Top-emitting AlasAlGaAs vertical cavity surface emitting lasers emitting at 765 nm with minimum threshold currents of 0.6 mA and threshold voltages of 1.9 V have been grown by MOVPE. In order to keep the growth time low, we investigated the possibility to grow these structures at growth rates of 5 μm/h. Special attention was paid to the homogeneity that can be achieved over a 2″ wafer under these growth conditions. Spatially resolved reflectivity measurements on GaAsAlAs distributed Bragg reflectors showed, that the growth rate varies less than 0.3% in the center of the wafer and decreases by 1% at the wafer edge.

We have fabricated AlAs/AlGaAs Vertical Cavity Surface Emitting Lasers (VCSELs) emitting at 765 nm with record performance. The VCSELs were fabricated using MOVPE and a combination of dry and wet etching for the lateral structuring of the laser posts. Minimum threshold currents of 600 μA and threshold voltages of 1.9 V are achieved for VCSELs with a mesa diameter of 26 μm. The maximum slope efficiencies are 0.46 W/A with wallplug efficiencies of 11.2 % at an output power of 1 mW. The maximum output powers for larger devices exceed 5 mW. To our knowledge these are the best performance characterstics for VCSELs operating in the 760 - 780 nm wavelength range. Compared to recently published data on 780 nm VCSELs in the GalnAsP/AlGalnP material system, the threshold currents ate more than a factor of 4 smaller, the wallpug efficiencies are a factor of 1.7 larger. We attribute the high performance to the accurate control over growth rates and aluminum contents, the layer design and the improved lateral current confinement by an additional lateral selective etching step. Spectral measurements show that the lasers operate single transverse mode over a wide current range with single mode output powers above 1 mW. A comparison with conventional mesa-etched VCSEL structures is made to demonstrate the impact of the additional lateral etching step on the device performance.

Technological problems stemming from high temperature operation of the sulfur resonator have hindered its development as a tunable, efficient, discharge pumped laser. The use of RF simmer discharges is shown to reduce previous temperature constraints by dissociating polyatomic sulfur molecules into the dimer, such that lasing is achieved when pumped by an XeCl excimer laser. The peak power output of the S 2 laser and the transmission spectra through sulfur discharges are used to infer the effectiveness of the discharge in dissociating the vapor.

This chapter reviews that organelles contain a complete apparatus for the synthesis of proteins. It is clear that, at least in most cases, organelle tRNAs are transcripts of the organelle genome. The limited number of tRNAs present in organelles in contrast to prokaryotes and the eukaryotic cytoplasm-poses an interesting problem. The chapter discusses the two hypotheses: (1) That organelles evolved via endosymbiosis, and (2) that organelles evolved through invagination and compartmentalization of function. It suggests that either certain codons are not utilized by organelles or that, because of “wobble” at the third position of the anticodon, or a few isoacceptors-all 61 “sense” codons may be translated. As codon recognition by aminoacyl-tRNAs is determined, solely by the tRNA component, these elements of the protein synthetic machinery are in large part, responsible for maintaining the fidelity of the genetic code. The aim of this chapter is to review the development and progress of organelle tRNA research and the aminoacyl-tRNA synthetases.

In high density near-field optical storage applications a laser diode is brought into close proximity of a recorded surface with the express purpose to circumvent the diffraction limit imposed upon the spot size, as schematically shown in Fig 1. In such a configuration, generally, there is no space for bulky elements employed in the usual far- field detection schemes. As an alternative, the disk induced effects of self-coupling and optical feedback, as manifested in modulation of diode voltage, operating wavelength or rear facet output power may be utilized for readout. In this paper, the issues of sensitivity, signal-to-noise-ratio, speed and other overall prospectus of such a near-field detection scheme are addressed via a theoretical analysis and numerical simulations. Utilizing advanced finite difference and finite element simulations to solve the complete vectorial Maxwell equations, we analyze optical self-coupling and emission from a very small aperture (VSA) (1) milled into the front metal coated facet of a laser diode(2). The calculated coupling coefficients were then applied as inputs to the dynamical laser model based on the weak optical feedback approximation (3). The stochastic Langevin forces were included for modeling spontaneous and shot noises. In Fig. 2 the side view of light intensity emitted from the front facet coating (SiO2-Al2O3-Ag - air interface ) is depicted. One can observe that the lateral intensity distribution is quite narrow (on the order of the subwavelength aperture size) within a small distances of the aperture (the near-field zone). In phase-change (PC) optical media, data is recorded in a thin alloys layer through laser induced heating. The area effected by the focused beam results in either an amorphous or crystalline mark depending on the temperature reached and cooling rate . We compared readback sensitivity of both edge emitters and VCSELs to a signal from the phase changing media (Fig. 3) when the detection is based on measuring the power output from the rear facet. We found that the absolute change of the rear facet output due to modulation of the external mirror reflectivity (marks on the PC disk) to be approximately the same for both types of lasers. Smaller "openness" and the larger (symmetric) mode area of VCSELs are compensated by a short cavity length leading to comparable sensitivity. The issues of magneto-optic detection using VSA laser diodes are also briefly discussed.