Fig. 1. A mirror characterization setup constructed at the 1-km endstation of BL29XUL. One of the most irritating problems in X-ray optics for 3 rd generation synchrotron radiation has been spatial fringes observed in the totally reflected beam by mirrors. The relatively high spatial co he re nc e of th e X- ra ys fr om 3 rd ge ne ra ti on so ur ce s ma ke s in te rf er en ce fr in ge s ca us ed by fi gu re e r r o r s i n m i r r o r s f a b r i c a t e d w i t h c o n v e n t i o n a l p o l i s h i n g t e c h n i q u e s . T o f a b r i c a t e h i g h e r - q u a l i t y mirro rs with less figur e- and slope -err ors is a chall enge to reali ze the coher ence pres ervin g optic s which are required for both 3 rd and the coming 4 th generation sources. A group from the Department of Precision Science and Technology of Osaka University and t h e S P r i n g - 8 O p t i c s G r o u p s t a r t e d c o l l a b o r a t i o n o n t h e f a b r i c a t i o n o f n e w - g e n e r a t i o n m i r r o r s i n February 2001. X-ray reflection properties are compared by observing the images of the reflected beam at different mirror-detector distances among mirrors fabricated with (i) a conventional polishing t e c h n i q u e , ( i i ) c h e m i c a l v a p o r i z a t i o n m a c h i n i n g ( C V M ) [ 1 ] , a n d ( i i i ) e l a s t i c e m i s s i o n m a c h i n i n g ( EEM ) [2]. A characterization setup was constructed at the one-kilometer experimental station of B L 2 9 X U [ 3 ] , u s i n g a s t a n d a r d d i f f r a c t o m e t e r f o r p r e c i s i o n o p t i c s [ 4 ] a s a m i r r o r o r i e n t a t o r , a n d Ham ama tsu Zoo min g Tub e as a hig h spa tia l-r eso lut ion ima ge det ect or ( Fig . 1 ). A sam ple mir ror prepared from a (001) Si slab was firstly prepared with a conventional polishing technique, a striped regi on was refi ned by a CVM tech niqu e, and then a part of the CVM- fini shed stri ped regi on was further refined by an EEM technique ( Fig. 2 )[5]. Characterization of Total Reflection Mirrors Fabricated with Chemical Vaporization Machining ( CVM ) and Elastic Emission Machining ( EEM ) Techniques 110 In Fig. 3 are shown images of reflected beam from a conventionally polished area (designated as Pr e- Ma ch in ed ), a CV M fi ni sh ed ar ea an d an EE M- CV M fi ni sh ed ar ea ta ke n at th re e di ff er en t sample-detector distances (166 mm, 566 mm, and 966 mm ). The surface profiles measured with an optical interferometric technique are also shown. A slight curvature of the conventionally polished r e g i o n g a v e r i s e t o a f o c u s i n g e f f e c t , c h a n g i n g t h e s i z e o f t h e r e f l e c t e d b e a m w i t h t h e d e t e c t o r po si ti on . Hi gh -c on tr as t in te rf er en ce fr in ge s ca n be ob se rv ed on th e pr e- ma ch in ed su rf ac e. CV M correction of the surface profile could remove the curvature, and bring the peak-to-valley height error to within several nm. Nevertheless, the fringe contrast in the reflected beam images still remain s . Additional EEM correction of the surface profile reduced the peak-to-valley height error to below 2 nm. The fringe contrast in the reflected beam images faded out for the EEM finished surface, except on the edge region where the edge effect is dominant. For the correction of surface figure with the EEM technique, an advanced metrology with h i g h a c c u r a c y i s q u i t e i m p o r t a n t . W e f o u n d t h a t t h e w i d e l y u s e d s u r f a c e p r o f i l e m e a s u r e m e n t technique, the Long Trace Profiler ( LTP ) [6] had insufficient spatial resolution for the fabrication of mirrors suppressin g interferenc e fringes. Therefore, stitching interferome try combining the ZYGO NEW-VIEW with large area Fizeau interferometer was developed. The surface profile measured with t h e n e w s t i t c h i n g t e c h n i q u e r e p r o d u c e d t h e o b s e r v e d b e a m p r o f i l e s f a i r l y w e l l b y c a l c u l a t i n g n u m e r i c a l l y t h e F r e s n e l - K i r c h h o f f i n t e g r a l f o r t h e i n c i d e n t f u l l - s p a t i a l l y - c o h e r e n t X - r a y s [ 5 ] . A n a l gorithm to retriev e the surface figure from beam images at different sample-detector distances was also successfully developed [7]. Since both CVM and EEM are based on chemical process es which occur in removing atoms f r o m t h e m i r r o r s u r f a c e , t h e y d o n o t d a m a g e t h e c r y s t a l l a t t i c e o f t h e w o r k s . T h e r e f o r e , t h e s e t e c h n i q u e s a r e e a s i l y a p p l i c a b l e t o B r a g g - d i f f r a c t i o n o p t i c a l e l e m e n t s s u c h a s m o n o c h r o m a t o r crystals. A good agreement between the observation and Fresnel-Kirchhof simulation has opened up a new possibility to fabricate figured mirrors for focusing optics with CVM and EEM. A pre l iminary prototype has already been fabricated, giving a 0.1 μ m wide line focus for 15 keV X-rays. Fig. 2. Sample mirror. A (001) surface of Si (50 mm × 100 mm ) was firstly finished with a conventional polishing technique (Pre-Machined Area). A striped area was refined by a CVM technique, and a part of this was further refined by an EEM technique. 111 References [1] Y. Mori et al. , Precision Engineering 9 (1987) 123. [2] Y. Mori et al. , Rev. Sci. Instrum. 71 (2000) 4620; Y. Mori et al. , Rev. Sci. Instrum. 71 (2000) 4627. [ 3 ] T. I s h ik a w a , K . Ta ma s a k u , M . Y a b a s h i, S . G o to , Y . Ta n a k a , H . Y a ma z a k i, K . Ta k e s h it a , H . Kimura, H. Ohashi, T. Matsushita and T. Ohata, Proc. SPIE 4145 (2001) 1. [4] K. Tamasku et al. , Nucl. Instrum. Methods A467-468 (2001) 686. [5] Y. Mori et al. , Proc. SPIE 4501 (2001) 30. [6] P. Z. Takacs, Proc. SPIE 749 (1987) 59; P. Z. Takacs and S. Qian, US Patent 4884679 (1989). [7] A. Souvorov, M. Yabashi, K. Tamasaku, T. Ishikawa, Y. Mori, K. Yamauchi, K. Yamamura and A. Saito, J. Synrotron Rad., submitted. F i g . 3 . I m a g e s o f r e f l e c t e d b e a m s f r o m c o n v e n t i o n a l l y p o l i s h e d (designated as Pre-Machined) area, CVM finished area and a CVM + EEM finished area recorded at 166 mm, 566 mm and 966 mm from the center of m i r r o r . C o r r e s p o n d i n g s u r f a c e p r o f i l e s m e a s u r e d w i t h a n o p t i c a l interferometer are shown. Glancing angle of 1.2 mrad at 15 keV X-rays. Yuzo Mori a and Tetsuya Ishikawa b (a) Osaka University (b) SPring-8 / JASRI ∑ RIKEN 112
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