Why Research Activities Fascinate Me

– Moments in which theoretical predictions were demonstrated experimentally –

In paper (a), I predicted an effect called the dramatic enhancement of high-harmonic generation. When it was published, a world-famous experimentalist commented, “It can’t be true!”  However, four years later, the theoretical prediction was demonstrated by a beautiful experiment done by a group at RIKEN, a leading research institute in Japan.  Details are included in paper (b).  The real pleasure of our theoretical research comes from the excitement of seeing predictions created through theories and computer simulations actually happening and presenting new opportunities for predictions—even if they turn out to be wrong eventually.  Our paper (c) was criticized by a well-known theorist.  But again, our predictions have recently been demonstrated in experiments conducted by a multi-national international project using a free-electron laser, details of which are included in paper (d).  Another prediction of mine in paper (e) has not been tested yet; however, it has led us to international collaborations with the Vienna University of Technology, the Imperial College of London, and the Max Born Institute in Berlin.
I always wonder why light, electrons, atoms, molecules, etc. precisely follow equations that are no more than human inventions.  Why do they know which paths to take?  Such paths are extremely difficult to calculate, even with supercomputers.  Studies on fundamental phenomena “unexpectedly” open ways to practical applications.  That is the reason I am always fascinated by scientific research.

【Journals】
(a) K. Ishikawa, Photoemission and ionization of He+ under simultaneous irradiation of fundamental laser and high-order harmonic pulses, Phys. Rev. Lett. 91, 043002 (2003).
(b) E. J. Takahashi, T. Kanai, K. L. Ishikawa, Y. Nabekawa, and K. Midorikawa, Dramatic enhancement of high-order harmonic generation, Phys. Rev. Lett. 99, 053904 (2007).
(c) K. L. Ishikawa and K. Ueda, Competition of resonant and nonresonant paths in resonance-enhanced two-photon single ionization of He by an ultrashort extreme-ultraviolet pulse, Phys. Rev. Lett. 108, 033003 (2012).
(d) R. Ma, K. Motomura, K. L. Ishikawa, et al., Photoelectron angular distributions for two-photon ionization of helium by ultrashort extreme ultraviolet free electron laser pulses, J. Phys. B 46, 164018 (2013).
(e) K. L. Ishikawa and K. Midorikawa, Above-threshold double ionization of helium with attosecond intense soft x-ray pulses, Phys. Rev. A 72, 013407 (2005).