Ultrashort in-plane semiconductor microlasers with high-reflectivity microstructured mirrors

We present very compact, as short as 20 m long, low-threshold in-plane semiconductor lasers operating at a wavelength of 980 nm, in which microstructured mirrors have been formed at both cavity ends by deep reactive ion etching (RIE). The back mirror consists of a seven-period third order Bragg reflector with a measured reflectivity of 95%. The front mirror has a similar configuration, but consists of three periods with a lower reflectivity (80%) in order to allow output coupling. Lasing has been achieved from 20 m long and 8 m wide devices exhibiting a current threshold of 7 mA. These are among the shortest in-plane Fabry–Perot electrically pumped lasers demonstrated to date. Design issues are discussed, along with experimental data from which values for the reflectivity of the mirrors are derived. State-of-the-art electron beam lithography (EBL) and high-aspect-ratio RIE have been used for device fabrication, while additional strategies are proposed for the further improvement of the device performance.     

Small-signal modulation characteristics for 1.5 μm lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers

The small-signal modulation characteristics of 1.5 m lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers and their temperature dependence have been calculated. It is found that the maximum bandwidth of the InGaNAs/GaAs quantum well lasers is about 2.3 times larger than that of the InGaAs/InP quantum well lasers due to the high differential gain which results from the large electron effective mass in the dilute nitride system. The slope efficiency for the 3 dB bandwidth as a function of optical density is twice as large for InGaNAs/GaAs as for InGaAs/InP quantum well lasers.     

Classical Roots of the Unruh and Hawking Effects

Although the Unruh and Hawking phenomena are commonly linked to field quantization in accelerated coordinates or in curved space-times, we argue that they are deeply rooted at the classical level. We maintain, in particular, that these effects should be best understood by considering how the special-relativistic notion of particle gets blurred when employed in theories including accelerated observers or in general-relativistic theories and that this blurring is an instantiation of a more general behavior arising when the principle of equivalence is used to generalize classical or quantum special-relativistic theories to curved space-times or accelerated observers. A classical analogue of the Unruh effect, stemming from the noninvariance of the notion of electromagnetic radiation as seen by inertial and accelerated observers, is illustrated by means of four gedanken-experimente. The issue of energy balance in the various cases is also briefly discussed.     

Measurement of Optical Constants of CVD-Diamond for Short-Wavelength Far-Infrared Lasers

A diagnostic system using short-wavelength far-infrared (FIR) lasers (40–70 m in wavelength) is now being developed for high density and large volume plasmas. In the wavelength region, a CVD-diamond is the excellent materials for optical windows of the laser and the plasma vessel and beam splitters of a multichannel interferometer. To design these optical elements, the optical constants (refractive index n, absorption coefficient and transmissivity T) of the CVD-diamond have been measured precisely by using FIR lasers of 48-, 57- and 71-m in wavelength. As an example, the result for 57.1511 m light is n = 2.383(1) ± 0.002, = 0.19 ± 0.05 cm^-1 and T = 97.5 ± 1.5% at 1.023 mm in thickness.     

Foundation for Quantum Computing

In this paper we introduce a minimal formal intuitionistic propositional Gentzen sequent calculus for handling quantum types, quantum storage being introduced syntactically along the lines of Girard's of course operator !. The intuitionistic fragment of orthologic is found to be translatable into this calculus by means of a quantum version of the Heyting paradigm. When realized in the category of finite dimensional Hilbert spaces, the familiar qubit arises spontaneously as the irreducible storage capable quantum computational unit, and the necessary involvement of quantum entanglement in the quantum duplication process is plainly and explicitly visible. Quantum computation is modelled by a single extra axiom, and reproduces the standard notion when interpreted in a larger category.     

Trilinear generally covariant equations

Field equations for n-frames h ^a that are possible in the theory of absolute parallelism are considered. It is shown that in three cases the equations can, after the substitution h ^a =H^pH ^a (H=det H ^a , p is an n-dependent constant), be written in a trilinear form that contains only the matrix H _a and its derivatives and not H ^a . It is shown that the equations are still regular for degenerate but finite matrices H _a if rank H _a 2.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 22–27, February, 1991.     

A Strategy for a Vanishing Cosmological Constant in the Presence of Scale Invariance Breaking

Recent work has shown that complex quantum field theory emerges as a statistical mechanical approximation to an underlying noncommutative operator dynamics based on a total trace action. In this dynamics, scale invariance of the trace action becomes the statement 0 = Re Tr T , with T the operator stress energy tensor, and with Tr the trace over the underlying Hilbert space. We show that this condition implies the vanishing of the cosmological constant and vacuum energy in the emergent quantum field theory. However, since the scale invariance condition does not require the operator T to vanish, the spontaneous breakdown of scale invariance is still permitted.     

R-matrix methods for studying nuclear effects in μCF

Properties ofR-matrix theory that are useful for studying muon-catalyzed fusion reactions are reviewed, and applications to the dt system are discussed, using both improved adiabatic and non-adiabatic (variational) wave functions. We give complex eigenvalues and - sticking fractions for the (L, v)=(0,0) and (0, 1) states of dt using variational Hamiltonian matrix elements that have been properly symmetrized by means of the Block operator. Expressions for the fusion rate and - sticking fraction are developed from a time-dependent theory that uses the complex-energy states corresponding to the poles of the systemS-matrix. These are shown to reduce with the appropriate approximations to the expressions and values commonly used. Additional nuclear effects on these quantities can easily be studied within the framework developed, but they are not expected to be large.     

Analysis of the effects of doping and barrier design on the small-signal modulation characteristics of long-wavelength multiple quantum well lasers

This theoretical work has modelled the small signal response of InGaAsP and InGaAlAs multiple quantum well (MQW) lasers based on an ambipolar carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated.For the InGaAsP-based system, the optimization for maximum 3 dB bandwitdth shows that the optimum width is about 5 nm for 1.1 m barriers and 7 nm for 1.2 m barriers. The optimum barrier bandgap wavelength is about 1.1 m for the barrier width of 6 nm, about 1.15 m for 8 nm and 10 nm barriers. The p-doped MQW exhibits a higher modulation bandwidth because of its high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the potential for a higher modulation bandwidth. For the InGaAlAs-based system, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 m, and 6 nm for 1.2 m. The optimum barrier bandgap wavelength is about 1.1 m for a barrier width of 4 nm, and about 1.2 m for 6, 8 and 10 nm.     

An Approach to Linear Scalable DH-PHEMT Model for Millimeterwave Application

This paper describes a scalable small-signal equivalent circuit for 0.25 m gatelength Double Heterojunction delta-doped PHEMTs. The scaling rules for all elements except the pad capacitances and bondwire inductances have been determined. Good agreement is obtained between simulation results and measured results for 2 times 20 m , 2 times 40 m, 2 times 60 m, 2 times 100 m gate width (number of gate fingers times unit gate width) DH PHEMT.     

The lasing mechanism of nuclear-pumped IR lasers at krypton and argon atomic transitions

For studying the lasing mechanism of nuclear-pumped IR lasers at krypton and argon atomic transitions, the kinetics of the plasma process is considered and computations are made for the energy and threshold characteristics of He-Kr (=2.52 m) and He-Ar (=1.79 m) lasers excited by uranium fission fragments. The calculated optimal pressures, mixture compositions, laser output powers and threshold characteristics agree satisfactorily with the experimental ones.     

Actively mode-locked 1.3 and 1.55 μm InGaAsP diode lasers

Active mode-locking of uncoated InGaAsP diode lasers having an external diffraction grating cavity was investigated experimentally. A high frequency r.f. signal and short-duration electrical pulses were used to drive the lasers. The pulse duration was measured by an ultrafast streak camera. Pulses as short as 13 ps at 1.3m and 29 ps at 1.55m were generated at a repetition rate of 1 GHz. The reason for obtaining broader pulses from the 1.55m laser which had the same structure as the 1.3m diode laser is explained.Formerly with GEC Hirst Research Centre, Wembley, Middlesex, UK.     

Instead of particles and fields: A micro realistic quantum “smearon” theory

A fully micro realistic, propensity version of quantum theory is proposed, according to which fundamental physical entities—neither particles nor fields—have physical characteristics which determine probabilistically how they interact with one another (rather than with measuring instruments). The version of quantum smearon theory proposed here does not modify the equations of orthodox quantum theory: rather it gives a radically new interpretation to these equations. It is argued that (i) there are strong general reasons for preferrring quantum smearon theory to orthodox quantum theory; (ii) the proposed change in physical interpretation leads quantum smearon theory to make experimental predictions subtly different from those of orthodox quantum theory. Some possible crucial experiments are considered.     

Monte-Carlo calculation of bound-state properties

We elaborate on the role of the Green's function Monte-Carlo method in connection with quantum few-body systems and their computational treatment algorithms for calculation of bound-state properties are presented. We report results obtained from Green's function Monte-Carlo calculations both of ground-state properties of the mesic moleculesdt,dd, andpd as well as of excited states of the three-dimensional anharmonic oscillator and thedt molecule.Deceased     

Matter and light wave interferometry in gravitational fields

We consider the problem of finding the quantum mechanical phase associated with the propagation of a particle in a given external gravitational field, and conclude that it ism ds. In weak fieldsh this allows us to calculate the gravitationally induced phase on a freely traveling particle as 1/2 h P dx whereP is the ordinary momentum. This formula has the expected Newtonian limit and is then used to calculate effects in matter wave interferometry such as those due to gravity waves and the dragging of the ether frame by rotating bodies. Light wave interferometry is then considered and is shown to be also described by 1/2 h K dx , whereK is the wave vector of the light, and the integral is along the path of the ray. Matter and light wave interferometry are compared in various cases.A preliminary version of this work was presented at the Grenoble Workshop on Neutron Interferometry, June 1978.     

AN EXTENSION OF “POPPER'S EXPERIMENT” CAN TEST INTERPRETATIONS OF QUANTUM MECHANICS

Karl Popper proposed a way to test whether a proposed relation of a quantum-mechanical state to perceived reality in the Copenhagen interpretation (CI) of quantum mechanics—namely that the state of a particle is merely an expression of what is known about the system—is in agreement with all experimental facts. A conceptual flaw in Popper's proposal is identified and an improved version of his experiment (called Extension step 1)—which fully serves its original purpose—is suggested. The main purpose of this paper is to suggest to perform this experiment. The results of this experiment predicted under the alternative assumptions that the CI or the many-worlds interpretation (MWI) is correct are shown to be identical. Only after a further modification (called Extension step 2) (the use of an ion isolated from the macroscopic environment as particle detector) the predictions using the respective interpretations become qualitatively different. This is because what is known by a human observer H can fail as a basis for the prediction of the statistical distribution of measurement results within the MWI in special cases: The temporal evolution of a system un-entangled with H (like the isolated ion) can depend on another system's state components that are entangled with states ortogonal to H. Thus—within the CI—for H they are known not to exist. Yet H can infer their existence by studying the evolution of the ion.     

Positivity of entropy production in nonequilibrium statistical mechanics

We analyze different mechanisms of entropy production in statistical mechanics, and propose formulas for the entropy production ratee() in a state . When is steady state describing the long term behavior of a system we show thate()0, and sometimes we can provee()>0.     

Fabrication and characteristics of double-fused vertical-cavity lasers

We discuss the fabrication process and characteristics of three consecutive runs of double-fused 1.5-m vertical-cavity lasers. We have measured light-current characteristics of over three hundred lasers with ten different diameters between 6 and 60 m and observe a yield of over 95%. The process and design improvements resulted in a low pulsed threshold current of 3 mA on a number of 6- and 8-m-diameter devices and threshold current density of 2 kA cm^–2 on 60-m-diameter devices at room temperature.     

Hermiticity of Quantum Observables Versus Commutation Relations

In order to obtain sum rules and spectral representations the Hermiticity property , A = A, of observables is used. It is shown that for certain and the property turns out to be inconsistent with the commutation relations that contain A. The known Schwinger paradox is explained by this inconsistency.