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Optically pumped lasing from AlGaN/AlN multiple quantum wells grown on single-crystalline AlN substrates with lasing thresholds as low as 6 kW/cm2 is demonstrated via the reduction of unintentional point defects in the active region and waveguide, which reduces the non-radiative recombination by 2 orders of magnitude. A higher lasing threshold of 11 kW/cm2 is observed for AlGaN barriers, owing to the reduced localization of electrons and holes in the wells. It is shown that for electrically injected UVC laser diodes, AlGaN barriers are essential.

The absorption spectra of Tb,Tm:YVO4 and Ho,Tm:YVO4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, Ai,j and ?i,j and the cross-relaxation probability are calculated in virtue of Judd?Ofelt and Dexter theories. The fluorescence lifetime of Tm3+ in the Tb3+ (or Ho3+) co-doped crystal is calculated. It indicates that the lifetime of initial level 3H4 of the laser transition can be shorter than that of terminal level 3F4 of the transition if the atomic percentage of Tb3+ (or Ho3+) ions is bigger than about 1 at%: namely, by means of the co-doping Tb3+ (or Ho3+) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P(4)th and the slope efficiency ?(4)s of the four-energy-level system, we obtain the relationship of threshold power P(4)th to the concentration of Tm3+ ions and discuss the effect of Tb3+ (or Ho3+) ion concentration on the laser threshold power P(4)th around 1.5?m wavelength. The result shows that Tb,Tm:YVO4 crystal is a better choice to make the laser at ~1.5?m wavelength than Ho,Tm:YVO4 crystal. We give the appropriate composition of (1?2) at% Tb, (1?2) at% Tm:YVO4, just for reference.

This review summarizes recent developments and successes in the theoretical modelling of the characteristics of semiconductor microcavity lasers. After a discussion of the basic laser properties, results of a quasi-equilibrium many-body theory are presented which are very useful for the understanding of microcavity laser operation not too far above the laser threshold. Non-equilibrium phenomena, such as spectral and kinetic hole burning as well as plasma heating effects, are analysed using a quantum kinetic approach. Comparisons with experimental observations are discussed, before open problems and future challenges are outlined.

We report for the first time on the observation of self-mode-locking in a diode pumped self-Q-switched (SQS) Nd3+,Cr4+:YAG laser. This phenomenon results from significant excited state absorption of the Cr4+ ions in the co-doped host during the SQS laser pulses. The self-mode-locking occurs already slightly above the SQS laser threshold. Experiments using relatively low saturable intensity achieved a modulation depth of more than 40%.

We studied the cavity solitons (CSs) and their switching in a semiconductor Fabry–Perot type microresonator where the active medium is multiple quantum well nanostructures. We take benefit of the full set of Maxwell–Bloch equations to describe the dynamical behavior of the system, since the rate equation model for a two-level system fails to explain the system when considering femtosecond time scales. Numerical simulations imply formation of stable CSs which is done by local carrier injection as the switching method. To switch off these CSs we used the same method but with negative amplitude of the injection function. It is also realized that the successive switching on/off of CSs by such a scheme is possible in this system.

We studied the carrier transport phenomena of the multiple-quantum-well (MQW) active region and their impact on the performance of aquamarine and green laser diodes (LDs) grown on polar and semipolar planes. The ballistic carrier transport mechanism was found to be dominant in the MQW region. For the c-plane, because of the high hole capture probability and slow escape rate, mainly the quantum wells (QWs) positioned close to the p-side are electrically pumped. The optical loss induced by the underpumped QWs further away from the p-side leads to significantly higher laser threshold current density and a longer lasing wavelength with increased number of QWs. These effects are not significant for semipolar LD structures.

In this paper we investigated cavity soliton switching in a VCSEL type semiconductor laser which has been driven by homogeneous holding beam. Using quadratic fitting of the gain curve we studied the incoherent switching technique for the controlling of cavity solitons in a VCSEL-type laser and we show the cavity soliton spontaneous mobility in this type of injection.

This paper reviews several topics related to optically pumped ZnO nanowire lasers. A systematic study of the various properties of a device as it evolves from the regime of amplified spontaneous emission to laser oscillation above threshold is presented. The key dependence of the laser threshold on nanowire diameter is demonstrated and explained by means of a thorough study of guided modes in semiconducting nanowires for a nanowire-on-substrate geometry. A 'head on' detection geometry is used to measure the far-field profile of a nanowire laser and thus identify the modes responsible for lasing. Finally, the temperature behavior of a nanowire laser is reported, and possible mechanisms that may be responsible for gain are suggested.

An analysis is made of the influence of weak diffuse scattering by mirrors on the characteristics of an unstable resonator. It is shown that even if the diffuse reflection coefficient is only Ddiff~10–2, the roughness of the mirror surface may give rise to a random scatter (~10–1) of the laser threshold and a considerable (~ 1) change in the distribution of the intensity on the resonator mirrors.

A theoretical investigation is made of influence of the saturation in amplifying and absorbing media on the competition between opposite waves in a ring laser resonator. An expression for the polarization of a gas in the field of opposite waves of unequal amplitude is derived free of any restrictions in relation to the wave intensity. This expression is used to calculate the width of the competition zone and the parameters of narrow concurrent resonances due to the presence of a nonlinearly absorbing cell in the resonator. The dependences of these quantities on the excess over the laser threshold are analyzed for various relationshops between the homogeneous and inhomogeneous line broadening in the active medium.

The possibility of obtaining population inversion between the 7 2P3/2 and 7 2S1/2 thallium levels is investigated, mercury being used as the pumping element. The inversion attained in a radio-frequency discharge at 39 Mc/s is estimated to be, under certain conditions, of the same order of magnitude as the laser threshold inversion.

An investigation was made of the distribution of the gas density in a discharge gap of a continuous-flow CO2 laser with a heated cathode. The influence of the cathode heating on the laser threshold was determined. It was established that the use of a heated cathode made it possible to increase the molecular gas content in the working mixture by improving the homogeneity of the discharge.

Plates cut from cadmium sulfide and selenide ingots were used as laser screens. The laser threshold was reduced considerably by chemomechanical polishing.

An experimental investigation was made of the influence of heat treatment of p?n junctions on the characteristics of epitaxial and diffused GaAs laser diodes. The laser threshold decreased after heat treatment because of increase of the gain factor and the reduction by a factor of 5?10 of the threshold current density. The output power increased because the internal quantum efficiency became greater. The internal optical losses increased severalfold, indicating some deterioration of the waveguide properties.

An investigation was made of the laser parameters of bulk cadmium sulfide single crystals grown by the static sublimation method. It was established that mechanical treatment of the electron-bombarded surface had a condiderable influence on these parameters. The laser threshold and efficiency obtained for a cleaved surface were close to the best results obtained for platelet crystals.