Obtaining Single Picosecond Pulses in a Short-Cavity Dye Laser with Switching of Lasing to the Saturable Absorber

A new method of lasing of single picosecond pulses in a short-cavity dye laser with spatial separation of the lasing medium and the saturable absorber in the case of pumping by nanosecond pulses with energies much higher than the oscillation threshold has been developed and experimentally realized. The method is based on the use of a high-Q, external cavity tuned to the amplification wavelength of the saturable absorber. The first picosecond pulse is lased at a lasing-medium wavelength and the subsequent pulses are lased at a saturable-absorber amplification wavelength.     

Realizations of standard quantum computational circuits by adiabatic evolution

We study the adiabatic equivalent of the standard quantum circuit of elementary logic operators. We propose a scheme for constructing time variations of the Hamiltonian. This scheme can be implemented sufficiently simply, for example, on nuclear spins controlled by radio-frequency pulses. As an illustration, we numerically simulate an adiabatic quantum algorithm for finding the permutation order for a system of five spins (qubits). __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 150, No. 3, pp. 461–472, March, 2007.     

Radar in observing and recognizing unusual aperiodic atmospheric formations

A study is made of the errors and incorrect interpretations involved in anomalous spots from atmospheric and ground objects on radar screens. Features are given for identifying areas from objects with anomalous characteristics. Conditions are considered for radio visibility of plasma anomalous objects, together with the scope for recognizing them with radars of various types working in various ranges.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 118–121, March, 1992.     

Dissipation of electronic excitation energy within a C60 [6:0]-hexaadduct carrying 12 pyropheophorbide a moieties

The synthesis and photophysical studies of a fullerene [6:0]-hexaadduct that carries 12 pyropheophorbide a units are reported. The synthesis started with the malonate 1, which was coupled under template conditions to C(60)() to give the hexaadduct 2. After removal of the protecting group with acid the dodecakis amino-substituted precursor compound 3 was generated. 3 was not isolated but directly reacted with the N-succinimid ester 4 of pyropheophorbide a (5), which delivered the desired fullerene [6:0]-hexaadduct 6 in excellent yield. The photophysical properties of 6 were studied and compared with those of the fullerene [5:1]-hexaadduct 7 with six pyropheophorbide a groups and the bispyropheophorbide a-fullerene [5:1]-hexaadduct 8. The pyropheophorbide a units in 6 undergo after light absorption very efficient energy transfer as well as partly excitonic interaction. The last process results in formation of energy traps, which could be resolved experimentally. Compared to the reference compounds 7 and 8, 6 has a higher probability of trap formation due to a higher local concentration of dye molecules and shorter distances between them. As a consequence, the excitation energy is delivered rapidly (within 23 ps) to the traps, resulting in decreases of the fluorescence, intersystem crossing, and singlet oxygen quantum yields in comparison with the values of the reference compounds.     

Electron spectroscopy as applied to the layer-by-layer analysis of hydrocarbon coatings produced by ion-plasma deposition

The results of the nondestructive layer-by-layer analysis of hydrocarbon coatings, which is carried out by means of the electron spectroscopy method, are presented. The coating is prepared using the ion-plasma-deposition technique. Analysis of the elemental composition is performed with the help of X-ray photoelectron and Auger electron spectroscopies. The hydrogen concentration is determined via elastic peak electron spectroscopy. The coating structure is investigated by means of electron energy-loss spectroscopy.     

Synthesis and photophysical properties of annulated dinuclear and trinuclear phthalocyanines

Metal-free mononuclear, dinuclear and trinuclear phthalocyanines were prepared by a mixed cyclotetramerisation of a 1,2,4,5-tetracyanobenzene derivative and 4,5-bis(2,6-dimethylphenoxy)phthalonitrile. For the first time, a pi-electron-conjugated trinuclear phthalocyanine was synthesised with phthalocyanine units connected by common annulated benzene rings. The Q band of the trinuclear compound in solution occurs at lambda = 944 nm whereas those of the dinuclear and mononuclear compounds are at lambda = 853/830 and 701/664 nm, respectively. Fluorescence quantum yields, fluorescence lifetimes and singlet-oxygen quantum yields of the compounds were determined.     

Secondary globular structure of copolymers containing amphiphilic and hydrophilic units: Computer simulation analysis

The coil-globule transition in copolymers composed of amphiphilic and hydrophilic monomer units has been studied by the computer simulation technique. It has been shown that the structure of globules formed in such systems substantially depends on the rate at which the solvent quality worsens. The globule resulting from slow cooling is cylindrical, and its core contains a large amount of hydrophilic groups. The globule formed upon rapid cooling takes the helical conformation, in which all hydrophilic groups are displaced to the periphery. One helix turn of such globules contains 3–5 units. In both cases, the backbone of the polymer chain forms a typical zigzag-shaped structure with an average angle between neighboring bond vectors of about 60°. This fact implies that globules of copolymers consisting of amphiphilic and hydrophilic units comprise secondary structure components.