Optic Design Specification Criteria
AXCO produces optics made to precise optimised specifications with submicron RMS accuracy and repeatablity. The taper profiles used are based on very-high-order polynomial series which are dynamically optimised in 3D for maximal flux concentration and transmission efficiency against a specific set of design constraints. These constraints comprise the physical equipment geometry, spectral features and beam characteristics desired. AXCO maintains highly accurate computer codes developed and refined against test results from actual optics made to conform to predicted ideal profiles, for configurations ranging from robotic X-ray microanalysis instruments for space missions through standard lab instruments to syncrotron beamline end-station microfocusing optics.
What X-ray beam characteristics can an AXCO optic produce?
Our optics can achieve many different beam geometries for a range of X-ray sources. The analogous conventional optical systems are lenses and cylindrically-symmetric mirrors. Using a pointlike or extended source, a beam can be produced that is either focused at some distance from the optic (1mm to 1m), parallel or divergent. Beam spot sizes at a specimen position from a few microns to several mm can be specified. In addition, nonuniform beam intensity profiles at the specimen may be advantageous where the spot size may be user-selectable by means of interchangeable apertures or collimators, to enhance relative performance from smaller beam sizes. Spectral characteristics are also designed into the optic - for bombardment sources, typically the primary spectral line energy is optimally reflected and higher energies suppressed. For synchrotron or continuum applications, an optical design is optimised for the energy band desired by the customer.
Do I need a custom designed optic?
Our experience is that new instruments usually require new optical profiles to be determined to produce an optimal result. We don't recommend a "close" existing design where we find we can produce a better result using a new custom design at reasonable cost. Often there is no cost penalty involved. Accordingly we welcome requests from scientists, engineers and OEMs for estimated improvement using an optimised optic design for their specific application and choice of equipment. We can also recommend alternatives for X-ray sources and analysis equipment to ideally complement our optics where requested. AXCO maintains no commercial arrangements with any OEMs and can provide impartial reccomendations.
What else goes with an optic?
Typically a primary beam shutter is employed either upstream of the optic (eg tube shield, synchrotron beam line etc.) or downstream where a significant performance increase is available in locating the optic closer to the source (e.g. most rotating anode sources, microfocus tubes). The optics are very radiation tolerant and will not degrade after many years in continuous exposure in the latter case. An exit-collimator is also typically placed just upstream of the specimen position to exclude scatter and limit the beam diameter to the specfied size. This is often interchangeable to provide different beam sizes and/or intensity distributions at the specimen. Some applications may include a filter or monochromator placed either side of the optic. AXCO can provide advice on what ancilliary beam conditioning components may be needed for a specified instrumental configuration.
How to request a performance estimate
When requesting a performance estimate for an optic within a customer-specifed application, we need the following information or an indication of [lack of] preference. Where an off-the-shelf OEM product is to be used please just specify make and model details. Any information supplied will be treated as strictly confidential.
* Laboratory X-ray sources *
1. X-ray source type (e.g., sealed tube, microfocus tube, rotating anode etc.)
2. Apparent X-ray source dimensions (diameter or height x width)
3. Minimum approach distance to X-ray source (Note - it is often highly advantageous to include a primary beam shutter located AFTER the optic, where possible, to permit closer approach to the source by the optic and hence greater flux collection solid-angle)
4. Permitted distance range between X-ray source and specimen positions including any equipment contraints - e.g. sample cells, goniometer arcs, tube shields etc.
5. Beam diameter at specimen (for large-diameter beams to be used with interchangeable apertures, specify max beam width and desired intensity distribution)
6. Beam focus position (if any) with respect to specimen position
7. Beam divergence (or convergence) limits at specimen
8. Desired X-ray wavelength, energy or source spectral line (e.g. Cu Ka, Mo Ka, etc.)
9. Any other constraints or requirements of the analysis technique desired (please detail).
* Synchrotron and FEL X-ray sources *
1. Type of source (bend magnet, undulator, wiggler etc.)
2. Upstream optics (if any)
3. Apparent beam dimensions at location for desired optic (height x width, FWHM etc.)
4. Beam divergence / convergence incident at desired optic location (or FWHM limits etc.)
5. Permitted distance range between desired optic position (beam source port, slits, window, etc.) and specimen position including any equipment constraints - e.g. sample cells etc.
6. Beam diameter desired at specimen (for large-diameter beams to be used with interchangeable apertures, specify max beam width and desired intensity distribution)
7. Beam focus position (if any) with respect to specimen position
8. Beam divergence (or convergence) limits at specimen
9. Desired X-ray energy range of operation
10. Any other constraints or requirements of the analysis technique desired (please detail).
What does the performance estimate actually mean?
This is, of course, the bottom line. Please see the definitions page for an explanation of the terms used in the performance estimate supplied by AXCO for your proposed X-ray analysis application.
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