- Email: [email protected]
Infrared facility at the Canadian light source
Infrared Physics & Technology 45 (2004) 383–387 www.elsevier.com/locate/infrared
Infrared facility at the Canadian light source T.E. May
*
Canadian Light Source, University of Saskatchewan-Saskatoon, 101 Perimeter Road, Saskatoon, SK S7N0X4, Canada Available online 19 March 2004
Abstract The Canadian Light Source (CLS) is constructing two beamlines for Infrared Spectroscopy using synchrotron radiation (IRSR). One will supply mid-Infrared (2–25 l) light to a Fourier Transform Infrared (FTIR) spectrometer and microscope for biological applications. The second will have a high resolution FTIR spectrometer for gas-phase and surface spectroscopy in the far-Infrared (beyond 25 l). The Infrared beamlines will use dipole bending magnet radiation from a special bend magnet port design which provides a 50 mrad square acceptance. Issues with the first mirror and photon mask design, as well as the beamline layout and features are discussed. 2004 Elsevier B.V. All rights reserved. PACS: 29.20.Dh; 41.60.Ap; 42.72.Ai Keywords: Infrared synchrotron radiation; Infrared source; Infrared spectroscopy; Infrared microscopy
1. Introduction The CLS is providing an Infrared facility via two beamlines, each serving a segment of the IRSR community. First light and commissioning is expected in 2004 for both mid and far infrared beamlines. These facility-owned beamlines will operate 24/7. Members of the Canadian infrared spectroscopy community are planning to develop a high-level infrared spectroscopy facility at the CLS, to be known as the Canadian Consortium for Synchrotron Infrared Spectroscopy (C2 SIRS). The purpose of C2 SIRS is to provide a comprehensive laboratory to perform spectroscopic experiments using IR synchrotron radiation that will be acces-
*
Tel.: +1-306-657-3552; fax: +1-306-657-3535. E-mail address: [email protected] (T.E. May).
sible to the entire Canadian spectroscopy community. In light of the national character of the facility, the beamline teams have representation from the three major spectroscopic communities: academic, industrial and government. CLS is owned by the University of Saskatchewan in Saskatoon. The 2.9 GeV electron storage ring has scheduled electron beam current up to 500 mAmp in full operation in 2008 [1]. Standard bending magnet radiation sources are used with a wide-angle 50 mrad Vertical by 50 mrad Horizontal aperture. Heat load and mirror design issues resulting from a wide vertical angle in a high-energy ring are discussed. 2. Front end Flux and brightness calculations were carried out (Fluxt.bas [2] and SRW [3]) using synchrotron radiation equations for bending magnets [4]. For
1350-4495/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.infrared.2004.01.010
384
T.E. May / Infrared Physics & Technology 45 (2004) 383–387
CLS, a maximum port size of 58 mrad · 58 mrad port, located 0.687 m from a bending magnet source (radius of the electron orbit is 7.1 m), was considered. At k ¼ 173 lm, the radiation opening angle equals the aperture size, so that a flux of 6aðDx=xÞðI=epÞ is expected, where a is the fine structure constant, Dx=x is the relative bandwidth, I is the ring current, and e is the electron charge [5]. Calculations were made to determine the performance of the mid and far infrared ports for a ring current of 100 mA. The mid-Infrared for microscopy can expect brightness on the order of 7 · 1015 Photons/s-0.1%bw-mm2 sr with flux on order of 2 · 1013 Photons/s-0.1%bw at 10 l. The far-Infrared can expect brightness on the order of 4 · 1014 Photons/s-0.1%bw-mm2 sr with flux on order of 1 · 1013 Photons/s-0.1%bw at 100 l [6]. A method for extracting the light from the vacuum, using a two-part mirror and photon mask to circumvent the high heat load is based on the BESSY II design.
3. Photon mask and mirror The integrated vertical power at the maximum design current of 500 mA is 69.7 W/mrad horizontal. The majority of the power is located within ±0.8 mrad of the orbital plane. This on-plane power must be removed from the first optical element as it cannot withstand this load without distortion. There are two practical ways to do this, either a slot to allow the high power to pass through or a tubular ‘‘finger’’ mask in front of the surface to absorb it. The first design concept mirror was one-piece with a slot to clear the highenergy photons. A similar design is employed at BESSY with the mirror in two pieces and mounted within a framework [7]. This is necessary to maintain planarity of the two surfaces. The alternative, a cooled finger mask similar to the ALS [8], is being modified to mask the mirror sides. The power intercepted by 55 mrad is 3850 W, over six times the ALS design. The sides of the mirror frame must be protected, 10 mrad wide masking has up to 700 W to dissipate per side. The mirror material will be Glidcop, coated with Aluminum. The side edge of the first optical element and mask
Fig. 1. Mask and mirror arrangement. Slot in mirror passes hard X-rays, mask surface is ribbed and at 8 incidence angle to spread heat flux.
must be beyond a minimum ‘‘stay-clear’’ distance (16 mm) from the electron beam itself to avoid acting as a limiting aperture to the electron beam. Fig. 1 shows the mask and mirror layout. The mask is located in front of the first mirror and is very close to the source, 600 mm away on the ‘‘inner’’ side, and will be dissipating 486 W at 200 mA current. The water cooled channel design will allow for non-boiling operation and maintain surface temperatures below 250 C. The Glidcop material design rules being followed have been alTable 1 Maximum values as guidelines allowed for Glidcop material in the UHV system
Temperature Compression stress Wall temperature Heat flux
APS rules
ESRF proposed rules
300 C
400 C or more <2· tensile ultimate strength >Boiling point (phase transition) 72 W/mm2
T.E. May / Infrared Physics & Technology 45 (2004) 383–387
tered in light of recent values from ESRF as we have flux density of 66 W/mm2 at the mask [9] (see Table 1). Keeping the cooling water below the critical boiling point is necessary to avoid vibrations of the mirror mount. The mirror has a small heat load that can be side cooled, and will be extractable from the chamber for maintenance.
4. Far-Infrared beamline optics For a particular wavelength, spectral resolution, and collimator focal length, there is a maximum aperture size that ensures that the incoming IR radiation is sufficiently parallel to give interference fringes in the Michelson interferometer, which is the heart of the FTIR. For example, to give Doppler-limited resolution (0.0008 cm1 ) of CO2 molecules at 200 K and 500 cm1 (k ¼ 20 lm), the required aperture diameter is only 0.8 mm for an f/4 FTIR. A synchrotron can deliver far more IR photons through this small aperture than can a thermal source like the globar normally used in IR spectrometers. The first optical element is a plane mirror sending the photon beam upwards. Following is an ellipsoidal mirror M2 sending the beam towards the ring wall and slightly demagni-
385
fying the source. The next optical element, outside the shield wall, is the diamond window of 20 mm diameter, and a wedge angle of 1. A plane mirror deflects the beam horizontally making it parallel to the spectrometer. The next ellipsoidal mirror makes an intermediate one-to-one image and sends the beam down towards another plane mirror which makes the beam horizontal again. The last ellipsoidal mirror demagnifies the beam by a factor of 2.38 and together with the demagnification of M2 results in the increase of the divergence from 55 to 152 mrad to match the F number of the spectrometer (F/6.58). The beam is not collimated due to diffraction losses over the distance between source and spectrometer. The FTIR will have a large optical retardation of several meters to achieve the 0.0008 wavenumber resolving power. After all the reflections, the polarization at the entrance of the spectrometer is vertically oriented. Fig. 2 shows the beamline layouts.
5. Mid-Infrared beamline optics The mid-IR beamline optical layout out differs from the Far IR to accommodate the shorter wavelength region. For the mid-IR a collimated
Fig. 2. (Left) Far-IR floor plan with Bruker IFS125HR FTIR and (right) is mid-IR layout with Bruker 66V and Hyperion microscope. Optical pathlength is 12 m for far-IR and 15 m for mid-IR.
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T.E. May / Infrared Physics & Technology 45 (2004) 383–387
Fig. 3. (Left) intensity at the focal plane of first ellipsoid after propagating the 500 lm (s polarized) radiation calculated at the front aperture and (right) intensity at the focal plane of second ellipsoid when 20 mm aperture is placed at focus of first ellipsoid. Propagations performed with Waveprop from Scientific Answers and Solutions.
output beam was considered, and is often used at other synchrotrons, but for the distances we have to cover we chose to refocus the beam twice between the source and spectrometer. The same design of the first mirror and photon mask are used for each beamline, and the first focusing ellipsoidal mirror, but the optics differ downstream from there. This is partly due to the difference in physical layout between the 02B1-1 port (mid) and 01B1-1 (far) bend magnet sections in the ring. Also, the acceptance of the microscope sets the usable beam size to 10 mm diameter at the FTIR of the mid-IR beamline.
wavelengths due to the large size of the focused image spot. The aperture and mirror edges act to diffract the beam that causes loss of light.
Acknowledgements The author thanks Wayne McKinney for reviewing the designs, Ruben Reininger and Bob Bosch for discussions on the optics, and Bill Barg on the mask and M1 design analysis. This work is based upon research conducted at the CLS, University of Saskatchewan, Saskatoon, which is supported by the Canadian Foundation for Innovation.
6. Diffraction spot size A geometrical ray trace does not show the effects of diffraction that appears on the beam due to port and mirror edges, and finite size of the optical elements. Additional calculations were needed to propagate the actual wavefront to determine how the beam is affected. See Fig. 3 which show the expected spot shape without a window, and with the window. The diamond window is chosen at 20 mm diameter to reduce the loss of light at the long
References [1] L.O. Dallin, D.M. Skopik, E.L. Hallin, J.C. Bergstrom, in: P. Pianetta (Ed.), SRI99, Stanford, CA, 1999, AIP Conference Proceedings, vol. 521, 1999, pp. 391–396. [2] C.J. Hirschmugl, Low frequency adsorbate-substrate dynamics for carbon monoxide/copper studied with infrared synchrotron radiation, Ph.D. thesis, Yale University, 1994. [3] O. Chubar, P. Elleaume, Accurate and efficient computation of synchrotron radiation, in: The Near Field Region,
T.E. May / Infrared Physics & Technology 45 (2004) 383–387 Proceedings of the EPAC’98 Conference, 22–26 June 1998, pp. 1177–1179. [4] Section 2, Center for X-Ray Optics X-Ray Data Booklet (LBL PUB490), April 1986, LBL, Univ. of Cal., Berkeley, CA 94720. [5] R.A. Bosch, Nucl. Instrum. Meth. A 454 (2000) 497–505. [6] T.E. May, R.A. Bosch, in: Synchrotron Radiation Instrumentation Conference, Madison, WI, Rev. Sci. Instrum. 73 (3) (2002) 1554–1556.
387
[7] W.B. Peatman, U. Schade, Rev. Sci. Instrum. 72 (3) (2001) 1620–1624. [8] M. Fong, N. Andresen, LBL-UC Engineering Note ‘‘M1 Finger Mask––Thermal Analysis’’, AL-60-80 SN M7620 March 18, 1997. [9] L. Zhang, J.C. Biasci, B. Plan, in: 2nd International Workshop on Mechanical Engineering Design of Synchrotron Radiation Equipment and Instrumentation (MEDSI02), ESRF, 2002.
Infrared facility at the Canadian light source T.E. May
*
Canadian Light Source, University of Saskatchewan-Saskatoon, 101 Perimeter Road, Saskatoon, SK S7N0X4, Canada Available online 19 March 2004
Abstract The Canadian Light Source (CLS) is constructing two beamlines for Infrared Spectroscopy using synchrotron radiation (IRSR). One will supply mid-Infrared (2–25 l) light to a Fourier Transform Infrared (FTIR) spectrometer and microscope for biological applications. The second will have a high resolution FTIR spectrometer for gas-phase and surface spectroscopy in the far-Infrared (beyond 25 l). The Infrared beamlines will use dipole bending magnet radiation from a special bend magnet port design which provides a 50 mrad square acceptance. Issues with the first mirror and photon mask design, as well as the beamline layout and features are discussed. 2004 Elsevier B.V. All rights reserved. PACS: 29.20.Dh; 41.60.Ap; 42.72.Ai Keywords: Infrared synchrotron radiation; Infrared source; Infrared spectroscopy; Infrared microscopy
1. Introduction The CLS is providing an Infrared facility via two beamlines, each serving a segment of the IRSR community. First light and commissioning is expected in 2004 for both mid and far infrared beamlines. These facility-owned beamlines will operate 24/7. Members of the Canadian infrared spectroscopy community are planning to develop a high-level infrared spectroscopy facility at the CLS, to be known as the Canadian Consortium for Synchrotron Infrared Spectroscopy (C2 SIRS). The purpose of C2 SIRS is to provide a comprehensive laboratory to perform spectroscopic experiments using IR synchrotron radiation that will be acces-
*
Tel.: +1-306-657-3552; fax: +1-306-657-3535. E-mail address: [email protected] (T.E. May).
sible to the entire Canadian spectroscopy community. In light of the national character of the facility, the beamline teams have representation from the three major spectroscopic communities: academic, industrial and government. CLS is owned by the University of Saskatchewan in Saskatoon. The 2.9 GeV electron storage ring has scheduled electron beam current up to 500 mAmp in full operation in 2008 [1]. Standard bending magnet radiation sources are used with a wide-angle 50 mrad Vertical by 50 mrad Horizontal aperture. Heat load and mirror design issues resulting from a wide vertical angle in a high-energy ring are discussed. 2. Front end Flux and brightness calculations were carried out (Fluxt.bas [2] and SRW [3]) using synchrotron radiation equations for bending magnets [4]. For
1350-4495/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.infrared.2004.01.010
384
T.E. May / Infrared Physics & Technology 45 (2004) 383–387
CLS, a maximum port size of 58 mrad · 58 mrad port, located 0.687 m from a bending magnet source (radius of the electron orbit is 7.1 m), was considered. At k ¼ 173 lm, the radiation opening angle equals the aperture size, so that a flux of 6aðDx=xÞðI=epÞ is expected, where a is the fine structure constant, Dx=x is the relative bandwidth, I is the ring current, and e is the electron charge [5]. Calculations were made to determine the performance of the mid and far infrared ports for a ring current of 100 mA. The mid-Infrared for microscopy can expect brightness on the order of 7 · 1015 Photons/s-0.1%bw-mm2 sr with flux on order of 2 · 1013 Photons/s-0.1%bw at 10 l. The far-Infrared can expect brightness on the order of 4 · 1014 Photons/s-0.1%bw-mm2 sr with flux on order of 1 · 1013 Photons/s-0.1%bw at 100 l [6]. A method for extracting the light from the vacuum, using a two-part mirror and photon mask to circumvent the high heat load is based on the BESSY II design.
3. Photon mask and mirror The integrated vertical power at the maximum design current of 500 mA is 69.7 W/mrad horizontal. The majority of the power is located within ±0.8 mrad of the orbital plane. This on-plane power must be removed from the first optical element as it cannot withstand this load without distortion. There are two practical ways to do this, either a slot to allow the high power to pass through or a tubular ‘‘finger’’ mask in front of the surface to absorb it. The first design concept mirror was one-piece with a slot to clear the highenergy photons. A similar design is employed at BESSY with the mirror in two pieces and mounted within a framework [7]. This is necessary to maintain planarity of the two surfaces. The alternative, a cooled finger mask similar to the ALS [8], is being modified to mask the mirror sides. The power intercepted by 55 mrad is 3850 W, over six times the ALS design. The sides of the mirror frame must be protected, 10 mrad wide masking has up to 700 W to dissipate per side. The mirror material will be Glidcop, coated with Aluminum. The side edge of the first optical element and mask
Fig. 1. Mask and mirror arrangement. Slot in mirror passes hard X-rays, mask surface is ribbed and at 8 incidence angle to spread heat flux.
must be beyond a minimum ‘‘stay-clear’’ distance (16 mm) from the electron beam itself to avoid acting as a limiting aperture to the electron beam. Fig. 1 shows the mask and mirror layout. The mask is located in front of the first mirror and is very close to the source, 600 mm away on the ‘‘inner’’ side, and will be dissipating 486 W at 200 mA current. The water cooled channel design will allow for non-boiling operation and maintain surface temperatures below 250 C. The Glidcop material design rules being followed have been alTable 1 Maximum values as guidelines allowed for Glidcop material in the UHV system
Temperature Compression stress Wall temperature Heat flux
APS rules
ESRF proposed rules
300 C
400 C or more <2· tensile ultimate strength >Boiling point (phase transition) 72 W/mm2
T.E. May / Infrared Physics & Technology 45 (2004) 383–387
tered in light of recent values from ESRF as we have flux density of 66 W/mm2 at the mask [9] (see Table 1). Keeping the cooling water below the critical boiling point is necessary to avoid vibrations of the mirror mount. The mirror has a small heat load that can be side cooled, and will be extractable from the chamber for maintenance.
4. Far-Infrared beamline optics For a particular wavelength, spectral resolution, and collimator focal length, there is a maximum aperture size that ensures that the incoming IR radiation is sufficiently parallel to give interference fringes in the Michelson interferometer, which is the heart of the FTIR. For example, to give Doppler-limited resolution (0.0008 cm1 ) of CO2 molecules at 200 K and 500 cm1 (k ¼ 20 lm), the required aperture diameter is only 0.8 mm for an f/4 FTIR. A synchrotron can deliver far more IR photons through this small aperture than can a thermal source like the globar normally used in IR spectrometers. The first optical element is a plane mirror sending the photon beam upwards. Following is an ellipsoidal mirror M2 sending the beam towards the ring wall and slightly demagni-
385
fying the source. The next optical element, outside the shield wall, is the diamond window of 20 mm diameter, and a wedge angle of 1. A plane mirror deflects the beam horizontally making it parallel to the spectrometer. The next ellipsoidal mirror makes an intermediate one-to-one image and sends the beam down towards another plane mirror which makes the beam horizontal again. The last ellipsoidal mirror demagnifies the beam by a factor of 2.38 and together with the demagnification of M2 results in the increase of the divergence from 55 to 152 mrad to match the F number of the spectrometer (F/6.58). The beam is not collimated due to diffraction losses over the distance between source and spectrometer. The FTIR will have a large optical retardation of several meters to achieve the 0.0008 wavenumber resolving power. After all the reflections, the polarization at the entrance of the spectrometer is vertically oriented. Fig. 2 shows the beamline layouts.
5. Mid-Infrared beamline optics The mid-IR beamline optical layout out differs from the Far IR to accommodate the shorter wavelength region. For the mid-IR a collimated
Fig. 2. (Left) Far-IR floor plan with Bruker IFS125HR FTIR and (right) is mid-IR layout with Bruker 66V and Hyperion microscope. Optical pathlength is 12 m for far-IR and 15 m for mid-IR.
386
T.E. May / Infrared Physics & Technology 45 (2004) 383–387
Fig. 3. (Left) intensity at the focal plane of first ellipsoid after propagating the 500 lm (s polarized) radiation calculated at the front aperture and (right) intensity at the focal plane of second ellipsoid when 20 mm aperture is placed at focus of first ellipsoid. Propagations performed with Waveprop from Scientific Answers and Solutions.
output beam was considered, and is often used at other synchrotrons, but for the distances we have to cover we chose to refocus the beam twice between the source and spectrometer. The same design of the first mirror and photon mask are used for each beamline, and the first focusing ellipsoidal mirror, but the optics differ downstream from there. This is partly due to the difference in physical layout between the 02B1-1 port (mid) and 01B1-1 (far) bend magnet sections in the ring. Also, the acceptance of the microscope sets the usable beam size to 10 mm diameter at the FTIR of the mid-IR beamline.
wavelengths due to the large size of the focused image spot. The aperture and mirror edges act to diffract the beam that causes loss of light.
Acknowledgements The author thanks Wayne McKinney for reviewing the designs, Ruben Reininger and Bob Bosch for discussions on the optics, and Bill Barg on the mask and M1 design analysis. This work is based upon research conducted at the CLS, University of Saskatchewan, Saskatoon, which is supported by the Canadian Foundation for Innovation.
6. Diffraction spot size A geometrical ray trace does not show the effects of diffraction that appears on the beam due to port and mirror edges, and finite size of the optical elements. Additional calculations were needed to propagate the actual wavefront to determine how the beam is affected. See Fig. 3 which show the expected spot shape without a window, and with the window. The diamond window is chosen at 20 mm diameter to reduce the loss of light at the long
References [1] L.O. Dallin, D.M. Skopik, E.L. Hallin, J.C. Bergstrom, in: P. Pianetta (Ed.), SRI99, Stanford, CA, 1999, AIP Conference Proceedings, vol. 521, 1999, pp. 391–396. [2] C.J. Hirschmugl, Low frequency adsorbate-substrate dynamics for carbon monoxide/copper studied with infrared synchrotron radiation, Ph.D. thesis, Yale University, 1994. [3] O. Chubar, P. Elleaume, Accurate and efficient computation of synchrotron radiation, in: The Near Field Region,
T.E. May / Infrared Physics & Technology 45 (2004) 383–387 Proceedings of the EPAC’98 Conference, 22–26 June 1998, pp. 1177–1179. [4] Section 2, Center for X-Ray Optics X-Ray Data Booklet (LBL PUB490), April 1986, LBL, Univ. of Cal., Berkeley, CA 94720. [5] R.A. Bosch, Nucl. Instrum. Meth. A 454 (2000) 497–505. [6] T.E. May, R.A. Bosch, in: Synchrotron Radiation Instrumentation Conference, Madison, WI, Rev. Sci. Instrum. 73 (3) (2002) 1554–1556.
387
[7] W.B. Peatman, U. Schade, Rev. Sci. Instrum. 72 (3) (2001) 1620–1624. [8] M. Fong, N. Andresen, LBL-UC Engineering Note ‘‘M1 Finger Mask––Thermal Analysis’’, AL-60-80 SN M7620 March 18, 1997. [9] L. Zhang, J.C. Biasci, B. Plan, in: 2nd International Workshop on Mechanical Engineering Design of Synchrotron Radiation Equipment and Instrumentation (MEDSI02), ESRF, 2002.