Akio Yazaki

Evolving shock-wave profiles measured in a silicon crystal by picosecond time-resolved x-ray diffraction

Picosecond time-resolved x-ray diffraction is used to probe single-crystal silicon under pulsed-laser irradiation (300 ps pulse at 1.4 J/cm2) at an interval of 60 ps. The observed rocking curves show shock compression of the silicon lattice by the laser irradiation. Uniaxial strain profiles perpendicular to the Si(111) plane are estimated using dynamical x-ray diffraction theory. The temporal and spatial evolution of the profiles indicates a propagating shock wave with the velocity of 9.4 km/s inside the silicon crystal. The observed maximum compression is 1.05%, which corresponds to a pressure of 2.18 GPa.

Ultrafast dark-field surface inspection with hybrid-dispersion laser scanning

High-speed surface inspection plays an important role in industrial manufacturing, safety monitoring, and quality control. It is desirable to go beyond the speed limitation of current technologies for reducing manufacturing costs and opening a new window onto a class of applications that require high-throughput sensing. Here, we report a high-speed dark-field surface inspector for detection of micrometer-sized surface defects that can travel at a record high speed as high as a few kilometers per second. This method is based on a modified time-stretch microscope that illuminates temporally and spatially dispersed laser pulses on the surface of a fast-moving object and detects scattered light from defects on the surface with a sensitive photodetector in a dark-field configuration. The inspectors ability to perform ultrafast dark-field surface inspection enables real-time identification of difficult-to-detect features on weakly reflecting surfaces and hence renders the method much more practical than in the...

Ultrafast web inspection with hybrid dispersion laser scanner

We report an ultrafast web inspector that operates at a 1000 times higher scan rate than conventional methods. This system is based on a hybrid dispersion laser scanner that performs line scans at nearly 100 MHz. Specifically, we demonstrate web inspection with detectable resolution of 48.6 μm/pixel (scan direction) × 23 μm (web flow direction) within a width of view of 6 mm at a record high scan rate of 90.9 MHz. We demonstrate the identification and evaluation of particles on silicon wafers. This method holds great promise for speeding up quality control and hence reducing manufacturing costs.

Picosecond structural dynamics in photoexcited Si probed by time-resolved x-ray diffraction

Direct observation of structural dynamics of a 300 ps laser irradiated silicon crystal is performed by means of picosecond time-resolved x-ray diffraction. Change in x-ray diffraction profiles corresponds to propagation of a strain pulse inside the sample with sound velocity. The strain profiles are simulated by considering carrier dynamics and thermoelastic treatment and well explain the experiments.

Picosecond Time-Resolved X-Ray Diffraction from Si(111) under High-Power Laser Irradiation

Picosecond time-resolved X-ray diffraction is used to observe Si(111) under 300 ps pulsed laser irradiation at a power density above the damage threshold. The pulsed X-rays (of about 9 ps pulse width) are generated by focusing a femtosecond laser on an Fe target. The rocking curves are obtained with a time step of 50 ps. The transient lattice compression (0.9% at maximum) driven by laser-induced dielectric breakdown is directly observed.

Picosecond Time-Resolved X-Ray Diffraction of a Photoexcited Silicon Crystal

Direct observation of the lattice dynamics of a photoexcited silicon crystal is performed by means of picosecond time-resolved X-ray diffraction. X-ray diffraction profiles from 300 ps laser-irradiated Si(111) are obtained at a time step of 50 ps. The results are in quantitative agreement with results of simulations based on dynamical diffraction theory, and are consistent with an interpretation based on acoustic wave propagation.

Picosecond time-resolved X-ray diffraction from a silicon crystal under laser-induced breakdown

Picosecond time-resolved X-ray diffraction is performed for a Si(111) under laserinduced breakdown using picosecond pulsed X-rays. Transient change in strain profiles due to the shock compression generated by laser-induced breakdown is observed. The propagating strain profiles inside the Si(111) are determined.

Picosecond Time‐Resolved X‐Ray Diffraction : Estimation of Local Pressure

We have performed time resolved X‐ray diffraction experiments with picosecond time resolution on Si single crystal compressed by laser irradiation. From the measured diffraction profiles, temporal and spatial distribution of the strain in the sample have been estimated using the direct search of optimization method based on the dynamical X‐ray diffraction theory. The maximum compression of 1.05% was measured at the irradiation power density of 4.7X109 W/cm2. We discussed pressure distribution analyzing observed data.

Transition from Expansion to Shock Compression in Laser Irradiated Si by Multiple Shots

Picosecond time‐resolved X‐ray diffraction measurements have been performed on laser irradiated Si single crystal. Two types of experiments were performed in air. In one set of experiments, single shot irradiation on the silicon (111) crystal was performed at an irradiance range of 1 – 10 GW/cm2. The results of X‐ray diffraction measurement showed both thermal expansion and transient elastic shock compression. It is deduced that the ablation threshold falls in the range in irradiance of 1 – 10 GW/cm2. The second set of experiments was performed with multiple shot irradiation in the range in irradiance of GW/cm2. Lattice compression due to the multiple laser irradiation was observed. This result indicates that multiple irradiation causes reduction of the ablation threshold.

Pump-probe x-ray diffraction for condensed matter in picosecond time domain

Transient lattice compression of a Si(111) crystal induced by pulsed laser is studied by the picosecond pulsed x-ray diffraction. The x-rays used are laser induced x-rays with a pulse duration of less than 6 ps. The laser beam of 300 ps is used for the pump beam. The lattice compression at 400 ps after laser irradiation (2.97×1010 W/cm2) is estimated to be about 4.2% from the observed shift of Bragg angles, which is beyond Hugoniot elastic limit of silicon has been reported.