Showing papers on "Phase (waves) published in 2009"
TL;DR: A new method for grating and side lobes suppression in ultrasound images is presented, based on an analysis of the phase diversity at the aperture data, which uses phase rather than amplitude information to perform the correction action.
Abstract: A new method for grating and side lobes suppression in ultrasound images is presented. It is based on an analysis of the phase diversity at the aperture data. Two coherence factors, namely the phase coherence factor (PCF) and the sign coherence factor (SCF), are proposed to weight the coherent sum output. Different from other approaches, phase rather than amplitude information is used to perform the correction action.
368 citations
TL;DR: In this paper, the authors derived the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition, which modifies the gravitational wave spectrum at large scales.
Abstract: We analytically derive the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition. In contrast to previous studies, we take into account the fact that turbulence and magnetic fields act as sources of gravitational waves for many Hubble times after the phase transition is completed. This modifies the gravitational wave spectrum at large scales. We also model the initial stirring phase preceding the Kolmogorov cascade, while earlier works assume that the Kolmogorov spectrum sets in instantaneously. The continuity in time of the source is relevant for a correct determination of the peak position of the gravitational wave spectrum. We discuss how the results depend on assumptions about the unequal-time correlation of the source and motivate a realistic choice for it. Our treatment gives a similar peak frequency as previous analyses but the amplitude of the signal is reduced due to the use of a more realistic power spectrum for the magneto-hydrodynamical turbulence. For a strongly first-order electroweak phase transition, the signal is observable with the space interferometer LISA.
312 citations
TL;DR: A novel and simple iterative phase compensation algorithm is proposed to compensate the nonsinusoidal phase error and experiments show that the proposed algorithm can be used for effective phase error compensation in practical phase-shifting FPP.
Abstract: The nonlinear intensity response of a digital fringe projection profilometry (FPP) system causes the captured fringe patterns to be nonsinusoidal waveforms and leads to an additional phase measurement error for commonly used three- and four-step phase-shifting algorithms. We perform theoretical analysis of the phase error owing to the nonsinusoidal waveforms. Based on the derived theoretical model, a novel and simple iterative phase compensation algorithm is proposed to compensate the nonsinusoidal phase error. Experiments show that the proposed algorithm can be used for effective phase error compensation in practical phase-shifting FPP.
297 citations
TL;DR: In this article, the carrier-envelope phase of a light pulse is measured in one shot using a single-shot measurement. But the phase of the light pulse can be measured in many separate pulses.
Abstract: When the length of a light pulse approaches that of just a few wavelengths, the difference in the phase of its field relative to its overall shape, or envelope becomes important in how the pulse interacts with matter. Accurate measurements of this carrier-envelope phase previously required averaging over many separate pulses. Now it can be measured in one shot.
268 citations
TL;DR: In this paper, the authors derived the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition, which modifies the gravitational wave spectrum at large scales.
Abstract: We analytically derive the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition. In contrast to previous studies, we take into account the fact that turbulence and magnetic fields act as sources of gravitational waves for many Hubble times after the phase transition is completed. This modifies the gravitational wave spectrum at large scales. We also model the initial stirring phase preceding the Kolmogorov cascade, while earlier works assume that the Kolmogorov spectrum sets in instantaneously. The continuity in time of the source is relevant for a correct determination of the peak position of the gravitational wave spectrum. We discuss how the results depend on assumptions about the unequal-time correlation of the source and motivate a realistic choice for it. Our treatment gives a similar peak frequency as previous analyses but the amplitude of the signal is reduced due to the use of a more realistic power spectrum for the magneto-hydrodynamical turbulence. For a strongly first-order electroweak phase transition, the signal is observable with the space interferometer LISA.
265 citations
TL;DR: Applying a phase-sensitive SPR polarimetry scheme and using gas calibration model, this work experimentally demonstrates the detection limit of 10(-8) RIU, which is about two orders of magnitude better compared to amplitude-sensitive schemes.
Abstract: We consider amplitude and phase characteristics of light reflected under the Surface Plasmon Resonance (SPR) conditions and study their sensitivities to refractive index changes associated with biological and chemical sensing. Our analysis shows that phase can provide at least two orders of magnitude better detection limit due to the following reasons: (i) Maximal phase changes occur in the very dip of the SPR curve where the vector of probing electric field is maximal, whereas maximal amplitude changes are observed on the resonance slopes: this provides a one order of magnitude larger sensitivity of phase to refractive index variations; (ii) Under a proper design of a detection scheme, phase noises can be orders of magnitude lower compared to amplitude ones, which results in a much better signal-to-noise ratio; (iii) Phase offers much better possibilities for signal averaging and filtering, as well as for image treatment. Applying a phase-sensitive SPR polarimetry scheme and using gas calibration model, we experimentally demonstrate the detection limit of 10(-8) RIU, which is about two orders of magnitude better compared to amplitude-sensitive schemes. Finally, we show how phase can be employed for filtering and treatment of images in order to improve signal-to-noise ratio even in relatively noisy detection schemes. Combining a much better physical sensitivity and a possibility of imaging and sensing in micro-arrays, phase-sensitive methodologies promise a substantial upgrade of currently available SPR technology.
261 citations
TL;DR: The first spectral numerical simulations of 16 orbits, merger, and ringdown of an equal-mass nonspinning binary black hole system were presented in this paper, where the waveform seen by an observer at infinity is determined from waveforms computed at finite radii by an extrapolation process accurate to <~0.01 radian in phase.
Abstract: The first spectral numerical simulations of 16 orbits, merger, and ringdown of an equal-mass nonspinning binary black hole system are presented. Gravitational waveforms from these simulations have accumulated numerical phase errors through ringdown of <~0.1 radian when measured from the beginning of the simulation, and <~0.02 radian when waveforms are time and phase shifted to agree at the peak amplitude. The waveform seen by an observer at infinity is determined from waveforms computed at finite radii by an extrapolation process accurate to <~0.01 radian in phase. The phase difference between this waveform at infinity and the waveform measured at a finite radius of r=100M is about half a radian. The ratio of final mass to initial mass is Mf/M=0.951 62±0.000 02, and the final black hole spin is Sf/Mf^2=0.686 46±0.000 04.
237 citations
01 Jan 2009
TL;DR: In this article, the authors characterized nonlinear features of flame dynamics by measuring the flame transfer functions for different input levels and provided a family of gain and phase curves, which constitute the Flame Describing Functions (FDF) and can be used to analyze self-sustained combustion oscillations.
Abstract: Nonlinear features of flame dynamics are characterized by measuring the flame transfer functions for different input levels. This provides a family of gain and phase curves, which constitute the Flame Describing Functions (FDF) and can be used to analyze self-sustained combustion oscillations. Experiments correspond to four different flame geometries established for the same injection conditions: a single conical flame (CF), a “V”-flame, an “M”-flame and a collection of small conical flames (CSCF) stabilized on a perforated plate. It is shown that the gain and phase evolve with the level of modulation and that the response notably depends on the steady-state configuration. In the conical flame case, the gain weakly depends on the level of modulation while the phase changes linearly with frequency at low amplitudes. At higher amplitudes the phase first evolves linearly and then saturates. In the “V” and “M”-flame cases the gain exceeds unity in an intermediate range of frequencies. In that range the gain decreases monotonically as the amplitude increases. The phase evolves in a quasi-linear fashion with frequency and is essentially independent of the amplitude. In the CSCF case the gain also exceeds unity in a narrow range of frequencies and drops first slowly and then more rapidly with the amplitude of input perturbations. The phase is also quasi-linear with frequency but its slope rises as the amplitude increases indicating that the time lag associated to heat release perturbations measured with respect to the incoming disturbances is augmented when the amplitude level becomes large. All these features strongly influence the nonlinear response of the flame, its dynamics under sustained oscillations and the steady-state level reached at the limit cycle.
228 citations
TL;DR: A closed-form approach for performing a Kramers-Kronig transform that can be used to rapidly and reliably retrieve the phase, and thus the resonant imaginary component, from a broadband coherent anti-Stokes Raman scattering spectrum with a nonflat background.
Abstract: We describe a closed-form approach for performing a Kramers–Kronig (KK) transform that can be used to rapidly and reliably retrieve the phase, and thus the resonant imaginary component, from a broadband coherent anti-Stokes Raman scattering (CARS) spectrum with a nonflat background. In this approach we transform the frequency-domain data to the time domain, perform an operation that ensures a causality criterion is met, then transform back to the frequency domain. The fact that this method handles causality in the time domain allows us to conveniently account for spectrally varying nonresonant background from CARS as a response function with a finite rise time. A phase error accompanies KK transform of data with finite frequency range. In examples shown here, that phase error leads to small (<1%) errors in the retrieved resonant spectra.
171 citations
TL;DR: In this article, Heil et al. verified the electrical asymmetry effect (EAE) in a geometrically symmetric dual-frequency CCRF discharge operated at 13.56 and 27.12MHz.
Abstract: Recently a novel approach for achieving separate control of ion flux and energy in capacitively coupled radio frequency (CCRF) discharges based on the electrical asymmetry effect (EAE) was proposed (Heil et al 2008 J. Phys. D: Appl. Phys. 41 165202). If the applied, temporally symmetric voltage waveform contains an even harmonic of the fundamental frequency, the sheaths in front of the two electrodes are necessarily asymmetric. A dc self-bias develops and is a function of the phase angle between the driving voltages. By tuning the phase, precise and convenient control of the ion energy can be achieved while the ion flux stays constant. This effect works even in geometrically symmetric discharges and the role of the two electrodes can be reversed electrically. In this work the EAE is verified using a particle in cell simulation of a geometrically symmetric dual-frequency CCRF discharge operated at 13.56 and 27.12MHz. The self-bias is a nearly linear function of the phase angle. It is shown explicitly that the ion flux stays constant within ±5%, while the self-bias reaches values of up to 80% of the applied voltage amplitude and the maximum ion energy is changed by a factor of 3 for a set of low pressure discharge conditions investigated. The EAE is investigated at different pressures and electrode gaps. As geometrically symmetric discharges can be made electrically asymmetric via the EAE, the plasma series resonance effect is observed for the first time in simulations of a geometrically symmetric discharge. (Some figures in this article are in colour only in the electronic version)
168 citations
TL;DR: Several demonstrations of two-dimensional Fourier-transform spectroscopy are presented, including an example of a phase-cycling scheme that reduces noise and a spectrum that accesses two-quantum coherences, where all excitation pulses require phase locking for detection of the signal.
Abstract: The JILA multidimensional optical nonlinear spectrometer (JILA-MONSTR) is a robust, ultrastable platform consisting of nested and folded Michelson interferometers that can be actively phase stabilized. This platform generates a square of identical laser pulses that can be adjusted to have arbitrary time delay between them while maintaining phase stability. The JILA-MONSTR provides output pulses for nonlinear excitation of materials and phase-stabilized reference pulses for heterodyne detection of the induced signal. This arrangement is ideal for performing coherent optical experiments, such as multidimensional Fourier-transform spectroscopy, which records the phase of the nonlinear signal as a function of the time delay between several of the excitation pulses. The resulting multidimensional spectrum is obtained from a Fourier transform. This spectrum can resolve, separate, and isolate coherent contributions to the light-matter interactions associated with electronic excitation at optical frequencies. To show the versatility of the JILA-MONSTR, several demonstrations of two-dimensional Fourier-transform spectroscopy are presented, including an example of a phase-cycling scheme that reduces noise. Also shown is a spectrum that accesses two-quantum coherences, where all excitation pulses require phase locking for detection of the signal.
TL;DR: In this article, the authors present the theory of how to achieve phase measurements with the minimum possible variance in ways that are readily implementable with current experimental techniques, and they consider both adaptive and nonadaptive measurement schemes.
Abstract: We present the theory of how to achieve phase measurements with the minimum possible variance in ways that are readily implementable with current experimental techniques. Measurements whose statistics have high-frequency fringes, such as those obtained from maximally path-entangled $(|N,0⟩+|0,N⟩)/\sqrt{2}$ (``NOON'') states, have commensurately high information yield (as quantified by the Fisher information). However, this information is also highly ambiguous because it does not distinguish between phases at the same point on different fringes. We provide schemes to eliminate this phase ambiguity in a highly efficient way, providing phase estimates with uncertainty that is within a small constant factor of the Heisenberg limit, the minimum allowed by the laws of quantum mechanics. These techniques apply to NOON state and multipass interferometry, as well as phase measurements in quantum computing. We have reported the experimental implementation of some of these schemes with multipass interferometry elsewhere. Here, we present the theoretical foundation and also present some additional experimental results. There are three key innovations to the theory in this paper. First, we examine the intrinsic phase properties of the sequence of states (in multiple time modes) via the equivalent two-mode state. Second, we identify the key feature of the equivalent state that enables the optimal scaling of the intrinsic phase uncertainty to be obtained. This enables us to identify appropriate combinations of states to use. The remaining difficulty is that the ideal phase measurements to achieve this intrinsic phase uncertainty are often not physically realizable. The third innovation is to solve this problem by using realizable measurements that closely approximate the optimal measurements, enabling the optimal scaling to be preserved. We consider both adaptive and nonadaptive measurement schemes.
TL;DR: In this paper, the phase shift for the electrons produced in the ionization channels leading to the X 2 ⌺ g +, v ǫ = 1, and vǫ Á = 2 states was observed for different states of the ion.
Abstract: We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field We measure the phase of the two-color two-photon ionization transition molecular phase for different states of the ion We observe a 09 shift for the electrons produced in the ionization channels leading to the X 2 ⌺ g + , vЈ = 1, and vЈ = 2 states We relate this phase shift to the presence of a complex resonance in the continuum By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short-lived states, which is often not accessible otherwise DOI: 101103/PhysRevA80011404 PACS numbers: 3380Eh, 3360ϩq, 4265Ky, 8253Kp Ionization of atoms and molecules by absorption of ul-trashort extreme ultraviolet xuv radiation provides rich structural information on the considered species The ioniza-tion process releases an electron wave packet, which can be described as a coherent superposition of partial waves The relative contributions and phases of the partial waves can be extracted from photoelectron angular distributions at a given energy 1 However, the temporal structure of the ejected wave packet, which is imposed by the phase relation between different energy components, is not accessible with such experiments To access this phase, one needs to couple two energy components of the electron wave packet and record the resulting interference This can be achieved by absorption of high-order harmonics of an infrared laser pulse in the presence of the fundamental field An intense laser pulse propagating in a gas jet produces coherent xuv radiation constituted of odd harmonics 2q +1 0 of the fundamental frequency 0 These harmonics are all approximately phase locked with the fundamental and form an attosecond pulse train APT 2 In photoionization experiments with high harmonics, the photoelectron spectrum exhibits equidistant lines resulting from single-photon ionization Fig 1a If an additional laser field with frequency 0 is added, two-photon ionization can occur: absorption of a harmonic photon accompanied by either absorption or stimulated emission of one photon 0 New lines sidebands appear in the spectrum, in between the harmonics Fig 1a Since two coherent quantum paths lead to the same sideband, interferences occur They are observed in an oscillation of the sideband amplitude as the delay between the probe ir and harmonic fields is scanned 2,3 This is the basis of the reconstruction of attosecond beating by interference of two-photon transitions RABBITT technique The phase of the oscillation is determined by the phase difference between consecutive harmonics phase locking and by additional phase characteristics of the ionization process The same process can be described in the time domain The APT creates a train of attosecond electron wave packets The additional laser field acts as an optical gate on the electrons , which can be used to retrieve the temporal profile of the electron wave packets 4,5 This temporal structure is set by the temporal shape of the APT but also by the photoion-ization process Thus, RABBITT measurements with a well-characterized APT give access to the spectral phase of the photoionization 6,7, ie, the temporal dynamics of photo-ionization Recently Cavalieri et al 8 reported a time-resolved measurement of photoionization of a solid target by a single attosecond pulse Conceptually this is close to RABBITT 4,5 but using of an APT rather than a single pulse has major advantages: i the production of APT is much less demanding; ii the spectrum of APT is a comb of narrow harmonics that can be used to identify different photoioniza-tion channels; iii the intensity of the ir beam must be of Ϸ10 11 W cm −2 for RABBITT and about 10 13 W cm −2 with single pulses 9, which can perturb the system Here we study the photoionization of nitrogen molecules with an APT and characterize the outgoing electron wave packets using the RABBITT technique We probe the region just above the ionization threshold of N 2 , which is spectro-scopically very rich 10–12 We show that the " complex resonance " at 723 nm 10,12,13 induces a Ϸ phase change in the molecular phase This effect strongly depends
TL;DR: In this paper, a robust algorithm is presented to estimate the specific differential phase, which is able to work on wrapped phases and keep up with the spatial gradients of rainfall, to provide a high-resolution specific differential phases.
Abstract: The specific differential phase Kdp is one of the important parameters measured by dual-polarization radar that is being considered for the upgrade of the current Next Generation Weather Radar (NEXRAD) system. Estimation of the specific differential phase requires computing the derivative of range profiles of the differential propagation phase. The existence of possible phase wrapping, noise, and associated fluctuation in the differential propagation phase makes the evaluation of derivatives an unstable numerical process. In this paper, a robust algorithm is presented to estimate the specific differential phase, which is able to work on wrapped phases and keep up with the spatial gradients of rainfall, to provide a high-resolution specific differential phase.
TL;DR: In this paper, a coherent fiber array system composed of densely packed fiber collimators with built-in capabilities for adaptive wavefront phase piston and tilt control at each collimator is discussed.
Abstract: We discuss development and integration of a coherent fiber array system composed of densely packed fiber collimators with built-in capabilities for adaptive wavefront phase piston and tilt control at each fiber collimator. In this system, multi-channel fiber-integrated phase shifters are used for phase locking of seven fiber collimators and the precompensation of laboratory-generated turbulence-induced phase aberrations. Controllable x and y displacements of the fiber tips in the fiber collimator array provide additional adaptive compensation of the tip and tilt phase aberration components. An additional control system is utilized for equalization of the intensity of each of the fiber collimator beams. All three control systems are based on the stochastic parallel gradient descent optimization technique. The paper presents the first experimental results of adaptive dynamic phase distortion compensation with an adaptive phase-locked fiber collimator array system.
TL;DR: This work experimentally tested the robustness of Berry's geometric phase for spin-1/2 particles in a cyclically varying magnetic field and demonstrated that the geometric phase contributions to dephasing due to adiabatic field fluctuations vanish for long evolution times.
Abstract: The geometric phase has been proposed as a candidate for noise resilient coherent manipulation of fragile quantum systems. Since it is determined only by the path of the quantum state, the presence of noise fluctuations affects the geometric phase in a different way than the dynamical phase. We have experimentally tested the robustness of Berry's geometric phase for spin-1/2 particles in a cyclically varying magnetic field. Using trapped polarized ultracold neutrons, it is demonstrated that the geometric phase contributions to dephasing due to adiabatic field fluctuations vanish for long evolution times.
01 Jan 2009
TL;DR: The JILA Multidimensional Optical Nonlinear SpecTRometer (JILA-MONSTR) as mentioned in this paper is a robust, ultra-stable platform consisting nested and folded Michelson interferometers that can be actively phase stabilized.
Abstract: The JILA Multidimensional Optical Nonlinear SpecTRometer (JILA-MONSTR) is a robust, ultra-stable platform consisting nested and folded Michelson interferometers that can be actively phase stabilized. This platform generates a square of identical laser pulses that can be adjusted to have arbitrary time delay between them, while maintaining phase stability. The JILA-MONSTR provides output pulses for nonlinear excitation of materials and phase-stabilized reference pulses for heterodyne detection of the induced signal. This arrangement is ideal for performing coherent optical experiments, such as multidimensional Fourier-transform spectroscopy, which records the phase of the nonlinear signal as a function of the time delay between several of the excitation pulses. The resulting multidimensional spectrum is obtained from a Fourier transform. This spectrum can resolve, separate and isolate coherent contributions to the light-matter interactions associated with electronic excitation at optical frequencies. To show the versatility of the JILA-MONSTR, several demonstrations of two-dimensional Fourier-transform spectroscopy are presented, including an example of a phase-cycling scheme that reduces noise.
TL;DR: In this article, a theoretical formalism to describe bimodal atomic force microscopy (AFM) experiments is developed. But it is not suitable for point-mass and continuous models of the cantilever tip system.
Abstract: We develop a theoretical formalism to describe bimodal atomic force microscopy (AFM) experiments. The theory relates observables such as amplitudes and phase shifts to physical properties of the tip-surface interaction. The theory is compatible with point-mass and continuous models of the cantilever-tip system. We explain the ability of the bimodal AFM to map compositional variations under the influence of very small conservative forces. This is achieved by representing the dependence of the phase shift or amplitude of one eigenmode with respect to the amplitude or phase shift of the other mode. The agreement obtained between the theory and the numerical simulations validates the theoretical formalism.
TL;DR: Output mode purities of Laguerre-Gaussian (LG) beams generated from four typical simultaneous amplitude and phase modulation methods with phase-only spatial light modulators (SLMs) are investigated.
Abstract: We investigate output mode purities of Laguerre–Gaussian
(LG) beams generated from four typical simultaneous amplitude and
phase modulation methods with phase-only spatial light modulators
(SLMs). Numerical simulations supposing the practical SLM, i.e., stepwise
phase modulation with a pixelated device, predict an output mode purity
of beyond 0.969 for the LG beams of less than radially and azimuthally
fifth order. Experimental results of generating LG beams are also
shown to demonstrate the effects of the simultaneous phase and amplitude
modulation.
TL;DR: In this paper, the authors demonstrate arbitrary phase control of a single photon without affecting the photon's amplitude profile and verify it with two-photon quantum interference measurements, demonstrating fermionic spatial behaviour of photon pairs.
Abstract: Although the phase of a coherent light field can be precisely known, this is not true for the phase of the individual photons that create the field, considered individually1. Phase changes within single-photon wave packets, however, have observable effects. In fact, actively controlling the phase of individual photons has been identified as a powerful resource for quantum communication protocols2,3. Here we demonstrate arbitrary phase control of a single photon. The phase modulation is applied without affecting the photon's amplitude profile and is verified by means of a two-photon quantum interference measurement4,5, demonstrating fermionic spatial behaviour of photon pairs. Combined with previously demonstrated control of a single photon's amplitude6,7,8,9,10, frequency11, and polarization12, the fully deterministic phase shaping presented here allows for the complete control of single-photon wave packets. Arbitrary phase control within a single photon wave packet is demonstrated and verified by two-photon quantum interference measurements. Combined with the previously demonstrated ability to control a single photon's amplitude, frequency and polarization, the phase shaping presented here allows for the complete control of single-photon wave packets.
TL;DR: A phase-reduction method is formulated for a general class of noisy limit cycle oscillators and it is found that the phase equation is parametrized by the ratio between time scales of the noise correlation and amplitude relaxation of the limit cycle.
Abstract: We formulate a phase-reduction method for a general class of noisy limit cycle oscillators and find that the phase equation is parametrized by the ratio between time scales of the noise correlation and amplitude relaxation of the limit cycle. The equation naturally includes previously proposed and mutually exclusive phase equations as special cases. The validity of the theory is numerically confirmed. Using the method, we reveal how noise and its correlation time affect limit cycle oscillations.
TL;DR: In this article, the Schrodinger equation for a hydrogen atom interact- ing with a linearly polarized laser pulse, whose electric field is given by Et = E0ftcos0t + with Gaussian carrier envelope ft = expt 2 / 2.
Abstract: Three alternative forms of harmonic spectra, based on the dipole moment, dipole velocity, and dipole acceleration, are compared by a numerical solution of the Schrodinger equation for a hydrogen atom interact- ing with a linearly polarized laser pulse, whose electric field is given by Et = E0ftcos0t + with Gaussian carrier envelope ft = expt 2 / 2 . The carrier frequency 0 is fixed to correspond to a wavelength of 800 nm. Spectra for a selection of pulses, for which the intensity I0 = c0E 0 , duration T, and carrier-envelope phase are systematically varied, show that, depending on , all three forms are in good agreement for "weak" pulses with I0 Ib, the over-barrier ionization threshold, but that marked differences among the three appear as the pulse becomes shorter and stronger I0 Ib. Except for scalings by powers of the harmonic frequency, the three forms differ from one another only by "limit contributions" proportional to the expectation values of the dipole moment ztf or dipole velocity ztf at the end tf of the pulse. For long, weak pulses the limit contributions are negligible, whereas for short, strong ones they are not. In the short, strong limit, where ztf 0 and therefore zt may increase without bound i.e., the atom may ionize, depending on ,a n "infinite-time" spectrum based on the acceleration form provides a convenient computational pathway to the corresponding infinite-time dipole-velocity spectrum, which is related directly to the experimentally measured "harmonic photon number spectrum" HPNS. For short, intense pulses the HPNS is quite sensitive to and exhibits not only the usual odd harmonics but also even ones. The analysis also reveals that most of the harmonic photons are emitted during the passage of the pulse. Because of the divergence of zt the dipole- moment form does not provide a numerically reliable route to the harmonic spectrum for very short few- cycle, very intense laser pulses.
TL;DR: It is shown that phase locking arises from hydrodynamics forces alone, and has its origin in the front-back asymmetry of the geometry of their flagellar waveform, and microorganisms can phase lock into conformations which minimize or maximize energy dissipation.
Abstract: Some microorganisms, such as spermatozoa, synchronize their flagella when swimming in close proximity. Using a simplified model (two infinite, parallel, two-dimensional waving sheets), we show that phase locking arises from hydrodynamics forces alone, and has its origin in the front-back asymmetry of the geometry of their flagellar waveform. The time evolution of the phase difference between coswimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase lock into conformations which minimize or maximize energy dissipation.
TL;DR: This work directly generates the Airy beam using a 3/2 phase pattern encoded onto an LCD, and experimental results show a deflection that depends on the square of the distance from the LCD and match theoretical predictions.
Abstract: Accelerated Airy beams have previously been generated using a cubic phase pattern that represents the Fourier transform of the Airy beam. The Fourier transform of this pattern is formed using a system length of 2f, where f is the focal length of the Fourier transform lens. In this work, we directly generate the Airy beam using a 3/2 phase pattern encoded onto an LCD. Experimental results show a deflection that depends on the square of the distance from the LCD and match theoretical predictions. However the system length is much shorter.
TL;DR: A novel approach, based on sub-wavelength spatial phase variations at the focus of high-order beams, to reconfigure the optical near field distribution near plasmonic nanostructures to selectively switch on and off hot-spots sites within a complex antenna architecture is reported.
Abstract: We report on a novel approach, based on sub-wavelength spatial phase variations at the focus of high-order beams, to reconfigure the optical near field distribution near plasmonic nanostructures. We first show how the introduction of phase jumps in the incident field driving a gap nanoantenna strongly affects its near field response. Beyond, we demonstrate the feasibility of exploiting this approach to selectively switch on and off hot-spots sites within a complex antenna architecture.
TL;DR: In this article, an interferometric scheme for unambiguous phase estimation with precision scaling at the Heisenberg limit that does not require adaptive measurements is presented. But it does not resolve the phase ambiguity that exists when multiple passes through a phase shift, or NOON states, are used to obtain improved phase resolution.
Abstract: We derive, and experimentally demonstrate, an interferometric scheme for unambiguous phase estimation with precision scaling at the Heisenberg limit that does not require adaptive measurements. That is, with no prior knowledge of the phase, we can obtain an estimate of the phase with a standard deviation that is only a small constant factor larger than the minimum physically allowed value. Our scheme resolves the phase ambiguity that exists when multiple passes through a phase shift, or NOON states, are used to obtain improved phase resolution. Like a recently introduced adaptive technique (Higgins et al 2007 Nature 450 393), our experiment uses multiple applications of the phase shift on single photons. By not requiring adaptive measurements, but rather using a predetermined measurement sequence, the present scheme is both conceptually simpler and significantly easier to implement. Additionally, we demonstrate a simplified adaptive scheme that also surpasses the standard quantum limit for single passes.
07 Jun 2009
TL;DR: In this paper, an integrated 60 GHz active and passive phase shifters for RF-path phase-shifting phased array transceivers are demonstrated. But the authors focus on the phase shifting approach for 60 GHz phased arrays.
Abstract: Integrated 60-GHz active and passive phase shifters for RF-path phase-shifting phased array transceivers are demonstrated in this paper. The reflection-type passive phase shifter achieves ≫180° phase variation across the 57GHz–64GHz band with insertion loss varying from 4.2dB–7.5dB at 60GHz. The active phase shifter employs vector-interpolation architecture and achieves 360° phase variation, −2dB gain, 12GHz 3dB bandwidth and 16.5dB noise figure at 60GHz. Measurements over process and temperature are also discussed and comparisons are drawn between active and passive phase shifting approach for 60GHz phased arrays.
TL;DR: A framework to reduce the unwrapping errors of the measurement system using a digital multiple-wavelength phase- shifting algorithm and significantly alleviated the measurement errors caused by the phase noise.
Abstract: We address a framework to reduce the unwrapping errors of the measurement system using a digital multiple-wavelength phase- shifting algorithm. In particular, the following framework is proposed: 1 smooth the raw phase by smoothing the sine and cosine images of the phase computation of the inverse tangent function; 2 locate and re- move the incorrectly unwrapped points by the monotonicity condition of the phase map; 3 obtain the unwrapped phase map for the shortest wavelength without smoothing; 4 detect holes and fill them to preserve as much useful information as possible. Experiments demonstrated that the proposed framework significantly alleviated the measurement errors caused by the phase noise. © 2009 Society of Photo-Optical Instrumentation
TL;DR: In this paper, it was shown that the condition for achieving the quantum Cramer-Rao bound of phase estimation in conventional two-path interferometers is that the state is symmetric with regard to an (unphysical) exchange of the two paths.
Abstract: It is shown that the condition for achieving the quantum Cramer-Rao bound of phase estimation in conventional two-path interferometers is that the state is symmetric with regard to an (unphysical) exchange of the two paths. Since path symmetry is conserved under phase shifts, the maximal phase sensitivity can be achieved at arbitrary bias phases, indicating that path-symmetric states can achieve their quantum Cramer-Rao bound in Bayesian estimates of a completely unknown phase.