On the Normality of $$\mathfrak F^{\omega}$$ -Abnormal Maximal Subgroups of Finite Groups

Mathematical Notes - In the paper, the notion of an $$\mathfrak F^{\omega}$$ -abnormal (and $$\mathfrak F^{\omega}$$ -normal) maximal subgroup of a finite group is introduced, where $$\mathfrak F$$...     

Broadly tunable compact continuous-wave Cr(2+):ZnS laser

We report the development of a continuous-wave, room-temperature Cr(2+) ZnS laser that is compact and tunable over 700 nm. The laser is pumped by a diode-pumped Er-fiber laser and generates 0.7 W of linearly polarized radiation at 2.35microm , at up to 40% slope efficiency. Cr(2+) ZnS directly diode-pumped at 1.6microm yields polarized radiation that is tunable over 400 nm at up to 25 mW of output power. A comparison of Cr(2+) ZnS with Cr ZnSe (70 mW, 350 nm) in a similar setup is given. As opposed to Cr ZnSe, the Cr ZnS laser is intrinsically polarized. Finally, we observe sensitization of the output radiation by a few milliwatts of the visible (470-500-nm) and near-infrared (740-770-nm) radiation.     

A cw room-temperature Ho,Tm:YLF laser pumped at 1.682 μm

We present the results obtained with a Ho,Tm:YLF crystal grown at a new crystal growth facility in Pisa. The optical quality of the sample has been tested by studying its performance as the active medium of a laser operating at 2.06 μm. We employed three different pump laser sources: a Ti:sapphire, a diode (both tuned at 793 nm) and, for the first time, a continuous-wave Co:MgF₂ laser, tuned at 1.682 μm. At room temperature the best slope efficiency was 30 % in the case of “red” pumping, and 59 % in the case of “infrared” excitation. The typical lasing threshold is about 100 mW. Received: 14 March 2001 / Revised version: 15 June 2001 / Published online: 19 September 2001     

Formylation of 1,2,3,4-tetrahydro-2,4,5-trimethylpyrrolo-1-2,c]pyrimidine. Its conversions to the 7-formyl derivative with opening of the tetrahydropyremidine ring

We have optimized the method for obtaining 1,2,3,4-tetrahydro-2,4,5-trimetkylpyrrolo[1,2-c]pyrimidine. We carried out the reactions of quaternization, forinylation, and opening of the tetrahydropyrinddine ring of its 7-formyl derivative and the oxime of this carbonyl compound.Russian University of International Friendship, Moscow 117923. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 534–539, April, 1995. Original article submitted March 14, 1995.     

Cyclic organic derivatives of hypophosphorous acid

2-H-1,3,2-Dioxa-, dithia-, diaza- and oxaazaphosphorinanes have been prepared by reducing corresponding phosphorichloridates; spectral and chemical properties of these compounds have been studied. These compounds were considered as initial members of series when investigating the stereochemistry of heterocycles substituted at the phosphorus. The examination of ¹H, ¹³C and ³¹P NMR spectra has shown that substitution of hydrogen at the phosphorus by axial halogen, alkyl, alkoxy and amido-groups is accompanied by shielding of 4,6-C atoms and deshielding of 4,6-axial protons; introduction of an axial Me group into γ-position to the P-H fragment causes a 30–40 ppm up-field shift of the resonance of the phosphorus nucleus.     

Study of local magnetic fields and magnetic ordering in fluid and solid matrices containing magnetite nanoparticles using TEMPOL stable radical

The stable nitroxide radical 2,2,6,6-tetramethyl-4-hydroxy-piperidin-1-oxyl (TEMPOL) has been applied as a sensor to study magnetite nanoparticles both in water suspension and in dried gelatin films. g-values and line widths of ESR spectra of the probe were found to be sensitive to the local magnetic fields of magnetic nanoparticles. Calculated on the basis of the sensor ESR spectra, local magnetic fields are stipulated by linear aggregates of magnetite nanoparticles formed in applied outer magnetic fields and are significantly lower than local magnetic fields estimated from the static magnetic measurements data.     

Directly diode-pumped Kerr-lens mode-locked Cr4+:YAG laser

A directly diode-pumped Kerr-lens mode-locked Cr4+:YAG laser is demonstrated for what is to our knowledge the first time. Pulses as short as 65 fs with up to 30 mW of average output power, at a central wavelength of 1569 nm, were obtained at a repetition rate of 100 MHz. Low-loss chirped mirrors have been used for dispersion compensation up to the third order. Comparison with an Yb-fiber-pumped configuration shows good prospects for improvement.     

Self-starting five optical cycle pulse generation in Cr<Superscript>4+</Superscript>:YAG laser

We report stable self-starting near-transform-limited 26-fs pulses at 250-mW output power from a Kerr-lens mode-locked (KLM) Cr⁴⁺:YAG laser using chirped mirrors in combination with prisms. The highest output power achieved in KLM regime was 600 mW at 55-fs pulse duration. The experimental results agree well with the results of theoretical analysis with respect to KLM self-starting ability and stability against continuous-wave and multi-pulse operation. Parameter ranges for stable transform-limited KLM pulses as well as the shortest achievable pulse durations are established. Using an InGaAs-InP semiconductor saturable absorber mirror we could obtain self-starting 57-fs pulses at the average output power of 200 mW. Two-photon absorption was found to be the main mechanism favoring the multiple-pulse operation. Received: 2 May 2002 / Revised version: 16 July 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +43-1/58801-38799, E-mail: sorokina@tuwien.ac.at