國家同步輻射研究中心出國報告書 出國人姓名 : 王端正 出國日期 :105 年 4 月 25 日至 29 日 目的地 ( 國家 城市 ): 中國, 蘇州

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1 國家同步輻射研究中心出國報告書 出國人姓名 : 王端正 出國日期 :105 年 4 月 25 日至 29 日 目的地 ( 國家 城市 ): 中國, 蘇州 參加會議名稱或考察 研究訓練地點 : 2016 先進光學製造與檢測技術研討會 The 8 th SPIE international Symposium on advanced optical manufacturing and testing technology ( 請自下一頁開始撰寫 )

2 一 目的參加 8th AOMATT, 先進光學製造與檢測技術研討會 (The 8 th SPIE international Symposium on advanced optical manufacturing and testing technology), 了解同步輻射光學測量, 各國實驗室的進展及追求的目標 二 行程 4 月 25 日由松山飛上海, 轉火車至蘇州 4 月 26 日 plenary presentation 4 月 27 日至 28 日聽口頭報告 4 月 29 日蘇州回台 三 內容摘要 : 本會議共分成 7 組, 我是參加其中一個 conference, Subnanometer accuracy measurement for synchrotron optics and X-ray optics. 會議中世界各國同步輻射光學測量有關的專家均與會, 共有 26 個口頭報告, 我代表 NSRRC, 第 11 個報告 講題為 Progress in upgrading long trace profiler in NSRRC. 此次研討會有幾個小主題, 各國實驗室現有能力及目標介紹, 儀器發展, 現場測量, 鏡子製造 參加人員有 PTB, Diamond, Bessy II, APS, NSLSII, SLAC, Spring -8, SSRF, BSRF, J-tec, Osaka 大學, Tokyo 大學及中國多個研究所 目前精密鏡子測量的目標是曲面鏡希望可達到 50nrad. 測量之儀器有 NOM, LTP, Zygo, sharper ( 新產品 ) 此困難點之解決除了系統之穩定性外還有校正之問題,NSLSII 錢石楠教授提出之移動式光學頭之概念, 可使誤差變小, 容易校正, 在會議上我也報告了我們自製的移動式光學頭鏡子測量數據, 給

3 大家良好印象 四 心得概述與建議 此次研討會約有 500 人參加, 口頭報告約 150 篇, 壁報展示 350 篇, 中國展示了在此領域的企圖心, 令人敬畏 在同步輻射光學測量之同行中, 如錢石楠教授之評論, 我們還不錯, 在經費及人力投入上尚須加強 會中談到 2018 IWXM 研討會 (X-ray optics metrology) 是否在台灣舉辦, 因 SRI2018 將在台灣舉辦, 北京同步輻射中心也想爭取, 我有發言, 在台灣舉辦可看看我們新的 TPS, 與會者也多位發言支持, 將向長官報告細節及聯絡 對中心的建議 從精密光學測量技術發展, 移動式光學頭應是以後主流, 我們已有一些基礎, 將在加強校正工作, 現場測量也適合本中心發展以追求光束線最佳性能

4 附件報告文章 Progress in upgrading a long trace profiler at NSRRC Duan-Jen Wang, Shang-Wei Lin, Shen-Yaw Perng NSRRC, 101 Shin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan, R.O.C. ABSTRACT A long trace profiler in NSRRC is used to develop a bendable mirror, for the mirror-mounting mechanism and to inspect the mirrors of TPS beamlines. We upgraded the air bearing, the motor and gear, the penta-mirror, the CCD and the software. ELCOMATT 3000 is our calibration reference. To maintain constant the measurement of the optical path, we adopted a scheme for a moving optical head that decreases the various optical paths through a focusing lens to avoid lens homogeneity. The measurement environment (temperature, vibration, air turbulence) is effectively controlled. In measuring a curved mirror (radius 9.7 m), the repeatability is below 0.1 rad. This paper describes the upgraded performance and engineering details. Key words: Long trace profiler, mirror measurement INTRODUCTION The storage ring of Taiwan Photon Source (TPS) in NSRRC was commissioned in New beamlines are constructed sequentially in various phases; they require varied functions such as a beam spot to have a micro-focus or nano-focus, phase-coherent preservation or ultra-high resolution. Some mirrors of these beamlines are required to have a slope error at a precise level about 0.1 rad rms. A long trace profiler (LTP) is a key tool to measure and to develop a bendable mirror and a mirror-mounting mechanism, and for the inspection of the mirrors of these beamlines. Although we upgraded the stability of a LTP below 0.1 rad rms 1, the accuracy of a LTP requires corrections in the measurement of a curved mirror; this correction depends on the particular optical path of the variously curved mirrors (size and curvature), which causes some uncertainty in the mirror measurement. The accuracy issues of a LTP were discussed by Shinan Qian 2 regarding the lateral beam motion, arising from the design of the optical layout, a non-perfect lens or mirror in the LTP optical system. To increase the accuracy of measurement of a curved mirror, we tested various schemes such as a Penta mirror 3, NOM 4 (as at BESSY II) and stitching schemes, but they had also some limitations of quality of the lens focus and otherwise. The stitching scheme was time-consuming and had an unknown stitching uncertainty. In this work, we adopted a scanning optical head to preserve a constant optical path, and discarded the penta prism. The constant optical path improves the calibration curve in measuring a curved mirror; discarding the penta prism or penta mirror decreases the imperfection of this optical component. To achieve a great level of measurement precision, the environment of the measurement and each component also contributes to the

5 measurement uncertainty. In this paper, we present the environment control, engineering details of the upgraded components and the performance of measurement of a flat or curved mirror. UPGRADED ITEMS OF A LTP Control of the environment in the metrology laboratory A controlled environment of a LTP is essential for its precise measurements, including the air temperature, air turbulence and vibration. In the set-up of the metrology laboratory, we chose a site on the ground floor to have a minimal ground vibration. The LTP is situated on a massive granite table to preserve the rigidity and a high damping performance to decrease the vibration from the ground. It has also a large thermal mass to assist the uniformity of temperature. The temperature in the metrology room is controlled within 0.1 o C in the LTP area over several days. To increase the stability of the temperature, the granite table is isolated with PVC shielding. The power dissipation of the motor is moved outside the shielding with water cooling. Figure 1 shows a picture of the LTP setup. Figure 2 shows the temperature within the LTP measurement cabin, which attains 0.01 o C rms over 24 h. To decrease the air turbulence, an extensible acrylic pipe is designed to shield the optical path; the air velocity within the pipe is about 1.8 cm/s. Figure 1.Setup of LTP in the metrology laboratory.

6 Figure 2.Temperature stability of the LTP measurement area. Air bearing stage The stability of the air bearing induces motion of the measurement beam during scanning. As discussed in the preceding section, if the optical components are imperfect, homogeneity or imperfections deteriorate the precision of measurement. Our LTP (from Continental Co.) is equipped with an air-bearing scanning stage for the penta-prism; the entire stage comprises a ceramic rail, an air-bearing stage (driven with a friction wheel and motor) and an encoder. We designed a new stage with a motor outside the sliding stage and driven with a traction wire to maintain a smooth motion. Figure 3 shows that the stability of the new air bearing during motion is about 2.5 rad rms. We upgraded the encoder with resolution 0.5 m. In the closed-loop control of the motor, the position accuracy is 0.5 m p-p, which benefits the position repeatability and the mirror measurement. Figure 3.Stability of the new air bearing during motion. CCD camera and software We adopted a CCD camera (Prosilica, 2448x2050 pixel, pixel size is 3.45micron) of 2D type. Of two signals on the CCD, one is the measurement beam that scans along the horizontal direction of the focusing lens; the reference beam is fixed nearly on the center but is kept a small distance from the measurement beam. The sensor

7 size is 8.5mmx7mm, equivalent to a maximum range about 8 mrad of angular measurement. The measurement signal on the CCD is an interference pattern; the weighted-centroid algorithm that we use to identify the valley point is more precise than the conventional method from fitting several points near the valley. During the measurement, the measuring result is the signal of the measurement beam minus the signal of the reference beam. The sample rate of this CCD is 20 frames per second. We take typically 20 readings to obtain a mean at each point. Scanning optical head Figure 4 shows the layout of the optical head. The measurement beam is directed downward to the inspecting mirror; the reference beam is directed to the right and horizontal of the reference mirror. Most optical components conform to great precision. The PBS and focusing lens are designed by Dr. Peter Tacks (BNL) and manufactured commercially. The reflection mirror, which has flatness λ/20, will be upgraded later. Figure 4.Layout of optical head. 1=Diode laser, 2= Wave front-splitting phase shift beam splitter, 3= Rotating half-wave plate, 4= Polarizing beam splitter, 5&6= Quarter-wave plates, 7=Stationary reference mirror, 8= Fourier transform lens, 9&10= Folding mirrors, 11= 2D Detector. Calibration According to the design of the scanning optical head, the optical path of the measurement beam is kept constant. The calibration is easy when we set a constant distance between the optical head and the test mirror. The autocollimator (Elcomatt 3000) adopted as a reference for the LTP calibration has an accuracy 0.5 rad over the total range according to the calibration data sheet. In this work, the Elcomatt was installed on a granite stand; two flat mirrors ( /100) were set up on the same tilting stage, one for the Elcomatt 3000, the other for the LTP. On adjusting the tilting stage, we obtain a reading from the LTP and the Elcomatt With this setup, we obtain linearity of the CCD as shown in Fig. 5. We found that, when the test mirror is remote from the focusing lens, the linearity deteriorates, which implies some lateral motion of the beam at the focusing lens. We generally take the distance as 15 cm; the mirror under test is then about 5 cm from the lower edge of the optical head. We found some ripple in the center region of the curve, the same as the data sheet of the autocollimator. In these conditions we simply take an average; one pixel on the CCD is then rad. In a detailed calibration, we must undertake calibration point by point.

8 optical head. Figure 5.Calibration of LTP with autocollimator, test mirror is at varied distance from the focus lens inside moving PERFORMANCE OF THE UPGRADED LTP Point Stability Before the scanning measurement of the LTP, we test the stability of a static point. With the optical head stationary and the beam directed to a static flat mirror, the CCD reading is recorded for a long time to observe a noise or perturbation from the environment. Figure 6 shows the stability and temperature during a measurement for 24 h. Controlling the temperature at the measurement area to o C rms and maintaining a good condition of air turbulence, we obtain stability 0.09 rad rms. The rate of sampling of the CCD is 20 data points per second.

9 Figure 6.Long-term stability of the LTP varied with temperature. Repeatability The repeatability of a scanning measurement is the sum of the result of the scanning effect and the point stability. Each data point is a mean of 20 readings. We take the mean of 10 scans, the slope difference relative to mean is shown in the following figures. Figure 7 shows the repeatability of a flat mirror (length 160mm) in 10 scans is 15.3nrad rms, equivalent to height repeatability 0.1 nm. Figure 8 shows the repeatability of a curved mirror (length 200mm) of radius 41.5 m in 10 scans; the repeatability is about 15.6 nrad rms, or, expressed as a height, 0.15 nm. The repeatability of a flat mirror is a little better than for a curved mirror, as also found in other facilities. Figure 7.Repeatability of a flat mirror measurement with scanning optical head mode

10 Figure 8.Repeatability of an elliptical mirror measurement with scanning optical head mode Measurement of a curved mirror of radius 10 m To demonstrate the advantage of the scanning optical head of the LTP, we measured a strongly curved mirror, radius 9.7 meter. Figure 9 show that we find the scheme of a scanning optical head to be better than the old LTP with a penta-prism. Figure 9.Slope error of a spherical mirror (radius 9.7 meter) with two scanning modes On Fly scan Under some conditions, we require a rapid measurement of a mirror profile. On fly scan scheme is to drive the optical head moving across the mirror without stopping and to record data without averaging, different from the

11 conventional scanning process of scan, stop, measure, which saves much time. According to Table 1, on fly scan over a mirror (length 500 mm) requires about 1 min, which somewhat decreases the precision. For a plane mirror the slope error is rad from a normal scan, 0.05 from on fly scan; for a mirror of radius 38 m, the slope error increases from 0.27 rad to 0.4 rad. Table1.Comparison of normal and on fly scan Item Normal scan On fly scan Mirror Slope error(urad) Scan velocity Flat mirror(l:160mm) ~3 s/point Radius:38m(L:200mm) ~3 s/point Radius:9.7m(L:50mm) ~3 s/point Scan Slope Scan Scan time(sec) error(urad) velocity time(sec) mm/s mm/s mm/s 50 CONCLUSION In this paper we describe the upgraded items of a LTP, including the temperature control, air turbulence, vibration, air bearing, CCD camera and software. A scanning optical head scheme was used to increase the precision and to simplify the calibration for the measurement of a curved mirror. The repeatability of a flat mirror in 10 scans is 15.3 nrad rms, equivalent to height repeatability 0.1 nm rms. For a curved mirror of radius 41.5 m, the repeatability in 10 scans is about 15.6 nrad rms, or, expressed as a height, 0.15 nm rms. In such a stable condition, on fly scan mode can be used for a quick measurement in a short time, as stated above. REFERENCES [1] Wang, D J., Lin S W., Chen H W., Fung, H S., Perng, S Y. Performance of upgraded long trace profiler at NSRRC,Journal of Physics, (2013). [2] Qian, Shinan. Scanning optical head with nontilted reference beam:assuring nanoradian accuracy for a new generation surface profiler in the large-slope tesying range, International journal of optics (2011) [3] Qian, Shinan., Wayne Lewis., Idir, Mourad. Nano-accuracy measurements and the surface profiler by use of monolithic hollow penta-prism for precision mirror testing Nuclear instruments and methods in physics research A A759, 36-43(2014) [4] Siewert, F., Buchheim, J., Boutet, S.,Williams., Montanez, GJ., Krzywinski Jacek., and Signorato, Riccardo., Ultra-precise characterization of LCLS hard X-ray focusing mirrors by high resolution slope measuring deflectometry Optics express (2012)

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