Research interests 

Introduction 

  When a material surface  is irradiated with a short pulse short pulse laser with energy exceeding the destruction threshold (ablation threshold) of the material, the surface is ablated (scattering and peeling), and periodic nano-structures (LIPSS: Laser Induced Periodic Surface Structures) are self-organized. The LIPSS has a inter-spacing of LIPSS shorter than the laser wavelength. However, its formation mechanism is unknown. Therefore, we are not known how small LIPSS can be produced, how to improve the uniformity of LIPSS. For the purpose of elucidating the formation mechanism of LIPSS, I have worked on the "short laser ablation" research by dividing into four processes from the viewpoint of laser-material interaction. I. In laser absorption process, it was clarified that the ions emitted from the laser-irradiated metal surface are involved in multiphoton absorption [Reference 1]. II. Then the electron emission due to a photoelectric field (decreased surface potential barrier) is induced. [Reference 2]. III. In addition, it is similar to the energy spectrum of the ions emitted during the formation of the periodic nano-structures, suggesting that the ions are emitted from the nano-space by the Coulomb explosion. IV. We found that the inter-space of LIPSS depends on laser fluence [References 3 and 4], and clarified that the formation mechanism involves the interaction between the laser and the laser-produced plasma [Reference 5]. In addition, the crystallinity of the material is amorphized by ablation [Reference 6], and the size of the periodic nano-structure is reduced to about 1/13 of the laser wavelength λ by irradiation with double pulse laser beam [Reference 7]. Furthermore, by optimizing the irradiation conditions, we have discovered various new phenomena such as the formation of LIPSS with extremely high periodicity (uniform periodicity) [Reference 8]. Understanding and controlling the interaction between the laser and the material is required to perform the desired nano-fabrication on the surface of the material.

Research goals

 The research goal is to work on basic research and applied research of nano-structures that are self-organized by short pulse lasers, elucidate the formation mechanism, and find novel functions that are manifested by adding nano-structures to the material surface. To explore new functions, we will develop laser functional material creation technology to create materials of the size required for measurement and evaluation. We would like to accelerate collaborative research and fusion research in the university and show our laboratory presence in the research fields of nano-structure formation and new functional material creation. 

Our work

In Tokai University,  We have built a double pulse laser machining system for the purpose of elucidating the formation of fine structures and its application. In addition, in applied research on the nano-structure that can be formed on the surface by laser irradiation, we will develop a laser functional material creation system that creates materials of the size (5 cm x 5 cm) required for measurement and evaluation in order to explore new functions. This will accelerate collaborative research and fusion research with the Q-LEAP Flagship program and joint research institutes, aiming for stronger collaboration than ever in the research fields of elucidating the mechanism of nano-structure formation and creating new functional materials. 

Tokai University has the Technology Joint Management Office established, maintained, and operated with the assistance of the Advanced Research Infrastructure Sharing Promotion Project in MEXT(the Ministry of Education, Culture, Sports, Science and Technology), and the Tokai University Imaging Research Center established based on the industry-academia collaboration comprehensive agreement by Nikon Co., Ltd. Adjacent to our laboratory, there are more than 35 material analyzers and 15 bio-imaging instruments. By utilizing an environment that enables rapid implementation from laser irradiation to analysis, not only with new collaboration for high-intensity laser interactions and laser micro/nano surface processing, but also the basics of micro/nano structure formation, new material applications, and bio-material research is going to be accelerated.  

 References

   1.     M. Hashida, A. Semerok, O. Govert, G. Petite, Y. Izawa, and J. F-. Wagner: "Ablation threshold dependence on pulse duration for copper", Appl. Surf. Sci. 197-198 (2002) 862-867. (citation:144)

   2.     M. Hashida, S. Namba, K. Okamuro, S. Tokita, S. Sakabe: "Ion emission from a metal surface through a multiphoton process and optical field ionization", Phys. Rev. B 81(2010) 115442-1-115442-5.  (citation:39)

  3.     K. Okamuro, M. Hashida*, Y. Miyasaka, Y. Ikuta, S. Tokita, and S. Sakabe: "Laser fluence dependence of periodic grating structures formed on metal surfaces under femtosecond laser pulse irradiation", Phys. Rev. B 82 (2010) 165417-1- 165417-5. (citation:147) *Corresponding author

  4.     M. Hashida, Y. Ikuta, Y. Miyasaka, S. Tokita, and S. Sakabe: "Simple formula for the interspaces of periodic grating structures self-organized on metal surfaces by femtosecond laser ablation", Appl. Phys. Lett. 102 (2013) 174106-1-174106-4.  (citation:34)

  5.     A. M. Gouda, H. Sakagami, T. Ogata, M. Hashida, S. Sakabe: "Formation mechanism of the periodic  grating structure by the surface plasma wave", Plasma Fusion Res. 11 (2016) 2401071-1-12401071-4. (citation:11) 

  6.     M. Hashida, Y. Miyasaka, Y. Ikuta, S. Tokita, and S. Sakabe: "Crystal structures on a copper thin film  with a surface of periodic self-organized nanostructures induced by femtosecond laser pulses", Phys. Rev. B 83 (2011) 235413-1-235413-5.  (citation:26)

  7.     M. Hashida, L. Gemini, T. Nishii, Y. Miyasaka, H. Sakagami, M. Shimizu, S. Inoue, J. Limpouch, T. Mocek, and S. Sakabe: "Periodic graing structures on metal self-organized by double pulse irradiation", J. Laser Micro/Nano Eng., 9 (2014) 234-237. (citation:14)

  8.     M. Hashida, Y. Furukawa, S. Inoue, S. Sakabe, S. Masuno, M. Kusaba, H. Sakagami, M. Tsukamoto: "Uniform LIPSS on titanium irradiated by two color double-pulse beam of femtosecond laser", J. Laser Appl. 32 (2020)022054-1-022054-4. (citation:2）