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J V Moloney

Publications and source records attributed to J V Moloney.

15 recordsLinked to original sources
PubMed2006

Phase locking and in-phase supermode selection in monolithic multicore fiber lasers.

We report a compact multicore fiber laser that utilizes an all-fiber approach for phase locking and in-phase supermode selection. By splicing passive coreless fibers of controlled lengths to both ends of an active 19-core fiber, we demonstrate that the fundamental in-phase supermode can be selectively excited with a completely monolithic fiber device, instead of conventional free-space and bulk optics, to achieve phase-locked operation for a multiemitter laser device.

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PubMed2005

Generation of watt-level single-longitudinal-mode output from cladding-pumped short fiber lasers.

We generate as much as 1.6 W of continuous-wave 1550 nm single-longitudinal-mode output from a cladding pumped Er-Yb codoped phosphate fiber laser. This power is to our knowledge among the highest in single-longitudinal-mode fiber lasers. The narrowband fiber Bragg grating output coupler is demonstrated to be an effective element for providing the single-longitudinal-mode selection.

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PubMed2005

Short-length microstructured phosphate glass fiber lasers with large mode areas.

We report fabrication and testing of the first phosphate glass microstructured fiber lasers with large Er-Yb-codoped cores. For an 11-cm-long cladding-pumped fiber laser, more than 3 W of continuous wave output power is demonstrated, and near single-mode beam quality is obtained for an active core area larger than 400 microm2.

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PubMed2005

Photoluminescence and terahertz emission from femtosecond laser-induced plasma channels.

Luminescence as a mechanism for terahertz emission from femtosecond laser-induced plasmas is studied. By using a fully microscopic theory, Coulomb scattering between electrons and ions is shown to lead to luminescence even for a spatially homogeneous plasma. The spectral features introduced by the rod geometry of laser-induced plasma channels in air are discussed on the basis of a generalized mode-function analysis.

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PubMed2004

Nonlinear optical pulse propagation simulation: from Maxwell's to unidirectional equations.

Spatial- and time-domain versions of the unidirectional pulse propagation equation (UPPE) are derived and compared from the point of view of their practical application in simulations of nonlinear optical pulse dynamics. A modification of the UPPE suitable for ultrathin optical waveguides, such as submicron silica wires, is also presented. We show in detail how various, previously published propagation equations follow from the UPPE in a unified way that clearly elucidates their underlying approximations and areas of applicability.

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PubMed2004

Dynamic nonlinear X waves for femtosecond pulse propagation in water.

Recent experiments involving femtosecond pulses in water displayed long-distance propagation analogous to that reported in air. We verify this phenomenon numerically and show that the propagation is dynamic as opposed to self-guided. Furthermore, we demonstrate that the propagation can be interpreted as being due to dynamic nonlinear X waves whose robustness and role in long-distance propagation follows from the interplay between nonlinearity and chromatic dispersion.

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PubMed2003

Physical factors limiting the spectral extent and band gap dependence of supercontinuum generation.

Based on simulations of femtosecond pulse propagation in water we elucidate the physical factors that limit the attainable spectral extent of supercontinuum generation in bulk media. In contrast to the standard scenario, where arrest of self-focusing collapse by multiphoton absorption and plasma defocusing are viewed as imposing a limit to supercontinuum broadening, we show that linear chromatic dispersion also plays a major role. This insight provides an intuitive explanation of the observed band gap dependence of the attainable supercontinuum generation in condensed media.

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PubMed2003

Relevance of symmetry for the synchronization of chaotic optical systems and the related Lang-Kobayashi model limitations.

Synchronization of chaotic semiconductor lasers has now been demonstrated experimentally in a variety of coupling schemes. Coupling methods include configurations where the transmitter laser system is itself chaotic and drives a receiver system, both lasers are individually chaotic, and both lasers induce the chaos through mutual coupling. The dynamics for each of these scenarios is in many cases adequately captured by the Lang-Kobayashi rate equation model. Such a simplified model, however, ignores fundamental aspects of the laser dynamics, such as the frequency and carrier density material susceptibility dependence, spatial hole burning effects, proper boundary conditions, and the fact that lasers may exhibit pronounced multilongitudinal dynamic behavior with and without the presence of a weak external feedback or injection. The model also cannot distinguish between many of the possible coupling geometries realizable in experiments. Using an interactive simulator based on the rigorous microscopic description of the light-matter interaction, we explore the unidirectionally coupled configuration, the relevance of symmetry for the synchronization achieved between two identical lasers, and the differences that arise when the traditional analysis through the Lang-Kobayashi model is compared to the full nonlinear partial differential equation model results.

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PubMed2002

Unidirectional optical pulse propagation equation.

A unidirectional optical pulse propagation equation, derived directly from Maxwell's equations, provides a seamless transition between various nonlinear envelope equations in the literature and the full vector Maxwell's equations. The equation is illustrated in the context of supercontinuum generation in air and is compared to a recent scalar model of Brabec and Krausz. Fully vectorial aspects of the model are illustrated in the context of extreme focusing of a femtosecond pulse.

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PubMed2002

Derivation of semiconductor laser mean-field and Swift-Hohenberg equations.

Bulk and quantum well semiconductor lasers by nature display fundamentally different physical characteristics relative to multilevel gas and solid state lasers. In particular, the refractive index is nonzero at peak gain and the peak gain can shift strongly with varying carrier density or temperature. Moreover, a quantum well laser gain may be strongly asymmetric if more than the lowest subband is populated. Rigorously computed and experimentally validated, gain and refractive index spectra are now available for a variety of quantum well structures emitting from the infrared to the visible. Active devices can be designed and grown such that the gain spectrum remains approximately parabolic for carrier density variations typically encountered in above threshold pumped broad area edge-emitting semiconductor lasers. Under this assumption, we derive a robust optical propagation model that tracks the important peak gain shifts and broadening as long as the gain remains approximately parabolic over the relevant energy range in a running laser. We next derive a multimode model where the longitudinal modes are projected out of the total field. The next stage is to derive a mean-field single longitudinal mode model for a wide aperture semiconductor laser. The mean-field model allows for significant cavity losses and widely different facet reflectivities such as occurs with antireflection- and high-reflectivity-coated facets. The single mode mean-field model is further reduced using an asymptotic expansion of the relevant physical fields with respect to a small parameter. The end result is a complex semiconductor Swift-Hohenberg description of a single longitudinal mode wide aperture laser. The latter should provide a useful model for studying scientifically and technologically important lasers such as vertical cavity surface emitting semiconductor lasers.

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PubMed2002

Achronal generalized synchronization in mutually coupled semiconductor lasers.

Heil et al. [Phys. Rev. Lett. 86, 795 (2001)] recently discovered achronal synchronization of chaos in mutually coupled semiconductor lasers. This paper offers an analytic interpretation of their experiment using a simple rate equation model. Local eigenvalue analysis shows that isochronal synchronization is unstable; achronal synchronization, on the other hand, is stable if a generalized synchronization function is introduced. Single- and multimode simulations have substantiated this rate equation interpretation. Finally, there is a brief examination of "chaos pass filtering."

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PubMed2001

Generation of electromagnetic pulses from plasma channels induced by femtosecond light strings.

We present a model that elucidates the physics underlying the generation of an electromagnetic pulse from a femtosecond laser induced plasma channel. The radiation pressure force from the laser pulse spatially separates the ionized electrons from the heavier ions and the induced dipole moment subsequently oscillates at the plasma frequency and radiates an electromagnetic pulse.

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PubMed2001

Polarization dynamics of femtosecond pulses propagating in air.

Polarization dynamics of femtosecond light pulses propagating in air is studied by computer simulation. A rich variety of dynamics is found that depends on the initial polarization state and power of the pulse. Effects of polarization on the plasma and supercontinuum generation are also discussed.

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PubMed1999

Electromagnetic shocks on the optical cycle of ultrashort pulses in triple-resonance Lorentz dielectric media with subfemtosecond nonlinear electronic Debye relaxation.

The dynamical evolution of an intense ultrashort sub-10-fs two-cycle optical pulse is considered as it propagates through a transparent third-order dielectric medium characterized by three resonance lines and a finite sub-fs relaxation time of the electronic nonlinearity. Numerical integration of the full Maxwell's equations incorporating triple-resonance Lorentz linear dispersion and Debye nonlinear dispersion, for a linearly polarized electromagnetic pulse centered at lambda(0)=1.24 microm in the normal dispersion region near the zero dispersion wavelength, shows the formation of shocks occurring on the optical cycle due to the generation of optical harmonics. The finite relaxation time of the nonlinear electronic response (sub-fs time scale) (i) slows down the steepening rate of the optical cycle; (ii) does not limit the generation of strongly phase matched optical harmonics, and consequently the development of infinitely sharp edges on the optical cycle producing its breaking when linear dispersion is not included; (iii) reduces the production of phase matched harmonics and consequently the sharpening of the jumps when dispersion is present, compared to the case of an instantaneous nonlinear response; and (iv) reduces the harmonic spectrum spreading and modulation at later times on the appearance of self-steepening of the electric field envelope.

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