Keywords:4D X-ray phase CT, X-ray Talbot interferometry, laser drilling into the polymers
We report the development of pink-beam 4D phase CT at BL28B2 at SPring-8 facility to observe fast phenomena related to the laser-induced drilling and engraving into the polymer. In our experimental configuration, the X-ray multilayer mirror was used to generate a pink-beam with a mean energy of 25 keV and an energy bandwidth of 10 % . The main purpose of the pink-beam was reduction of radiation damage to samples and tailoring the spectrum of X-ray beam fit to the X-ray Talbot interferometer (XTI) used for phase CT. The XTI was composed of a π/2 phase grating (G1) and an amplitude grating (G2) with a pitch of 5.3 µm. 4D phase CT was performed with the continuous fringe scanning technique to record a movie of differential phase images. In the continuous fringe scanning technique, during 5 continuous sample rotations, G1 was continuously moved by a distance equal to the grating pitch (5.3 µm). In this study, we improved the time for recording differential phase images during 180° sample rotation from previously reported 2 s  to 1 s. The improved temporal resolution was achieved by increasing of frame rate of X-ray detector from 1000 fps to 2000 fps while the number of projections per 180° rotation was maintained at a value of 400. The developed pink-beam 4D phase CT set-up was applied to observe laser-induced drilling into the poly (methyl methacrylate) (PMMA).
We successfully visualized the bubbling phenomenon during laser drilling into the PMMA. We successfully demonstrated that pink-beam 4D phase CT can be used to study laser drilling into the polymers and we promoted synchrotron radiation to study industry-relevant issues.
 A. Momose, H. Takano, M. Hoshino, Y. Wu, K. Vegso, SPIE Proc. 10391 (2017) 103910Y