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Design and implementation of VUV-CD and LD measurements using an ac modulated polarizing undulator
Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
Design and implementation of VUV-CD and LD measurements using an ac modulated polarizing undulator K. Yagi-Watanabea,∗ , T. Yamadaa , M. Tanakab , F. Kanekoc , T. Kitadac , Y. Ohtac , K. Nakagawad a
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan b Graduate School of Science and Engineering, Waseda University, Okubo 3-14-9-702, Shinjuku-ku, Tokyo 169-0072, Japan c Graduate School of Cultural Studies and Human Science, Kobe University, Tsurukabuto, Nada-ku, Kobe 657-8501, Japan d Faculty of Human Development, Kobe University, Tsurukabuto, Nada-ku, Kobe 657-8501, Japan Available online 2 March 2005
Abstract VUV circular dichroism (CD) and linear dichroism (LD) have been successfully measured at wavelengths beyond the conventional limit by using an ac modulated polarizing undulator. We have developed CD and LD measuring technique by polarization modulation at the source, without using transmission type polarizing modulator, to extend to the coverage to wavelengths shorter than 140 nm. AIST developed in 1986 ac polarizing undulator by using a electron storage ring “TERAS” based on an original concept. The undulator which can produce any desired polarization of vertical- and horizontal-linear polarization (VLP and HLP) and right- and left-handed circular polarization (RCP and LCP) is specially well suited to both measurements of CD and LD. With this undulator, the polarization alternate in the order of VLP–RCP–HLP– RCP–VLP–LCP–HLP–LCP–VLP–, i.e. when circular polarization is modulated in f Hz, linear polarization alters in 2f Hz. This allows us simultaneous measurements of CD and LD. Since the TERAS can produce ac-modulated polarized radiation of wavelength as short as 40 nm, it is expected to have CD and LD measurement extended to 40 nm. © 2005 Elsevier B.V. All rights reserved. Keywords: Circular dichroism; Linear dichroism; Undulator; Polarization modulation; Alanine
1. Introduction Circular dichroism (CD) and linear dichroism (LD) spectroscopies can be provided useful information about asymmetric and anisotropic properties of matter [1]. CD spectroscopy measures the difference in absorption between left and right circularly polarized light and is particularly useful for studying chiral molecules. LD is the difference in absorption of light linearly polarized parallel and perpendicular to an orientation axis, and is used with the oriented system. CD and LD spectroscopies are type of polarization modulation spectroscopy. The polarization modulation spectroscopy was restricted to the region from visible to ultra∗
Corresponding author. E-mail address: [email protected] (K. Yagi-Watanabe).
0368-2048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2005.01.132
violet. Commercially available CD spectropolarimeter using mercury or xenon lamp as light source have a coverage to 190 nm wavelength. Recently, effort have been paid to the extension of CD measurement to VUV through the combination of synchrotron radiation with photoelastic modulator, and SR facilities in the world have embarked on the race for developing CD technology in VUV [2–5]. However the conventional method using transmission type optical elements as polarizing modulator could not measure at wavelength shorter than 110 nm in principle, and 140 nm in practice. We have developed CD/LD measuring technique by polarization modulation at the source, without using transmission type polarizing modulator, to extend to the coverage to wavelengths shorter than 140 nm. Onuki developed in 1986 ac polarizing undulator (Onuki type crossed undulator) by using a electron storage ring TERAS at AIST [6]. Although the use of the undulator for VUV-CD measurement was first described
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K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
about 10 years ago [7,8], development of applications in the chiral molecules have been much more recent. In this paper, we prove experimentally the feasibility of achieving VUVCD/LD by polarization modulation method using the polarizing undulator. Since the TERAS can produce ac-modulated polarized radiation of wavelength as short as 40 nm by changing the energy of the stored beam from 300 to 760 MeV, it is expected to have CD/LD measurement extended to 40 nm. This would be epoch-making accomplishment based on synchrotron radiation from AIST’s original ac modulated polarization undulator.
2. VUV-CD/LD instruments A beam line BL-5 at TERAS has been designed for optimum performance for polarization modulation spectroscopy using the polarizing undulatior in the wavelength range from 70 to 250 nm. Fig. 1 shows optical layout of the BL-5 and a schematic diagram of the data-acquisition system. A goldcoated concave mirror is located 11,000 mm from the undulator which forms an image of the source at the entrance slit of a monochromator. Before the mirror there are two sets of four-blade slits which cuts out the stray radiation and defines the optical axis. The radiation is monochromized with a monochromator (Acton, VM-502) and irradiated to a sample. The light was detected with sodium salicylate and photomultiplier. In the electron storage ring TERAS, four-period Onukitype crossed undulator [6] is installed as light source. Bandwidth of the radiation from four-period undulator has about 30%, which is relatively wide and suited for spectrophotometry [9,10]. The peak wavelength of the undulator radiation is selected by varying the electron beam energy, E. Wavelength of first harmonic peak was 180 nm with E =
350 MeV, 150 nm with E = 400 MeV. This can be covered the wavelength range from 110 to 220 nm for spectrophotometry. Polarization characteristics of the radiation from the undulator has been reported in the previous papers [7,10]. Even a short four-period undulator can produce a high degree of polarization. To get precise knowledge of polarization of the light emerging from the monochromator, we have made polarization analysis using a reflection-polarimeter [11–13]. We got Stokes parameters as function of the undulator phase retardation, φ in the wavelength range from 150 to 220 for E = 350 MeV, from 110 to 180 for E = 400 MeV. The degree of polarization keeps at more than 80% in the wavelength region over 50 nm. Detailed description of the polarization modulation spectroscopy measurements with the polarizing undulator is described in our other paper [14]. Original concept of VUVCD/LD measurements can also find in a previous paper [15]. In this brief paper, it can be mentioned only summarily. The Onuki type crossed undulator which can produce any desired polarization states of vertical- and horizontal-linear polarization (VLP and HLP) and right- and left-handed circular polarization (RCP and LCP) is specially well suited to both measurements of CD and LD. With this undulator, the polarization alternate in the order of VLP–RCP–HLP–RCP– VLP–LCP–HLP–LCP–VLP–, i.e. when circular polarization is modulated in f Hz, linear polarization alters in 2f Hz. The time-course structures of the phase retardation φ and the second parameter S1 (degree of linear polarization) and fourth parameter S3 (circular polarization) of Stokes vector are indicated in Fig. 2 [14]. This allows us simultaneous measurements of CD and LD. A fractional difference in the absorption with polarization modulation was detected by a lock-in amplifier; CD with referring frequency f and LD with frequency 2f .
Fig. 1. Optical layout of beam line BL-5 at TERAS and block diagram of signal processing and data-acquisition system.
K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
1017
surement using ac-modulated polarizing undulator is giving correct spectrum.
4. LD measurements
Fig. 2. The time-course structures of the phase retardation φ and Stokes parameters S1 (degree of linear polarization) and S3 (circular polarization).
3. CD measurements We have obtained CD spectra of amino acid films from 130 to 210 nm for evaluation. Fig. 3 shows CD spectra of l- and d-alanine films on a c-axis cut MgF2 substrate, where each spectrum was subtracted by the spectrum of its substrate. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 1F-mode. Detailed description of sample preparation and Fuller discussion of the CD spectra will be reported elsewhere. Let us now look at validity of our CD measurements. Using a commercially purchased CD spectrometer (J-720WI, JASCO), we have measured CD spectra on the same samples in wavelength higher than 185 nm for comparison. Curves indicated by solid and dotted lines in Fig. 3 are the CD spectra measured with the J-720WI. In the wavelength range of 190–210 nm, the CD spectra measured with the undulator are in good agreement with the spectra recorded with the J720WI. l-Ala and d-Ala films show symmetrical positive and negative peaks at around 185 nm, respectively [16]. It is entirely fair to say that our CD mea-
Fig. 3. CD spectra of l- and d-alanine films on a c-axis cut MgF2 substrate, where µ is the circular dichroic absorption coefficient. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 1Fmode.
LD is used with systems that are either intrinsically oriented or are oriented during the experiment. When we operate lock-in amplifier 2F-mode, a signal should correspond to the difference in intensity of the VLP and HLP. To confirm this experimentally, we made measurement on reflected light from KBr(1 0 0) cleaved surface at oblique incidence in the horizontal plane. In this case, the lock-in signal should be equivalent to (Rp − Rs )/(Rp + Rs ), where Rp is the component of specular reflection parallel to the plane of incidence (reflection of HLP light), and Rs the perpendicular component (VLP). The data shown in Fig. 4 were measured for light incidence angles, θ = 30◦ and 45◦ over the range from 120 to 190 nm with E = 400 MeV. The sample was cleaved in air and then put into the sample chamber. The measurements were performed at room temperature. The obtained data have been corrected by the degree of polarization which measured previously by the polarimeter [14]. The specular reflectance of a substance at an angle of incidence θ, measured from the surface normal, is related to the complex index of refraction by the generalized Fresnel reflection coefficients [17]. The optical constants of single crystal of KBr have been described in the literature [18]. A solid and dotted lines in the figure are the curves calculated by use of Palik’s compilation of the optical constant data [18]. The experimental results gives a good agreement with the calculated results. They agree precisely over a wavelength region of 130–170 nm, i.e. within the first harmonic band of the undulator radiation. Beyond
Fig. 4. Experimental and calculated results of the (Rp − Rs )/(Rp + Rs ) spectra of KBr(1 0 0) cleaved surface. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 2F-mode.
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K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
this wavelength range, we can see some discrepancy. Being distant from the peak wavelength of the radiation, degree of polarization and light intensity were gradually reduced. We can say that our polarization modulation method gives definite information of LD and becomes a very useful method.
ture, Sports, Science and Technology, based on the screening and counselling by the Atomic Energy Commission. We wish to thank the staff of linac group, AIST for machine operation.
References 5. Concluding remarks We have developed VUV-CD/LD measuring technique by polarization modulation at the source, without using transmission type polarization modulator. We have successfully measured CD and LD spectra at wavelength beyond the conventional limit by utilizing the ac modulated Onuki-type crossed undulator at TERAS. The new technique has made it possible to measure CD/LD in the VUV region and combined CD/LD studies are expected to reveal detailed molecular structure and about interaction between molecules. CD spectra are necessarily accompanied by artifacts which originate from the interaction between the macroscopic anisotropies of a sample such as linear birefringence (LB) and LD, and the non-ideal characteristics of polarization modulation instruments. Since the LB and LD of an anisotropic sample are usually one or two orders of magnitude larger than the CD, the latter is easily drowned by the linear effects.
Acknowledgements A part of this study was financially supported by the Budget for Nuclear Research of the Ministry of Education, Cul-
[1] A. Rodger, B. Nord´en, Circular Dichroism and Linear Dichroism, Oxford University Press, 1997. [2] B.A. Wallace, J. Synchrotron Rad. 7 (2000) 289. [3] D.A. Clarke, G. Jones, J. Synchrotron Rad. 11 (2004) 142. [4] N. Ojima, K. Sakai, T. Fukuzawa, K. Gekko, Chem. Lett. 2000 (2000) 832. [5] N. Ojima, K. Sakai, K. Matsuo, T. Matsui, T. Fukuzawa, H. Nakatame, M. Taniguchi, K. Gekko, Chem. Lett. 2001 (2001) 522. [6] H. Onuki, Nucl. Instrum. Meth. A 246 (1986) 94. [7] K. Yagi, M. Yuri, H. Onuki, J. Phys. Soc. Jpn. 63 (1994) 3941. [8] K. Yagi, M. Yuri, H. Onuki, Rev. Sci. Instrum. 66 (1995) 1592. [9] K. Yagi, H. Onuki, S. Sugiyama, T. Yamazaki, Rev. Sci. Instrum. 63 (1992) 396. [10] K. Yagi, M. Yuri, S. Sugiyama, H. Onuki, Rev. Sci. Instrum. 66 (1995) 1993. [11] T. Koide, T. Shidara, M. Yuri, Nucl. Instrum. Meth. A 336 (1993) 368. [12] T. Koide, T. Shidara, T. Miyahara, M. Yuri, Rev. Sci. Instrum. 66 (1995) 1923. [13] L. Nahon, C. Alcaraz, Appl. Opt. 43 (2004) 1024. [14] T. Yamada, K. Yagi-Watanabe, M. Tanaka, F. Kaneko, T. Kitada, Y. Ohta, K. Nakagawa, Rev. Sci. Instrum., in preparation. [15] K. Yagi, H. Onuki, J. Electron Spectros. Relat. Phenom. 80 (1996) 429. [16] K. Nakagawa, M. Tanaka, F. Kaneko, T. Kitada, Y. Ohta, A. Aguri, F. Fujii, A. Yokoya, K. Yagi-Watanabe, T. Yamada, in this proceedings. [17] J.A.R. Samson, Techniques of Vacuum Ultraviolet Spectroscopy, Pied, 1967, p. 304. [18] E.D. Palik, Handbook of Optical Constants of Solids II, Academic Press, 1991, p. 989.
Design and implementation of VUV-CD and LD measurements using an ac modulated polarizing undulator K. Yagi-Watanabea,∗ , T. Yamadaa , M. Tanakab , F. Kanekoc , T. Kitadac , Y. Ohtac , K. Nakagawad a
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan b Graduate School of Science and Engineering, Waseda University, Okubo 3-14-9-702, Shinjuku-ku, Tokyo 169-0072, Japan c Graduate School of Cultural Studies and Human Science, Kobe University, Tsurukabuto, Nada-ku, Kobe 657-8501, Japan d Faculty of Human Development, Kobe University, Tsurukabuto, Nada-ku, Kobe 657-8501, Japan Available online 2 March 2005
Abstract VUV circular dichroism (CD) and linear dichroism (LD) have been successfully measured at wavelengths beyond the conventional limit by using an ac modulated polarizing undulator. We have developed CD and LD measuring technique by polarization modulation at the source, without using transmission type polarizing modulator, to extend to the coverage to wavelengths shorter than 140 nm. AIST developed in 1986 ac polarizing undulator by using a electron storage ring “TERAS” based on an original concept. The undulator which can produce any desired polarization of vertical- and horizontal-linear polarization (VLP and HLP) and right- and left-handed circular polarization (RCP and LCP) is specially well suited to both measurements of CD and LD. With this undulator, the polarization alternate in the order of VLP–RCP–HLP– RCP–VLP–LCP–HLP–LCP–VLP–, i.e. when circular polarization is modulated in f Hz, linear polarization alters in 2f Hz. This allows us simultaneous measurements of CD and LD. Since the TERAS can produce ac-modulated polarized radiation of wavelength as short as 40 nm, it is expected to have CD and LD measurement extended to 40 nm. © 2005 Elsevier B.V. All rights reserved. Keywords: Circular dichroism; Linear dichroism; Undulator; Polarization modulation; Alanine
1. Introduction Circular dichroism (CD) and linear dichroism (LD) spectroscopies can be provided useful information about asymmetric and anisotropic properties of matter [1]. CD spectroscopy measures the difference in absorption between left and right circularly polarized light and is particularly useful for studying chiral molecules. LD is the difference in absorption of light linearly polarized parallel and perpendicular to an orientation axis, and is used with the oriented system. CD and LD spectroscopies are type of polarization modulation spectroscopy. The polarization modulation spectroscopy was restricted to the region from visible to ultra∗
Corresponding author. E-mail address: [email protected] (K. Yagi-Watanabe).
0368-2048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2005.01.132
violet. Commercially available CD spectropolarimeter using mercury or xenon lamp as light source have a coverage to 190 nm wavelength. Recently, effort have been paid to the extension of CD measurement to VUV through the combination of synchrotron radiation with photoelastic modulator, and SR facilities in the world have embarked on the race for developing CD technology in VUV [2–5]. However the conventional method using transmission type optical elements as polarizing modulator could not measure at wavelength shorter than 110 nm in principle, and 140 nm in practice. We have developed CD/LD measuring technique by polarization modulation at the source, without using transmission type polarizing modulator, to extend to the coverage to wavelengths shorter than 140 nm. Onuki developed in 1986 ac polarizing undulator (Onuki type crossed undulator) by using a electron storage ring TERAS at AIST [6]. Although the use of the undulator for VUV-CD measurement was first described
1016
K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
about 10 years ago [7,8], development of applications in the chiral molecules have been much more recent. In this paper, we prove experimentally the feasibility of achieving VUVCD/LD by polarization modulation method using the polarizing undulator. Since the TERAS can produce ac-modulated polarized radiation of wavelength as short as 40 nm by changing the energy of the stored beam from 300 to 760 MeV, it is expected to have CD/LD measurement extended to 40 nm. This would be epoch-making accomplishment based on synchrotron radiation from AIST’s original ac modulated polarization undulator.
2. VUV-CD/LD instruments A beam line BL-5 at TERAS has been designed for optimum performance for polarization modulation spectroscopy using the polarizing undulatior in the wavelength range from 70 to 250 nm. Fig. 1 shows optical layout of the BL-5 and a schematic diagram of the data-acquisition system. A goldcoated concave mirror is located 11,000 mm from the undulator which forms an image of the source at the entrance slit of a monochromator. Before the mirror there are two sets of four-blade slits which cuts out the stray radiation and defines the optical axis. The radiation is monochromized with a monochromator (Acton, VM-502) and irradiated to a sample. The light was detected with sodium salicylate and photomultiplier. In the electron storage ring TERAS, four-period Onukitype crossed undulator [6] is installed as light source. Bandwidth of the radiation from four-period undulator has about 30%, which is relatively wide and suited for spectrophotometry [9,10]. The peak wavelength of the undulator radiation is selected by varying the electron beam energy, E. Wavelength of first harmonic peak was 180 nm with E =
350 MeV, 150 nm with E = 400 MeV. This can be covered the wavelength range from 110 to 220 nm for spectrophotometry. Polarization characteristics of the radiation from the undulator has been reported in the previous papers [7,10]. Even a short four-period undulator can produce a high degree of polarization. To get precise knowledge of polarization of the light emerging from the monochromator, we have made polarization analysis using a reflection-polarimeter [11–13]. We got Stokes parameters as function of the undulator phase retardation, φ in the wavelength range from 150 to 220 for E = 350 MeV, from 110 to 180 for E = 400 MeV. The degree of polarization keeps at more than 80% in the wavelength region over 50 nm. Detailed description of the polarization modulation spectroscopy measurements with the polarizing undulator is described in our other paper [14]. Original concept of VUVCD/LD measurements can also find in a previous paper [15]. In this brief paper, it can be mentioned only summarily. The Onuki type crossed undulator which can produce any desired polarization states of vertical- and horizontal-linear polarization (VLP and HLP) and right- and left-handed circular polarization (RCP and LCP) is specially well suited to both measurements of CD and LD. With this undulator, the polarization alternate in the order of VLP–RCP–HLP–RCP– VLP–LCP–HLP–LCP–VLP–, i.e. when circular polarization is modulated in f Hz, linear polarization alters in 2f Hz. The time-course structures of the phase retardation φ and the second parameter S1 (degree of linear polarization) and fourth parameter S3 (circular polarization) of Stokes vector are indicated in Fig. 2 [14]. This allows us simultaneous measurements of CD and LD. A fractional difference in the absorption with polarization modulation was detected by a lock-in amplifier; CD with referring frequency f and LD with frequency 2f .
Fig. 1. Optical layout of beam line BL-5 at TERAS and block diagram of signal processing and data-acquisition system.
K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
1017
surement using ac-modulated polarizing undulator is giving correct spectrum.
4. LD measurements
Fig. 2. The time-course structures of the phase retardation φ and Stokes parameters S1 (degree of linear polarization) and S3 (circular polarization).
3. CD measurements We have obtained CD spectra of amino acid films from 130 to 210 nm for evaluation. Fig. 3 shows CD spectra of l- and d-alanine films on a c-axis cut MgF2 substrate, where each spectrum was subtracted by the spectrum of its substrate. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 1F-mode. Detailed description of sample preparation and Fuller discussion of the CD spectra will be reported elsewhere. Let us now look at validity of our CD measurements. Using a commercially purchased CD spectrometer (J-720WI, JASCO), we have measured CD spectra on the same samples in wavelength higher than 185 nm for comparison. Curves indicated by solid and dotted lines in Fig. 3 are the CD spectra measured with the J-720WI. In the wavelength range of 190–210 nm, the CD spectra measured with the undulator are in good agreement with the spectra recorded with the J720WI. l-Ala and d-Ala films show symmetrical positive and negative peaks at around 185 nm, respectively [16]. It is entirely fair to say that our CD mea-
Fig. 3. CD spectra of l- and d-alanine films on a c-axis cut MgF2 substrate, where µ is the circular dichroic absorption coefficient. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 1Fmode.
LD is used with systems that are either intrinsically oriented or are oriented during the experiment. When we operate lock-in amplifier 2F-mode, a signal should correspond to the difference in intensity of the VLP and HLP. To confirm this experimentally, we made measurement on reflected light from KBr(1 0 0) cleaved surface at oblique incidence in the horizontal plane. In this case, the lock-in signal should be equivalent to (Rp − Rs )/(Rp + Rs ), where Rp is the component of specular reflection parallel to the plane of incidence (reflection of HLP light), and Rs the perpendicular component (VLP). The data shown in Fig. 4 were measured for light incidence angles, θ = 30◦ and 45◦ over the range from 120 to 190 nm with E = 400 MeV. The sample was cleaved in air and then put into the sample chamber. The measurements were performed at room temperature. The obtained data have been corrected by the degree of polarization which measured previously by the polarimeter [14]. The specular reflectance of a substance at an angle of incidence θ, measured from the surface normal, is related to the complex index of refraction by the generalized Fresnel reflection coefficients [17]. The optical constants of single crystal of KBr have been described in the literature [18]. A solid and dotted lines in the figure are the curves calculated by use of Palik’s compilation of the optical constant data [18]. The experimental results gives a good agreement with the calculated results. They agree precisely over a wavelength region of 130–170 nm, i.e. within the first harmonic band of the undulator radiation. Beyond
Fig. 4. Experimental and calculated results of the (Rp − Rs )/(Rp + Rs ) spectra of KBr(1 0 0) cleaved surface. The modulation frequency of undulator was 2 Hz and lock-in amplifier was operated 2F-mode.
1018
K. Yagi-Watanabe et al. / Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 1015–1018
this wavelength range, we can see some discrepancy. Being distant from the peak wavelength of the radiation, degree of polarization and light intensity were gradually reduced. We can say that our polarization modulation method gives definite information of LD and becomes a very useful method.
ture, Sports, Science and Technology, based on the screening and counselling by the Atomic Energy Commission. We wish to thank the staff of linac group, AIST for machine operation.
References 5. Concluding remarks We have developed VUV-CD/LD measuring technique by polarization modulation at the source, without using transmission type polarization modulator. We have successfully measured CD and LD spectra at wavelength beyond the conventional limit by utilizing the ac modulated Onuki-type crossed undulator at TERAS. The new technique has made it possible to measure CD/LD in the VUV region and combined CD/LD studies are expected to reveal detailed molecular structure and about interaction between molecules. CD spectra are necessarily accompanied by artifacts which originate from the interaction between the macroscopic anisotropies of a sample such as linear birefringence (LB) and LD, and the non-ideal characteristics of polarization modulation instruments. Since the LB and LD of an anisotropic sample are usually one or two orders of magnitude larger than the CD, the latter is easily drowned by the linear effects.
Acknowledgements A part of this study was financially supported by the Budget for Nuclear Research of the Ministry of Education, Cul-
[1] A. Rodger, B. Nord´en, Circular Dichroism and Linear Dichroism, Oxford University Press, 1997. [2] B.A. Wallace, J. Synchrotron Rad. 7 (2000) 289. [3] D.A. Clarke, G. Jones, J. Synchrotron Rad. 11 (2004) 142. [4] N. Ojima, K. Sakai, T. Fukuzawa, K. Gekko, Chem. Lett. 2000 (2000) 832. [5] N. Ojima, K. Sakai, K. Matsuo, T. Matsui, T. Fukuzawa, H. Nakatame, M. Taniguchi, K. Gekko, Chem. Lett. 2001 (2001) 522. [6] H. Onuki, Nucl. Instrum. Meth. A 246 (1986) 94. [7] K. Yagi, M. Yuri, H. Onuki, J. Phys. Soc. Jpn. 63 (1994) 3941. [8] K. Yagi, M. Yuri, H. Onuki, Rev. Sci. Instrum. 66 (1995) 1592. [9] K. Yagi, H. Onuki, S. Sugiyama, T. Yamazaki, Rev. Sci. Instrum. 63 (1992) 396. [10] K. Yagi, M. Yuri, S. Sugiyama, H. Onuki, Rev. Sci. Instrum. 66 (1995) 1993. [11] T. Koide, T. Shidara, M. Yuri, Nucl. Instrum. Meth. A 336 (1993) 368. [12] T. Koide, T. Shidara, T. Miyahara, M. Yuri, Rev. Sci. Instrum. 66 (1995) 1923. [13] L. Nahon, C. Alcaraz, Appl. Opt. 43 (2004) 1024. [14] T. Yamada, K. Yagi-Watanabe, M. Tanaka, F. Kaneko, T. Kitada, Y. Ohta, K. Nakagawa, Rev. Sci. Instrum., in preparation. [15] K. Yagi, H. Onuki, J. Electron Spectros. Relat. Phenom. 80 (1996) 429. [16] K. Nakagawa, M. Tanaka, F. Kaneko, T. Kitada, Y. Ohta, A. Aguri, F. Fujii, A. Yokoya, K. Yagi-Watanabe, T. Yamada, in this proceedings. [17] J.A.R. Samson, Techniques of Vacuum Ultraviolet Spectroscopy, Pied, 1967, p. 304. [18] E.D. Palik, Handbook of Optical Constants of Solids II, Academic Press, 1991, p. 989.