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High performance micromachining of sapphire by laser induced plasma assisted ablation(LIPAA)using GHz burst mode femtosecond pulses

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Opto-Electronic Science 2024年第6期3卷 20-29页

作者： Kotaro Obata Shota Kawabata Yasutaka Hanada godai Miyaji Koji Sugioka RIKEN Center for Advanced Photonics(RAP) Wako-shiSaitama 351-0198Japan Faculty of Engineering Tokyo University of Agriculture and TechnologyKoganeiTokyo 184-8588Japan Graduate School of Science and Technology Hirosaki UniversityHirosakiAomori 036-8561Japan

GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire *** a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.

关键词： femtosecond laser GHz burst mode ablation LIPAA laser induced plasma assisted ablation sapphire

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固体推进剂火箭的装药形状和长度-直径比

航空兵器 1966年第3期 16-21页

作者： tomifumi godai 选义

在本文中,作者讨论如何确定长径此L/D和用于固体推进剂火箭中的装药的几何形状。为了实现火箭要求的飞行性能,火箭的质量比λ,火箭的初始重量与发动机横断面积比W/A,比冲和燃烧的持续时间应固定在一定的范围。比冲取决于推进剂的种类。... 详细信息

在本文中,作者讨论如何确定长径此L/D和用于固体推进剂火箭中的装药的几何形状。为了实现火箭要求的飞行性能,火箭的质量比λ,火箭的初始重量与发动机横断面积比W/A,比冲和燃烧的持续时间应固定在一定的范围。比冲取决于推进剂的种类。如果采用相同的质量比,空气阻力较小将带来较好的性能,所以希望W/A尽可能大。

关键词：固体推进剂火箭几何形状星型装药火箭发动机长度

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日本现在和未来航天运输计划评论

国外导弹与航天运载器 1990年第11期 6-15页

作者： tomifumi godai 孙国庆

本文评论了日本当今航天科学领域和应用领域的航天运输计划。在航天科学领域,至今仍使用四级固体火箭M-3SⅡ。而实际应用领域则用液体和固体推进的三级H-1火箭以及现正处于研制中,计划11992年首次飞行的高性能的二级H-Ⅱ火箭。本文简要... 详细信息

本文评论了日本当今航天科学领域和应用领域的航天运输计划。在航天科学领域,至今仍使用四级固体火箭M-3SⅡ。而实际应用领域则用液体和固体推进的三级H-1火箭以及现正处于研制中,计划11992年首次飞行的高性能的二级H-Ⅱ火箭。本文简要介绍了这三种火箭。而对未来航天运输计划,主要有三家航天机构在进行研究和研制,其中有H-Ⅱ轨道飞机HOPE,单级亚轨道科学飞机,HIMES,单级入轨全重复使用航天飞机等。本文介绍了每种的方案及发展步骤。

关键词：航天飞机运载火箭航天运输日本

Two-dimensional laser-induced periodic surface structures formed on crystalline silicon by GHz burst mode femtosecond laser pulses

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International Journal of Extreme Manufacturing 2023年第1期5卷 212-220页

作者： Shota Kawabata Shi Bai Kotaro Obata godai Miyaji Koji Sugioka RIKEN Center for Advanced Photonics 2-1 HirosawaWakoSaitama 351-0198Japan Department of Applied Physics Tokyo University of Agriculture and Technology2-24-16 NakachoKoganeiTokyo 184-8588Japan

Femtosecond laser pulses with GHz burst mode that consist of a series of trains of ultrashort laser pulses with a pulse interval of several hundred picoseconds offer distinct features in material processing that cannot be obtained by the conventional irradiation scheme of femtosecond laser pulses(single-pulse mode).However,most studies using the GHz burst mode femtosecond laser pulses focus on ablation of materials to achieve high-efficiency and high-quality material *** this study,we explore the ability of the GHz burst mode femtosecond laser processing to form laser-induced periodic surface structures(LIPSS)on *** is well known that the direction of LIPSS formed by the single-pulse mode with linearly polarized laser pulses is typically perpendicular to the laser polarization *** contrast,we find that the GHz burst mode femtosecond laser(wavelength:1030 nm,intra-pulse duration:220 fs,intra-pulse interval time(intra-pulse repetition rate):205 ps(4.88 GHz),burst pulse repetition rate:200 kHz)creates unique two-dimensional(2D)*** regard the formation mechanism of 2D LIPSS as the synergetic contribution of the electromagnetic mechanism and the hydrodynamic ***,generation of hot spots with highly enhanced electric fields by the localized surface plasmon resonance of subsequent pulses in the bursts within the nanogrooves of one-dimensional LIPSS formed by the preceding pulses creates 2D ***,hydrodynamic instability including convection flow determines the final structure of 2D LIPSS.

关键词： GHz burst laser-induced periodic surface structures(LIPSS) surface nanostructuring 2D nanostructures

GHz bursts in MHz burst(BiBurst) enabling high-speed femtosecond laser ablation of silicon due to prevention of air ionization

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International Journal of Extreme Manufacturing 2023年第2期5卷 208-214页

作者： Kotaro Obata Francesc Caballero-Lucas Shota Kawabata godai Miyaji Koji Sugioka RIKEN Center for Advanced Photonics 2-1 HirosawaWako-shiSaitama 351-0198Japan Department of Applied Physics Tokyo University of Agriculture and Technology2-24-16 NakachoKoganeiTokyo 184-8588Japan

For the practical use of femtosecond laser ablation, inputs of higher laser intensity are preferred to attain high-throughput material removal. However, the use of higher laser intensities for increasing ablation rates can have detrimental effects on ablation quality due to excess heat generation and air ionization. This paper employs ablation using BiBurst femtosecond laser pulses, which consist of multiple bursts(2 and 5 bursts) at a repetition rate of 64 MHz, each containing multiple intra-pulses(2–20 pulses) at an ultrafast repetition rate of 4.88 GHz, to overcome these conflicting conditions. Ablation of silicon substrates using the BiBurst mode with 5 burst pulses and 20 intra-pulses successfully prevents air breakdown at packet energies higher than the pulse energy inducing the air ionization by the conventional femtosecond laser pulse irradiation(single-pulse mode). As a result, ablation speed can be enhanced by a factor of23 without deteriorating the ablation quality compared to that by the single-pulse mode ablation under the conditions where the air ionization is avoided.

关键词： BiBurst mode GHz burst laser ablation silicon air ionization