Igor V. Ermakov

Alkaline hydrolysis of polyacrylonitrile, 1. Structure of the reaction products

The alkaline bydrolysis of a polyacrylonitrile suspension was carried out in a water/ethanol mixture at 75%. The product structure was studied by means of solid state 13 C NMR spectroscopy. The hydrolyzed samples contain up to 20% of amidines, which are formed in the nearest neighborhood of the COONa groups. Amidines are relatively stable under the given reaction conditions up to almost complete conversion of the nitrile groups, then being hydrolyzed gradually into amides. After complete hydrolysis of the amidines, the resulting poly[(acryl amide)-co-(sodium acrylate)] exhibits a Bernoulli triad distribution of the comonomer units. The data obtained might be useful in elucidating the reaction mechanism.

BaWO4 crystal for quasi-cw yellow Raman laser

The possibility to use BaWO4 solid state Raman laser for conversion of quasi-cw laser radiation has been demonstrated. The operation of yellow Raman laser with 1 kHz repetition rate and pulse width 10-600 ns under pumping with second harmonic of Nd3+:YLiF4 laser (527 nm) was investigated. The 1st Stokes (544 nm) and 2nd Stokes (583 nm) component radiation with promising characteristics was obtained at 1-10 W pump power.

Two-photon polarization spectroscopy of LiF crystals with F2 laser color centers

The paper reports on a measurement and calculation of the dependence of LiF: F2 luminescence polarization and intensity on the polarization of high-power laser radiation (λex=1064 nm) producing two-photon excitation of F2 centers. It is shown that the two-photon transition results in the excitation of a previously unknown electronic level of F2 centers of the A1g symmetry.

Stimulated Raman scattering in barium nitrate crystal in the external optical cavity

Barium nitrate Raman laser pumped with nanosecond YAG:Nd laser is investigated. High energy conversion efficiencies to the first, second, and third Stokes components up to 60%, 35%, and 25%, respectively, are obtained. Results on development of Raman laser for the eye safe spectral region are presented.

Polarization investigations of two-photon excitation of F3+ color centers in LiF crystals and analysis of excited-state symmetry

The peculiarities of energy levels structure of laser-active F3+ color centers in LiF crystals were studied. The dependencies of polarization and fluorescence intensity of LiF crystals with F3+ centers against polarization of powerful laser irradiation which originates two-photon excitation of F3+ centers, were measured and calculated. It was shown that the two-photon transition leads to the excitation of unknown previously spin-singlet electronic state, possessing 1A1 wavefunction symmetry.

Singlet-singlet, singlet-triplet, and triplet-triplet transitions for F3+ color centers in LiF crystals

New spin-triplet electronic states of laser-active F3+ color centers in LiF crystals are discovered. The triplet-triplet absorption spectra from low laying 3E state to the high laying states, triplet-triplet 3T(alpha ) yields 3E fluorescence spectrum and 3E yields 1A1 triplet-singlet phosphorescence spectrum are measured. Temperature dependencies of nonradiative singlet-triplet 1E yields 3E and triplet- singlet 3E yields 1A1 transitions probability are found. The influence of spin-triplet states on the LiF:F3+ color center laser characteristics is discussed. The new way of obtaining of tunable oscillation in wide visible range using triplet-triplet transition is offered.

Polarization dependence of luminescence induced by two-photon excitation in LiF crystals with F 3 + laser color centers and the symmetry of the excited state

The energy level structure of F3+ laser color centers in crystals of LiF is discussed. A high-power laser (λex=920 nm) is used to excite luminescence from LiF crystals with F3+ centers via two-photon absorption, and the dependence of the polarization and intensity of this luminescence on the polarization of the laser light is measured and calculated. It is shown that the two-photon transition involves the excitation of a previously unknown state of the F3+ center—a spin singlet whose wave function has 1A1 symmetry.