The third-generation attosecond light source

Katsumi Midorikawa

RIKEN Center for Advanced Photonics

Since breaking the barrier of 1fs in 2001, attosecond science has progressed rapidly for two decades, supported by advances in ultrafast laser technology and an understanding of the interaction of strong optical fields with matter. Attosecond pulses allow us to capture the motion of electrons in a variety of materials and are expected to bring about revolutionary progress in basic science fields such as physics, chemistry, and biology.

Research on attosecond pulses has changed significantly around 2010. Before 2010, the Ti:S laser was the de facto standard as the driving light source, so the cutoff energy was limited to about 100 eV and the repetition rate was typically 1 kHz [1]. After 2010, the mid-infrared (MIR) optical parametric amplifier (OPA) became the mainstream of the driving source [2]. Owing to the quadratic dependence of the cutoff energy on the driving wavelength, the harmonic photon energy was extended to over 300 eV, reaching the water-window spectral region, by using a MIR OPA [3]. However, the increase in driving wavelength results in a significant decrease in conversion efficiency due to the combined effects of the electron wave packet spreading and the increase in the harmonic order. In order to compensate for the low photon flux associated with the low conversion efficiency, attempts to optimize the waveform of the driving laser pulse [4] as well as to increase the driving laser energy [5] and repetition rate [6] have been pursued vigorously. In this talk, I will present our efforts over the last decade for the generation of intense isolated attosecond pulses.

References
[1] M. Chini, K. Zhao, and Z. Chang, Nat. Photon. 8, 178 (2014)
[2] K. Midorikawa, Nat. Photo. 16, 267 (2024)
[3] E. J. Takahashi, T. Kanai, K. L. Ishikawa, Y. Nabekawa, and K. Midorikawa, K. Phys. Rev. Lett. 101, 253901 (2008)
[4] B. Xue, Y. Tamaru, Y. Fu, H. Yuan, P. Lan, O. D. Mücke, A. Suda, K. Midorikawa, and E. J. Takahashi, Sci. Adv. 6, eaay2802 (2020)
[5] E. J. Takahashi, P. Lan, O. D. Mücke Y. Nabekawa, and K. Midorikawa, Nat. Commun. 4, 2691 (2013)
[6] U. Elu, M. Baudisch, H. PIRES, P. Tani, M. H. Frosz, F. Köttig, A. Erolov, P. St.t. Russell, and J. Biegert, Optica 4, 1024 (2017)