Showing papers in "Journal of The Optical Society of America B-optical Physics in 2003"
TL;DR: In this paper, a multipole method for calculating the modes of microstructured optical fibers is described, which uses a multi-hole expansion centered on each hole to enforce boundary conditions accurately and matches expansions with different origins by use of addition theorems.
Abstract: We describe a multipole method for calculating the modes of microstructured optical fibers. The method uses a multipole expansion centered on each hole to enforce boundary conditions accurately and matches expansions with different origins by use of addition theorems. We also validate the method and give representative results.
419 citations
TL;DR: In this article, an approach for the fabrication of optical waveguides by focused low-repetition-rate femtosecond laser pulses is described. But the main limitation of this approach is the strong asymmetry of the waveguide profile.
Abstract: We describe a novel approach for the fabrication of optical waveguides by focused low-repetition-rate femtosecond laser pulses. This approach overcomes the main limitation of the technique, i.e., the strong asymmetry of the waveguide profile. By use of an astigmatic beam and suitably controlling both beam waist and focal position in tangential and sagittal planes, it is possible to shape the focal volume in such a way as to obtain waveguides with a circular transverse profile and of the desired size. This technique is applied to the fabrication of active waveguides in Er:Yb-doped glass substrates. The waveguides are single mode at 1.5 μm and exhibit propagation losses of ∼0.25 dB/cm and an internal gain of 1.4 dB at 1534 nm.
360 citations
TL;DR: In this article, a simple imaging method for direct determination of single-molecule orientations is presented that uses a wide-field epifluorescence microscope and a sensitive CCD camera.
Abstract: A simple imaging method for direct determination of single-molecule orientations is presented that uses a wide-field epifluorescence microscope and a sensitive CCD camera. Imaging is performed with slight defocusing of the optics, allowing for direct determination of single-molecule orientation based on the characteristic intensity distribution of the defocused images. Exact wave-optical calculations of these defocused images are presented and are in good agreement with the measurements. These calculations represent what is to the authors’ knowledge the first complete wave-optical modeling of defocused imaging of dipole emitters at an interface; the peculiarities of dipole emission at an interface and the vector effects of that emission and of imaging with a high-numerical-aperture objective are taken into account.
358 citations
TL;DR: In this article, the authors measured the spectroscopic properties of Yb:YAG with different Yb3+ concentrations by using the Fuchtbauer-Ladenburg formula and the reciprocity method.
Abstract: Measurements are reported of the spectroscopic properties (absorption and emission spectra, stimulated-emission cross section, and radiative lifetime) of (YbxY1-x)3Al5O12 for nominal x values of 0.025, 0.05, 0.1, 0.2 and 0.3 at temperatures of 15–300 K. The emission cross sections of Yb:YAG with different Yb3+ concentrations were determined by use of the Fuchtbauer–Ladenburg formula and the reciprocity method. At low temperatures, the product (στ) of the effective stimulated-emission cross section and the radiative lifetime is greater than at room temperature for all concentrations. Product στ is nearly independent of Yb3+ concentration at a given temperature. These results will aid in the design of high-power thin disk lasers by use of highly doped Yb:YAG.
245 citations
TL;DR: In this paper, a low-noise resonant electro-optic modulator based on high-Q whispering gallery modes was implemented and the modulator was used as a receiver to detect nanowatt microwave radiation.
Abstract: We report on the experimental observation of efficient all-resonant three-wave mixing using high-Q whispering-gallery modes. The modes were excited in a millimeter size toroidal cavity fabricated from LiNbO3. We implemented a low-noise resonant electro-optic modulator based on this wave mixing process. We observe an efficient modulation of light with coherent microwave pumping at 9 GHz with applied power of approximately 10 mW. Used as a receiver, the modulator allows us to detect nanowatt microwave radiation. Preliminary results with a 33-GHz modulator prototype are also reported. We present a theoretical interpretation of the experimental results and discuss possible applications of the device.
222 citations
TL;DR: In this article, the authors report on experiments featuring two special laser cooling techniques for ions which are stored in Paul traps, and demonstrate ground state cooling of a single trapped ion, which is a prerequisite for an ion-based quantum processor.
Abstract: Laser cooling was first proposed in 1975 by Hansch and Schawlow, and simultaneously by Wineland and Dehmelt. After some general remarks on laser cooling in traps we report on experiments featuring two special laser cooling techniques for ions which are stored in Paul traps. With both techniques we demonstrate ground state cooling of a single trapped ion. Ground state cooling of one or a string of ions might help to improve ion-based frequency standards, and is a prerequisite for an ion-based quantum processor.
206 citations
TL;DR: In this paper, the degradation of optical and radio frequency standards that are due to the instability in the transmission channel has been measured and active noise cancellation is demonstrated to improve the transfer stability of the fiber link.
Abstract: Optical and radio frequency standards located in JILA and National Institute of Standards and Technology (NIST) laboratories have been connected through a 3.45-km optical fiber link. An optical frequency standard based on an iodine-stabilized Nd:YAG laser at 1064 nm (with an instability of ∼4×10-14 at 1 s) has been transferred from JILA to NIST and simultaneously measured in both laboratories. In parallel, a hydrogen maser-based radio frequency standard (with an instability of ∼2.4×10-13 at 1 s) is transferred from NIST to JILA. Comparison between these frequency standards is made possible by the use of femtosecond frequency combs in both laboratories. The degradation of the optical and rf standards that are due to the instability in the transmission channel has been measured. Active noise cancellation is demonstrated to improve the transfer stability of the fiber link.
189 citations
TL;DR: In this paper, the effect of light forces on atoms when the field is enclosed in an optical resonator of high finesse is discussed, and the authors identify the dynamical coupling between the light field intensity and the atomic motion as the central mechanism underlying the cavity-induced cooling.
Abstract: We review the modifications and implications of the effect of light forces on atoms when the field is enclosed in an optical resonator of high finesse. The systems considered range from a single atom strongly coupled to a single mode of a high-Q microcavity to a large ensemble of atoms in a highly degenerate quasi-confocal resonator. We set up general models that allow us to obtain analytic expressions for the optical potential, friction, and diffusion. In the bad-cavity limit the modified cooling properties can be attributed to the spectral modifications of light absorption and spontaneous emission in a form of generalized and enhanced Doppler cooling. For the strong coupling regime in a good cavity, we identify the dynamical coupling between the light field intensity and the atomic motion as the central mechanism underlying the cavity-induced cooling. The dynamical cavity cooling, which does not rely on spontaneous emission, can be enhanced by multimode cavity geometries because of the effect of coherent photon redistribution between different modes. The model is then generalized to include several distinct frequencies to account for more general trap geometries. Finally we show that the field-induced buildup of correlations between the motion of different particles plays a central role in the scaling behavior of the system. Depending on the geometry and parameters, its effect ranges from strong destructive interference, slowing down the cooling process, to self-organized crystallization, implying atomic self-trapping and faster cooling to lower temperatures by cooperative coherent scattering.
175 citations
TL;DR: In this article, the authors investigated nonlinear absorption of Rhodamine B dye in methanol and water near resonance (532 nm) on the higher energy (435 nm) and lower energy (600 nm) sides of the absorption band using an open-aperture Z-scan technique with nanosecond pulses.
Abstract: We have investigated nonlinear absorption of Rhodamine B dye in methanol and water near resonance (532 nm) on the higher-energy (435 nm) and lower-energy (600 nm) sides of the absorption band, using an open-aperture Z-scan technique with nanosecond pulses. We observed reverse saturable absorption (RSA) at 435 nm in both of the solvents, and a transition from saturable absorption (SA) to RSA with an increase in either intensity or concentration at 600 nm in methanol. A transition from RSA to SA with an increase in concentration at 600 nm was observed with water as the solvent. We used theoretical analysis based on rate equations to determine the two-photon and excited-state absorption coefficients from the experimental results.
167 citations
TL;DR: A review of laser cooling and trapping techniques can be found in this article, where three main features are discussed: quantization of atomic motion, effects of the multilevel structure of atoms, and effects of polychromatic light.
Abstract: A review is presented of some of the principal techniques of laser cooling and trapping that have been developed during the past 20 years. Its approach is primarily experimental, but its quantitative descriptions are consistent in notation with most of the theoretical literature. It begins with a simplified introduction to optical forces on atoms, including both cooling and trapping. Then its three main sections discuss its three selected features, (1) quantization of atomic motion, (2) effects of the multilevel structure of atoms, and (3) the effects of polychromatic light. Each of these features is an expansion in a different direction from the simplest model of a classical, two-level atom moving in a monochromatic laser field.
165 citations
TL;DR: In this article, the enhancement of two-photon absorption (TPA) in a series of porphyrins and tetraazaporphyrins was studied by measuring the absolute TPA cross sections with 100-fs-duration pulses in two ranges of laser wavelengths, from 1100 to 1500 and from 700 to 800 nm.
Abstract: We study the enhancement of two-photon absorption (TPA) in a series of porphyrins and tetraazaporphyrins by measuring the absolute TPA cross sections with 100-fs-duration pulses in two ranges of laser wavelengths, from 1100 to 1500 and from 700 to 800 nm. The cross section in the Q transition region is σ2∼1–10 GM (where 1 GM=10-50 cm4 s-1 photons-1), a value that is explained by partial lifting of the prohibition that is due to a parity selection rule. In the Soret transition region we find σ2 enhancement by ∼1 order of magnitude owing to the Q transition, which acts as a near-resonance intermediate state, and also owing to the presence of gerade energy levels, which we identify in this spectral region. In tetraazaporphyrins symmetrically substituted with strong electron acceptors, we find further enhancement (up to σ2∼1600 GM). As a possible application, we demonstrate for the first time to our knowledge the photosensitization of singlet-oxygen luminescence by TPA in porphyrin.
TL;DR: In this paper, the behavior of several simultaneously trapped, micrometer-sized particles in a fiber-optical trap consisting of two opposing single-mode fibers delivering counter-propagating, near-IR laser beams strongly depends on the size of the particles.
Abstract: The behavior of several simultaneously trapped, micrometer-sized particles in a fiber-optical trap consisting of two opposing single-mode fibers delivering counterpropagating, near-IR laser beams strongly depends on the size of the particles. Whereas beads that are considerably larger than the laser wavelength are pressed against each other in an axial line, smaller beads spontaneously arrange themselves into regular chains of equidistantly separated particles suspended in space with increasing separation for increasing bead diameter. A simple model based on self-organization by means of diffraction from the particles is capable of explaining the basic features of our experimental observations in the investigated range of bead diameters and refractive indices.
TL;DR: In this article, a short-pulse tunable soft x-ray free electron laser source based on the self-amplified spontaneous emission process (SEM) was proposed.
Abstract: The construction of short-pulse tunable soft x-ray free electron laser sources based on the self-amplified spontaneous emission process will provide a major advance in capability for dense plasma-related and warm dense matter (WDM) research. The sources will provide 1013 photons in a 200-fs duration pulse that is tunable from approximately 6 to 100 nm. Here we discuss only two of the many applications made possible for WDM that has been severely hampered by the fact that laser-based methods have been unavailable because visible light will not propagate at electron densities of ne≥1022 cm-3. The next-generation light sources will remove these restrictions.
TL;DR: In this paper, the role of confinement loss in small-core Holey fibers was investigated to optimize the design of practical highly nonlinear fibers, and it was shown that the dispersive properties of some of the designs are suitable for a range of device applications.
Abstract: Holey fibers with small-core dimensions relative to the optical wavelength and large air-filling fractions offer tight mode confinement and are therefore attractive for highly nonlinear fiber applications. We investigated the role of confinement loss in these small-core fibers to optimize the design of practical highly nonlinear fibers. We found that silica holey fibers can exhibit effective nonlinearities as great as 52 W-1 km-1 and that the confinement loss can be less than the losses of standard fiber types. We show that the dispersive properties of some of the designs are suitable for a range of device applications.
TL;DR: In this paper, a vector theory of the stimulated Raman scattering process is developed for describing the polarization effects in fiber-based Raman amplifiers, and it is found that polarization-mode dispersion (PMD) induces large fluctuations in an amplified signal.
Abstract: A vector theory of the stimulated Raman scattering process is developed for describing the polarization effects in fiber-based Raman amplifiers. We use this theory to show that polarization-mode dispersion (PMD) induces large fluctuations in an amplified signal. It is found that PMD-induced fluctuations follow a log-normal distribution. We also discuss the random nature of the polarization-dependent gain (PDG) in Raman amplifiers. Using the concept of a PDG vector, we find the probability distribution of PDG in an analytic form and use it to show that both the mean and the standard deviation of PDG depend on the PMD parameter inversely when the effective fiber length is much larger than the PMD diffusion length. We apply our theory to study how PDG can be reduced by scrambling pump polarization randomly and show that the mean value of PDG is directly proportional to the degree of pump polarization.
TL;DR: In this article, the authors describe the motion of these optical phase singularities as the relative phase or amplitude of two interfering collinear nonconcentric beams is varied, and the creation and the annihilation of vortices are found.
Abstract: Composite optical vortices may form when two or more beams interfere. Using analytical and numerical techniques, we describe the motion of these optical phase singularities as the relative phase or amplitude of two interfering collinear nonconcentric beams is varied. The creation and the annihilation of vortices are found, as well as vortices having translational velocities exceeding the speed of light.
TL;DR: In this article, the effect of total external reflection on metal-dielectric nanostructures is investigated when light from vacuum is incident onto these materials at an angle exceeding the critical angle defined by Snell's law.
Abstract: Metamaterials composed of metal-dielectric nanostructures are engineered to have an effective refractive index less than unity at optical wavelengths. The effect of total external reflection is demonstrated when light from vacuum is incident onto these materials at an angle exceeding the critical angle defined by Snell’s law. Novel approaches are discussed to derive the effective index of refraction from the reflection and refraction properties of finite slabs. The effect of losses and dispersion are analyzed in the visible range of frequencies by consideration of the measured properties of silver. The differences among ultralow refractive-index metamaterials, photonic bandgap materials, and metals are discussed. Remarkably, a bandgap is not required to obtain total external reflection.
TL;DR: In this paper, a detailed investigation of strontium magneto-optical trap (MOT) dynamics is presented, such as temperature, atom number and density, and loss channels and lifetime, with respect to various trap parameters.
Abstract: We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1S0–1P1 88Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkaline-earth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87Sr MOT. A dual-isotope (87Sr and 88Sr) MOT is also demonstrated.
TL;DR: In this article, the authors presented a model for cooling thulium-doped heavy-metal fluorozirconate glass to 19 K below ambient with a multiple-pass pump scheme, which represents over an order of magnitude increase from the previously reported single pass geometry.
Abstract: Recent developments in cooling thulium-doped heavy-metal fluoride glass are presented. Thulium-doped fluorozirconate (ZBLANP) is cooled to 19 K below ambient with a multiple-pass pump scheme. This represents over an order of magnitude increase from the previously reported single-pass geometry. The results agree with a simple model for anti-Stokes fluorescence cooling that includes considerations of quantum efficiency and parasitic heating mechanisms. Issues relating to a practical optical refrigerator are examined, including a general model for the effects of multiple pump passes.
TL;DR: In this article, an all-optical microwave frequency standard based on coherent population trapping (CPT) in 85Rb is developed, where the CPT resonances are detected by an ordinary edge-emitting diode laser in a simple optical setup.
Abstract: An all-optical microwave frequency standard based on coherent population trapping (CPT) in 85Rb is developed. The CPT resonances are detected by an ordinary edge-emitting diode laser in a simple optical setup. A buffer-gas mixture is carefully optimized to yield a narrow linewidth and a reduced temperature dependence of the resonance frequency. With the developed system we are able to measure ultranarrow optically induced hyperfine CPT resonances at <20 Hz, which is in good agreement with the linewidth calculated from experimental parameters. The frequency of an RF-signal generator has been stabilized to the CPT resonance between the two mF=0 magnetic sublevels. The relative frequency stability (square root of Allan variance) follows a slope of 3.5×10-11 τ-1/2(1 s<τ<2000 s). The best stability of 6.4×10-13 is reached at an integration time of τ=2000 s. This stability is sufficient for many high-precision applications. Frequency-shift measurements were made to evaluate the frequency dependencies on the operation parameters.
TL;DR: In this article, the phase relationship between the two pulses is measured to be ±π/2, which is related to theoretical predictions obtained from a Ginzburg-Landau distributed model.
Abstract: In a passively mode-locked fiber ring laser, we report the experimental observation of relative phase locking of pulses in a wide variety of cases. Relative phase locking is observed in bunches of N pulses separated by more than 20 pulse widths as well as in close pulse pairs. In the latter case, the phase relationship between the two pulses is measured to be ±π/2, which is related to theoretical predictions formerly obtained from a Ginzburg–Landau distributed model. We have developed a simplified numerical model adapted to our laser, which keeps its essential features while significantly reducing the number of free parameters. The agreement with the experiment is excellent.
TL;DR: In this article, the authors model particle formation by considering the hydrodynamics of material expansion into vacuum, and find that the ejected material can be quenched 1-3 orders of magnitude more efficiently than thermal conduction quenches the residual bulk surface.
Abstract: Ablation driven by intense, femtosecond laser pulses offers a novel route to fabrication of nanometer-sized particles. I model particle formation by considering the hydrodynamics of material expansion into vacuum. Modeling reveals rapid material dilution and cooling. Vacuum expansion is found to quench the ejected material 1–3 orders of magnitude more efficiently than thermal conduction quenches the residual bulk surface. Efficient quenching implies that solid-phase particles are produced rapidly (in ≪1 ns) following laser excitation; this may allow unique material states to be frozen within the ejected particles. Finally, the mean particle size is estimated to range from ∼1 to ∼10 nm for initial lattice temperatures ranging from 0.3 to 10 eV.
TL;DR: In this paper, the issue of 3D out-of-plane losses was addressed analytically by means of an incoherent approximation, assuming separability both for the dielectric map and for the electric field, this approach is valid for defects such as in-plane microcavities, PhC-based waveguides, bends and couplers.
Abstract: Waveguide modes in two-dimensional (2-D) photonic crystals (PhCs) deeply etched through monomode slab waveguides, e.g., AlGaAs/GaAs, GaAs/AlOx, or InP/GaInAsP, suffer from radiation losses that are strongly affected by the air hole depth and shape. The issue of three-dimensional (3-D) out-of-plane losses is addressed analytically by means of an incoherent approximation. Assuming separability both for the dielectric map and for the electric field, this approach is valid for defects such as in-plane microcavities, PhC-based waveguides, bends and couplers. Out-of-plane scattering is translated into an effective imaginary index in the air holes, so that 3-D losses can be cast in a simple 2-D calculation. The case of cylindroconical holes is treated, and the validity of this approach is experimentally confirmed by transmission measurements through simple PhC slabs.
TL;DR: In this article, the morphology-dependent resonances split into N higher-Q modes, in direct analogy with other types of oscillators, for a structure consisting of N-coupled microspheres or ring resonators, and for odd numbers of identical lossless coupled rings, the circulating intensity in the innermost ring increases exponentially with N.
Abstract: Using iterative methods we demonstrate that, for a structure consisting of N-coupled microspheres or ring resonators, the morphology-dependent resonances split into N higher-Q modes, in direct analogy with other types of oscillators. Moreover, for odd numbers of identical lossless coupled rings, the circulating intensity in the innermost ring increases exponentially with N when there is strong coupling to even-numbered rings and weak coupling to odd-numbered rings.
TL;DR: In this article, an adiabatic taper design in three dimensions for coupling light into photonic crystal defect waveguides in a square lattice of circular dielectric rods is presented.
Abstract: We present an adiabatic taper design in three dimensions for coupling light into photonic crystal defect waveguides in a square lattice of circular dielectric rods. The taper is a two-stage structure in which the first stage makes the transition from a dielectric waveguide to a coupled-cavity waveguide. The second stage subsequently transforms the waveguide mode from an index-guided mode to a band-gap-guided mode. We discuss differences between the two-dimensional device and its three-dimensional slab version.
TL;DR: In this paper, the authors show that the observed signal in transmission and selective reflection spectroscopy is actually an interferometric mixture of the optical responses as provided in both transmission and in reflection by a long macroscopic cell.
Abstract: Transmission spectroscopy in an ultrathin vapor cell, which has been recently demonstrated as a new method of sub-Doppler spectroscopy in the optical domain, is revisited. We show that, because of an unavoidable Fabry–Perot effect, the observed signal—in transmission spectroscopy and selective reflection spectroscopy as well—is actually an interferometric mixture of the optical responses as provided in transmission and in reflection by a long macroscopic cell. After the derivation of a very general solution, we restrict ourselves to the case of a linear interaction with the resonant laser. We finally discuss the application to a two-level atom for which analytical expressions are given, in the large Doppler limit, for FM transmission and reflection signals.
TL;DR: In this paper, a three-dimensional, metallic photonic crystal is realized and its absorption measured at infrared wavelengths, and the metallic absorption rate was found to be suppressed in the photonic bandgap regime (λ∼8-20 μm).
Abstract: A three-dimensional, metallic photonic crystal is realized and its absorption measured at infrared wavelengths. The metallic absorption rate is found to be suppressed in the photonic bandgap regime (λ∼8–20 μm). On the other hand, order-of-magnitude absorption enhancement is observed at the photonic band edge (λ∼5.8 μm). The enhancement is attributed to the slower group velocity of light at the photonic band edge, a longer photon–matter interaction length, and a finite intrinsic absorption of tungsten.
TL;DR: In this article, the existence of electromagnetic surface modes and surface plasma waves in the interface of a one-dimensional photonic crystal and a metal was demonstrated, and it was shown that these modes can be excited and observed without prism or grating configurations even under normal incidence from vacuum.
Abstract: We demonstrate the existence of electromagnetic surface modes and surface plasma waves in the interface of a one-dimensional photonic crystal and a metal. These modes can exist in the region in which bandgaps of the photonic crystal overlap and in the region below the plasma frequency of a metal in the frequency wave-vector space. An analytic dispersion relation to determine the existence of these electromagnetic surface modes is obtained, and it is shown that these modes can be excited and observed without prism or grating configurations even under normal incidence from vacuum.
TL;DR: In this paper, the authors investigated the effect of the accumulated thermal effect (ATE) in femtosecond closed-aperture Z-scan measurements by varying the repetition rate of the incident pulse for a dye solution in CHCl3.
Abstract: Accumulated thermal effect (ATE), which can be an artifact in femtosecond closed-aperture Z-scan measurements, was investigated by varying the repetition rate of the incident pulse for a dye solution in CHCl3. It was found that the measurement is affected by two-photon-absorption-induced ATE, even at a low repetition rate of 1 kHz. The relaxation time of the ATE was found to be tens of milliseconds by time-resolved thermal-lens experiments and simulations, which is consistent with the observed repetition-rate dependence of the Z-scan measurements. The simulations for various commonly used solvents also exhibited that the ATE can be prominent in hydrocarbon and halogenated hydrocarbon solvents and inconspicuous in alcohols and water.
TL;DR: In this article, a comparison of Tm,Ho:YLF, Tm Ho:LuLF, and TmHo:LuAG was performed under identical experimental conditions.
Abstract: A comparison of Tm,Ho:YLF; Tm,Ho:LuLF; and Tm,Ho:LuAG crystals under identical experimental conditions showed that Tm,Ho:LuLF yielded significantly better performance. The thermal expansion coefficients were measured. These crystals were experimentally characterized in the spectral region of 680 nm and 780 nm accessible to laser diodes. The effective energy storage lifetimes of the Ho 5I7 manifold at room temperature were measured experimentally. At 10 Hz and 273 K, free-running laser output energy in excess of 17 mJ was obtained in Tm,Ho:YLF compared with 30 mJ in Tm,Ho:LuLF and 24.4 mJ in Tm,Ho:LuAG. The slope efficiencies with respect to the incident pump energy were 7.4%, 12.9%, and 11.6%, respectively. The temperature dependence of the output energies of these lasers was investigated.