2004 Fiscal Year Final Research Report Summary
Nanostructure analysis and laser damage mechanism of ultra-precision polished surface of calcium fluoride single crystals for high-power DUV applications.
| Project/Area Number |
14350077
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
機械工作・生産工学
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| Research Institution | Chubu University |
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Principal Investigator |
OHNISHI Naoyuki CHUBU UNIVERSITY, Faculty of Engineering, Associate Professor, 工学部, 助教授 (60201977)
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| Co-Investigator(Kenkyū-buntansha) |
NAMBA Yoshiharu CHUBU UNIVERSITY, Faculty of Engineering, Professor, 工学部, 教授 (40029129)
YOSHIDA Kunio OSAKA INSTITUTE of TECHNOLOGY, Faculty of Engineering, Professor, 工学部, 教授 (70029338)
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| Project Period (FY) |
2002 – 2004
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| Keywords | ultra-precision polishing / atomic surface propert / scanning probe microscopy / calcium fluoride / transmission electron microscopy / deep ultra-violet laser |
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| Research Abstract |
High power, Deep Ultra Violet (DUV) lasers are expected to be light sources for optical lithography, laser microprocessing, and laser fusion. High purity, DUV-grade calcium fluoride (CaF_2) single crystal material is the only candidate for such optics. The requirements for the CaF_2 surface are to have a high precision figure and an ultra-smooth surface, even though the CaF_2 crystal is difficult to polish because it is soft and has a relatively high thermal expansion coefficient. In order to increase the laser induced damage threshold, the polished surface must be extremely smooth and without subsurface damage caused by finishing. In this research, high purity calcium fluoride (111) single crystals have been float polished in order to obtain the highest quality surfaces. Float polishing is a means of obtaining the smoothest surfaces without introducing subsurface damage. The finished surfaces were observed with a Nomarski differential interference contrast microscope, two optical profilers, a scanning probe microscope and two transmission electron microscopes. The following conclusions can be drawn from the results of this research project.
1. A flatness of 31.9 nm p -v and 6.03 nm rms were obtained on 90-mm-diameter area samples by 80 min of float polishing after optical polishing.
2. It is clear from high resolution transmission electron microscope images, scanning probe microscope and Nomarski differential interference contrast microscope observations that there is no subsurface damage in the float-polished CaF_2 single crystal sample.
3. The float-polished surface is formed from a perfect (111) lattice with small atomic steps, so that the polished surface roughness depends on the mismatch between the sample surface and the (111) planes.
4. A surface roughness of 0.059 nm Ra, 0.077 nm rms, and 0.72 nm Ry was obtained by the float polishing process, as measured on a 1 x 1 □m area with an SPM.
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Research Products
(40 results)
