Time resolved photodissociation of small peptide ions

A new instrument has been constructed whose purpose is to study time-resolved photodissociation (TRPD) of small peptide ions. Laser desorption of neutral peptides is combined with laser photoionization in an ion trap followed by thermalization, laser photodissociation and time of flight mass analysis. Ionization and excitation take place through an aromatic chromophore at the C-terminus of the peptide whereas dissociation produces the immonium ion at the N-terminus. The long-range purpose is to uncover the role of IVR in unimolecular fragmentations of peptide radical cations. One avenue is the determination of microcanonical rate constants at a well-defined internal energy E for a series of peptides possessing the same chromophore, undergoing the same fragmentation but having a variable number of degrees of freedom. This paper demonstrates the feasibility of the method and provides the first attempts at rate measurements for the peptide leucyl tyrosine (LeuTyr). Received 6 January 2002 Published online 13 September 2002     

Models,predictions, and experimental measurements of far-infrared NH3-laser dynamics and comparisons with the Lorenz-Haken model

Dynamics of the intensity and optical field amplitude of a coherently pumped far-infrared NH₃-laser are measured and characterized. The experimental findings in certain parameter ranges closely follow the dynamics of the Lorenz model and its generalization for laser systems. Similarities and some specific differences are found in geometrical or statistical characterizations of the attractors. The experimental results are also consistent with the results of a model of optically pumped three-level lasers which takes into account the presence of a multiplicity of velocity groups as well as three-level coherence effects. For a certain region in parameter space, this far more complex model with a much larger phase space produces results similar to the dynamics of the Lorenz model. The model also provides explanations of differences between the experimental results and results from the Lorenz model.     

Exponential recovery of low frequency fluctuations in a diode laser with optical feedback

We show that the recovery after each power drop on the chaotic low frequency fluctuations in a semiconductor laser with optical feedback follows an exponential envelope. The time constant for such exponential behavior was experimentally measured. This recovery time constant and the average time interval between consecutive drops have different dependences when measured as function of the pump current.     

Site-selective luminescence of Bi in the YBO3 host under vacuum ultraviolet excitation at low temperature

(Y_0.99Bi_0.01)BO₃ phosphor was prepared and its luminescent properties were investigated using the synchrotron radiation instrument in this paper. Site-selective luminescence of Bi³⁺ in the YBO₃ host was demonstrated by exciting/monitoring with different wavelengths at low temperature in this research. At the same time, the energy transfer between the centers of Bi³⁺ ions occupying different symmetric sites was observed. The excited energy levels of Bi³⁺ were identified through assigning the emission and excitation spectra. The paths and mechanism of energy transfer between the centers of Bi³⁺ occupying different symmetric sites were discussed finally.     

Concentration and Temperature Dependences of YBO3：Bi^3＋ Luminescence under Vacuum Ultraviolet Excitation

Bi^3＋ doped YB03 phosphors are prepared by solid state reaction and their luminescent properties are investi- gated by using synchrotron radiation instrument, Concentration and temperature dependences of YBO3：Bi3＋ luminescence under VUV/UV excitation is observed, The emission and excitation spectra are assigned, and the mechanism for these phenomena is explored, which result from the energy transfer between Bi^3＋ ions occupying different sites in YB03 crystal lattice.     

The laser pulse from a rf waveguide CO2 laser

The behaviour of a rf-excited waveguide CO₂ laser in the pulse regime is studied experimentally. The specific time sections of the pulse have been defined and described in detail. The output pulse evolution versus input power, pressure of the laser mixture, output coupling, repetition frequency and pulse width has been investigated. The spectral content of the pulse has been analysed. A model explaining the effect of laser tuning during the pulse duration is given. The ultrahigh pulse (UHP), defined as the pulse for which the bulge effect occurs, is predicted. Received: 22 October 2002 / Revised version: 13 January 2003 / Published online: 26 March 2003 RID="*" ID="*"Corresponding author. Fax: +48-71/3203-189, E-mail: eda@zr.ita.pwr.wroc.pl     

Noise as reliability screening for semiconductor lasers

The low-frequency electrical noise in semiconductor lasers is measured and used for device-reliability screening, which is a sensitive and non-destructive method. In the experiment, we developed some approaches to improve the validity of reliability screening by using noise criteria. A new method of determining the threshold level of noise criteria is given. The experimental results show that this method is effective. Received: 26 September 2002 / Revised version: 28 January 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +86-431/462-7013, E-mail: huguijun@sina.com     

Incorporation of selective population transfer and homo-spin decoupling into selective one-dimensional experiments

The incorporation of selective population transfer (SPT) and homo-spin decoupling (HSD) into selective one-dimensional (1D) experiments has been shown to be very useful in obtaining information on the elucidation of the structure of organic compounds. To demonstrate this, the determination of the relative configuration of the sugar moiety of Mi-saponins has been presented.