A. G. Deryagin

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.

Self-sustained pulsation in the oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

The authors report the observation of strong self-pulsations in molecular-beam epitaxy–grown oxide-confined vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots. At continuous-wave operation, self-pulsations with pulse durations of 100–300ps and repetition rates of 0.2–0.6GHz were measured. The average optical power of the pulsations was 0.5–1.0mW at the laser continuous-wave current values of 1.5–2.5mA.

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.

Nonvanishing turn-on delay in quantum dot lasers

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.

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.

Switching between generation of two quantum states in quantum-well laser diodes

The dynamics of emission spectra in semiconductor quantum-well lasers generating from two quantum states have been experimentally studied. In the case of electric pumping with 100-ns pulses, the lasing via transitions from the ground state is switched off and the emission from an excited state is switched on within 10–50 ns after laser turn-on. The switching is accompanied by a dip in the intensity of lasing, the duration of which depends on the pumping pulse amplitude. The observed phenomenon is explained in terms of gain clamping and redistribution of the carrier concentration between the ground and excited states.

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.

Optical trapping with Bessel beams generated from semiconductor lasers

In this paper, we study generation of Bessel beams from semiconductor lasers with high beam propagation parameter M2 and their utilization for optical trapping and manipulation of microscopic particles including living cells. The demonstrated optical tweezing with diodegenerated Bessel beams paves the way to replace their vibronic-generated counterparts for a range of applications towards novel lab-on-a-chip configurations.