The optical properties, Faraday effect and Verdet constant of ceramic terbium gallium garnet (TGG) have been measured at 1064 nm, and were found to be similar to those of single crystal TGG at room temperature. Observed optical characteristics, laser induced bulk-damage threshold and optical scattering properties of ceramic TGG were compared with those of single crystal TGG. Ceramic TGG is a promising Faraday material for high-average-power YAG lasers, Yb fiber lasers and high-peak power glass lasers for inertial fusion energy drivers.

The degradation of infrastructure (e.g., tunnels) can cause serious accidents. Periodic inspection to detect internal concrete defects using the hammering method is recognized as a major preventive measure to eliminate accidents. However, the hammering method does not provide remote sensing or quantitative evaluation, and it is often time-consuming. It is of key importance to overcome these challenges, in order to improve inspector’s safety, reduce human errors, and successfully adapt the inspection methods to various types of infrastructure. Inspection methods for the detection of internal concrete defects employ ultrasound waves,¹ 2. 3. ^{– 4} thermography,⁵ 6. ^{– 7} and electromagnetic waves,⁸ 9. ^{– 10} which have been proposed to overcome the above challenges. However, taking into account the long track record of the hammering method, further efforts are required to enable large-scale applicability of these methods. Recently, a technique, which employs high-power directional sound source and scanning laser Doppler vibrometer, was proposed.^11,12 A remarkable distinction of this technique, which employs sound source, is the usage of audible detection frequencies, similar to the hammering method. Using the sound source, inspection speed of 0.5 Hz¹¹ was achieved.

The temperature dependence of the laser-induced damage threshold on optical coatings was studied in detail for laser pulses from 123 K to 473 K at different temperature. For pulses longer than a few picoseconds, the laser-induced damage threshold of coated substrates increased with decreasing temperature. This temperature dependence was reversed for pulses shorter than a few picoseconds. We describe the physics models to explain the observed scaling. The electron avalanche is essential to explain the differences in the temperature dependence.

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.

There is no evaluation method currently available to assess intraoperative pedicle screw fixation (PSF) strength. In this study, we established a laser‐based resonance frequency analysis (RFA) system with high‐speed, noncontact, quantitative measurements of PSF. Clinical investigations in the future can assess surgical failure risk of implants. We investigated the characteristics of the laser RFA and compared them with the conventional methods. We inserted a pedicle screw in the vertebral pedicle of human cadaver or model bone, followed by screw pull‐out, peak torque, implant stability quotient (ISQ) value obtained by the magnetic dental RFA system, and fixation force of laser RFA. We compared the outcomes using best‐fit linear or logarithmic approximations. For the model bone study, the resonance frequency (RF) versus peak torque/pull‐out force (POF) demonstrated strong correlations using logarithmic approximation (vs. peak torque: R = 0.931, p < .001, vs. POF: R = 0.931, p < .001). RF strongly correlated with the ISQ value using linear approximation (R = 0.981, p < .001). For the cadaveric vertebrae study, the correlation coefficients between RF and the peak torque/POF were significant regardless of approximation method (peak torque: logarithmic: R = 0.716 vs. linear: R = 0.811; p < .001) (POF: logarithmic: R = 0.644 vs. linear: R = 0.548; p < .05). Thus, the results of this study revealed a constant correlation between RFA and conventional methods as a measurement validation, predicting favorable support for intraoperative PSF. RFA has the potential to be a new index for evaluating the implant fixation force.

Laser remote sensing (LRS) using irradiation of high-power laser pulses provides characteristic vibrations (CVs) which are accompanied by internal deterioration. While the principle of LRS is the same as that of the traditional hammering inspection, optimizing the irradiation parameters of laser pulses for vibrating samples is essential for effective LRS. In this study, the frequencies and magnitudes of CVs on a concrete specimen exhibiting a mock inside defect were evaluated by laser pulse irradiation and pendulum impact. When laser pulses were irradiated, the magnitude of CVs increased linearly with increasing laser pulse energy, and higher-order vibration was observed. On the other hand, an optimal spot size was indicated by the non-linear correlation between the fluence and the magnitude of CVs. To obtain an effective LRS, we propose that both high laser fluence and an optimized laser spot size are essential.