A Nd : glass laser system with the additional selective devices based on electro-optical Pockels cells and fast-response deflectors makes it possible to produce light pulses with a contrast not less than 10⁶ by means of the amplification of chirped pulses. Focusing such laser pulses on a target, we were able to achieve an intensity of 10¹⁷ W/cm², which provided an opportunity to produce a high-temperature plasma, which emitted both bremsstrahlung and line radiation. The efficiency of energy conversion these processes reached several tenths of a percent. The efficiencies of energy conversion into X-ray emission are compared for short (1.5 ps) and long (50 ns) pulses. Reasonable agreement between the experimental data and the results of numerical simulations is achieved.