Frequency doubling of Yb-doped fiber laser to 515 nm

Operation of Yb-doped fiber laser (YDFL) at short wavelengths (about 1030 nm) is known to be possible with relatively short active fibers. Frequency doubling of such a laser is studied. It is shown that, in contrast to conventional YDFLs, operating around 1080 nm, the short-wavelength YDFL does not exhibit significant spectral broadening induced by nonlinear effects. Thus, the generated spectrum remains narrower than the FBG reflection profile, which allows an almost twofold intracavity intensity enhancement. Consequently, the second harmonic generation in the KTP crystal placed inside the YDFL cavity appears more effective than the generation in the single-pass scheme by an order of magnitude. An output power of about 0.4 W at a wavelength of 515 nm is demonstrated.     

Theorems of law of large numbers type for functionals of products of independent random matrices

A limit theorem of the type of the law of large numbers is proved using the martingale method.Translated fromTeoriya Sluchainykh Protsessov, Vol. 15, pp. 16–19, 1987.     

Determination of the ratio of the axial-vector to the vector coupling constant for weak interaction in triton beta decay

Data on the chemical shifts of the half-lives of atomic and molecular tritium are used to determine the ratio of the axial-vector to the vector coupling constant for weak interaction in triton beta decay. The result is (G_A/G_V)_t=?1.2646±0.0035.     

Introduction of a tritium label into nucleoside analogs modified in their carbohydrate residues

The synthesis has been effected of arabinofuranosylcytosine, -uracil, and -adenine, and of ftorafur [tegafur] and acyclovir, all containing a tritium label. The introduction of tritium was effected by reductive dehalogenation and desulfuration and also by the isotope exchange reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 95–99, January, 1988.     

Atomic effects accompanying the beta decay of tritium

The results of the first experiment designed to measure the difference between the beta-decay constants of atomic and molecular tritium Δλ=λ_a–λ_m are presented. The experimental scheme calls for the creation of two identical samples of a gas mixture containing helium-4 and molecular tritium followed by the treatment of one of them for the purpose of bringing the tritium into the atomic state. The value of Δλ is determined by comparing the growth rates of the ratio of the concentration of radiogenic helium-3 to the concentration of helium-4 in the samples with molecular and atomic tritium. The value Δλ=(4.6±0.8)×10⁻¹² s⁻¹, which corresponds o a relative change in the decay constant amounting to ∼0.26%, is obtained. Zh. Tekh. Fiz. 69, 19–21 (September 1999)