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International audience; A Markov model of semiconductor nanolaser is constructed in order to describe finely the effects of quantum fluctuations in the dynamics of the laser, in particular by considering the transition to lasing. Nanolasers are expected to contain only a small number of emitters, whose semiconductor bands are simulated using true carrier energy states. The model takes into account carrier-carrier interactions in the conduction and valence bands, but the result is a huge Markov chain that is often too demanding for direct Monte-Carlo simulation. We introduce here a technique to split the whole chain into two subchains, one referring to thermalization events within the bands and the other to laser photonic events of interest. The model is applied to the analysis of laser transition and enlightens the coexistence of a pulse regime triggered by the quantum nature of the photon with the birth of the known coherent cw regime. This conclusion is highlighted by calculated time traces. We show that on the ultrasmall scale of nanolasers, we are unable to define perfectly the threshold.

High quality La 2 CaB 10 O 19 single crystals doped with Pr 3+ ions were grown by means of the top seeded solution growth method. The concentration of Pr 3+ ions in the starting melt was equal to 4 at%, which, due to small distribution coefficient, in consequence gave single crystals containing 2.5 at% of Pr 3+ ions. The piezoelectric coefficients were measured for the pure and Pr +3 doped crystals. The principal changes under influence of the nanosecond pulsed 1064 nm Nd:YAG laser were observed for the LCBO nanocrystallites incorporated into the polymer matrices. The introduction of the Pr 3+ ions favors enhanced piezoelectric constants. In turn the nanocrystallites with enhanced piezoelectricity lead to the enhanced laser threshold damage.

CW mirrorless laser operation at 1840 nm at room temperature was observed in buried rib waveguides of KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 fabricated by structuring KY(WO4) substrates by Ar-ion milling and subsequent liquid phase epitaxial growth of the active layer on these substrates. Laser efficiency and laser threshold seems to change with the width of the channels fabricated.

The dependence of the refractive index and emission line-width of laser crystals on the atomic parameters of ions in the crystals has been analyzed qualitatively. As a result, an empirical relationship between laser threshold and chemical composition of laser crystals is proposed and demonstrated by some oxide crystals. The relation may be useful for the investigations of laser crystals.

We compare orientational relaxation phenomena of a light-emitting polymer and a, spectroscopically similar, conventional laser dye in solutions of comparable viscosity. The orientational relaxation time of the laser dye is found to be very much smaller than that of the polymer. This result is attributed to the large difference in shape between the two light-emitting materials. We demonstrate that these very different reorientation times have a major influence on the operation of a gain-switched laser based on these gain media, in particular on its threshold.

A scaling law obeyed by photon number fluctuations near threshold in the Ginzberg-Landau theory of second order phase transition is described. Normalized factorial moments are found to scale as F r ∼ F β r 2 , r ⩾ 3. The results from photon counting experiments on laser fluctuations near threshold are shown to support this scaling law. It is found that β r = ( r − 1) v , where v = 1.304. Implication of the scaling behavior is discussed.

Oxazine-170 was introduced into glasses obtained by the sol-gel method from methoxysilane. Absorption and emission of the dye were studied as a function of preparation conditions of the glasses. Extinction coefficients and quantum efficiencies of the mono-cationic form of the dye reveal much higher values than the neutral and di-cation forms. Laser threshold for the mono-cationic form in glasses is calculated to be 29 kW/cm 2 per pulse for 620 nm pumping wavelength and 67 kW/cm 2 for 578 nm pumping wavelength.

Spectral and dynamical changes in the fluorescence of Nd 3+ in the Ca 3 Ga 2 Ge 3 O 12 garnet have been investigated as a function of Nd concentration. These experimental results are then used to interpret the increase observed in the laser threshold with the Nd content.

Nd:Sr 5 (PO 4 ) 3 F, known as Nd:S-FAP, is a new material for efficient and miniature diode-laser pumped solid-state lasers. By using a laser-diode pump operating at 805.4 nm, Nd:S-FAP has been successfully lased at 1.328 μm. A slope efficiency of 33.5% and a laser threshold of 18.5 mW have been measured. The theoretical formulas for threshold power and slope efficiency were given and the theoretical estimation agreed with the experimental result.

We have studied the laser performance of Nd: KGW and Nd: YAG rods by monitoring the 1.06 μm laser emission at 78.5 K and 300 K. Our observations indicate that the laser efficiency from Nd: KGW is much higher than from Nd: YAG at these two temperatures. The laser threshold in Nd: KGW is lower at 78.5 K than at 300 K but it is always lower than that in Nd:YAG.

Intercavity absorptions is known to lead to an enormous enhancement in the detectability of absorbing species. Here the time development of this enhancement of this enhancement is investigated in order to fix a typical time scale such measurements. This is done with a Pockles cell in front and inside a flashlamp pumped dye laser resonator. The enhancement of absorption steeply increases at laser threshold and then levels off during the letter part of the laser pulse. By Q-switching a dye laser it is demonstrated that on a time resolution of 20 nsec extinctions as low as 10 -4 can be measured with an enhancement of two orders of magnitude.

We use the positive P representation approach to treat the nonlinear problem of a two-photon correlated-spontaneous-emission laser. An approximate positive P function is obtained in steady state. We discuss the influence of the laser intensity on squeezing and find that squeezing in the phase quadrature decreases with increasing laser intensity near the laser threshold.

We study the time evolution of a good cavity unidirectional single mode homogeneously broadened ring laser when the losses are slowly varied linearly in time. In the small intensity regime an exact solution is obtained. In this way we can characterize the delayed first laser threshold, the width of the dynamically induced hysteresis and the long time solution. Our results agree with recent experiments performed on a Ar + laser.

Laser emission cross-sections of the 1077 nm and 1370 nm emissions of Nd3+ in 3Ga2S3 (0.85)La2S30.15Nd2S3 (GLS) and 3Al2S3 (0.872)La2S30.128Nd2S3 (ALS) were obtained from the calculated matrix elements of Nd3+ in the glasses, experimentally measured intensity parameters, emission half-widths and lifetimes. The laser threshold power for side pumping in the chalcogenide glasses is much lower than for ED-2 glass.

A condition for which cooperative processes can be dominate purely random processes is established, and a threshold relation obtained. It is shown that for this condition the system under consideration behaves in a manner markedly different from its normal behaviour. In particular, for photon processes the occurrence of anomalously large emissions of correlated, and in some instances coherent, radiation emitted from very hot, high-density systems is predicted. These emissions have been observed in several plasma experiments. For a gas laser, the laser threshold behavior as a function of the gas density is predicted and is found to agree well with experiment.

Experimental results on quantum well laser operation in magnetic fields B < 12 T are reported. For B perpendicular (B⊥) to the quantum well a shĩft toward higher photon energy of ~ 0.5 meV/T is observed, with the laser threshold current decreasing significantly. In parallel magnetic fields (B∥) no significant effect is measured, thus confirming the built-in two-dimensional character of the electron gas.

Fluctuation-dissipation theorems for systems in non-thermal equilibrium are derived and are applied to the study of the laser threshold region.