Effect of inhomogeneous broadening of submonolayer quantum dots on the generation of vertical-cavity laser with saturable absorber

The experimental dependences for a laser based on submonolayer quantum dots (QDs) without an absorber were used to calculate the energy characteristics of a semiconductor laser based on QDs and quantum wells with a saturable absorber under bistable lasing conditions; the data obtained make it possible to implement a monolithic version of this laser. All of the mechanisms of carrier relaxation and QD filling, which are important for experiment, are taken into account. The effect of inhomogeneous QD broadening over resonant frequency is considered. The laser mode shift that is caused by an increase in the pump current is found to limit the lasing power. It is shown that the choice of active and passive layers with inhomogeneously broadened QDs makes it possible to obtain bistable lasing in the entire range of available pump currents.     

Magnetic resonance in a [{Cr(CN)<Subscript>6</Subscript>} {Mn(S)-<Emphasis Type="Italic">pn</Emphasis>H-(H<Subscript>2</Subscript>O)}] · H<Subscript>2</Subscript>O single-crystal molecular ferrimagnet

The variations in the magnetic resonance spectra accompanying the transition from the paramagnetic to ferrimagnetic state in [{Cr(CN)₆} {Mn(S)-pnH-(H₂O) }] · H₂O orthorhombic chiral molecular crystals were studied. The dependence of the EPR linewidth on temperature in the proximity of the transition point T_C = 38 K argues for the two-dimensional character of spin ordering. The spin resonance line was found to undergo exchange narrowing at T > T_C. The ferrimagnetic phase has an easy magnetization axis coinciding with the a crystallographic axis.     

Depolarization of luminescence of polyatomic molecules in the gas phase as a method of determining the efficiency of collisional transfer of angular momentum

The theory of collisional depolarization of luminescence of extended polyatomic molecules in rarefiedgases is considered. The interrelation between the frequency of collisions, the relaxation time of the angular momentum, and the cross section of the luminescence depolarization is established, and the dependence of these parameters on the efficiency of an abrupt change in the angular momentum is calculated. The use of the theory of collisions of solids in the Enskog approximation made it possible to take into account the effect of the shape and mass of colliding molecules on the degree of depolarization. It is established that, in terms of this theory, there exists a limiting efficiency of an abrupt change in the angular momentum, which, however, does not attain the value proposed in the model of strong collisions (Jdiffusion). The dependence of the depolarization of luminescence of 1,4-di-(2-5-p-tolyloxazolyl) benzene molecules on the concentration of a buffer gas (argon) is measured. It is found that about five collisions with Ar atoms are required for randomization of the angular momentum of these molecules.     

Single-Lobe Single-Wavelength Lasing in Ultrabroad-Area Vertical-Cavity Surface-Emitting Lasers Based on the Integrated Filter Concept

We have studied broad-area vertical-cavity surface-emitting lasers grown in the antiwaveguiding approach (AVCSELs). The AVCSEL-type devices were fabricated in the ridge stripe geometry with openings in the top contact layer. Surface lasing was realized and evaluated for the devices with and without the integrated absorber section, acting as a selective filter for the emission modes propagating at finite tilt angle with respect to the normal to the surface (F-AVCSEL). It was found that the conventional AVCSEL device lases in high-order excited modes, tilted with respect to the normal to the surface, while lower order modes evolve at higher current densities causing a dramatic broadening of the emission spectrum. On the contrary, the F-AVCSEL emission is composed of a single spectral feature, which remains hardly affected up to the highest current densities >10 kA/cm². The far-field pattern is composed of a single zero-angle lobe with a beam divergence defined by the size of the opening in the top contact. No spectral features due to parasitic high-order modes were observed. The Gaussian-type single-wavelength surface-emitting lasing with an output power of 70 mW was realized in all-epitaxial wavelength-selective filter concept.     

Synthesis and molecular structure of chlorostannyl derivatives of carbonyl(cyclopentadienyl)nitrosylmanganese

The reaction of [CpMn(CO)(NO)]₂ (I) with an equimolar amount of tin dichloride in THF at room temperature gave the product of tin insertion into the Mn-Mn bond, the carbonyl nitrosyl complex [CpMn(CO)(NO)]₂SnCl₂ (II). The same complex was formed on treatment of CpMn(CO)(NO)SnCl₃ with sodium borohydride. Treatment of I with an excess of anhydrous tin dichloride under the same conditions gave the trinitrosyl complex Cp₂Mn₂(NO)(μ-NO)₂SnCl₃ (III). According to X-ray diffraction, II contains a Mn-Sn-Mn chain with highly shortened Mn-Sn bonds (2.5570(2) and 2.5754(2) Å). Compound III contains a Mn-Mn-Sn chain (Mn-Mn, 2.5358(10); Mn-Sn, 2.5604(8) Å) with the Mn-Mn bond supplemented by two nitrosyl bridges and one terminal NO group.     

Influence of optical losses on the dynamic characteristics of linear arrays of near-infrared vertical-cavity surface-emitting lasers

The effect of the level of internal and external optical losses on the dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) in the spectral region of 850 nm is studied. It is shown that an increase in optical losses leads to a decrease in the speed of laser response and to the predominance of thermal effects, while a decrease in losses for the output of radiation brings about an increase in the response speed of the laser and the dominance of damping of the effective modulation frequency. Linear matrix emitters with the 1 × 4 format based on fast-response VCSEL with individual element addressing are produced and studied. Individual laser emitters with a current-aperture diameter of 5–7 μm provide lasing in the continuous-wave mode at room temperature in the region of 850 nm with threshold currents no higher than 0.5 mA, a differential efficiency no lower than 0.6 W/A, a modulation frequency as high as 20 GHz, and a MCEF factor of ～10 GHz/mA^1/2.