報告書番号

H05001

タイトル（和文）

音響光学レーザ偏向器を用いた高速度撮影技術の開発 -―放電現象・衝撃波に伴う密度変化の計測および可視化―-

タイトル（英文）

Development of High-Speed Imaging Technique Using an Acousto-Optic Laser Deflector －Visualization and measurement of density variations accompanying discharges and shockwaves－

概要 （図表や脚注は「報告書全文」に掲載しております）

音響光学偏向器を用いたレーザ光強度分布の高速度撮影技術を開発した。高速度撮影に従来用いられている装置に比べ，本手法はレーザ光などの高輝度光の入射に対し損傷の危険性が低い。本手法の時間応答特性，画質，解像度を評価した結果，密度変化を時間分解能約1μ秒，距離1mにおいて空間分解能約0.2mmで捉えられることが分かった。本手法を用いて火花放電のレーザ干渉計測を行い，電子密度約2E+24/m3を得た。また，単一の火花放電に対して異なる時間遅延におけるレーザ干渉縞を撮影する高速コマ撮り手法を開発した。また，リーダ，ストリーマなどの放電前駆現象に伴う密度変化を発光と同時に捉え，高圧電極先端から進展するストリーマの密度変化と発光強度の相関は極性によって大きく異なることを示した。また，火花放電および空気中レーザ絶縁破壊に伴う衝撃波を可視化し，衝撃波が420～490m/sの速度で伝播する様子を観察した。

概要 （英文）

A technique for high-speed imaging of laser beam intensity distribution using an acousto-optic deflector was developed. Compared to a gated image intensifier, which is commonly used for high-speed imaging applications, this method is less susceptible to damage due to incident light of high intensity, such as laser light. The time response, image quality, and spatial resolution of the high-speed imaging technique were evaluated, which showed that density variations could be visualized with a temporal resolution of about 1 microsecond and an angular resolution of about 0.2 mrad, which corresponds to a spatial resolution of 0.2 mm for a measurement distance of 1 m. The high-speed imaging technique was applied to laser interferometry to measure the electron density of impulse spark discharges in air, and an electron density of approximately 2E+24/m3 was obtained. Furthermore, a method for imaging laser interference fringes corresponding to different delay times relative to a spark discharge was developed, and 4 frames showing the time evolution of the fringes were recorded on a single video frame of an ordinary CCD camera. Laser interferometry was also used to visualize density variations accompanying pre-discharge phenomena such as leaders and streamers. Simultaneous observations of density variations and optical emission showed that the relation between the magnitude of density variation and emission intensity for streamers eminating from a needle electrode depends largely on the polarity. The technique was also applied to shadowgraphy to visualize shockwaves accompanying spark discharges in air and laser-induced breakdown in air, which showed that shockwaves propagated outward from the discharge region at a speed of 420 m/s to 490 m/s.

報告者

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