- Email: [email protected]
Modeling infrared beam lines with Shadow and Zemax
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Vibrational Spectroscopy xxx (2014) xxx–xxx
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Modeling infrared beam lines with Shadow and Zemax夽 Timothy May ∗ , Alan Duffy Canadian Light Source, 44 Innovation Boulevard, Saskatoon, S7N 2V3 SK, Canada
a r t i c l e
i n f o
Article history: Available online xxx Keywords: Synchrotron infrared Microspectroscopy Spectromicroscopy Raytrace
a b s t r a c t Ray tracing software is an important tool in the design and develop infrared beam lines. It provides layout coordinates, beam shape and size at mirrors, location of foci and performance estimates. Of the software that models reflective optics, a combination of Shadow [1] and Zemax [2] are discussed. Shadow generates light source rays from its accurate model of synchrotron bend magnets to provide realistic ray distributions. The optical path is traced from this source via optical components to a final image. Although Shadow makes the entire ray trace it has limited graphics and export capability that are features of Zemax. The source rays and optical coordinates generated by Shadow can be used by Zemax to position the optics and launch the rays to simulate the actual system. A conversion of the synchrotron source generated in Shadow that Zemax can use is presented. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Optical ray tracing software is an essential tool in the design the optics that takes light from an electron storage ring to an experimental sample for analysis. The optics form a “beam line” and the light ranges from hard X-rays through the infrared (IR). To provide the broadest bandwidth of IR photons, reflective mirror optics and IR transmitting window materials are used to couple the light from the ultra-high vacuum environment of the storage ring to the Fourier Transform IR spectrometers used by researchers at the beam line. The high brightness of the ring sources make them ideal for IR microscopy and ultra-high resolution far-IR spectroscopy [3]. Software to handle the unique characteristics of synchrotron radiation (SR) sources has been developed that is not related to commercially available packages such as CodeV, Oslo and Zemax which have no models of electron beam sources. Programs such as Shadow, XOP and RAY [1,4] take into account the energy and distribution of photons and model refraction and reflection with geometric rays. This specialized software can generate the distribution of rays and angles of launch for a variety of SR sources but dipole bend magnets are primarily used for IR work (exclusive of Free Electron Lasers). Synchrotron Radiation Workshop [5] and other software packages model various types of SR sources – bend magnets and
夽 Paper presented at the 7th International Workshop on Infrared Microscopy and Spectroscopy with Accelerator-Based Sources (WIRMS), Melbourne, Australia, 10–13th November 2014. ∗ Corresponding author. Tel.: +1 306 657 3552; fax: +1 306 657 3535. E-mail address: [email protected] (T. May).
insertion devices – by propagating electric field vectors as wave fronts along a system of ideal optics. These use arrays of amplitude and phase to model diffraction, interference and polarization effects but geometric rays as such are not available. The ray and wavefront methods are often combined in the analysis and design of IR beam lines [6,7] However, specialized SR programs do not offer good visualization of optical elements locations, or allow data export to other design or CAD packages for the construction and testing of the beam lines. Conventional ray tracing software with SR sources enables better analysis of beam footprints and expanded capability of mirror surface profiles, display in 2 and 3D views, and inclusion of beam outlines in vacuum systems within CAD designs. Most SR beam lines operate in the vacuum ultraviolet or X-ray regions, and use specialized mirrors and components at grazing incidence angles that differ considerably from conventional optical systems. This article explains the process of converting an SR source generated by the long-used code Shadow to a form usable by the commercial package Zemax for implementing designs of IR beam lines. 2. Method Shadow generates a set of light rays emitted by the electron beam. These are randomly distributed along the electron orbit defined by the accelerator parameters which include the bending magnet radius of the electron orbit, the energy (GeV) and the characteristics of the electron beam lattice, waists and the emission angles both vertical and horizontal. Shadow produces a file of ray positions and angles plus some flags for energy and lost rays. The rays originate from a section of the orbit within the bend magnet,
http://dx.doi.org/10.1016/j.vibspec.2014.08.009 0924-2031/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
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the length of which is determined by the bend radius and the horizontal angular width of the beam extracting port. This is usually some tens of milliradians leading to source lengths of hundreds of mm. This source length makes the depth of the source a factor in re-imaging at the sample. Observing this effect in the ray trace is easier in the commercial package due to its tools and better graphics. Light gets emitted tangentially to the electron beam as it bends in the magnetic field, due to the electron’s extreme energy relative to its rest mass, hence producing synchrotron emission. The photon angle of emission is dependent on its energy, with the high energy (keV) X-ray’s angle being very close to the plane of the electron orbit, and increasing as the photon energy decreases, attaining tens of mrad for the IR. A light source having an angle dependence upon photon energy is not common so no commercial package includes a SR source model. The Zemax can take in a ray distribution made by Shadow with proper rearrangement of the components as will be discussed. 2.1. Shadow source The source generated by Shadow is a list of comma separated variables with each row representing one ray. Up to N = 20,000 rays are possible in Shadow version 2.3 and a million in the newest Shadow 3 [8]. Each ray has 12 parameters, 6 more if polarization is considered. The first twelve ray components are: 3 space coordinates (x,y,z), 3 direction cosines (x ,y ,z ), 3 electric field components (Ei ), a flag for lost ray (l), a wavenumber value (k) giving its energy and an ordinal value (n) to identify it uniquely. The columns are ordered thus: x y z x y z Ex Ey Ez l k n. N rows of these ray values are double precision and comma separated. The source rays with the desired parameters are generated by running the Shadow routine ‘Source’. This produces the file Begin.dat which contains the rays in binary format. Optical elements (OE) are added as desired and the whole system is traced from source to the last OE by running ‘Trace’. Post processing of the Begin.dat file is done using the TRANSLATE command in Shadow. This makes a text file with comma separated variables with the name you specify, e.g. “IRsource.txt”. Shadow’s system information command SYSINFO generates a file with a table of xyz lab coordinates of the pole locations of all the OEs modeled in Shadow. A pole is a unit vector located at center of the OE surface and normal to it. Shadow places OEs given the distance and angles to the next element, starting from the source, so all the spatial geometry is computed and can be added into the Zemax lens editor as discussed below. Distance units are either mm or cm. The cloud of source points for the far-IR source at the Canadian Light Source is shown in Fig. 1. 2.2. Source file conversion Zemax can use a text file with the ray list as an input but this differs in format from the Shadow list. The coordinate system of Shadow differs from Zemax convention: photons propagate along Y axis in Shadow but along Z axis in Zemax. The conversion is straightforward and amenable to automation via script or code. The conversion entails selecting columns and processing as follows. The 3 Ei component columns and the ordinal value column are removed. Both spatial and angular coordinates columns are swapped – the y and z coordinate columns as well as the y and z columns. The x and x columns change sign. The flag (l = 1) column at the end is kept; it now acts as “unit intensity” for Zemax. Finally a header line with two values is added to the top of the new file. The first value is the number of rays and the second is a unit # which indicates the distance scale to Zemax: 2 = cm, 4 = mm. Now the order of columns relative to the original labels is: −x z y −x z y l k (the last two being intensity and optional wavelength). This file can be a space or tab separated array of 8 columns by N rows of rays with a header
Fig. 1. Cloud of IR source points for rays from Shadow. The length scales are compressed: 400 mm Y by 4 mm X by 0.2 mm Z. The rays (not shown) would point toward the left (positive Y-direction) in a roughly conical fan tangent to the orbit.
line and saved with a new name having .DAT extension, for example “IRRay.DAT”, and located in the Zemax\Sources\ folder. Fig. 2 shows the resulting file for a 100 m wavelength source. Shadow is limited in the long wavelength IR compared to X-rays in that only single energy photons are generated rather than a range of energies. This is partly due to large angles of emission compared to X-rays, internal small angle approximations that fail below 1 eV (1 m wavelength corresponds to 10,000 cm−1 ) and the need to designate “Exact synchrotron” in the source calculation to avoid approximation. If sources at different photon energy are made in Shadow, the k flag can be changed to a wavelength value, in microns, to indicate which photon energies these rays represent. These rows could be added to another source file with one or more differing wavelengths to build up a range of ray energies. Thus combining ray files for differing energies allows beams of varying emission angle to be traced together. Zemax can color the rays differently for each k wavelength value. Up to 1 million rays may be read directly in the source text file; Zemax will convert larger files to a binary format for up to 4 billion rays. Spreadsheet software or a script can be written to automate this conversion. Shadow’s VUI version in XOP has a macro capability that could be used to loop through incremental k values and make sets of rays to combine in one Begin file, contact author for details. 2.3. Zemax setup Zemax has a mode called “non-sequential” that allows for a file of rays to be read in as the object of the system. In Zemax a Lens Design Editor (LDE) spreadsheet is used to define the optical surfaces and starts with an object type called “source file” in which the new ray file name is entered. The LDE displays this in the object comments, and the number of layout and analysis rays is designated, up to N for either. The layout rays are a subset of the total analyzed ones. The source can be placed anywhere in lab frame coordinate space, with any angular orientation. It is best to leave it at the origin (0,0,0) as the lab frame coordinates of all the OEs can be used from Shadow as direct inputs into the LDE coordinates for each object. Otherwise an offset needs to be applied to each OE’s location. A wavelength is assigned in microns to each k flag number in the wavelength table. One then places the OEs from Shadow into the Zemax LDE as objects, with coordinates from the SYSINFO
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
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ARTICLE IN PRESS T. May, A. Duffy / Vibrational Spectroscopy xxx (2014) xxx–xxx
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Fig. 2. Example of the text files before and after conversion. Shadow output file (upper) has 12 columns with 6 shown here, Zemax source file (lower) has 7 (or 8 for wavelength). The columns have been swapped and the optional wavelength value has been left out.
file, and orients them as needed. Shadow orients OE rotations relative to an optic axis that can change direction after each encounter with the next OE surface, while Zemax objects start with each surface normal to the global Z direction. Rotation angles are adjusted as needed and the correct orientation of an object or mirror can be checked with rapid tracing in Zemax. The source rays and two mirrors from the beam line are shown in Fig. 3. The “standard surface” is specified in Zemax with a conic equation used to define radius of curvature at the vertex of the object (here a surface of revolution with the vertex on-axis) and parameters to define type of curve – sphere, parabola, ellipse, etc. The placement of off-axis aspheres is challenging in that the objects have their vertex location set by the LDE coordinates, not the pole location of the OE surface to which Shadow refers. This means that offsets from the vertex to the pole need to be calculated (using CAD) so that the rays hit the desired part of the surface and at the correct angle of incidence. Once completed in layout the system may be observed and plotted in a number of displays for 2 and 3D examination. The footprint of the actual ray distribution may be seen on the mirror surfaces or anywhere along the path, at foci, windows or detectors that are arbitrarily placed along the ray path. Fig. 4 shows the ray pattern intersecting a vacuum window near the focus of the beam line for 100 micron wavelength (100 cm−1 ). In Zemax these patterns are viewed on detector surfaces; in Shadow
Fig. 4. Ray pattern in Zemax at an intermediate focus by a vacuum window of the IR beam line. This shape is characteristic of the wide angle port collecting IR synchrotron radiation. A demagnified image is focused further along the beam line at the IR spectrometer aperture.
they are plotted from “star.xx” files where xx is the OE number. The model containing rays, surfaces and volume objects may now be exported as a STEP file (model.stp) to CAD software so the beam ray bundle can be used to design chambers and mounts and placed into the facility layout. 3. Results The combination of Shadow source rays and Zemax plotting ability makes a powerful tool for evaluating the optical design. Changes in the layout can be made and effects observed rapidly; actual footprints of the beam can be seen on mirror surfaces and at detectors wherever placed. Zemax can adjust mirror parameters by optimizing merit functions that can for instance adjust focus and on realistic rays, a feature not available in Shadow. Making use of the wave propagation capability of Zemax is a future goal. Acknowledgements
Fig. 3. Beam line in Zemax starting with source arc within bend magnet outline. Rays travel to right reflecting up from mirror 1 sending rays to mirror 2 and then into the page toward focus at vacuum window. The footprint of the beam is seen on the second mirror rectangle.
Research described in this paper was performed at the Canadian Light Source, which is funded by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
G Model VIBSPE-2390; No. of Pages 4
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4
Institutes of Health Research, the Government of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan. References [1] Shadow is part of XOP: www.esrf.eu/Instrumentation/software/data-analysis/ xop2.3/shadowvui (April, 2014). [2] Zemax-EE Version 13, http://zemax.com/home (April, 2014).
[3] G.L. Carr, G.P. Williams, SPIE Conf. Proc. 3153 (1997) 51–58. [4] F. Schafers, in: A. Erko, M. Idir, T. Krist, A. Michette (Eds.), Modern Developments in X-Ray and Neutron Optics, vol. 137, Springer-Verlag, Berlin, 2008, pp. 9–39, Chap. 2. [5] http://www.esrf.eu/Accelerators/Groups/InsertionDevices/Software/SRW (April, 2014). [6] A. Nucara, S. Lupi, P. Calvani, Rev. Sci. Instrum. 74 (2003) 3934–3942. [7] M. Frogley, G. Cinque, AIP Conf. Proc. 1214 (2010) 29–31. [8] M. Sanchez del Rio, N. Canestrari, F. Jiang, F. Cerrina, J. Synchrotron Radiat. 18 (2011) 708–716.
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
ARTICLE IN PRESS
VIBSPE-2390; No. of Pages 4
Vibrational Spectroscopy xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Vibrational Spectroscopy journal homepage: www.elsevier.com/locate/vibspec
Modeling infrared beam lines with Shadow and Zemax夽 Timothy May ∗ , Alan Duffy Canadian Light Source, 44 Innovation Boulevard, Saskatoon, S7N 2V3 SK, Canada
a r t i c l e
i n f o
Article history: Available online xxx Keywords: Synchrotron infrared Microspectroscopy Spectromicroscopy Raytrace
a b s t r a c t Ray tracing software is an important tool in the design and develop infrared beam lines. It provides layout coordinates, beam shape and size at mirrors, location of foci and performance estimates. Of the software that models reflective optics, a combination of Shadow [1] and Zemax [2] are discussed. Shadow generates light source rays from its accurate model of synchrotron bend magnets to provide realistic ray distributions. The optical path is traced from this source via optical components to a final image. Although Shadow makes the entire ray trace it has limited graphics and export capability that are features of Zemax. The source rays and optical coordinates generated by Shadow can be used by Zemax to position the optics and launch the rays to simulate the actual system. A conversion of the synchrotron source generated in Shadow that Zemax can use is presented. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Optical ray tracing software is an essential tool in the design the optics that takes light from an electron storage ring to an experimental sample for analysis. The optics form a “beam line” and the light ranges from hard X-rays through the infrared (IR). To provide the broadest bandwidth of IR photons, reflective mirror optics and IR transmitting window materials are used to couple the light from the ultra-high vacuum environment of the storage ring to the Fourier Transform IR spectrometers used by researchers at the beam line. The high brightness of the ring sources make them ideal for IR microscopy and ultra-high resolution far-IR spectroscopy [3]. Software to handle the unique characteristics of synchrotron radiation (SR) sources has been developed that is not related to commercially available packages such as CodeV, Oslo and Zemax which have no models of electron beam sources. Programs such as Shadow, XOP and RAY [1,4] take into account the energy and distribution of photons and model refraction and reflection with geometric rays. This specialized software can generate the distribution of rays and angles of launch for a variety of SR sources but dipole bend magnets are primarily used for IR work (exclusive of Free Electron Lasers). Synchrotron Radiation Workshop [5] and other software packages model various types of SR sources – bend magnets and
夽 Paper presented at the 7th International Workshop on Infrared Microscopy and Spectroscopy with Accelerator-Based Sources (WIRMS), Melbourne, Australia, 10–13th November 2014. ∗ Corresponding author. Tel.: +1 306 657 3552; fax: +1 306 657 3535. E-mail address: [email protected] (T. May).
insertion devices – by propagating electric field vectors as wave fronts along a system of ideal optics. These use arrays of amplitude and phase to model diffraction, interference and polarization effects but geometric rays as such are not available. The ray and wavefront methods are often combined in the analysis and design of IR beam lines [6,7] However, specialized SR programs do not offer good visualization of optical elements locations, or allow data export to other design or CAD packages for the construction and testing of the beam lines. Conventional ray tracing software with SR sources enables better analysis of beam footprints and expanded capability of mirror surface profiles, display in 2 and 3D views, and inclusion of beam outlines in vacuum systems within CAD designs. Most SR beam lines operate in the vacuum ultraviolet or X-ray regions, and use specialized mirrors and components at grazing incidence angles that differ considerably from conventional optical systems. This article explains the process of converting an SR source generated by the long-used code Shadow to a form usable by the commercial package Zemax for implementing designs of IR beam lines. 2. Method Shadow generates a set of light rays emitted by the electron beam. These are randomly distributed along the electron orbit defined by the accelerator parameters which include the bending magnet radius of the electron orbit, the energy (GeV) and the characteristics of the electron beam lattice, waists and the emission angles both vertical and horizontal. Shadow produces a file of ray positions and angles plus some flags for energy and lost rays. The rays originate from a section of the orbit within the bend magnet,
http://dx.doi.org/10.1016/j.vibspec.2014.08.009 0924-2031/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
G Model VIBSPE-2390; No. of Pages 4
ARTICLE IN PRESS T. May, A. Duffy / Vibrational Spectroscopy xxx (2014) xxx–xxx
2
the length of which is determined by the bend radius and the horizontal angular width of the beam extracting port. This is usually some tens of milliradians leading to source lengths of hundreds of mm. This source length makes the depth of the source a factor in re-imaging at the sample. Observing this effect in the ray trace is easier in the commercial package due to its tools and better graphics. Light gets emitted tangentially to the electron beam as it bends in the magnetic field, due to the electron’s extreme energy relative to its rest mass, hence producing synchrotron emission. The photon angle of emission is dependent on its energy, with the high energy (keV) X-ray’s angle being very close to the plane of the electron orbit, and increasing as the photon energy decreases, attaining tens of mrad for the IR. A light source having an angle dependence upon photon energy is not common so no commercial package includes a SR source model. The Zemax can take in a ray distribution made by Shadow with proper rearrangement of the components as will be discussed. 2.1. Shadow source The source generated by Shadow is a list of comma separated variables with each row representing one ray. Up to N = 20,000 rays are possible in Shadow version 2.3 and a million in the newest Shadow 3 [8]. Each ray has 12 parameters, 6 more if polarization is considered. The first twelve ray components are: 3 space coordinates (x,y,z), 3 direction cosines (x ,y ,z ), 3 electric field components (Ei ), a flag for lost ray (l), a wavenumber value (k) giving its energy and an ordinal value (n) to identify it uniquely. The columns are ordered thus: x y z x y z Ex Ey Ez l k n. N rows of these ray values are double precision and comma separated. The source rays with the desired parameters are generated by running the Shadow routine ‘Source’. This produces the file Begin.dat which contains the rays in binary format. Optical elements (OE) are added as desired and the whole system is traced from source to the last OE by running ‘Trace’. Post processing of the Begin.dat file is done using the TRANSLATE command in Shadow. This makes a text file with comma separated variables with the name you specify, e.g. “IRsource.txt”. Shadow’s system information command SYSINFO generates a file with a table of xyz lab coordinates of the pole locations of all the OEs modeled in Shadow. A pole is a unit vector located at center of the OE surface and normal to it. Shadow places OEs given the distance and angles to the next element, starting from the source, so all the spatial geometry is computed and can be added into the Zemax lens editor as discussed below. Distance units are either mm or cm. The cloud of source points for the far-IR source at the Canadian Light Source is shown in Fig. 1. 2.2. Source file conversion Zemax can use a text file with the ray list as an input but this differs in format from the Shadow list. The coordinate system of Shadow differs from Zemax convention: photons propagate along Y axis in Shadow but along Z axis in Zemax. The conversion is straightforward and amenable to automation via script or code. The conversion entails selecting columns and processing as follows. The 3 Ei component columns and the ordinal value column are removed. Both spatial and angular coordinates columns are swapped – the y and z coordinate columns as well as the y and z columns. The x and x columns change sign. The flag (l = 1) column at the end is kept; it now acts as “unit intensity” for Zemax. Finally a header line with two values is added to the top of the new file. The first value is the number of rays and the second is a unit # which indicates the distance scale to Zemax: 2 = cm, 4 = mm. Now the order of columns relative to the original labels is: −x z y −x z y l k (the last two being intensity and optional wavelength). This file can be a space or tab separated array of 8 columns by N rows of rays with a header
Fig. 1. Cloud of IR source points for rays from Shadow. The length scales are compressed: 400 mm Y by 4 mm X by 0.2 mm Z. The rays (not shown) would point toward the left (positive Y-direction) in a roughly conical fan tangent to the orbit.
line and saved with a new name having .DAT extension, for example “IRRay.DAT”, and located in the Zemax\Sources\ folder. Fig. 2 shows the resulting file for a 100 m wavelength source. Shadow is limited in the long wavelength IR compared to X-rays in that only single energy photons are generated rather than a range of energies. This is partly due to large angles of emission compared to X-rays, internal small angle approximations that fail below 1 eV (1 m wavelength corresponds to 10,000 cm−1 ) and the need to designate “Exact synchrotron” in the source calculation to avoid approximation. If sources at different photon energy are made in Shadow, the k flag can be changed to a wavelength value, in microns, to indicate which photon energies these rays represent. These rows could be added to another source file with one or more differing wavelengths to build up a range of ray energies. Thus combining ray files for differing energies allows beams of varying emission angle to be traced together. Zemax can color the rays differently for each k wavelength value. Up to 1 million rays may be read directly in the source text file; Zemax will convert larger files to a binary format for up to 4 billion rays. Spreadsheet software or a script can be written to automate this conversion. Shadow’s VUI version in XOP has a macro capability that could be used to loop through incremental k values and make sets of rays to combine in one Begin file, contact author for details. 2.3. Zemax setup Zemax has a mode called “non-sequential” that allows for a file of rays to be read in as the object of the system. In Zemax a Lens Design Editor (LDE) spreadsheet is used to define the optical surfaces and starts with an object type called “source file” in which the new ray file name is entered. The LDE displays this in the object comments, and the number of layout and analysis rays is designated, up to N for either. The layout rays are a subset of the total analyzed ones. The source can be placed anywhere in lab frame coordinate space, with any angular orientation. It is best to leave it at the origin (0,0,0) as the lab frame coordinates of all the OEs can be used from Shadow as direct inputs into the LDE coordinates for each object. Otherwise an offset needs to be applied to each OE’s location. A wavelength is assigned in microns to each k flag number in the wavelength table. One then places the OEs from Shadow into the Zemax LDE as objects, with coordinates from the SYSINFO
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
G Model VIBSPE-2390; No. of Pages 4
ARTICLE IN PRESS T. May, A. Duffy / Vibrational Spectroscopy xxx (2014) xxx–xxx
3
Fig. 2. Example of the text files before and after conversion. Shadow output file (upper) has 12 columns with 6 shown here, Zemax source file (lower) has 7 (or 8 for wavelength). The columns have been swapped and the optional wavelength value has been left out.
file, and orients them as needed. Shadow orients OE rotations relative to an optic axis that can change direction after each encounter with the next OE surface, while Zemax objects start with each surface normal to the global Z direction. Rotation angles are adjusted as needed and the correct orientation of an object or mirror can be checked with rapid tracing in Zemax. The source rays and two mirrors from the beam line are shown in Fig. 3. The “standard surface” is specified in Zemax with a conic equation used to define radius of curvature at the vertex of the object (here a surface of revolution with the vertex on-axis) and parameters to define type of curve – sphere, parabola, ellipse, etc. The placement of off-axis aspheres is challenging in that the objects have their vertex location set by the LDE coordinates, not the pole location of the OE surface to which Shadow refers. This means that offsets from the vertex to the pole need to be calculated (using CAD) so that the rays hit the desired part of the surface and at the correct angle of incidence. Once completed in layout the system may be observed and plotted in a number of displays for 2 and 3D examination. The footprint of the actual ray distribution may be seen on the mirror surfaces or anywhere along the path, at foci, windows or detectors that are arbitrarily placed along the ray path. Fig. 4 shows the ray pattern intersecting a vacuum window near the focus of the beam line for 100 micron wavelength (100 cm−1 ). In Zemax these patterns are viewed on detector surfaces; in Shadow
Fig. 4. Ray pattern in Zemax at an intermediate focus by a vacuum window of the IR beam line. This shape is characteristic of the wide angle port collecting IR synchrotron radiation. A demagnified image is focused further along the beam line at the IR spectrometer aperture.
they are plotted from “star.xx” files where xx is the OE number. The model containing rays, surfaces and volume objects may now be exported as a STEP file (model.stp) to CAD software so the beam ray bundle can be used to design chambers and mounts and placed into the facility layout. 3. Results The combination of Shadow source rays and Zemax plotting ability makes a powerful tool for evaluating the optical design. Changes in the layout can be made and effects observed rapidly; actual footprints of the beam can be seen on mirror surfaces and at detectors wherever placed. Zemax can adjust mirror parameters by optimizing merit functions that can for instance adjust focus and on realistic rays, a feature not available in Shadow. Making use of the wave propagation capability of Zemax is a future goal. Acknowledgements
Fig. 3. Beam line in Zemax starting with source arc within bend magnet outline. Rays travel to right reflecting up from mirror 1 sending rays to mirror 2 and then into the page toward focus at vacuum window. The footprint of the beam is seen on the second mirror rectangle.
Research described in this paper was performed at the Canadian Light Source, which is funded by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009
G Model VIBSPE-2390; No. of Pages 4
ARTICLE IN PRESS T. May, A. Duffy / Vibrational Spectroscopy xxx (2014) xxx–xxx
4
Institutes of Health Research, the Government of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan. References [1] Shadow is part of XOP: www.esrf.eu/Instrumentation/software/data-analysis/ xop2.3/shadowvui (April, 2014). [2] Zemax-EE Version 13, http://zemax.com/home (April, 2014).
[3] G.L. Carr, G.P. Williams, SPIE Conf. Proc. 3153 (1997) 51–58. [4] F. Schafers, in: A. Erko, M. Idir, T. Krist, A. Michette (Eds.), Modern Developments in X-Ray and Neutron Optics, vol. 137, Springer-Verlag, Berlin, 2008, pp. 9–39, Chap. 2. [5] http://www.esrf.eu/Accelerators/Groups/InsertionDevices/Software/SRW (April, 2014). [6] A. Nucara, S. Lupi, P. Calvani, Rev. Sci. Instrum. 74 (2003) 3934–3942. [7] M. Frogley, G. Cinque, AIP Conf. Proc. 1214 (2010) 29–31. [8] M. Sanchez del Rio, N. Canestrari, F. Jiang, F. Cerrina, J. Synchrotron Radiat. 18 (2011) 708–716.
Please cite this article in press as: T. May, A. Duffy, Modeling infrared beam lines with Shadow and Zemax, Vib. Spectrosc. (2014), http://dx.doi.org/10.1016/j.vibspec.2014.08.009