Masud Mansuripur is professor and Chair of Optical Data Storage at the College of Optical Sciences of the University of Arizona in Tucson. He is the author of four books and over 250 technical papers in peer-reviewed journals. Dr. Mansuripur's areas of interest include optical and magnetic data storage, electromagnetic theory, information theory, and problems associated with radiation pressure and photon momentum inside material media.

**Publications**(76)

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*R*, mass

*m*, and total electrical charge

*q*, having an oscillatory angular velocity Ω(

*t*) around a fixed axis, is a model for a magnetic dipole that radiates an electromagnetic field into its surrounding free space at a fixed oscillation frequency ω. An exact solution of the Maxwell-Lorentz equations of classical electrodynamics yields the self-torque of radiation resistance acting on the spherical shell as a function of

*R*,

*q*, and ω. Invoking the Newtonian equation of motion for the shell, we relate its angular velocity Ω(

*t*) to an externally applied torque, and proceed to examine the response of the magnetic dipole to an impulsive torque applied at a given instant of time, say,

*t*= 0. The impulse response of the dipole is found to be causal down to extremely small values of

*R*(i.e., as

*R*→ 0) so long as the exact expression of the self-torque is used in the dynamical equation of motion of the spherical shell.

**. While the angular spread of the**

*k**k*-vectors gives rise to diffractive effects, it is the frequency-dependence of the refractive index of the host medium that is commonly associated with optical dispersion. When the spectral distribution of the wave-packet is confined to a narrow band of frequencies, and also when the spread of the

*k*-vectors is not too broad, it is possible, under certain circumstances, to obtain analytical expressions for the local and/or global trajectory of the packet’s envelope as it evolves in time. This paper is an attempt at a systematic description of the underlying physical assumptions and mathematical arguments leading to certain well-known properties of narrowband electromagnetic wave-packets in the presence of diffractive as well as (temporally) dispersive effects.

*g*= 2, for Zeeman splitting, for relativistic corrections to Schrödinger’s equation, for Darwin’s term, and for the correct 1/2 factor in the spin-orbit coupling energy.

*without*the need to renormalize the particle’s mass – or to discard undesirable infinities. The relativistic expression of self-force known as the Abraham- Lorentz-Dirac equation is derived in two different ways. Certain properties of the self-force are examined, and an approximate formula for the self-force, first proposed by Landau and Lifshitz, is discussed in some detail.

*R*<30 Ω/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thin film coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (

_{s}*V*= 720 mV) and short-circuit current-density (

_{oc}*J*= 0.96 mA/cm

_{sc}^{2}), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (

*V*= 782 mV) and a decent short-circuit current (

_{oc}*J*= 3.96 mA/cm

_{sc}^{2}), with roughly 1.5% optical-to-electrical conversion efficiency.

_{s}) of ~ 200 Ω/sq and ~ 150 Ω/sq, respectively.

*without*the need for hidden entities, provided that the Einstein-Laub laws of force and torque are used in place of the standard Lorentz law. Einstein and Laub published their paper in 1908, but the simplicity of the conventional Lorentz law overshadowed the subtle features of their formulation which, at first sight, appears somewhat complicated. However, that slight complication turns out to lead to subsequent advantages in light of Shockley’s discovery of hidden momentum, which occurred more than a decade after Einstein had passed away. In this paper, we show how the Einstein-Laub formalism handles the underlying problems associated with certain paradoxes of classical electrodynamics involving a static distribution of electric charges and a magnet whose magnetization slowly fades away in time. The Einstein-Laub laws of electromagnetic force and torque treat these paradoxes with elegance and without contradicting the existing body of knowledge, which has been confirmed by more than one and a half century of theoretical and experimental investigations.

_{g}of the material (both positive entities), and not the phase refractive index n =√με , which is negative in negative-index media. One approach to investigating the exchange of momentum between electromagnetic waves and material media is via the Doppler shift phenomenon. In this paper we use the Doppler shift to arrive at an expression for the radiation pressure on a mirror submerged in a negative-index medium. In preparation for the analysis, we investigate the phenomenon of Doppler shift in various settings, and show the conditions under which a so-called “inverse” Doppler shift could occur. We also argue that a recent observation of the inverse Doppler shift upon reflection from a negative-index medium cannot be correct, because it violates the conservation laws.

_{o}carry energy in the amount of ħω

_{o}, where ħ is Planck’s reduced constant, enables one to relate the Doppler shift to the amount of energy exchanged. Under certain circumstances, the knowledge of exchanged energy leads directly to a determination of the momentum transferred from the photon to the material body, or vice versa.

_{EM}(r,t)=E(r, t)×H(r,t)/c

^{2}emerges as the universal electromagnetic momentum that does not depend on whether the field is propagating or evanescent, and whether or not the host media are homogeneous, transparent, isotropic, linear, dispersive, magnetic, hysteretic, negative-index, etc. Any variation with time of the total electromagnetic momentum of a closed system results in a force exerted on the material media within the system in accordance with the generalized Lorentz law.

_{EM}= S(r,t)/c

^{2}. Here S(r, t) = E(r, t)×H(r, t) is the Poynting vector at point r in space and instant t in time, E and H are the local electromagnetic fields, and c is the speed of light in vacuum. The above statement is true irrespective of whether the waves reside in vacuum or within a ponderable medium, which medium may or may not be homogeneous, isotropic, transparent, linear, magnetic, etc. When a light pulse enters an absorbing medium, the force experienced by the medium is only partly due to the absorbed Abraham momentum. This absorbed momentum, of course, is manifested as Lorentz force (while the pulse is being extinguished within the absorber), but not all the Lorentz force experienced by the medium is attributable to the absorbed Abraham momentum. We consider an absorptive/ reflective medium having the complex refractive index n

_{2}+i κ

_{2}, submerged in a transparent dielectric of refractive index n

_{1}, through which light must travel to reach the absorber/reflector. Depending on the impedance-mismatch between the two media, which mismatch is dependent on n

_{1}, n

_{2}, κ

_{2}, either more or less light will be coupled into the absorber/reflector. The dependence of this impedance-mismatch on n

_{1}is entirely responsible for the appearance of the Minkowski momentum in certain radiation pressure experiments that involve submerged objects.

_{EM}(r,t)=E(r,t)×H(r,t)/c

^{2}, whether the field is in vacuum or in a ponderable medium. [Homogeneous, linear, isotropic media are typically specified by their electric and magnetic permeabilities ε

_{ο}ε(ω) and μ

_{ο}μ(ω).] The electromagnetic momentum residing in a ponderable medium is often referred to as Abraham momentum. When an electromagnetic wave enters a medium, say, from the free space, it brings in Abraham momentum at a rate determined by the density distribution Ρ

_{EM}(r,t), which spreads within the medium with the light's group velocity. The balance of the incident, reflected, and transmitted (electromagnetic) momenta is subsequently transferred to the medium as mechanical force in accordance with Newton's second law. The mechanical force of the radiation field on the medium may also be calculated by a straightforward application of the generalized form of the Lorentz law. The fact that these two methods of force calculation yield identical results is the basis of our claim that the equations of electrodynamics (Maxwell + Lorentz) comply with the momentum conservation law. When applying the Lorentz law, one must take care to properly account for the effects of material dispersion and absorption, discontinuities at material boundaries, and finite beam dimensions. This paper demonstrates some of the issues involved in such calculations of the electromagnetic force in magnetic dielectric media.

*p*of the slit array is comparable to (or somewhat below) the incident wavelength λ

_{o}, the Bloch mode method requires only the 10-20 lowest-order modes of the slit array to achieve stable solutions; we find the Bloch mode method to be an effective tool for studying dielectric-filled apertures in highly conductive hosts.

^{8}), microsphere resonators possess a narrow reflection bandwidth. This feature enables construction of single-frequency fiber lasers even when the cavity is long. We also propose and demonstrate an active Q-switched fiber laser using a high-Q micro-sphere resonator as the Q-switching element. The laser cavity consists of an Er-doped fiber as the gain medium, a glass micro-sphere reflector (coupled through a fiber taper) at one end of the cavity, and a fiber Bragg grating reflector at the other end. The reflectivity of the micro-sphere is modulated by changing the gap between the micro-sphere and the fiber taper. Active Q-switching is realized by oscillating the micro-sphere in and out of contact with the taper. Nonlinear effects (such as stimulated Raman lasing) were also observed in our setup at relatively low pump powers.

_{2}Te

_{3}pseudo-binary compound film is investigated with sub-nanosecond laser pulses using a pump-and-probe technique. We also use a two-laser static tester to estimate the onset time of crystallization under a 2.0-μs-pulse excitation. Experimental results indicate that the formation of a melt-quenched amorphous mark is completed in about one nanosecond, but crystalline mark formation on an as-deposited amorphous region requires several hundred nanoseconds. Simple arguments based on heat diffusion are used to explain the time scale of amorphization and the threshold for creation of a burned-out hole on the phase-change film.

^{c}, a general-purpose scalar diffraction modeling program, to observe the effects on the error signals due to focusing lens misalignment, Seidel aberrations, and optical crosstalk (feedthrough) between the focusing and tracking servos. Using the results of the astigmatic/push-pull system as a basis for comparison, a novel focus/track-error detection technique that utilizes a ring toric lens is evaluated as well as the obscuration method (focus error detection only).

_{O}. If desired, the trellis may be confined in the beginning and/or at the end to a subset of states. We then show a simple method of enumeration that assigns a number to each code word in the trellis according to is lexicographic order. All the necessary information for enumerative encoding and decoding of binary data will be subsequently stored in an array of size L

_{O}X (Omega) ; both encoding and decoding can be achieved with a few simple operations using this table. In short, arbitrarily long blocks of data can be encoded into sequences that satisfy arbitrary constraints, with algorithms that are easy to implement. Since no additional constraints are imposed, the rates approach Shannon's noiseless channel capacity in the limit of long sequences. We present ideas for correction of random errors that occur in modulated sequences, so that errors in readout can be corrected prior to demodulation. The post-modulation error correction codes are necessary when modulation code words are long, in which case small errors can destroy large quantities of data. Also introduced in this paper is a simple, efficient algorithm for burst-error-correction. The primary application of the ideas of this paper is in the area of data encoding/decoding as applied in magnetic and optical data storage systems.

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The ultimate limit in data storage is imposed by the available signal-to-noise ratio (SNR) in readout. We discuss the sources of signal, noise, and jitter in optical data storage, and examine various techniques for evaluating their contributions to the readout waveform. We also describe methods of improving the signal and reducing the noise as practiced today, as well as promising techniques for future devices. Examples from conventional as well as novel optical storage systems will be used to clarify the underlying concepts.

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