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A method for generation of droplet quasi-Bessel beams using a conical lens with a rounded tip is demonstrated. The study of the longitudinal distribution of the intensity of the obtained quasi-Bessel beam showed that, due to the interference of two wavefronts that occurred as the generating beam passed through the rounded axicon, periodical intensity pulsations that looked like "drops" of light occurred in the resulting beam. These light beams can be used for micromanipulation of biological objects and in super-resolution microscopy. The application of an axicon with a rounded tip for generation of a droplet beam allows considerable simplification and miniaturization of the experimental setup, which paves the way for multiple practical applications. [ABSTRACT FROM AUTHOR]

Fiber-coupled semiconductor lasers are studied under pumping with high-power short current pulses. Appropriate parameters of the current pumping make it possible to substantially reduce the output pulse duration to 80 ps for a single-mode laser and 120 ps for a wide-stripe multimode laser at a pump pulse duration of 1 ns and to 40 ps for the single-mode laser at a pump pulse duration of 0.5 ns. [ABSTRACT FROM AUTHOR]

In this paper, we studied Bessel beams obtained using an axicon with a substantially rounded apex. A study of the interference of two wave fronts arising from the refraction of the generating beam on an imperfect axicon showed that rounding its apex results in periodic pulsations of intensity in the resultant quasi-Bessel beam resembling visually the "droplets" of light. The proposed mathematical model demonstrates excellent agreement with the experiment. [ABSTRACT FROM AUTHOR]

We examine the response of a pulse pumped quantum dot laser both experimentally and numerically. As the maximum of the pump pulse comes closer to the excited-state threshold, the output pulse shape becomes unstable and leads to dropouts. We conjecture that these instabilities result from an increase of the linewidth enhancement factor α as the pump parameter comes close to the excitated state threshold. In order to analyze the dynamical mechanism of the dropout, we consider two cases for which the laser exhibits either a jump to a different single mode or a jump to fast intensity oscillations. The origin of these two instabilities is clarified by a combined analytical and numerical bifurcation diagram of the steady state intensity modes. [ABSTRACT FROM AUTHOR]

Broad-stripe edge-emitting semiconductor lasers have been used to obtain propagation-invariant (nondiffracting) light beams with powers and diameters of the central ray acceptable for optical manipulation and tweezing. The results of investigations of the propagation of Bessel beams generated from broad-stripe lasers with spectrally selective resonator show that the spatial homogeneity of emission plays a much greater role than the temporal coherence in the formation of Bessel beams. The main factors limiting the length of non-diffracting beam propagation (without distortion of the central ray) are the astigmatism and multimode character of laser radiation. [ABSTRACT FROM AUTHOR]

A turn-on of a quantum dot semiconductor laser is analyzed in detail both theoretically and experimentally. We show that quantum dot lasers have a nonlinear damping rate which strongly affects laser turn-on dynamics due to the non-instantaneous capture of carriers to a dot. It results in nonvanishing turn-on delay even at very high pumping in good agreement with experiment. [ABSTRACT FROM AUTHOR]

Output radiation focusing in AlGaAs/GaAs quantum-well curved-grating distributed Bragg reflector (c-DBR) lasers has been theoretically and experimentally studied. It is established that the focal spot size for c-DBR lasers is determined to a considerable extent by the spectral perfection of laser radiation. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A turn on of a quantum dot (QD) semiconductor laser simultaneously operating at the ground state (GS) and excited state (ES) is investigated both experimentally and theoretically. We find experimentally that the slow passage through the two successive laser thresholds may lead to significant delays in the GS and ES turn ons. The difference between the turn-on times is measured as a function of the pump rate of change ɛ and reveals no clear power law. This has motivated a detailed analysis of rate equations appropriate for two-state lasing QD lasers. We find that the effective time of the GS turn on follows an ɛ−1/2 power law provided that the rate of change is not too small. The effective time of the ES transition follows an ɛ−1 power law, but its first order correction in ln(ɛ) is numerically significant. The two turn ons result from different physical mechanisms. The delay of the GS transition strongly depends on the slow growth of the dot population, whereas the ES transition only depends on the time needed to leave a repellent steady state. [ABSTRACT FROM AUTHOR]