Theoretical study on how to improve the properties of x-ray lasers by designing targets

The target used in x-ray lasers (XRL) is designed as an one-dimensional photonic crystals (1D PC’s) with 12 bilayers of SiO₂ and TiO₂, at the center of which a defect layer made of target material is embedded. The optical thicknesses of the target layer and each layer of the others are one-half and one-quarter of the pumping laser wavelength, respectively, so that the pumping laser is the localized mode of the 1D PC’s. Compared with the common slab target, the pumping laser intensity in the target layer will be enhanced by about two orders. This is very important to the progress of x-ray lasers towards compactness, shorter wavelength, and higher-conversion efficiency. The gain coefficient will increase by a factor of five, hence, the target length in saturated XRL is reduced to one-fifth. X-ray laser intensity will increase by about four orders, and so does the conversion efficiency. The average ionization state increases with pumping laser intensity, therefore, x-ray lasers will shift towards shorter wavelength.