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We consider two semiconductor lasers coupled face to face under the assumption that the delay time of the injection is small. The model under consideration consists of two coupled rate equations, which approximate the coupled Lang-Kobayashi system as the delay becomes small. We perform a detailed study of the synchronized and antisynchronized solutions for the case of identical systems and compare results from two models: with the delay and with instantaneous coupling. The bifurcation analysis of systems with detuning reveals that self-pulsations appear via bifurcations of stationary (i.e., continuous wave) solutions. We discover the connection between stationary solutions in systems with detuning and synchronous (also antisynchronous) solutions of coupled identical systems. We also identify a codimension 2 bifurcation point as an organizing center for the emergence of chaotic behavior.

We extend the quasi-steady-state approximation (QSSA) with respect to the class of differential systems as well as with respect to the order of approximation. We illustrate the first extension by an example which cannot be treated in the frame of the classical approach. As an application of the second extension we prove that the trimolecular autocatalator can be approximated by a fast bimolecular reaction system. Finally we describe a class of singularly perturbed systems for which a higher order QSSA can easily be obtained.

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A compact and effcient source of amplitude-squeezed light is described. It employs a semi-monolithic degenerate MgO:LiNbO(3) optical parametric amplifier pumped by a frequency-doubled Nd:YAG laser at 532 nm. Injection-seeding of the amplifier by a 1064 nm wave permits active stabilization of the cavity length and stable operation. At a pump power of 380 mW, a maximum noise reduction of 6.5 dB in the amplitude fluctuations of the 0.2 mW 1064 nm wave was detected. The average detected noise reduction in continuous operation over 14 minutes was 6.2 dB. Taking the detection effciency into account, this corresponds to a squeezing of 7.2 dB in the emitted wave.