State-of-the-art intense ultrashort extreme ultraviolet (XUV) and soft X-ray (SX) pulse sources such as high-order harmonic generation (HHG, phenomenon in which laser light is converted to light with integer multiples of the laser frequency) and X-ray free electron lasers are expected to open a way to investigate new aspects of light-matter interaction. This is not only interesting as fundamental science but also may serve as a basis of advanced optical technology related to ultrafast phenomena and real-time biomolecular structure imaging.

　Nonlinear, nonperturbative effects and electronic correlation often play an essential role in the generation and application of ultrashort intense XUV and SX pulses. The best theoretical method to study such phenomena is based on the time-dependent Schrodinger equation (TDSE). In the present project, we study the generation, measurement and application of ultrashort XUV and SX pulses (especially HHG), with TDSE and other theoretical tools. Our recent achievements include two-photon double ionization of He, attosecond double-slit experiment, the HHG dramatic enhancement (DE) (Fig. 1) and its application to single attosecond pulse generation (Fig. 2).

　The fruits of this ongoing project will greatly contribute to technological innovation such as the creation of unique atomic and molecular states, the observation of atomic and molecular wave function, and the control of intra-atomic electron dynamics with the attosecond time scale.