Luminescence properties of divinylbenzene and methylmethacrylate copolymers

This article describes our attempts to produce ”nonexcimer” polymer systems by means of rigid fixation of chromophore groups positioned between two vinyl bonds. Divinylbenzene and methylmethacrylate copolymers were chosen as such systems. Study of the optical properties of synthesized copolymers showed their constancy in a wide region of specific concentrations of chromophore groups. The absence of luminescent properties modification in a wide concentrations range proves the possibility of eliminating the intrasystem energy traps by means of rigid fixation of chromophores in polymer.     

Novel approach to a perfect lens

Within the framework of an exact analytical solution of Maxwell equations in a space domain, it is shown that optical scheme based on a slab with negative refractive index (n = −1) (Veselago lens or Pendry lens) does not possess focusing properties in the usual sense. In fact, the energy in such systems does not go from object to its “image,” but from object and its “image” to an intersection point inside a metamaterial layer, or vice versa. A possibility of applying this phenomenon to a creation of entangled states of two atoms is discussed. The article is published in the original.     

Nonlinear optical effects of near-IR femtosecond laser radiation on the morphology and structure of a nerve cell in the field of an optical trap

Changes in the morphology and structure of a neuron cell in the process of manipulating it with an femtosecond laser tweezers operating at a wavelength of 800 nm are examined. The changes in the morphology and structure are caused by the nonlinear optical absorption and multiphoton excitation of cell biomacromolecules by femtosecond pulses of light. The cell nucleus is demonstrated to be destroyed by focused femtosecond laser radiation (FLR). Changes in the state of the cytoplasmic nucleoproteins and the hydrophobicity of the plasmatic membrane under the action of FLR focused inside the cell are observed. By the example of the simultaneous displacement of the neuron with a cw laser and cutting of a neuron with FLR, the operation of holographic optical manipulator and a scalpel based on the use of femtosecond and cw lasers is considered. The possibility of the simultaneous microsurgical operation with several optical foci of FLR is demonstrated.     

Polarization-bistable vertical-cavity surface-emitting lasers: application for optical bit memory

We summarize recent results on polarization-bistable vertical-cavity surface-emitting lasers (VCSELs) and their application to optical buffer memory. All-optical flip-flop operation with very low switching energies and high repetition rates is achieved. An optical buffer memory consisting of a two-dimensional array of polarization-bistable VCSELs, in which the bit state of the optical signal, “0” or “1”, is stored as a lasing linear polarization state of 0 or 90°. Input data stored as the polarization states of the first VCSEL are transferred to the polarization states of the second VCSEL. In our experiments with 980 nm polarization-bistable VCSELs, 10 Gbit/s optical buffering, 2-bit optical buffering, and a shift register function have been successfully demonstrated.     

Plasmonic resonance enhancement of single gold nanorod in two-photon photopolymerization for fabrication of polymer/metal nanocomposites

We investigated the plasmonic resonance enhanced two-photon photopolymerization (PETPP) using the isolated chemical synthesized gold nanorods for fabrication of polymer/metal nanocomposites. The isolated gold nanorods with the plasmonic resonance band around 750 nm covered by photoresist were irradiated by a femtosecond laser with the wavelength of 780 nm. The PETPP trigged by the plasmonic resonance enhancement of gold nanorods was localized only in the distance smaller than 30 nm from the surface of gold nanorods, which matched the distance of plasmonic resonant enhanced field of the gold nanorod. The shapes of obtained polymer/gold nanocomposites were changed from the “dumbbell” to the “ellipsoid” with the increase of laser irradiating intensity used for PETPP. This study would provide a potential method for fabricating the plasmonic nanomaterials and nanostructures of polymer/metal nanocomposites, which could be expected to be applied in the emerging fields such as nanophotonics, nanobiosensor, nanolithography.     

Ionization of a two-electron atom in a strong electromagnetic field

A one-dimensional model of a helium atom in an intense field of a femtosecond electromagnetic pulse has been constructed using the Hartree technique. “Exact” calculations have been compared to the approximations of “frozen” and “passive” electrons. A nonmonotonic dependence of the single-electron ionization probability on the radiation intensity has been detected. Minima in the ionization probability are due to multiphoton resonances between different atomic states due to the dynamic Stark effect. We suggest that the ionization suppression is due to the interference stabilization in this case. Zh. éksp. Teor. Fiz. 112, 470–482 (August 1997)     

Exponential sums with continuous arguments,interference and factorization

We take advantage of the interesting connection between truncated exponential sums with continuous arguments (CTES) in number theory and interference in Physics in order to investigate the challenging problem of factoring large numbers. In particular we develop a novel method of factorization based on the use of an optical computer able to reproduce “CTES interferograms” by exploiting polychromatic interference. The scaling properties at the core of such “factoring” interferograms allows, in principle, the prime number decomposition of several large integers.     

Characteristic of a negative corona discharge in active media of Xe(6p−5d) and eximer lasers

The article contains results of a study of electric and optical characteristics of a negative corona discharge in a “needles-grid” electrode system in the mixtures He/Xe and He/Xe(Kr)/HCl, which are used in periodic pulsed electric-discharge Xe(6p−5d), XeCl, and KrCl lasers. The corona discharge was ignited in a multielectrode system whose length is commensurable with the length of the active medium of the lasers. Voltage-current characteristics, radiation spectra of the discharge plasma, and the dependences of the radiation intensity of atomic spectral lines and the band λ=308 nm of XeCl (B-X) on parameters of the corona discharge are studied. For the mixture He/Xe the corona discharge exists as a spatially homogeneous discharge that is intermediate between corona and glow discharges and is transformed into an anode streamer at higher charge voltages. Collisional purification of the 6p states of the Xe atom by helium was observed. In the mixture He/Xe/HCl the corona discharge is ignited in the form of individual generation zones and a dark external region and can be used in electric systems for pumping the active media of XeCl and KrCl lasers. Uzhgorod State University, 46, Pidgirna St., Uzhgorod, 294000, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 205–210, March–April, 1998.     

Effect of the state of a quantized electromagnetic field on the interaction with an atom with allowance for the continuum

This paper studies the effect of a transition into the continuous spectrum on the “collapse” and “revival” of population oscillations in an atom. It is shown that at large values of the mean number of photons in a radiation field and in conditions of weak ionization the phenomena of collapse and revival can still be observed, but the amplitude of population oscillations decreases exponentially because of the damping of the level. The interaction of a quantized electromagnetic field with a Λ system of an atom when one state is continuous is examined. Expressions are derived for the probability of “survival” of the atom when the quantized field was initially in a state with a given number of photons and when it was in a coherent state. An approximate calculation of the sum in averaging over the photon number distribution in the case of a coherent field leads to expressions for the probabilities of survival of the atom that transform into expressions, as the mean number of photons tends to infinity, corresponding to the case of a field in the representation of a fixed number of photons. The possibility of a stable state existing in a coherent quantized field is examined. It is found that for a Λ system the condition for the existence of a stable state remains valid in the case of a coherent state of the field when the photon number is large. Zh. éksp. Teor. Fiz. 113, 1193–1205 (April 1998)     

A vision for laser induced particle acceleration and applications

High intensity lasers interacting with solid and gas targets can produce energetic beams of electrons, protons, heavy ions, photons and neutrons. There is the potential for producing “table top” sources of radiation for many different applications.     

Double radiooptical resonance in <Superscript>87</Superscript>Rb atomic vapor in cells with antirelaxation wall coating

The object of investigation is double radiooptic resonance in ⁸⁷Rb atomic vapor contained in a cell covered by an antirelaxation coating. The Dicke narrowing is studied in terms of the quantum-kinetic approach. It is found that optical pumping using a laser with a “wide” radiation spectrum makes it possible to improve the short-term stability of the frequency standard by an order of magnitude compared with a narrow-spectrum laser.     

Lateral field instability and six-wave mixing in a diode laser with broad active area

The electromagnetic field inside a nonlinear active medium of a laser is considered as a system of counterpropagating waves. Such an approach changes radically an earlier studied behavior of the lateral field instability due to self-deformaion (or self-focusing). In our calculations we used an expression for a laser field in the form of two “strong” counterpropagating waves whose complex amplitudes have weak perturbations. Amplitude perturbations of each of the “strong” waves can be presented by two spatial harmonics corresponding to two weak perturbation waves with wave vectors making some tilted angle ±φ with the cavity axis. Thus six waves would participate in the interaction: two counterpropagating strong waves and two pairs of weak waves. Using this approach, we have developed a theory for the propagation of four “weak” perturbation waves in a nonlinear amplifying medium in the presence of two counterpropagating “strong” waves. It is shown that perturbation waves with tilted angle φ⋍0.5–1.2° inside the active region, and respecively, with the side lobes of the far-field pattern at ∼1.7–4°, have the greatest growth increment. These perturbation waves produce lateral intensity modulation with period 10–30 μm for the 0.85 μm lasing wavelength. The appearance of such waves corresponds to the instability threshold of a homogeneous lateral distribution of optical power in a diode laser. The present theory makes it possible to investigate the stability of the homogeneous lateral optical intensity distribution in a diode laser of any design. This allows one to choose a suitable design of a laser with a homogeneous lateral distribution at high radiation power. Translated from Preprint No. 43 (1992) of the Lebedev Physics Institute, Russian Academy of Sciences.     

Watching it boil: Continuous observation for the quantum zeno effect

The quantum Zeno effect (QZE) is often associated with the ironic maxim, “a watched pot never boils”, although the notion of “watching” suggests a continuous activity at odds with the usual (pulsed measurement) presentation of the QZE. We show how continuous watching can provide the same halting of decay as the usual QZE, and, for incomplete hindrance, we provide a precise connection between the interval between projections and the response time of the continuous observer. Thus, watching closely, but not so closely as to halt the “boiling”, is equivalent to—gives the same degree of partial hindrance as—pulsed measurements with a particular pulsing rate. Our demonstration is accomplished by treating the apparatus for the continuous watching as a fully quantum object. This in turn allows us a second perspective on the QZE, in which it is the modified level structure of the combined system/apparatus Hamiltonian that slows the decay. This and other considerations favor the characterization “dominated time evolution” for the QZE.     

Substantiation of the mechanism of biphoton nonresonance excitation of molecules of bacteriochlorophyll of purple bacteria by femtosecond pulses

In a series of published experimental works, there has been observed nonresonance biphoton excitation, by femtosecond IR pulses (1250–1500 nm) of molecules of bacteriochlorophyll-a and the pigment in the composition of light-absorbing natural “antenna” complexes of photosynthesizing purple bacteria. The authors of these works believe that IR quanta excite hypothetical forbidden levels of pigments of these bacteria in the dual frequency range of 625–750 nm. In this study, an alternative mechanism of intramolecular electron transport apparently responsible for this phenomenon is suggested and substantiated. The mechanism should manifest itself in powerful electric fields, which are achieved in the pulses of picofemtosecond lasers.     

Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime

Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated.     

Analysis of the cluster formation in two-component cylindrical bottle-brush polymers under poor solvent conditions. A simulation study

Two-component bottle-brush polymers, where flexible side chains containing N = 20, 35 and 50 effective monomers are grafted alternatingly to a rigid backbone, are studied by Molecular Dynamics simulations, varying the grafting density s \sigma and the solvent quality. Whereas for poor solvents and large enough s \sigma the molecular brush is a cylindrical object with monomers of different type occupying locally the two different halves of the cylinder, for intermediate values of s \sigma an axially inhomogeneous structure of “pearl-necklace” type is formed, where microphase separation between monomers of different type within a cluster takes place. These “pearls” have a strongly non-spherical ellipsoidal shape, due to the fact that several side chains cluster together in one “pearl”. We discuss the resulting structures in detail and we present a comparison with the single-component bottle-brush case.     

Non-envelope formulation for femtosecond optical pulses in semiconductors

We analyze the response of an ensemble of 1s-excitons driven by a femtosecond optical pulse, beyond traditional “slowly varying amplitudes” approach. For optical pulses of a given duration it is shown that the off-resonance optical field can evolve into a stable soliton with nonzero asymptotic behavior. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 380–384 (10 March 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

A neutron reflectometry study of polystyrene network interfaces

We have used neutron reflectometry to measure interfacial widths between two polystyrene films, where either one or both films are crosslinked. The observed interfacial width between two networks is larger than the size expected for “dangling ends”, which suggests motion of heterogeneous regions of the networks. In the case when one of the networks is replaced by a linear polymer, the interfacial profile can be asymmetric with a diffusion “front” of linear polymer penetrating the network to a length scale of up to 200 ?. In the case of a more densely crosslinked network and a high molecular weight linear polymer the interface is symmetric implying negligible penetration. Received: 4 December 1996 / Revised: 13 October 1997 / Accepted: 23 December 1997     

A New Book of Numbers: On the Precise Definition of Quantum Variables and the Relationships between Mathematics and Physics in Quantum Theory

Following Asher Peres’s observation that, as in classical physics, in quantum theory, too, a given physical object considered “has a precise position and a precise momentum,” this article examines the question of the definition of quantum variables, and then the new type (as against classical physics) of relationships between mathematics and physics in quantum theory. The article argues that the possibility of the precise definition and determination of quantum variables depends on the particular nature of these relationships.     

Laser frequency offset locking scheme for high-field imaging of cold atoms

We present a simple and flexible frequency offset locking scheme developed for high-field imaging of ultra-cold atoms which relies on commercially available RF electronics only. The main new ingredient is the use of the sharp amplitude response of a “home-made” RF filter to provide an error signal for locking the lasers. We were able to offset lock two independent diode lasers within a capture range of hundreds of MHz, and with a tuning range of up to 1.4 GHz. The beat-note residual fluctuations for offset locked lasers are below 2 MHz for integration times of several hundreds of seconds.