Spectral superbroadening of self-focused picosecond laser pulses in D2O

Intense picosecond light pulses of a mode-locked Nd: glass laser at _L =1054 nm (fundamental wavelength) and _SH =527 nm (second harmonic wavelength) are passed through a sample of D₂O under self-focusing conditions. Spectrally structured superbroadened, spatially bell-shaped emission in the forward direction is obtained. Primary generation processes are pump-pulse-degenerate stimulated parametric four-photon interaction (₁ + _{1 3} + ₄) and stimulated Raman scattering (_{1 R} + ), which occur concurrently (₁= _L or _SH angular pump frequency, #x03C9; _R first Stokes frequency, #x03C9; signal frequency, #x03C9;₃ signal frequency, #x03C9;₄ idler frequency). The parametric four-photon interaction occurs under collinear non-phase-matched conditions and under longitudinally phase-matched, transversally non-phase-matched (erenkov-like) conditions. Subsequent interaction processes are pump-pulse-nondegenerate four-photon interaction of the type ₁ + _{R 3} + ₄, coherent antiStokes Raman scattering (CARS, ₁ + ₁ – _{4 3}), inverse Raman scattering ( _A + ₁ + ), and cascading light up-conversion of the type ₁ + _(i) – _{R (i+1)}.     

Ferromagnetic resonance in media with an inhomogeneous saturation magnetization

The method of transition probabilities is used to calculate the line width of ferromagnetic resonance in a medium with an inhomogeneous saturation magnetization. It is shown that in addition to linear (with respect to the Fourier components of the function describing inhomogeneities) terms, the perturbation Hamiltonian must include also quadratic terms. The frequency dependence of the contribution of the porosity to H is fundamentally different from the frequency dependence of the magnetic anisotropy contribution. This anisotropy contribution H_a() decreases on increase in the frequency and has a maximum at = (2/3)_M, whereas the porosity contribution H_p increases on increase in the frequency and vanishes at = (2/3)_M.deceasedTranslated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp.48–52, December, 1980.     

Some results on electronic two- and one photon raman scattering in CdS

Two photon Raman scattering (TPRS) via virtually excited biexcitons is observed in CdS over a rather large spectral region in a scattering configuration which favours stimulated emission. We observe either a pure longitudinal exciton or-for the first time—a bound exciton (I ₂) as final state particles. Furthermore, the anomaly in the relation between _exc and _R at _exc= E_blex is observed for the first time in a II–VI compound, indicating an energy of the ₁ biexciton level of 5.098 eV in agreement with two photon absorption measurements. With an applied magnetic fieldB, the corresponding shift of the exciton eigenenergies can be observed. For the longitudinal exciton, the diamagnetic shift is 0.35 meV atB=10T forBc in agreement with theoretical predictions. In this configuration also a stimulated one photon spin flip Raman scattering is observed, yielding the well known electronicg-value of 1.78.     

The modular group and super-KMS functionals

Every normal, faithful, self-adjoint functional on a von Neumann algebraA canonically determines a one-parameter-weakly continuous *-automorphism group (the analog of the modular group) and a canonical ₂ grading onA, commuting with . We show that the functional satisfies the weak super-KMS property with respect to and Furthermore, we prove that and are the unique pair of a-weakly continuous one-parameter *-automorphism group and a grading of the algebra, commuting with each other, with respect to which is weakly super-KMS. The above results thus provide a complete extension of the theory of Tomita and Takesaki to the nonpositive case.Supported in part by the National Science Foundation under Grant DMS-8922002.     

The third-order electric susceptibilities of NaCl and KCl monocrystals

The dispersion of the third-order electric susceptibilities(; , , –) and(; , 0, 0) of NaCl and KCl monocrystals has been calculated by means of experimental data on the electro-optic Kerr effect. The result has been obtained by using semi-classical models of anharmonic oscillators. An ionic contribution to the electro-optic coefficients has been presented. From the result obtained it follows that the third-order electric susceptibilities are of the order of 10^–22 m² V^–2.     

Averaged electron Green function and CDW pinning in one-dimensional random potential

The averaged retarded electron Green functionG ⁺(,k) in 1d disordered metal is calculated using the Berezinsky diagram technique. Using the Gorkov's theory it is shown, that the substitution of inG ⁺ (,k) by the square of the external frequency atk=0 gives the dependence of Fröhlich conductivity _F(). This dependence describes the impurity pinning of CDW in 1d disordered metals. The good agreement of this dependence with experimental data Zeller et al. about _F() in quasi-1d conductor KCP is found     

Third order nonlinear optical difference frequency generation in KH2PO4, TiO2, LiNbO3, CaCO3, ZnO and CdS

Third-order nonlinear optical susceptibilities of different crystals have been measured relative to LiNbO₃ by observing collinear phase-matched difference frequency generation ₁=2 ₂– ₄. The two incident light waves have been produced by a ruby laser ( ₂, ₂=694.3 nm) and by induced Raman scattering ( ₄, ₄=765.8 nm). With noncollinear phase-matching the number of nonlinear processes and the possibilities to determine nonlinear coefficients is much larger than in the collinear case. Therefore the theory of Raman-type third order interactions has been extended to noncollinear propagation of the interacting waves. The theory has been tested experimentally for CdS.     

Determination of the time correlation functions of vibrational and rotational relaxation from the anti-stokes Raman scattering lines using the method of direct Fourier transformation of the observed profiles I VV * (ω) and I VH * (ω)

It is shown that the difficulties in obtaining the correlation functions of rotational _2R(t) and vibrational _v(t) relaxation associated with the construction of the profile of isotropic scattering from the observed profiles I _VV ^* () and I _VH ^* () with subsequent Fourier transformation of the constructed profile can be eliminated by a Fourier transformation of the profiles I _VV ^* () and I _VH ^* () directly with subsequent normalization of the obtained correlation functions G _VV ^* (t) and G _VH ^* (t) at the time t=0. The correlation functions _2R(t) and _v(t) are obtained from the profiles of the Stokes and anti-Stokes Raman scattering lines. It is established that for lines with comparatively high polarization (p < 0.20) the correlation function _2R(t) and _v(t) obtained by processing the observed profiles of the Stokes and anti-Stokes lines are almost identical.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 8–13, September, 1980.     

A theory of 1/f noise

Letu() be an absolutely integrable function and define the random process where thet _i are Poisson arrivals and thes _i, are identically distributed nonnegative random variables. Under routine independence assumptions, one may then calculate a formula for the spectrum ofn(t), S _n(), in terms of the probability density ofs, p_s(). If any probability density p_s() having the property p_s() I for small is substituted into this formula, the calculated S_n() is such that S_n() 1 for small . However, this is not a spectrum of a well-defined random process; here, it is termed alimit spectrum. If a probability density having the property p_s() for small , where > 0, is substituted into the formula instead, a spectrum is calculated which is indeed the spectrum of a well-defined random process. Also, if the latter p_s is suitably close to the former p_s, then the spectrum in the second case approximates, to an arbitrary, degree of accuracy, the limit spectrum. It is shown how one may thereby have 1/f noise with low-frequency turnover, and also strict 1/f ^1– noise (the latter spectrum being integrable for > 0). Suitable examples are given. Actually, u() may be itself a random process, and the theory is developed on this basis.     

Excited-state absorption and third-order optical nonlinearities in symmetric π-electron organic molecules

Excited-State Absorption (ESA), Two-Photon Absorption (TPA) and the third-order polarizability (;,, – ) have been investigated for a model dichloride derivative of a symmetrically substituted benzylidene analine (SBAC), using a multielectron configuration-interaction procedure. The calculations indicate that SBAC exhibits ESA across the visible region of the spectrum, but that it is not as extensive as for molecules such as the phthalocyanines. The magnitude of the third-order polarizability is dominated by resonance enhancement from a very strongA _g B _u one-photon absorption. The calculated off-resonance value for (;,, – ) suggests that SBAC is a potential candidate for ultrafast switching applications.     

The Transit Time Effect of a Modulated Electron Beam

Energy change of an electron beam is studied numerically when it transits a rf field gap of width L. For a premodulated beam, the transit time L/0> for maximum energy extraction is shortened to 0.475 T (T=2/, 0> is the average velocity of the electrons) when the modulation frequency _m is matched to the rf field frequency . Enhancement of the extraction efficiency _o is dependent on the modulation coefficient h₁ and h₂. For a uniform beam with V=500 kV, _o is less than 2%. _o reaches 11% for a prebunched beam with h₁=0.7 and h₂=0.1 and will surpass 20% for an ideally modulated beam.     

A discrete spectrum of solutions of the wave equation with strong cubic nonlinearity

The nonlinear wave equation, _tt –+³=0, has many solutions that are periodic in time and localized in space, all with infinte energies. The search for spherically symmetric solutions that are well represented by the simple approximation, (r, t)A(r) sin t, leads to a discrete spectrum of solutions{ _N (r, t; )}. The solutions are nonlinear wavepackets, and they can be regarded as particles. The asymptotic theory () of the motion of the guiding center of theNth wavepacket, in the presence of a specified potential, is characterized by an infinite mechanical mass and an infinte interaction mass, and they are compatible. The rest mass in the classical relativistic mechanics of guiding centers ism ₀ c ²= _N ; i.e. the spectrum { _N } determines a spectrum of Planck's constants.On leave (1972–73) Université de Paris VI, Département de Mécanique, 75 Paris 5^e, France.     

Влияние катодной обл асти на динамические свойства тлеющего разряда в во дороде

. . , , I-om 1957 .     

Vacuum ultraviolet 178.7 nm emission in sodium vapour under two-photon resonance excitation

We have observed a fixed wavelength emission at 178.7 nm in sodium vapour under 578.7 nm two-photon resonance excitation. The proposed non-linear wave mixing scheme is described by _{178.7 nm} = 2_L + _{465.7 nm}; where _178.7 is the 178.7 nm photon frequency, _L is the laser-photon frequency, and _465.7 is the 465.7 nm photon frequency. This 465.7 nm emission comes from another six-wave mixing process involving two hyper-electronic Raman scattering photons. The excitation spectrum of the 178.7 nm emission has a typical multiwave mixing pattern with a competing effect appearing at higher temperatures under two-photon resonance excitation. Numerical analysis indicates that this vacuum ultraviolet emission has a poor phase-match condition that will depress the emission intensity to a certain extent. This makes the observation more difficult compared with other reported four-wave mixing generated emissions. Fortunately, on the one hand, it is enhanced by quasi-auto-ionization resonance when the 3s–5s transition is coupled to the sodium continuum by a 330.2 nm photon. On the other hand, its wavelength sits so close to the sodium Cooper minimum that weak absorption will not suppress this vacuum ultraviolet emission further.     

The Statistics of the Trajectory of a Certain Billiard in a Flat Two-Torus

We consider a billiard in the punctured torus obtained by removing a small disk of radius >0 from the flat torus ², with trajectory starting from the center of the puncture. In this case the phase space is given by the range of the velocity only. Let (), and respectively R(), denote the first exit time (length of the trajectory), and respectively the number of collisions with the side cushions when ² is being identified with [0,1)². We prove that the probability measures on [0, ) associated with the random variables and R are weakly convergent as 0⁺ and explicitly compute the densities of the limits. Research partially supported by ANSTI grant C6189/2000.     

Pulsed NMRON oscillatory free induction decay signals in the angular distribution of gamma radiation from plated60CoFe

Results for an inhomogeneously broadened⁶⁰CoFe NMRON sample have been obtained for gamma detected single pulse (nutation) and two pulse (free induction decay) experiments in the region of intermediate-to-lowR(=₁/). Here ₁ is the angular frequency measure of the strength of the ferromagnetically enhanced RF field at the nucleus and is the HWHM of the inhomogeneously broadened line. Comparisons of the oscillatory FID signals obtained are made with the theoretical predictions of the following paper [6].     

Radiation damping of waves in a cold magnetized two-component plasma

It is shown in this paper that the damping decrements of electromagnetic waves with right circular polarization and the decrements of plasma oscillations near the cyclotron and hybrid frequencies in a strong magnetic field _eBpe are proportional to the square of the cyclotron frequencies _eB and _iB. In a weak magnetic field _eBpe the damping decrements of all modes are proportional to the square of the plasma oscillation frequencies _pe, _pi. Taking account of ions results in a nonzero damping decrement for electromagnetic waves with left circular polarization.Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, p. 8–11, October, 1982.In conclusion, I am grateful to L. S. Kuz'menkov and P. Polyakov for constant attention to the research and for useful remarks.     

Experimental survey of the sticking problem in muon catalyzed dt fusion

The sticking process dt + n, which constitutes the most severe limit to the number of fusions which a muon can catalyze, is reviewed. Many attempts were made to determine by calculations and measurements the probability for initial sticking _s ⁰ (immediately after dt fusion) and for final sticking _s (after the came to rest). Previous results based on neutron disappearance rates and on the observation of -X-rays were controversial and also in some disagreement with theory. New data are reported from PSI on direct observation of final sticking, using a setup with the St. Petersburg ionization chamber. These data mark a significant improvement in reliability and may clarify questions concerning previous discrepancies. The new results is _s(0.56±0.04)%, lower than the theory prediction _s=(0.65±0.03)%, at medium density.     

Double phase-matched cascaded fifth harmonic generation in single nonlinear medium by focussed laser beam

Generation of a fifth harmonic by the cascading of two phase-matched third-order processes in a single centrosymmetric nonlinear medium with a focused fundamental beam is investigated theoretically. With the help of analytical and numerical investigations the optimized conditions for maximum conversion into the fifth harmonic are found. In general the optimal position of focusing depends on the values of the mismatches k₁ and k₂ for both steps of the third order cascading (++=3; 3++=5). It is shown that for best efficiency this method of fifth harmonic generation requires specially chosen k_1,opt and k_2,opt and focusing in the center of the nonlinear media. If the phase matching parameters are fixed and they deviate from the optimal values, then the optimal strength of focusing and position of the focus spot should be calculated according to the analysis presented here. PACS 42.65.-k; 42.65.Ky; 42.79.Nv     

Normal mode configuration in an inorganic medium containing defects

The vibrational structure in an inorganic medium containing defects is analyzed as a function of the frequency of the applied field. Since the dispersion relations for the medium are nonlinear, the configuration of the normal modes depends differently upon and . It is shown that exponential damping of the optic branches is observed for <₀, and that the structure of these modes changes significantly over the range 0<<₀, so that only in the neighborhood of ₀ does it correspond to long wavelength vibrations with configurations of stress deviator waves.Institute for the Physics of Strength and Materials Science, Russian Academy of Sciences, Siberian Division. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 87–90, October, 1994.