Artificial joint acetabular cup stability is essential for successful total hip arthroplasty. However, a quantitative evaluation approach for clinical use is lacking. We developed a resonance frequency analysis (RFA) system involving a laser system that is fully contactless. This study aimed to investigate the usefulness of laser RFA for evaluating acetabular cup stability. First, the finite element method was performed to determine the vibration mode for analysis. Second, the acetabular cup was press-fitted into a reamed polyurethane cavity that replicated the human acetabular roof. The implanted acetabular cup was vibrated with pulse laser irradiation and the induced vibration was detected with a laser Doppler vibrometer. The time domain signal from the vibrometer was analyzed by fast Fourier transform to obtain the vibration frequency spectrum. After laser RFA, the pull-down force of the acetabular cup was measured as conventional implant fixation strength. The frequency of the first highest amplitude between 2 kHz and 6 kHz was considered as the resonance peak frequency, and its relationship with the pull-down force was assessed. The peak frequency could predict the pull-down force (R² = 0.859, p < 0.000). Our findings suggest that laser RFA might be useful to measure acetabular cup stability during surgery.

We discuss requirements on relativistic-irradiance (I₀ > 10¹⁸ W/cm²) high-power (multi-terawatt) ultrashort (femtosecond) lasers for efficient generation of high-order harmonics in gas jet targets in a new regime discovered recently (Pirozhkov et al., 2012). Here, we present the results of several experimental campaigns performed with different irradiances, analyse the obtained results and derive the required laser parameters. In particular, we found that the root mean square (RMS) wavefront error should be smaller than ~100 nm (~λ/8). Further, the angular dispersion should be kept considerably smaller than the diffraction divergence, i.e., μrad level for 100–300-mm beam diameters. The corresponding angular chirp should not exceed 10⁻² μrad/nm for a 40-nm bandwidth. We show the status of the J-KAREN-P laser (Kiriyama et al., 2015; Pirozhkov et al., 2017) and report on the progress towards satisfying these requirements.

The initial stages of the femtosecond (fs) laser ablation process of gold, platinum, and tungsten were observed by single-shot soft x-ray imaging technique. The formation and evolution of soft x-ray Newton’s rings (NRs) were found for the first time. The soft x-ray NRs are caused by the interference between the bulk ablated surface and nanometer-scale thin spallation layer; they originate from the metal surface at pump energy fluence of around 1 J/cm2 and work as a flying soft x-ray beam splitter.

At the Kansai Photon Science Institute (KPSI, Kyoto, Japan), there are three unique high-power laser facilities. Here, we introduce the features of each facility and some experimental studies, which will be useful to users as a reference.

A recombination plasma soft X-ray laser that is associated with Li-like Aluminum ion Al¹⁰⁺ 3d-4f transition (wavelength: 15.47 nm) was investigated to increase the gain coefficient. By optimizing the time interval of the 16-pulse train, higher-density plasma with a low temperature could be generated, and thus, we obtained the gain coefficient of 9.84 cm⁻¹ at the pump laser pulse energy which was as low as 3 J. To further enhance the X-ray laser output energy, the single resonator which was installed by using a Mo/Si multilayer mirror that has a high reflectivity of 0.45 at 15.5 nm, and the X-ray spectrum after the double pass in the lasing medium was measured. As a result, the output intensity was increased to be 1.5 times higher than t=when it was compared with those that were conducted with no X-ray mirror.