The problem of delivering a multimode pump to a single mode core is considered. Original designs of double-clad fiber amplifiers are analyzed. A slab pump geometry of a fiber amplifier is suggested. The partially coherent pump should be coupled to the narrow slab which supports propagation of the pump and absorbs highest modes of the core, then the core itself has no need to be single-mode. The slab plays the role of cladding in conventional double-clad fibers. Such a cladding has no need to surround the core and its refractive index can be higher than that of the core. Then the highest modes of the slab are absorbed at the very beginning of the amplifier. This allows for tapering of the slab, providing almost constant pump power in the core. The end result is a the high efficiency of a compact device with scaling to high pump power. We provide the key design formulars for such a device.
Any nonlinear interaction, in principle, can produce non-classical state. The Kerr nonlinearity seems to be the simplest one. Since papers [1-3], it seemed that as the squeezed states, as the Schriidinger cat ones can be produced by the self-modulation. The squeezing was really observed [ 3] in such a scheme. As for cats, Ref. {4,5] mention the large distance of propagation and linear absorption as factors which make the experimental realization unlike. Note that neither the large distance of propagation nor the linear absorption are fundamental reasons why the Schrödinger cat cannot be obtained by such a manner.
Distortions of the wave front in the Earth 'a atmosphere is discuued. The approximation of distortions of the wave localized in the thin layer is considered. The model to construct random realizations of the field with the given structure function is suggested. But the lower atmospheric layers give relatively small contribution to the distortion of wavefronts. In the first approximation the role of the thickneBB of the atmosphere may be described by the linear diffraction equation. It gives the estimation of the density of the dislocations of the wave front of the initial plane wave. It is shown that for this case this density is less than 1 dislocation per 100 square meters, at least for the good seeing condition. Recommendations to use flexible mirrors if the optical path in the atmosphere is leas than 10 km. and the segment mirror if the optical path is greater than 50 km. are suggested. The short program to simulate the wave fronts realizations to count dislocations is supplied.
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