Ryohei Hanayama

Multiple-surface interferometry of highly reflective wafer by wavelength tuning.

The surface shape and optical thickness variation of a lithium niobate (LNB) wafer were measured simultaneously using a wavelength-tuning interferometer with a new phase-shifting algorithm. It is necessary to suppress the harmonic signals for testing a highly reflective sample such as a crystal wafer. The LNB wafer subjected to polishing, which is in optical contact with a fused-silica (FS) supporting plate, generates six different overlapping interference fringes. The reflectivity of the wafer is typically 15%, yielding significant harmonic signals. The new algorithm can flexibly select the phase-shift interval and effectively suppress the harmonic signals and crosstalk. Experimental results indicated that the optical thickness variation of the LNB wafer was measured with an accuracy of 2 nm.

Tunable phase-extraction formulae for simultaneous shape measurement of multiple surfaces with wavelength-shifting interferometry

The interferometric surface measurement of single or stacked parallel plates presents considerable technical difficulties due to multiple-beam interference. To apply phase-shifting methods, it is necessary to use a pathlength-dependent technique such as wavelength scanning, which separates interference signals from various surfaces in frequency space. The detection window for frequency analysis has to be optimized for maximum tolerance against frequency detuning due to material dispersion and scanning nonlinearities, as well as for suppression of noise from other frequencies. We introduce a new class of phase-shifting algorithms that fulfill these requirements and allow continuous tuning of phase detection to any frequency of interest. We show results for a four-surface stack of nearparallel plates, measured in a Fizeau interferometer.

1 Hz fast-heating fusion driver HAMA pumped by a 10 J green diode-pumped solid-state laser

A Ti : sapphire laser HAMA pumped by a diode-pumped solid-state laser (DPSSL) is developed to enable a high-repetitive inertial confinement fusion (ICF) experiment to be conducted. To demonstrate a counter-irradiation fast-heating fusion scheme, a 3.8 J, 0.4 ns amplified chirped pulse is divided into four beams: two counter-irradiate a target with intensities of 6 × 1013 W cm−2, and the remaining two are pulse-compressed to 110 fs for heating the imploded target with intensities of 2 × 1017 W cm−2. HAMA contributed to the first demonstration by showing that a 10 J class DPSSL is adaptable to ICF experiments and succeeded in DD neutron generation in the repetition mode. Based on HAMA, we can design and develop an integrated repetitive ICF experiment machine by including target injection and tracking.

Head-On Inverse Compton Scattering X-rays with Energy beyond 10 keV from Laser-Accelerated Quasi-Monoenergetic Electron Bunches

Inverse Compton X-rays from laser-accelerated multiple electron bunches are observed. A Ti:sapphire laser (pulse energy: 500 mJ; pulse width: 150 fs) beam is divided into two beams. The main beam is focused onto an edge of a helium gas jet to accelerate electrons to energies of 14 and 23 MeV, which inversely scattered the head-on colliding secondary laser beam into 6 and 12 keV X-rays; this agrees well with that calculated from the electron spectra obtained. This demonstrates a first on-axis inverse Compton scattering X-ray energy detection beyond 10 keV induced by laser-accelerated electrons.

Multilayered polycrystallization in single-crystal YSZ by laser-shock compression

A single shot of an ultra-intense laser with 0.8 J of energy and a pulse width of 110 fs (peak intensity of W cm−2) is divided into two beams and the two beams counter-irradiated onto a 0.5 mm-thick single crystal yttria-stabilized zirconia (YSZ), changing the YSZ into a multilayered polycrystalline state. The laser-driven shock wave of the intensity 7.6 Pa penetrated the crystal as deep as 96 m, causing formation of a four-layered structure (the first layer from the surface to 12 m, the second from 12 to 28 m, the third from 28 to 96 m, and the fourth from 96 to 130 m, respectively). The grain size of the first layer was 1 m, while that of the second layer was broken into a few tens nanometers. The grain size of the third layer was a few hundred nanometers to a few ten micrometers. The area deeper than 96 m remained as a single crystal. The plasma heat wave might remelt the first layer, resulting in the grain size becoming larger than that of the second layer. The surface polycrystallization seems to maintain the residual stresses frozen in the film thickness direction. Our experimentally observed spatial profile of the grain size can be explained by this shock and heat waves model.

Measurement of the surface shape and optical thickness variation of a polishing crystal wafer by wavelength tuning interferometer

Interferometric surface measurement of parallel plates presents considerable technical difficulties owing to multiple beam interference. To apply the phase-shifting technique, it is necessary to use an optical-path-difference-dependent technique such as wavelength tuning that can separate interference signals in the frequency domain. In this research, the surface shape and optical thickness variation of a lithium niobate wafer for a solid Fabry-Perot etalon during the polishing process were measured simultaneously using a wavelength-tuning Fizeau interferometer with a novel phase shifting algorithm. The novel algorithm suppresses the multiple beam interference noise and has sidelobes with amplitudes of only 1% of that of the main peak. The wafer, which was in contact with a supporting glass parallel plate, generated six different interference fringes that overlapped on the detector. Wavelength-tuning interferometry was employed to separate the specific interference signals associated with the target different optical paths in the frequency domain. Experimental results indicated that the optical thickness variation of a circular crystal wafer 74 mm in diameter and 5-mm thick was measured with an uncertainty of 10 nm PV.

A trial for a reliable shape measurement using interferometry and deflectometry

Phase measuring deflectometry is an emerging technique to measure specular complex surface, such as aspherical surface and free-form surface. It is very attractive for its wide dynamic range of vertical scale and application range. Because it is a gradient based surface profilometry, we have to integrate the measured data to get surface shape. It can be cause of low accuracy. On the other hand, interferometry is accurate and well-known method for precision shape measurement. In interferometry, the original measured data is phase of interference signal, which directly shows the surface shape of the target. However interferometry is too precise to measure aspherical surface, free-form surface and usual surface in common industry. To assure the accuracy in ultra-precision measurement, reliability is the most important thing. Reliability can be kept by cross-checking. Then I will propose measuring method using both interferometer and deflectometry for reliable shape measurement. In this concept, global shape is measured using deflectometry and local shape around flat area is measured using interferometry. The result of deflectometry is global and precise. But it include ambiguity due to slope integration. In interferometry, only a small area can be measured, which is almost parallel to the reference surface. But it is accurate and reliable. To combine both results, it should be global, precise and reliable measurement. I will present the concept of combination of interferometry and deflectometry and some preliminary experimental results.

Development of a zero-method interferometer by means of dynamic generation of reference wave front

In this report, we propose a zero-method interferometer by means of dynamic generation of reference wave front using liquid crystal type spatial light modulator (LCoS-SLM). This interferometer was developed to aim to measure the shape of complex plane, such as aspherical plane. It is difficult for interferometer to measure such a surface which include large inclination, because of the problem of saturation of interference fringe. To overcome this problem, and to enlarge the dynamic range of interferometer, we attempted to combine interferometer and zero-method. Zero-method is characterized by its wide dynamic range. To apply zero-method to interferometer, SLM is adopted to configure variable reference surface. The basic configuration of the developed interferometer is Twyman-Green interferometer. A SLM is placed instead of reference mirror. In this interferometer, the shape of a target is measured using interference between object wave front and reference wave front that is generated using SLM. At first, the SLM generates flat wave front. And the detected phase map is fed back to the SLM. Then the difference between object wave front and detected phase map in the first turn. The operation is recursively repeated until the phase range of detected phase map becomes under the threshold. Then the generated wave front should become equal to the target shape. In this report, the basic idea of zeromethod interferometer using LCoS-SLM is verified through several numbers of simulative experiments.

Small lens testing method using phase shift shearing interferometer

In this report, lens testing method for small lenses is discussed. Cylindrical or aspherical lenses are included to the scope of this report in addition to spherical lenses. A shearing interferometer is applied for the measurement. That consists of a plane parallel plate for inducing lateral shear for the test beam. This method is robust to disturbances because it is a common path interferometry. Moreover it is not necessary to prepare reference lens. For these reasons it can be said that this method is practical and is good for using at actual factories.

1-Hz Bead-Pellet Injection System for Fusion Reaction Engaged by a Laser HAMA Using Ultra-Intense Counter Beams

Abstract The injection and engagement of pellets using laser beam irradiation is one of the key technologies to realize a laser-driven inertial fusion energy (IFE) reactor. We irradiated ultra-intense laser (11 TW: 0.6 J/110 fs 2 beams with a focal intensity of 510 W/cm) in counter configuration on flying 1-mm-diameter deuterated polystyrene beads beyond 600 pellets on an average at 1 Hz and 10 min per cycle for 4 years. An injection system delivers pellets with free-fall that consists of a header for pellet delivery by disk rotation and a detection unit for synchronizing the motion of a pellet for laser engagement in time. During laser irradiation, the free-falling pellet placement was at Δx = 1 mm, Δy = 0.4 mm on a plane perpendicular to the falling direction, and Δz = 0.1 mm in the falling direction at the moment of laser irradiation. Using a two-directional probe shadowgraph system, we succeeded in aligning the pellet-falling position with a laser engagement probability greater than 70%; the probability improved from the previous experiments wherein the probabilities were less than 20%. As a result, the shot probability is 27% for gamma-ray generation resulting from ultra-intense laser-matter interactions and 22% for detection of signals corresponding to fusion neutrons with a maximum yield of 4 10 n/shot. The neutron reaction induced from an integrated system of pellet injector and laser is a decisive step in the research and development of an IFE reactor.