Generation of coherent continua in soft X rays using a carrier-envelope phase-controlled few-cycle infrared light source

We have developed a sub-two-cycle intense infrared light source using novel BiB₃O₆ (BIBO)-based optical parametric amplifiers for the generation of high harmonics in soft X rays. The cutoff of high harmonics has extended to ~320 eV, which is well beyond the carbon K edge. The spectral structures and their dependences on the carrier-envelope phase strongly suggest the generation of single isolated attosecond bursts. The method holds promise for extending the energy scale of attosecond sciences from extreme ultraviole to soft X rays, as well as for realizing element-specific ultrafast spectroscopy using high harmonics.