CN103453991B - Method for improving spectral resolution of soft X-ray flat focal field spectrometer - Google Patents
Method for improving spectral resolution of soft X-ray flat focal field spectrometer Download PDFInfo
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- CN103453991B CN103453991B CN201310306376.0A CN201310306376A CN103453991B CN 103453991 B CN103453991 B CN 103453991B CN 201310306376 A CN201310306376 A CN 201310306376A CN 103453991 B CN103453991 B CN 103453991B
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Abstract
The invention provides a method for improving spectral resolution of a soft X-ray flat focal field spectrometer. A method that optical gratings are used for partitioning is adopted, on the premise that the structure of the spectrometer is not changed, trough type parameters of various partitions are respectively designed, diffraction efficiency of each partition is changed, and thus aberrations are further corrected to improve the spectral resolution. The method has the advantages that in the manufacturing of the optical gratings, partitioning is carried out in the direction vertical to stripes, different trough type parameters are respectively designed, distribution of the diffraction efficiency of each partition is changed, and the aberrations are further corrected; on the premise of guaranteeing the diffraction efficiency, proper partition structure trough type parameters are selected, resolution of wave lengths with serious aberrations is improved, resolution of other wave lengths is not influenced, and thus the spectrometer obtains good resolution on the whole use wave band.
Description
Technical field
The present invention relates to the flat burnt field spectrometer working in Soft X-Ray Region, for X ray plasma diagnostics, being specifically related to a kind of spectral resolution raising method of soft X-ray flat focal field spectrometer, utilizing grating partitioning technique to improve the spectral resolution of spectrometer when not changing spectrometer architecture parameter.
Background technology
Prior art 1(Performance of laminar-type holographic grating for a soft x-ray flat-fieldspectrograph in the0.7-6nm region) equal the structure of burnt field spectrometer as shown in Figure 1, concave grating used not only has dispersion function and also has imaging characteristic concurrently, do not need other image-forming component, therefore spectrometer can accomplish miniaturization.This system to light spectrum image-forming in a plane, can easily be coupled with the planar detector such as CCD, microchannel plate and streak camera compared to Rowland circle imaging system (imaging on a circle), be widely used in plasma diagnostics at present, element density of electronic states detects and soft x-ray laser research and development etc.
Prior art 2(Development of wavelength-dispersive soft X-ray emission spectrometers fortransmission electron microscopes-an introduction of valence electron spectroscopy fortransmission electron microscopy) spectral resolution is as the important indicator of spectral instrument, and improving spectral resolution has very important meaning.For the flat burnt field spectrometer of shortwave, the raising of current spectral resolution depends on conventional means, as reduced entrance slit width, increases light spectrum image-forming distance etc.But all there is more corresponding problem in these methods: reduce may be more serious while slit width promotes spectral resolution loss luminous flux; Increase the problem that light spectrum image-forming distance exists two aspects, one, spectrometer architecture becomes large, be difficult to accomplish miniaturization, its two, identical spectral range spectral image face width degree is become large, when the short of width of planar detector is to receive whole image planes, need plane of motion detector in the direction of the width repeatedly to receive data to obtain whole spectral image, make complex system like this, and cannot real-time be realized.The present invention considers from grating angle, when not changing system architecture, improves the spectral resolution of system by changing grating structural parameter.
Prior art 3(http: //www.horiba.com/cn/scientific/products/diffraction-gratin gs/catalog/variable-groove-depth-vgd/, Fabrication and evaluation of a wideband multilayer laminar-typeholographic grating for use with a soft-x-ray flat-field spectrograph in the region of1.7keV) content that provides of network address is HORIBA Jobin Yvon company changes grating zones of different blaze wavelength by continuously changing groove depth on stripe direction, the subregion mentioned in document is then grating is being divided into 3 regions perpendicular on the direction of grating fringe, and be coated with different assembly of thin films respectively, to obtain diffraction efficiency higher under different incidence angles degree simultaneously.Above-mentioned two kinds of gratings are all utilize subregion to obtain high diffraction efficiency of grating, the present invention is perpendicular to different grating grooved parameter (the Laminar grooved of zoning design on stripe direction, different accounts for wide ratio and groove depth) to change the diffraction efficiency of each subregion to incident light, the aberration of further some wave band of correction, thus the spectral resolution improving spectrometer.
Summary of the invention
For the imaging characteristics of grenz ray eliminating aberration concave grating, the present invention proposes a kind of spectral resolution raising method of soft X-ray flat focal field spectrometer, utilize the method for grating subregion, the grooved parameter of each subregion is designed respectively under the prerequisite not changing spectrometer architecture, change the diffraction efficiency of each subregion, thus revise aberration further to improve spectral resolution.
The technical solution used in the present invention is: a kind of spectral resolution raising method of soft X-ray flat focal field spectrometer, the method comprises the steps:
Step 1, determine the use wavelength of spectrometer, then determine the structural parameters of spectrometer;
Step 2, basis determine the linear-density distribution of parameter optimization eliminating aberration concave grating and the radius-of-curvature of grating substrate, then optimize the trench structure parameter of grating according to linear-density distribution to obtain comparatively ideal diffraction efficiency in whole use wave band;
Step 3, according to the grating correlation parameter after optimizing, analyze the meridian focusing curve of grating and the deviation of ideal focusing straight line, and tentatively determine the wavelength that needs to revise aberration further;
Step 4, ray tracing method analysis is utilized to put down the imaging of burnt field spectrometer, the result of verification step 3 also finally determines wavelength to be revised, because the incident angle of diverse location on light to grating is different with corresponding line density, namely there is certain difference in diffraction efficiency, in ray tracing, therefore consider the impact of diffraction efficiency;
Step 5, perpendicular on stripe direction, subregion is being carried out to grating, analyze each subregional imaging characteristic on wavelength to be optimized: grating is evenly divided into 3 regions, in point range figure, the spectral image in 3 regions is staggered, be convenient to center and the width of the spectral image observing regional, determine the quality of each regional imaging thus;
Step 6, the difference existed due to each regional imaging, for wavelength to be optimized, the ratio that each regional imaging is shared in final imaging can be adjusted, namely suppress aberration compared with the diffraction efficiency of large regions, promote the diffraction efficiency in the better region of aberration, thus weaken aberration further, promote spectral resolution;
Step 7, grating adopt Laminar grooved, therefore can by designing the groove depth of each subregion and accounting for wide ratio and adjust diffraction efficiency; Due to the change of subregion grooved parameter, the diffraction efficiency of corresponding whole wave band all can change, and therefore will consider its impact on other wavelength diffractive efficiency while grooved Selecting parameter;
Step 8, the Kr+ laser instrument of 413.1nm is utilized to carry out holographic exposure, obtain photoresist mask, according to the design parameter of step 7, utilize incinerator technology multidomain treat-ment photoresist mask, obtain in the error range allowed and account for wide ratio needed for each district, then utilize ion beam etching technology to etch groove depth needed for each district respectively, finally on grating, be coated with 100 ~ 150nm thick gold membrane.
Principle of the present invention is:
The invention provides a kind of spectral resolution raising method of soft X-ray flat focal field spectrometer, first according to the use wavelength of user demand determination spectrometer, then determine the structural parameters of spectrometer; According to the radius-of-curvature of the linear-density distribution and grating substrate of determining parameter optimization grating, then optimize the trench structure of grating according to linear-density distribution to obtain comparatively ideal diffraction efficiency in whole use wave band; Ray tracing method analysis is utilized to put down the imaging of burnt field spectrometer, because the incident angle of diverse location on light to grating is different with corresponding line density, namely there is certain difference in diffraction efficiency, therefore in ray tracing, consider the impact of diffraction efficiency, according to the difference that each wavelength place aberration exists, aberration can be revised further, to improve spectral resolution; Perpendicular on stripe direction, subregion is being carried out to grating, analyze the imaging characteristics in each district respectively, here 3 regions are evenly divided into grating, ray tracing method is utilized to analyze each subregion imaging features, can find that the aberration of some each subregion of wavelength exists obvious difference, utilize this characteristic to adjust the diffraction efficiency of each subregion, suppress the serious region of aberration to improve the spectral resolution of spectrometer; Due to the change of subregion grooved, the diffraction efficiency of corresponding whole wave band all can change, the selection of therefore final grooved parameter, diffraction efficiency that in whole wave band, aberration is large should be made as far as possible low and diffraction efficiency that aberration is little is as far as possible high, but pay the utmost attention to the diffraction efficiency reducing the large corresponding wavelength of aberration when ensureing overall diffraction efficiency.Preferably, the use wavelength of spectrometer is determined in step 1, then the structural parameters of spectrometer are determined, be specially: entrance slit is to raster center distance 237mm, imaging surface is 235mm to the distance of raster center, 1200 lines/mm the grating incident angle being used in 5 ~ 20nm is 87 °, and the 2400 lines/mm grating incident angle being used in 0.7 ~ 6nm is 88.65 °.
Advantage of the present invention and good effect are:
1, for eliminating aberration concave grating, along carrying out subregion perpendicular to stripe direction in manufacturing process, designing different grooved parameters respectively, changing its diffraction efficiency distribution, revise aberration further.
2, under the prerequisite ensureing diffraction efficiency, select suitable partitioned organization grooved parameter, improve the resolution of the more serious wavelength of aberration, and do not affect the resolution of other wavelength, thus make spectrometer obtain good resolution on whole use wave band.
Accompanying drawing explanation
Fig. 1 soft X-ray flat focal field spectrometer structural representation;
Fig. 2 center line density is the meridian focusing curve of 2400 lines/mm grating;
The light spectrum image-forming of Fig. 3 spectrometer (2400 lines/mm grating) in use wave band;
Fig. 4 grating subregion schematic diagram (the corresponding each regional center line density of numeral);
The imaging features of Fig. 5 grating zones of different (0.7,1.2,1.5,2,4.5 and 6nm);
Under the different partitioned parameters of Fig. 6 0.8,0.8 ± 0.8/50nm trace point range figure and resolution;
Under the different partitioned parameters of Fig. 7 1.1,1.1 ± 1.1/50nm trace point range figure and resolution;
Under the different partitioned parameters of Fig. 8 4.0,4.0 ± 4.0/50nm trace point range figure and resolution.
Embodiment
The present invention is further illustrated below in conjunction with drawings and the specific embodiments.
The structure that soft X-ray flat focal field spectrometer is commonly used as shown in Figure 1, core parts concave grating as spectrometer mainly contains two large classes: 1200 and 2400 lines/mm, correspond respectively to different use wave bands (wavelength coverage as 1200:5 ~ 20nm, 2400:0.7 ~ 6nm or lower).Concave grating possesses the function of dispersion and imaging simultaneously, and dispersion function can be realized by grating, and imaging function is realized by the linear-density distribution and spherical substrate radius-of-curvature optimizing grating.The optimization of line density is the whole use wave band considering spectrometer, therefore be difficult to can there be comparatively ideal anaberration effect to each wavelength, namely the aberration of some wavelength is little, and the aberration of some wavelength is relatively large, and the present invention weakens light spectrum image-forming aberration further for this situation exactly.
The concrete technical scheme that technical solution problem of the present invention adopts:
1, the use wavelength of spectrometer is determined, then the structural parameters of spectrometer are determined, most parameters depends on the structure of standard, entrance slit is to raster center distance 237mm, imaging surface is 235mm to the distance of raster center, incident angle determines primarily of use wavelength, and the 1200 lines/mm grating incident angle being generally used in 5 ~ 20nm is 87 °, and the 2400 lines/mm grating incident angle being used in 0.7 ~ 6nm is 88.65 °.
2, according to determining the linear-density distribution of parameter optimization eliminating aberration concave grating and the radius-of-curvature of grating substrate, the trench structure parameter of grating is then optimized according to linear-density distribution to obtain comparatively ideal diffraction efficiency in whole use wave band.
3, according to the grating correlation parameter after optimizing, analyze the meridian focusing curve of grating and the deviation of ideal focusing straight line and use the light spectrum image-forming size of each wavelength in wave band, determine the wavelength needing to revise aberration further.As Fig. 2 gives the focusing curve of grating, Fig. 3 provides imaging corresponding to several wavelength (grating parameter is see document Performance of laminar-typeholographic grating for a soft x-ray flat-field spectrograph in the0.7-6nm region), can find out that the aberration at each wavelength place there are differences, can find out that aberration is all more serious in 0.7 ~ 1.3nm wave band from focusing curve and spectral image size, therefore aberration corresponding to this wave band can be revised further, to improve spectral resolution.
4, perpendicular on stripe direction, subregion is being carried out to grating, analyzing respectively and treat the imaging characteristics optimizing wave band Nei Ge district further.The number of partitions is more many in theory more can revise aberration better, but considers process complexity, is only evenly divided into 3 regions to grating here, as shown in Figure 4.Fig. 5 gives the imaging of each subregion under several use wavelength, stagger in the horizontal direction for the ease of observing, there is obvious difference (size and centre-height) in the aberration of some each subregion of wavelength place, the present invention is exactly the diffraction efficiency utilizing this characteristic to adjust each subregion, suppresses the serious region of aberration to improve the spectral resolution of spectrometer.
5, grating adopts Laminar grooved, therefore can by designing the groove depth of each subregion and accounting for wide ratio and adjust diffraction efficiency; Due to the change of subregion grooved parameter, the diffraction efficiency of corresponding whole wave band all can change, and therefore will consider its impact on other wavelength diffractive efficiency while grooved Selecting parameter.
6, Kr+ laser instrument (413.1nm) is utilized to carry out holographic exposure, obtain photoresist mask, according to the subregion grooved parameter of design, utilize incinerator technology multidomain treat-ment photoresist mask, obtain in the error range allowed and account for wide ratio needed for each district, then utilize ion beam etching technology to etch groove depth needed for each district respectively, finally on grating, be coated with 100 ~ 150nm thick gold membrane.
Embodiment 1:
The grating chosen in document (Performance of laminar-type holographic grating for a soft x-ray flat-fieldspectrograph in the0.7-6nm region) carries out zoning design, raster center line density is 2400gs/mm, and line density parameter is b
2=-62, b
3=40007.5, b
4=-369802.6, substrate curvature radius is 15920mm, and use wave band is 0.7-6nm.
According to Fig. 2 and Fig. 3 analysis, the aberration of 0.7 ~ 1.3nm wave band is comparatively serious, therefore chooses this wave band and does further optimization.First, as grating is divided into region I, II and III by Fig. 4, under investigating each wavelength, the imaging characteristic (Fig. 5) of different grating region, can find out that the aberration of region I and II is larger, and trizonal inconocenter is not at a height, therefore causes the aberration of this wave band more serious.According to analysis above, in order to weaken aberration further, should the diffraction efficiency of inhibition zone I and II, the diffraction efficiency of lifting region III.Grating integral channel shape parameter in document for accounting for wide ratio 0.28, groove depth 4.5nm, the grating grooved parameter after subregion: what region I, II and III were corresponding account for wide ratio is respectively 0.2,0.2 and 0.425, and groove depth is respectively 15,15 and 4.5nm.Utilize consider diffraction efficiency impact ray tracing method, obtain the point range figure as shown in Fig. 6,7,8, trace wavelength be λ and λ ± λ/50(λ be respectively 0.8,1.1 and 4.0nm).In wave band to be optimized, the resolution at 0.8nm place is brought up to 383,1.1nm from 135 and is brought up to 620 from 346, gives the resolution at the wavelength 4.0nm place of unoptimizable wave band simultaneously, becomes 1035 from original 959.Therefore the resolution of design to wavelength to be optimized of subregion grating is significantly improved, and does not affect the resolution of other wavelength simultaneously.
Embodiment 2:
Grating is all example 1, the subregion grooved parameter of design: what region I, II and III were corresponding account for wide ratio is respectively 0.1,0.2 and 0.425, and groove depth is respectively 15,15 and 4.5nm.Ray tracing result is in Fig. 6,7,8, and at 0.8nm, spectral resolution changes not quite compared to example 1, becomes 425 from 383, at 1.1nm place, then rises to 712 from 620, and for 4.0nm, spectral resolution is changed to 1169 by 1035.Example 2, compared to example 1, further suppress the diffraction efficiency in larger aberration region, spectral resolution is had again raising to a certain degree.
The not disclosed in detail part of the present invention belongs to the known technology of this area.
Although be described the illustrative embodiment of the present invention above; so that the technician of this technology neck understands the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.
Claims (1)
1. the spectral resolution raising method of a soft X-ray flat focal field spectrometer, it is characterized in that, the method comprises the steps:
Step 1, determine the use wavelength of spectrometer, then determine the structural parameters of spectrometer;
Step 2, basis determine the linear-density distribution of parameter optimization eliminating aberration concave grating and the radius-of-curvature of grating substrate, then optimize the trench structure parameter of grating according to linear-density distribution to obtain comparatively ideal diffraction efficiency in whole use wave band;
Step 3, according to the grating correlation parameter after optimizing, analyze the meridian focusing curve of grating and the deviation of ideal focusing straight line, and tentatively determine the wavelength that needs to revise aberration further;
Step 4, ray tracing method analysis is utilized to put down the imaging of burnt field spectrometer, the result of verification step 3 also finally determines wavelength to be revised, because the incident angle of diverse location on light to grating is different with corresponding line density, namely there is certain difference in diffraction efficiency, in ray tracing, therefore consider the impact of diffraction efficiency;
Step 5, perpendicular on stripe direction, subregion is being carried out to grating, analyze each subregional imaging characteristic on wavelength to be optimized: grating is evenly divided into 3 regions, in point range figure, the spectral image in 3 regions is staggered, be convenient to center and the width of the spectral image observing regional, determine the quality of each regional imaging thus;
Step 6, the difference existed due to each regional imaging, for wavelength to be optimized, the ratio that each regional imaging is shared in final imaging can be adjusted, namely suppress aberration compared with the diffraction efficiency of large regions, promote the diffraction efficiency in the better region of aberration, thus weaken aberration further, promote spectral resolution;
Step 7, grating adopt Laminar grooved, therefore can by designing the groove depth of each subregion and accounting for wide ratio and adjust diffraction efficiency; Due to the change of subregion grooved parameter, the diffraction efficiency of corresponding whole wave band all can change, and therefore will consider its impact on other wavelength diffractive efficiency while grooved Selecting parameter;
Step 8, the Kr+ laser instrument of 413.1nm is utilized to carry out holographic exposure, obtain photoresist mask, according to the design parameter of step 7, utilize incinerator technology multidomain treat-ment photoresist mask, obtain in the error range allowed and account for wide ratio needed for each district, then utilize ion beam etching technology to etch groove depth needed for each district respectively, finally on grating, be coated with 100 ~ 150nm thick gold membrane.
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Non-Patent Citations (3)
| Title |
|---|
| Soft x-ray monochromator with a varied-space plane grating for synchroton radiation: design and evaluation;Masaaki Itou et al;《APPLIED OPTICS》;19890101;第28卷(第1期);第146-153页 * |
| Varied-line-spacing laminar-type holographic grating for the standard soft X-ray flat-field spectrograph;Masato Koike et al;《Proceedings of SPIE》;20001231;第4146卷;第163-170页 * |
| 宽光谱平像场全息凹面光栅的优化研究;皮道锐 等;《物理学报》;20100228;第59卷(第2期);第1009-1016页 * |
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