Radiation conditions are introduced as an exact method to truncate numerical solutions of the timedependent Schrödinger-equation at the boundaries of the numerical grid. A rigorous derivation of radiation conditions is given by the Green-function method for one-and three-dimensional regions. An accurate finitedifference representation is obtained for a one-dimensional region. The method is applied to calculations of strong-field photoionization. The calculation of ionization probabilities and energy spectra by the truncated solution is illustrated. ͓S1050-2947͑97͒06107-6͔PACS number͑s͒: 32.80.Rm, 31.15.Ϫp

A relativistic treatment of strong-field photoionization based on the phase-space-averaging method is presented. A procedure is described for preparing a relativistic microcanonical ensemble of the atomic ground state and for calculating the final compensated energies for relativistic electrons. The method is applied to over-the-barrier ionization of hydrogen with ultrashort laser pulses. Ionization probabilities and electron energy spectra have been obtained for laser pulse amplitudes near and well above the atomic unit. The results are in excellent agreement with previous experiments under similar conditions. In sufficiently strong fields, saturation of ionization is shown to limit the attainable electron energies.

The study of degradation process in high-power laser diodes, in particular, high-power laser bars, has become increasingly important as the output power of these devices continues to rise. We present a "by-emitter" degradation analysis technique, which examines degradation processes at both the bar and emitter levels. This technique focuses on understanding the dynamic mechanisms by which packaging-induced strain and operating conditions lead to the formation of defects and subsequent emitter and bar degradations. In the example presented, we examine a highly compressively strained bar, where thermally induced current runaway is found to be an important factor in the bar degradation and eventual device failure

Laser modules for single mode fiber (SMF) coupling of frequency stabilized diode lasers are so far mainly realized with ridge lasers due to their good beam quality. Tapered lasers are beam sources with a beam quality which is nearly as good as that of a ridge laser but with a higher optical output power. Therefore they have the potential for a higher SMF-coupled power than ridge lasers. It will be shown how the radiation of a tapered laser or amplifier can be frequency stabilized and coupled into a SMF in a compactly build module. To couple a tapered laser different coupling systems, using cylindrical lenses either crossed or in combination with rotational lenses are possible. The advantages, problems and coupling results of those systems will be illustrated. For many applications it is necessary to stabilize the frequency of the laser. This can be achieved for example by a fiber bragg grating, written in the SMF in which the laser is coupled or by a volume holographic grating, applied to a lens in the coupling system. Another possibility is the use of a tapered amplifier, which is stabilized by a fiber bragg grating on the backside of the amplifier

During the last few years high power diode laser arrays have become well established for direct material processing due to their high efficiency of more than 50%. But standard broad-area waveguide designs are susceptible to modal instabilities and filamentations resulting in low beam qualities. The beam quality increases by more than a factor of four by using tapered laser arrays, but so far they suffer from lower efficiencies. Therefore tapered lasers are mainly used today as single emitters in external resonator configurations. With increased output power and lifetime, they will be much more attractive for material processing and for pumping of fiber amplifiers. High efficiency tapered mini bars emitting at a wavelength of 980 nm are developed, and in order to qualify the bars, the characteristics of single emitters and mini bars from the same wafer have been compared. The mini bars have a width of 6 mm with 12 emitters. The ridge waveguide tapered lasers consist of a 500 µm long ridge and a 2000 µm long tapered section. The results show very similar behavior of the electro-optical characteristics and the beam quality for single emitters and bars. Due to different junction temperatures, different slope efficiencies were measured: 0.8 W/A for passively cooled mini bars and 1.0 W/A for actively cooled mini-bars and single emitters. The threshold current of 0.7 A per emitter is the same for single emitters and emitter arrays. Output powers of more than 50 W in continuous wave mode for a mini bar with standard packaging demonstrates the increased power of tapered laser bars

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