Sequences of picosecond pulses with a total energy in the pulse train of about 1 mJ are transmitted through a hollow-core photonic-crystal fibre with a core diameter of approximately 14 μm. The fluence of laser radiation coupled into the core of the fibre under these conditions exceeds the breakdown threshold of fused silica by nearly an order of magnitude. The laser beam coming out of the fibre is then focused to produce a breakdown on a solid surface. Parameters of laser radiation were chosen in such a way as to avoid effects related to the excitation of higher order waveguide modes and ionization of the gas filling the fibre in order to provide the possibility to focus the output beam into a spot with a minimum diameter, thus ensuring the maximum spatial resolution and the maximum power density in the focal spot.

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A polycapillary x-ray lens is an effective element for radiation control. However, owing to the influence of several factors (efficiency of radiation capture by the capillary, absorption of radiation during its propagation through the capillary, etc.), a photon energy exists at which the lens has a maximum efficiency. The value of this energy is mainly determined by the diameter of the individual capillaries. In this paper, a new generation of polycapillary lenses with a combined structure is proposed. The developed lens consists of structures with different channel sizes and glass types. Capillary channels with larger sizes transport radiation of lower energies more effectively and capillary channels with smaller sizes transport radiation of higher energies more effectively. A comparison of the characteristic parameters of conventional lenses with a homogeneous structure and of new lenses with a combined structure was carried out. Examples of applications of these new lenses are given.

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