An optical fiber communications system with Raman amplification of the signal radiation comprises a broadband pump radiation source, or, preferably a multiplicity of pump radiation sources. The sources are selected to result in a pump radiation spectrum such that pump radiation intensity in the fiber core is less than a critical intensity I.sub.c. In particular, the average intensity of pump radiation in a first spectral interval, centered on any wavelength .lambda..sub.p in the pump radiation spectrum and of width equal to the Brillouin line width of the fiber at .lambda..sub.p, is to be less than that average intensity in the first spectral interval that results in conversion of 10% of the radiation in the first spectral interval to stimulated Brillouin radiation. Use of a multiplicity of pump sources not only can reduce pump noise and pump depletion due to stimulated Brillouin scattering, but typically also can result in enhanced system reliability and lower cost. In a preferred embodiment, the invention is a soliton fiber communications system, with pump radiation injected at one or more intermediate fiber locations.

A method and apparatus are provided for the holographic examination of the internal features of cavities and passageways of a structure. The apparatus employs a laser beam source positioned external of the structure coupled to a multilayer fiber waveguide which conveys the reference beam and object beam, in at least two different layers of the multilayer fiber, which combine in a holographic recordation means to form a hologram of the internal features of the structure, or under certain circumstances a holographic interferogram of the selected features is formed.

A method and apparatus are provided for the holographic examination of the internal features of cavities and passageways of a structure. The apparatus employs laser beam sources positioned within the structure to form a laser reference beam and laser object beam which combine in a holographic recordation means to form a hologram of the internal features of the structure, or under certain circumstances a holographic interferogram of the selected features is formed.

An exposure apparatus includes a first dispersing element for dispersing substantially parallel laser light, from a laser, with respect to the wavelength to provide light beams of wavelength units, a first optical system for collecting each light beam of a wavelength unit from the first dispersing element, a wavelength selecting device for passing a predetermined wavelength region of light, of the light beams of wavelength units each being collected by the first optical system, a second optical system for receiving the light from the wavelength selecting device and providing parallel light beams of wavelength units, and a second dispersing element for combining the parallel light beams of wavelength units from the second optical system, the second dispersing element having substantially the same angular dispersion as that of the first dispersing element and a direction of dispersion opposite to that of the first dispersing element.

A pulsed solid state laser system is disclosed which utilizes a plurality of individual laser rods which are sequentially pumped and whose beans are combined into a single interleaved output bean. The individual laser rods are pumped at an average power level which is below that for maximum output power from each rod, thereby obviating the need for refrigeration cooling. A compact optical system is disclosed which permits a constant beam size even at different pump levels and other advantages. A compact cooling system is also disclosed.