Second generation X-ray lasers

High harmonic amplification is shown in an optical-field ionized X-ray laser. The 4d-4p X-ray line of Kr8+ at 32.8 nm, which has a close match to the 25th harmonic of the infrared laser, was amplified up to 200 times. The energy-extraction regime was also achieved, which depended on the level of seeding. This second-generation X-ray laser is fully polarized, has low divergence and shows a high degree of coherence. The duration is also expected to be short, fulfilling the requirements for an ultra-intense tabletop X-ray laser. Conditions for higher energy output are also suggested.