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An improved optical design for a microscopy beam line at Hefei
Nuclear Instruments and Methods in Physics Research A246 (1986) 655-657 North-Holland, Amsterdam
655
AN I M P R O V E D OPTICAL D E S I G N FOR A M I C R O S C O P Y BEAM LINE AT HEFEI Yong-Gang SU, Shao-Jun FU, Yun-Wu ZHANG National Synchrotron Radiation Laboratory, University of Science and Technology of China (USTC), Hefei, Anhui, P.R. China
An improved optical design for a microscopy beam line at Hefei is presented, utilizing a linear monochromator which consists of a diaphragm and a condenser zone plate selected from several ones with different parameters for different wavelength ranges. The progress and plan for the construction of these condenser zone plates are also described.
In September 1983, we presented a preliminary optical design for a scanning microscopy beam line at Hefei [1]. At the beginning of 1985, our machine group modified the magnet lattice of the Hefei 800 MeV storage ring. Table 1 gives the new optical parameters of this source at the center of port 6A and the HBLS (high brightness light source) optical configuration for the microscopy beam line [2]. To avoid the deterioration of the microscope resolution due to any changes in source diameter or source position, we are setting a pinhole of 0.2 m m diameter in the vacuum chamber of the bending magnet, about 0.5 m away from the synchrotron radiation source [3,4]. Recently, an optical design of the scanning X-ray microscope was presented [5]. Some optical requirements to the beam line (a linear monochromator and so on) are listed in table 2. Fig. 1 shows the schematic of the optical arrangement of a beam line and a microscope downstream at Hefei Synchrotron Radiation Laboratory (HESYRL). The optical parameters of the beam line are presented in table 3 and matched to the new source parameters as well as the optical requirements mainly from the scanning microscopy experimental station. On our beam line, a linear monochromator consisting of a condensor zone plate with outermost diameter D and a diaphragm with diameter d is to produce a partial coherent p h o t o n beam, whose temporal coherence would be given approximately by R = ?~/zl -~ D / 2 d [6] and spatial coherence is adequate for diffraction-limited performance of a microscope objective
within the divergence angle that fulfills the coherence condition d sin 0'_< ?, [7]. In the case of our microscope we have D ' << g ' where D ' is the outermost diameter of micro zone plate (MZP) and g ' is the distance between the diaphragm and the MZP, thus sin 0' -- 0' = D ' / g ' and the variable o=~rdD'/2?~g'<_~r/2. Therefore we learn that the coherence degree of the illuminating photon beam on M Z P would b e [ # I = [ 2 J l ( v ) / v I > 0.8(1/~ I = 1 at the centre axis) according to the partial coherent light theory [8]. So we selected the different diameters of the diaphragms shown in table 3 for 2.3, 3.2 and 4.5 nm respectively to support a coherent illumination for the M Z P and thus the good correlation of vibrations between any two points on the light wavefront within the divergence angle 0' to form a diffraction-limited spot at the image plane after MZP. In fact, we would prepare a series interchangable diaphragms whose diameters range from 5 to about 40 /xm for the different wavelength over the whole region 2.0-5.0 nm. Then we choose the CZP diameter D to satisfy the relation D >__2dR where the spectral resolution of this linear monochromator R = 200 fulfills the temporal coherence requirement R = ~ / A ~ >_n ' / 0 . 6 [9] for the illumination of the M Z P with a total zone number n'. An adjustable diaphragm could be mounted upstream to the CZP to shield the useless photon beam whose solid angle is bigger than that accepted by the CZP. The last four lines on table 3 indicate the parameters of three CZPs, named CZP23, CZP32, CZP45 respec-
Table 1 Main optical parameters in the center of port 6A at Hefei 800 MeV ring HBLS optical configuration Wavelength (nm) Synchrotron source height when k = 0.1 (mm) Synchrotron source divergence when k = 0.1 (mrad) Photon flux (photon/(s ,~ mrad)) 0168-9002/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
2.3 0.19 0.72 1.6 X 1014
3.2 0.19 0.82 1.4 X 1014
4.5 0.19 0.94 1.1 X 1014
IV(a). LITHOGRAPHY/MICROSCOPY/TOMOGRAPHY
656
Y.-G, Suet al. / Microscopy beam line at Hefei
Table 2 Some optical requirements to the beam line 2.0-5.0 nm (especially 2.3, 3.2 and 4.5 nm) 200 > 105 photons/(s 1% bandwidth)
Wavelength region Monochromator resolving power R Photon flux at exit spot of the microscope Microzone plate (MZP) has to be illuminated spatial coherently
Table 3 Beam line parameters 2.3 8.6 10 000 600 16.67 3.45 566 2286 0.377
Wavelength ?~ (rim) Diaphragm diameter (d < h0') (/~m) Distance between pinhole and CZP g (ram) Distance between CZP and diaphragm b (mm) Demagnification of CZP V = g / b d p / h CZP outermost diameter D > 2dR (mm) Focal length of CZP at first order F (mm) CZP zone number n Width of CZP outermost zone A r, (~tm) =
tively, used for three wavelength ranges centered at 23, 32 a n d 45~, that are mainly considered during our design a n d are very i m p o r t a n t to the morphological study and microanalysis of the biological specimens. In order to cover the whole wavelength region 2.0-5.0 nm, we might m o u n t the C Z P on a ball slide so that the position of C Z P relative to the pinhole or the dia p h r a g m could be adjusted within the range of a b o u t 20 cm. Table 4 describes the wavelength coverage situation while the C Z P s are slided along the optical axis. There are two small wavelength ranges overlapping 2.73-2.79 n m a n d 3.85-3.88 nm. While sliding CZP, the distance beween the pinhole a n d the d i a p h r a g m ( g + b) will be constant, i.e., the axial position of the d i a p h r a g m will never be changed to make the m o v e m e n t of some complicated apparatuses (e.g. M Z P a n d end window) unnecessary. Now let us estimate the p h o t o n flux at the exit spot ADJUSTABLE DIAPHRAGM SYNCEROTRON SOURCE
~~P
P!~HOLE
DIAPHRAGM MZP
~ |
~9000
PECIMEN
3.2 12.0 10 000 600 16.67 4.8 566 3180 0.377
4.5 16.9 10 000 600 16.67 6.75 566 4472 0.377
of the microscope. M u c h light is lost during transporting through the b e a m line a n d the microscope. Table 5 lists the estimated flux losses on the way from synchrotron radiation source to the end spot for 3.2 n m as an example. The total loss factor throughout the b e a m line a n d microscope is 3.4 × 107. Assuming the electron b e a m current is 150 mA, that would result in 3.0 × 105 p h o t o n s / s at the exit spot of our microscope. Additionally, from the s u m m e r of 1984, we began to construct a laboratory for m a n u f a c t u r i n g the soft X-ray a n d V U V optical c o m p o n e n t s such as zone plates a n d gratings. N o w a h o m e m a d e A r + laser system whose full spectral o u t p u t could reach to a b o u t 9 W at 30 A current, a 2.4 x 1.2 m 2 vibration-isolation table, some optical elements a n d the attached adjustable mechanics are in position to work. We have used them to fabricate some zone plate p a t t e r n s on the normal holographic plates a n d coated the AZ1350 photoresists, gold and polyimide o n the glass for testing the processes. N o w a special optical system is being designed at our university a n d an ion b e a m etching machine is being manufactured at an i n s t r u m e n t a t i o n institute for fabricating some novel optical elements at HESYRL. After the optical design of this scanning microscope b e a m line, our work is to be focused on m a n u f a c t u r i n g the condenser zone plates a n d on designing the mechanics, vacuum a n d electronics for this b e a m line.
mm
Table 4 Sliding CZP to cover the wavelength region 2.0-5.0 nm CZP number
CZP23
g (mm) b (mm) )~ (nm)
9890-10110 710-490 1.97-2.79
CZP32
CZP45
300 mm
Fig. 1. Schematic of a beam line and a microscope optics at HESYRL.
9890-10110 " 710-490 2.73-3.88
9890-10110 710-490 3.85-5.45
Y. -G. S u e t al. / Microscopy beam line at Hefei
Table 5 Photon flux losses estimation throughout the beam line and microscope for ?, = 3.2 nm Item At the pinhole (0.6 mm/0.2 mm) 2 At the CZP (0.82 mrad/0.4 mrad) 2 4% efficiency of the CZP 10% efficiency of the apodized phase MZP ~o (emitted from diaphragm)/w' (accepted by MZP) Two 70% transmitting foils on beam line and end window 1% bandwidth from source/0.5 % bandwidth from mono. (R = 200)
Loss factor 9 4.2 25 10 900 2 2
W e would like to acknowledge Prof. G. Schmahl a n d his research group at G~Sttingen University a n d BESSY for their very useful papers sent to us, Prof. I. L i n d a u a n d his research group at SSRL, S t a n f o r d University for their very helpful materials a n d effective s u p p o r t to us, Dr. R. J o h n s o n for his continuous help a n d advice, Prof. E. Spiller at I B M for the valuable materials mailed to us. T h a n k s are also due to Prof. Xing-shu Xie a n d his research group, the m a c h i n e group at H E S Y R L a n d our
657
o t h e r colleagues in C h i n a for the very helpful a n d significant discussions.
References [1] Yong-gang Su and Lu Fang, Nucl. Instr. and Meth. 222 (1984) 9. [2] Yu-ming Jin and Long-kang Chen, HESYRL Internal Report, Hefei (July 1985). [3] B. Niemann, in: X-Ray Microscopy, eds., G. Schmahl and D. Rudolph (Springer, Berlin, 1984) p. 217. [4] R.W. Klaffky, M.R. Howells, G.P. Williams, P.Z. Takacs and J.B. Godel, Nucl. Instr. and Meth. 195 (1982) 162, fig. 10. [5] Xing-shu Xie, Shi-xiu Kang, Cheng-zhi Jia and Tao Jin, these Proceedings (Synchrotron Radiation Instrumentation, Stanford, 1985) Nucl. Instr. and Meth. A246 (1986) 698. [6] B. Niemann, D. Rudolph and G. Schmahl, Nucl. Instr. and Meth. 208 (1983) 367. [7] E. Spiller, in: X-ray Microscopy, eds., G. Schmahl and D. Rudolph (Springer, Berlin, 1984) p. 226. [8] M. Born and E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975) ch. 10. [9] M. Howells and J. Kirz, Coherent Soft X-rays in High Resolution Imaging, Presented at the Topical Meeting on Free Electron Generation of Extreme UV Coherent Radiation, Brookhaven National Laboratory (Sep. 19-22, 1983).
IV(a). LITHOGRAPHY/MICROSCOPY/TOMOGRAPHY
655
AN I M P R O V E D OPTICAL D E S I G N FOR A M I C R O S C O P Y BEAM LINE AT HEFEI Yong-Gang SU, Shao-Jun FU, Yun-Wu ZHANG National Synchrotron Radiation Laboratory, University of Science and Technology of China (USTC), Hefei, Anhui, P.R. China
An improved optical design for a microscopy beam line at Hefei is presented, utilizing a linear monochromator which consists of a diaphragm and a condenser zone plate selected from several ones with different parameters for different wavelength ranges. The progress and plan for the construction of these condenser zone plates are also described.
In September 1983, we presented a preliminary optical design for a scanning microscopy beam line at Hefei [1]. At the beginning of 1985, our machine group modified the magnet lattice of the Hefei 800 MeV storage ring. Table 1 gives the new optical parameters of this source at the center of port 6A and the HBLS (high brightness light source) optical configuration for the microscopy beam line [2]. To avoid the deterioration of the microscope resolution due to any changes in source diameter or source position, we are setting a pinhole of 0.2 m m diameter in the vacuum chamber of the bending magnet, about 0.5 m away from the synchrotron radiation source [3,4]. Recently, an optical design of the scanning X-ray microscope was presented [5]. Some optical requirements to the beam line (a linear monochromator and so on) are listed in table 2. Fig. 1 shows the schematic of the optical arrangement of a beam line and a microscope downstream at Hefei Synchrotron Radiation Laboratory (HESYRL). The optical parameters of the beam line are presented in table 3 and matched to the new source parameters as well as the optical requirements mainly from the scanning microscopy experimental station. On our beam line, a linear monochromator consisting of a condensor zone plate with outermost diameter D and a diaphragm with diameter d is to produce a partial coherent p h o t o n beam, whose temporal coherence would be given approximately by R = ?~/zl -~ D / 2 d [6] and spatial coherence is adequate for diffraction-limited performance of a microscope objective
within the divergence angle that fulfills the coherence condition d sin 0'_< ?, [7]. In the case of our microscope we have D ' << g ' where D ' is the outermost diameter of micro zone plate (MZP) and g ' is the distance between the diaphragm and the MZP, thus sin 0' -- 0' = D ' / g ' and the variable o=~rdD'/2?~g'<_~r/2. Therefore we learn that the coherence degree of the illuminating photon beam on M Z P would b e [ # I = [ 2 J l ( v ) / v I > 0.8(1/~ I = 1 at the centre axis) according to the partial coherent light theory [8]. So we selected the different diameters of the diaphragms shown in table 3 for 2.3, 3.2 and 4.5 nm respectively to support a coherent illumination for the M Z P and thus the good correlation of vibrations between any two points on the light wavefront within the divergence angle 0' to form a diffraction-limited spot at the image plane after MZP. In fact, we would prepare a series interchangable diaphragms whose diameters range from 5 to about 40 /xm for the different wavelength over the whole region 2.0-5.0 nm. Then we choose the CZP diameter D to satisfy the relation D >__2dR where the spectral resolution of this linear monochromator R = 200 fulfills the temporal coherence requirement R = ~ / A ~ >_n ' / 0 . 6 [9] for the illumination of the M Z P with a total zone number n'. An adjustable diaphragm could be mounted upstream to the CZP to shield the useless photon beam whose solid angle is bigger than that accepted by the CZP. The last four lines on table 3 indicate the parameters of three CZPs, named CZP23, CZP32, CZP45 respec-
Table 1 Main optical parameters in the center of port 6A at Hefei 800 MeV ring HBLS optical configuration Wavelength (nm) Synchrotron source height when k = 0.1 (mm) Synchrotron source divergence when k = 0.1 (mrad) Photon flux (photon/(s ,~ mrad)) 0168-9002/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
2.3 0.19 0.72 1.6 X 1014
3.2 0.19 0.82 1.4 X 1014
4.5 0.19 0.94 1.1 X 1014
IV(a). LITHOGRAPHY/MICROSCOPY/TOMOGRAPHY
656
Y.-G, Suet al. / Microscopy beam line at Hefei
Table 2 Some optical requirements to the beam line 2.0-5.0 nm (especially 2.3, 3.2 and 4.5 nm) 200 > 105 photons/(s 1% bandwidth)
Wavelength region Monochromator resolving power R Photon flux at exit spot of the microscope Microzone plate (MZP) has to be illuminated spatial coherently
Table 3 Beam line parameters 2.3 8.6 10 000 600 16.67 3.45 566 2286 0.377
Wavelength ?~ (rim) Diaphragm diameter (d < h0') (/~m) Distance between pinhole and CZP g (ram) Distance between CZP and diaphragm b (mm) Demagnification of CZP V = g / b d p / h CZP outermost diameter D > 2dR (mm) Focal length of CZP at first order F (mm) CZP zone number n Width of CZP outermost zone A r, (~tm) =
tively, used for three wavelength ranges centered at 23, 32 a n d 45~, that are mainly considered during our design a n d are very i m p o r t a n t to the morphological study and microanalysis of the biological specimens. In order to cover the whole wavelength region 2.0-5.0 nm, we might m o u n t the C Z P on a ball slide so that the position of C Z P relative to the pinhole or the dia p h r a g m could be adjusted within the range of a b o u t 20 cm. Table 4 describes the wavelength coverage situation while the C Z P s are slided along the optical axis. There are two small wavelength ranges overlapping 2.73-2.79 n m a n d 3.85-3.88 nm. While sliding CZP, the distance beween the pinhole a n d the d i a p h r a g m ( g + b) will be constant, i.e., the axial position of the d i a p h r a g m will never be changed to make the m o v e m e n t of some complicated apparatuses (e.g. M Z P a n d end window) unnecessary. Now let us estimate the p h o t o n flux at the exit spot ADJUSTABLE DIAPHRAGM SYNCEROTRON SOURCE
~~P
P!~HOLE
DIAPHRAGM MZP
~ |
~9000
PECIMEN
3.2 12.0 10 000 600 16.67 4.8 566 3180 0.377
4.5 16.9 10 000 600 16.67 6.75 566 4472 0.377
of the microscope. M u c h light is lost during transporting through the b e a m line a n d the microscope. Table 5 lists the estimated flux losses on the way from synchrotron radiation source to the end spot for 3.2 n m as an example. The total loss factor throughout the b e a m line a n d microscope is 3.4 × 107. Assuming the electron b e a m current is 150 mA, that would result in 3.0 × 105 p h o t o n s / s at the exit spot of our microscope. Additionally, from the s u m m e r of 1984, we began to construct a laboratory for m a n u f a c t u r i n g the soft X-ray a n d V U V optical c o m p o n e n t s such as zone plates a n d gratings. N o w a h o m e m a d e A r + laser system whose full spectral o u t p u t could reach to a b o u t 9 W at 30 A current, a 2.4 x 1.2 m 2 vibration-isolation table, some optical elements a n d the attached adjustable mechanics are in position to work. We have used them to fabricate some zone plate p a t t e r n s on the normal holographic plates a n d coated the AZ1350 photoresists, gold and polyimide o n the glass for testing the processes. N o w a special optical system is being designed at our university a n d an ion b e a m etching machine is being manufactured at an i n s t r u m e n t a t i o n institute for fabricating some novel optical elements at HESYRL. After the optical design of this scanning microscope b e a m line, our work is to be focused on m a n u f a c t u r i n g the condenser zone plates a n d on designing the mechanics, vacuum a n d electronics for this b e a m line.
mm
Table 4 Sliding CZP to cover the wavelength region 2.0-5.0 nm CZP number
CZP23
g (mm) b (mm) )~ (nm)
9890-10110 710-490 1.97-2.79
CZP32
CZP45
300 mm
Fig. 1. Schematic of a beam line and a microscope optics at HESYRL.
9890-10110 " 710-490 2.73-3.88
9890-10110 710-490 3.85-5.45
Y. -G. S u e t al. / Microscopy beam line at Hefei
Table 5 Photon flux losses estimation throughout the beam line and microscope for ?, = 3.2 nm Item At the pinhole (0.6 mm/0.2 mm) 2 At the CZP (0.82 mrad/0.4 mrad) 2 4% efficiency of the CZP 10% efficiency of the apodized phase MZP ~o (emitted from diaphragm)/w' (accepted by MZP) Two 70% transmitting foils on beam line and end window 1% bandwidth from source/0.5 % bandwidth from mono. (R = 200)
Loss factor 9 4.2 25 10 900 2 2
W e would like to acknowledge Prof. G. Schmahl a n d his research group at G~Sttingen University a n d BESSY for their very useful papers sent to us, Prof. I. L i n d a u a n d his research group at SSRL, S t a n f o r d University for their very helpful materials a n d effective s u p p o r t to us, Dr. R. J o h n s o n for his continuous help a n d advice, Prof. E. Spiller at I B M for the valuable materials mailed to us. T h a n k s are also due to Prof. Xing-shu Xie a n d his research group, the m a c h i n e group at H E S Y R L a n d our
657
o t h e r colleagues in C h i n a for the very helpful a n d significant discussions.
References [1] Yong-gang Su and Lu Fang, Nucl. Instr. and Meth. 222 (1984) 9. [2] Yu-ming Jin and Long-kang Chen, HESYRL Internal Report, Hefei (July 1985). [3] B. Niemann, in: X-Ray Microscopy, eds., G. Schmahl and D. Rudolph (Springer, Berlin, 1984) p. 217. [4] R.W. Klaffky, M.R. Howells, G.P. Williams, P.Z. Takacs and J.B. Godel, Nucl. Instr. and Meth. 195 (1982) 162, fig. 10. [5] Xing-shu Xie, Shi-xiu Kang, Cheng-zhi Jia and Tao Jin, these Proceedings (Synchrotron Radiation Instrumentation, Stanford, 1985) Nucl. Instr. and Meth. A246 (1986) 698. [6] B. Niemann, D. Rudolph and G. Schmahl, Nucl. Instr. and Meth. 208 (1983) 367. [7] E. Spiller, in: X-ray Microscopy, eds., G. Schmahl and D. Rudolph (Springer, Berlin, 1984) p. 226. [8] M. Born and E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975) ch. 10. [9] M. Howells and J. Kirz, Coherent Soft X-rays in High Resolution Imaging, Presented at the Topical Meeting on Free Electron Generation of Extreme UV Coherent Radiation, Brookhaven National Laboratory (Sep. 19-22, 1983).
IV(a). LITHOGRAPHY/MICROSCOPY/TOMOGRAPHY