dielectric object that we obtain within the framework of classical electrodynamics. The electric field operator is expressed as a function of the polarization density field operator by means of the dyadic Green's function for the free space. The statistical functions of these operators are classical functionals of the statistics of the initial conditions of the matter field operators and of the electromagnetic field operators, whose kernels are linear or multilinear expressions of the impulse response of the dielectric object. We keep the polarization and the electromagnetic field distinct to enable the treatment of the polarization and electromagnetic fluctuations on equal footing. We expand the polarization density field operator in terms of the static longitudinal and transverse modes of the object to diagonalize the Coulomb and Ampere interaction energy terms of the Hamiltonian in the Coulomb gauge. We expand the radiation fields in terms of the transverse plane wave modes of free space. Few static longitudinal and transverse modes are needed to calculate each element of the impulse response matrix for dielectric objects with sizes of the order up to $\min\limits_{\omega}\{c_0/[\omega \sqrt{|{\chi}(\omega)|}]\}$ where ${\chi}(\omega)$ is the susceptibility of the dielectric.

Butterfly-shaped ultra slim piezoelectric ultrasonic linear motor

In this paper, we use nonequilibrium molecular dynamics modeling to investigate the thermal properties of monolayer hexagonal boron nitride nanoribbons under uniaxial strain along their longitudinal axis. Our simulations predict that hexagonal boron nitride shows an anomalous thermal response to the applied uniaxial strain. Contrary to three dimensional materials, under uniaxial stretching, the thermal conductivity of boron nitride nanoribbons first increases rather than decreasing until it reaches its peak value and then starts decreasing. Under compressive strain, the thermal conductivity of monolayer boron nitride ribbons monolithically reduces rather than increasing. We use phonon spectrum and dispersion curves to investigate the mechanism responsible for the unexpected behavior. Our molecular dynamics modeling and density functional theory results show that application of longitudinal tensile strain leads to the reduction of the group velocities of longitudinal and transverse acoustic modes. Such a phonon softening mechanism acts to reduce the thermal conductivity of the nanoribbons. On the other hand, a significant increase in the group velocity (stiffening) of the flexural acoustic modes is observed, which counteracts the phonon softening effects of the longitudinal and transverse modes. The total thermal conductivity of the ribbons is a result of competition between these two mechanisms. At low tensile strain, the stiffening mechanism overcomes the softening mechanism which leads to an increase in the thermal conductivity. At higher tensile strain, the softening mechanism supersedes the stiffening and the thermal conductivity slightly reduces. Our simulations show that the decrease in the thermal conductivity under compressive strain is attributed to the formation of buckling defects which reduces the phonon mean free path.