V. I. Kuchinskii

Generation of propagation-invariant light beams from semiconductor light sources

We have studied the possibility of generating propagation-invariant (nondiffracting) light beams using various semiconductor sources of radiation. The propagation-invariant (Bessel) beams have been generated using cone-shaped lenses (axicones) with an apical angle of 178° and 170°, which provided beams with a central spot diameter of 100 and 10 μm, respectively. The radiation sources were represented by various types of light-emitting diodes, quasi-single-mode semiconductor vertical-cavity surface-emitting lasers and broad-stripe (100 μm) edge-emitting laser diodes. It is demonstrated that these semiconductor light sources offer a promising basis for the generation of propagation-invariant light beams in various devices (including optical tweezers) intended for manipulating micro- and nanodimensional objects.

Study of non-diffracting light beams from broad-stripe edge-emitting semiconductor lasers

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.

Anomalous dynamic characteristics of semiconductor quantum-dot lasers generating on two quantum states

Dynamics of the emission spectra of semiconductor quantum dot (QD) lasers generating on two quantum states has been experimentally studied. Being pumped with 30-ns current pulses, a QD laser ceased to generate 2–5 ns after switch-on and exhibited a pause up to 10 ns or longer, depending on the pumping pulse amplitude. After the subsequent switch-on, the laser generated short (200–300 ps) pulses of emission from the excited state of QDs followed by minima of comparable duration (dark pulses) corresponding to the ground-state emission. This behavior is explained in terms of the laser Q-switching due to the charge carrier density redistribution between the excited and ground states.

Superfocusing of mutimode semiconductor lasers and light-emitting diodes

The problem of focusing multimode radiation of high-power semiconductor lasers and light-emitting diodes (LEDs) has been studied. In these sources, low spatial quality of the output beam determines theoretical limit of the focal spot size (one to two orders of magnitude exceeding the diffraction limit), thus restricting the possibility of increasing power density and creating optical field gradients that are necessary in many practical applications. In order to overcome this limitation, we have developed a method of superfocusing of multimode radiation with the aid of interference. It is shown that, using this method, the focal spot size of high-power semiconductor lasers and LEDs can be reduced to a level unachievable by means of traditional focusing. An approach to exceed the theoretical limit of power density for focusing of radiation with high propagation parameter M2 is proposed.

Room temperature midinfrared electroluminescence from GaInAsSbP light emitting diodes

Room temperature electroluminescence in the midinfrared near 4μm is reported from GaInAsSbP light emitting diodes grown on GaSb by liquid phase epitaxy. Comparison of the electro- and photoluminescence revealed that light is generated on the p side of the diode. The energy shift (24meV) is consistent with band gap narrowing and recombination via band tail states due to the Zn doping (1×1018cm−3) in the p layer of the structure. The temperature dependent behavior of the luminescence and the improved emission intensity was attributed to recombination from localized states arising from electrostatic potential fluctuations due to compositional inhomogeneities in these alloys.

High power Bessel beams from EP-VECSELs

We report on demonstration of non-diffracting (Bessel) beams from Electrically Pumped Vertical External Cavity Surface Emitting Lasers (EP-VECSELs), with output powers ranging up to hundreds of milliwatts and central lobe diameters of 10-100 μm with propagation lengths up to few tens of centimeters. To our knowledge, this is the best result for Bessel beams generated from semiconductor light sources and is comparable to that achievable from vibronic lasers.

Midinfrared photoluminescence and compositional modulation in pentanary GaInAsPSb alloys grown by liquid phase epitaxy

Room temperature photoluminescence is reported from GaInAsSbP pentanary alloys grown by liquid phase epitaxy on GaSb. The epitaxial layers exhibited emission in the midinfrared between 3 and 4μm. Investigation of the structural and photoluminescence properties revealed localization effects associated with potential fluctuations in the pentanary alloy arising from compositional modulation.

GaInAsSb/GaSb heterostructures grown in the spinodal decay region by liquid-phase epitaxy from Sb-enriched solution-melts

Nearly isoperiodic solitary Ga1−xInxAsySb1−y/GaSb heterostructures, in which the composition of the solid solution should be found inside the region of spinodal decay (x⩽0.4), were grown by liquid-phase epitaxy from solution-melts enriched with antimony. On the basis of the results of a study of structural and luminescence properties of Ga1−xInxAsySb1−y/GaSb heterostructures we have determined the main conditions ensuring reproducible growth of epitaxial layers, homogeneous in the composition of their solid solutions in the region where the existence of processes of spinodal and binodal decay have been theoretically predicted. It is shown that the magnitude and sign of the deformation which the layer undergoes during growth and also the thickness of the layer are the main factors influencing the properties of the growing GaInAsSb solid solutions in the spinodal-decay zone.

Dropout dynamics in pulsed quantum dot lasers due to mode jumping

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.

Non-diffracting beams from surface-emitting lasers

We present an overview of recent advances in generation of non-diffracting (Bessel) beams from surface-emitting lasers, such as electrically and optically pumped VECSELs, and discuss their applications in optical trapping/tweezing and manipulation of micromachines. Our experiments on VECSEL-generated watt power level Bessel beams with central lobe diameters of a few to tens micrometers suggest that the semiconductor surface-emitting lasers are the best candidates for replacement of gas and solid-state counterparts for power-demanding applications in optical manipulation.