CN111580207A - Higher harmonic suppression filter disc for 50-100 nm wave band and preparation method thereof - Google Patents

Higher harmonic suppression filter disc for 50-100 nm wave band and preparation method thereof Download PDF

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CN111580207A
CN111580207A CN202010534058.XA CN202010534058A CN111580207A CN 111580207 A CN111580207 A CN 111580207A CN 202010534058 A CN202010534058 A CN 202010534058A CN 111580207 A CN111580207 A CN 111580207A
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film
harmonic suppression
suppression filter
filter
thin film
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金宇
陈溢祺
朱忆雪
冀斌
朱东风
朱运平
金长利
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Suzhou Hongce Photoelectric Technology Co ltd
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    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/20Filters
    • G02B5/208Filters for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation

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Abstract

The invention provides a higher harmonic suppression filter sheet for a 50-100 nm waveband and a preparation method thereof, and belongs to the technical field of optical elements. The harmonic suppression filter sheet includes a first Al film, a Yb thin film, and a second Al film, which are sequentially stacked. In the invention, the Yb thin film has an absorption edge at about 46nm, the transmissivity of the filter disc prepared by using the Yb thin film is obviously compared before and after the absorption edge, the first Al film and the second Al film are easy to oxidize, and dense Al can be generated2O3Thereby protecting the Yb thin film from oxidation. The filter sheet provided by the invention can effectively inhibit higher harmonics within a wavelength range of 50-100 nm. The transmittance of the harmonic suppression filter is measured, and the result shows that the harmonic suppression filter can effectively suppress harmonic in the wavelength range of 50-95 nm.

Description

Higher harmonic suppression filter disc for 50-100 nm wave band and preparation method thereof
Technical Field
The invention relates to the technical field of optical elements, in particular to a higher harmonic suppression filter disc for a 50-100 nm waveband and a preparation method thereof.
Background
In synchrotron radiation light sources, beam lines in the Vacuum Ultraviolet (VUV) to soft X-ray wavelength range typically use grazing incidence grating monochromators. The grating monochromator disperses incident light into discrete diffraction orders according to the wavelength of the incident light and the grating period. Higher harmonics are introduced when the grazing incidence angle of the grating in the grating monochromator is small enough to reflect short wavelength incident light. The vacuum ultraviolet band covers resonance lines of a large number of light elements, and a high-sensitivity measurement and analysis means can be provided for the research of the components and the structure of the material; particularly, the L absorption edge of H, the HeI line and the OI line are also positioned in the wave band, and the method has wide application prospect in the fields of celestial physics, atmospheric physics, astronomy and the like. However, higher harmonics can create background in the photoelectron spectrum, particularly in the absorption spectrum of the photon excitation. Similarly, for the calibration of the optical element in this wavelength band, the higher harmonics will also bring errors to the test result. Therefore, for the above applications, it is most critical to effectively suppress the higher harmonics and ensure the spectral purity of the test light source.
In order to effectively suppress higher harmonics, various synchrotron radiation light sources have been extensively studied. Such as filters, harmonic suppression mirrors, and noble gas absorption cells. In the wave band of 50-100 nm, due to the strong absorption characteristic of the material, the research on the optical filter is very limited. Harmonic suppression devices used in this wavelength range are based essentially on rare gas absorption cells with vacuum differential systems (e.g. Chkhalo, n.i., Drozdov, et al. thin film multilayer filters for solar EUV telescopes, Applied Optics,2016,55(17), 4683). The thin film filter made of special material can be used to suppress the higher harmonics in the wavelength range of 5-50 nm (Zr, Si, Al, Mg) and higher than 104nm (LiF) (such as Torma, P.T., et Al. ultra-thin silicon nitride X-ray windows, IEEE transaction son Nuclear Science,2013,60(2), 1311-materials 1314). However, no filter is currently used in the wavelength range of 50-100 nm, because almost all available materials have strong absorption characteristics in this wavelength range.
Disclosure of Invention
In view of the above, the present invention provides a harmonic suppression filter for a 50-100 nm band and a method for manufacturing the same. The filter sheet provided by the invention can effectively inhibit higher harmonics within a wavelength range of 50-100 nm.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a higher harmonic suppression filter sheet for a 50-100 nm waveband, which comprises a first Al film, a Yb thin film and a second Al film which are sequentially stacked.
Preferably, the Yb thin film has a thickness of 100 to 500 nm.
Preferably, the Yb thin film has a thickness of 300 nm.
Preferably, the first Al film and the second Al film each have a thickness of 15 nm.
Preferably, the Yb thin film is of a circular structure, and the diameter of the circular structure is 8-20 mm.
The invention also provides a preparation method of the higher harmonic suppression filter disc in the technical scheme, which comprises the following steps:
and sequentially coating a first Al film, a Yb thin film and a second Al film to obtain the higher harmonic suppression filter disc.
Preferably, the coating is an evaporation coating or a magnetron sputtering coating.
Preferably, the background air pressure of the evaporation coating is lower than 2 × 10-5Pa。
The invention provides a higher harmonic suppression filter disc (Al/Yb/Al filter disc) for a 50-100 nm waveband, which comprises a first Al film, a Yb thin film and a second Al film which are sequentially stacked. In the invention, the Yb thin film has an absorption edge at about 46nm, the transmissivity of the filter disc prepared by using the Yb thin film is obviously compared before and after the absorption edge, the first Al film and the second Al film are easy to oxidize, and dense Al can be generated2O3Thereby protecting the Yb thin film from oxidation. The invention providesThe filter sheet can effectively suppress higher harmonics within a wavelength range of 50-100 nm. The transmittance of the higher harmonic suppression filter is measured, and the result shows that the higher harmonic suppression filter can effectively suppress harmonic within the wavelength range of 50-95 nm. The 840-line/mm grating is used for researching the higher harmonic of NSRL BL08B beam line at 50-80 nm, and the Al/Yb/Al filter is used for researching the harmonic suppression capability of BLO8B beam line, and the experimental result shows that the content of the higher harmonic is extremely high under the condition of no higher harmonic suppression filter at the wavelength of 50-80 nm. At 80nm, the intensity of the higher harmonics is ten times the intensity of the fundamental. After the higher harmonic suppression filter disc is added into the optical path, the higher harmonics with the wavelength higher than 10nm can be effectively suppressed.
Drawings
FIG. 1 is a layout diagram of a test experiment of a higher harmonic suppression filter according to the present invention;
FIG. 2 is a theoretical transmittance curve of Yb filter sheets with different thicknesses in a wavelength band of 10-100 nm;
FIG. 3 is a theoretical transmittance curve of Al/Yb/Al filter sheets with different thicknesses in a band of 10-100 nm;
FIG. 4 is a harmonic suppression ratio curve of Al/Yb/Al filter sheets with different thicknesses in a wave band of 50-100 nm;
FIG. 5 is a diffraction spectrum obtained by scanning with a detector under different incident wavelengths;
FIG. 6 is the ratio of the higher harmonic to fundamental signal strength of the NSRL metering station before and after insertion of the Al/Yb/Al filter;
FIG. 7 is a graph showing the harmonic behavior of an Al/Yb/Al filter with a wavelength of 50 nm;
FIG. 8 is a transmittance curve of the Al/Yb/Al filter after the harmonic influence is removed in the actual measurement, theoretical calculation and actual measurement results;
FIG. 9 shows the fitting results of two membrane systems of Al/Yb/Al filter;
FIG. 10 shows Yb and its oxide Yb2O3Al and its oxide Al2O3And YbAl compound formed by diffusion of Yb and Al3And Yb and Al in the wavelength range of 40 to 80 nm.
Detailed Description
The invention provides a higher harmonic suppression filter (Al/Yb/Al filter) for a 50-100 nm waveband, which comprises a first Al film, a Yb (ytterbium) thin film and a second Al film which are sequentially stacked.
In the present invention, the Yb thin film preferably has a thickness of 100 to 500nm, more preferably 300 nm.
In the present invention, the first Al film and the second Al film each preferably have a thickness of 15 nm.
In the invention, the Yb thin film is preferably a circular structure, and the diameter of the circular structure is preferably 8-20 mm.
The invention also provides a preparation method of the higher harmonic suppression filter disc in the technical scheme, which comprises the following steps:
and sequentially coating a first Al film, a Yb thin film and a second Al film to obtain the higher harmonic suppression filter disc.
In the present invention, the plating film is preferably an evaporation plating film or a magnetron sputtering plating film.
In the present invention, the background gas pressure of the evaporation coating film is preferably lower than 2 × 10-5Pa。
In the invention, when a transmission filter calibration experiment is carried out, the reflectivity meter works in a transmission mode, and the test experimental arrangement of the higher harmonic suppression filter is shown as figure 1. In fig. 1, the transmission grating is preferably a 840line/mm, gold-plated film, self-supporting transmission grating.
In order to further illustrate the present invention, the following describes in detail the harmonic suppression filter for 50-100 nm band and the preparation method thereof, but they should not be construed as limiting the scope of the present invention.
In the embodiment of the invention, the optical performance of the filter is characterized in Beijing synchrotron radiation device and national synchrotron radiation laboratories (BSRF and NSRL).
Example 1
A higher harmonic suppression filter disc for a 50-100 nm waveband comprises a first Al film, a Yb thin film and a second Al film which are sequentially stacked, wherein the thickness of the Yb thin film is divided into100, 200, 300, 400 and 500nm respectively, and the first Al film and the second Al film are both 15nm thick, and are prepared by an evaporation coating method, wherein the background air pressure is 2 × 10 during the preparation process-5Pa. The Yb thin film was a circular structure having a diameter of 8 mm. The thickness of the Yb thin film and the first and second Al films in the filter were measured by a quartz crystal resonator. The Al/Yb/Al filter produced in this example was calibrated using a reflectometer at the NSRL BL08B metering line station.
Yb filter disc: pure Yb filters with thicknesses of 100, 200, 300, 400 and 500nm, respectively.
FIG. 2 shows the theoretical transmittance of Yb filter sheets with different thicknesses in the wavelength range of 10-100 nm, which shows that Yb (ytterbium) has an absorption edge around 46nm, and the Yb filter transmittance is very obviously compared before and after the absorption edge.
However, Yb is chemically more reactive and will slowly oxidize in air, whereas Yb is2O3The optical properties differ greatly from Yb. Therefore, 15nm Al protective layers were plated on both sides of Yb. Al will form dense Al2O3Thereby protecting Yb from oxidation. FIG. 3 is a theoretical transmittance curve of Al/Yb/Al filter sheets with different thicknesses in a wavelength band of 10-100 nm, and FIG. 4 is a harmonic suppression ratio curve of Al/Yb/Al filter sheets with different thicknesses in a wavelength band of 50-100 nm. As can be seen from FIGS. 3 to 4, in the BSRF 3B1 beam line, harmonics around 10nm were detected. Therefore, in order to effectively suppress the harmonics of about 10nm, the filter of the present invention is finally determined to be a 300nm Yb thin film, and 15nm Al films are deposited on both surfaces of the Yb thin film.
A signal with a relatively good signal to noise ratio is not obtained due to a too low flux in the band above 80 nm. Therefore, the test band is 50-80 nm. And performing spectrum calibration tests of adding the Al/Yb/Al filter disc and not adding the Al/Yb/Al filter disc at intervals of 5nm at a wave band of 50-80 nm to obtain the harmonic suppression effect of the Al/Yb/Al filter disc.
Test results
Spectrum calibration test
The results of the transmission grating diffraction spectrum test with and without the Al/Yb/Al filter are shown in FIG. 5. According to the grating equation: dsin θ is m (λ/n), where d is the grating constant, n is 1 represents the fundamental wave with wavelength λ, and m is the fundamental diffraction order. n.gtoreq.2 represents a higher harmonic having a wavelength of lambda/n.
The integrated intensity of each diffraction peak signal can be obtained by integrating the area of each diffraction peak. And then the integral intensity of the higher harmonic signal is compared with the integral intensity of the fundamental wave signal, so that the ratio of the higher harmonic to the fundamental wave signal can be obtained. The results of the individual wavelength ratios are given in FIG. 6, where IHFor integration of the intensity of the harmonic signal, IFThe intensity is integrated for the fundamental signal. At 50nm, higher harmonic signals of 1/2, 1/3 to 1/7 of the fundamental wave can be observed. At 80nm, higher harmonics of 1/2 to 1/10 of the fundamental wave can be observed. The longer the wavelength, the more complex the distribution of the higher harmonics and the higher the proportion of the higher harmonics in the fundamental wave. At a wavelength of 80nm, the intensity of the higher harmonics is already approximately 10 times that of the fundamental signal.
Note that the higher order diffraction peaks are superimposed and cannot be resolved due to the lower minimum angular resolution of the detector rotation. The angular position of each higher harmonic can be obtained through a grating formula, specific higher harmonic information in the diffraction signal of the large bump can be obtained by carrying out multimodal fitting on the diffraction signal of the large bump which cannot be analyzed, and when the wavelength is 50nm, the fitting is carried out on the signal in the wider and larger diffraction peak in the graph 7. From the test results, it can be seen that most of the higher harmonics are effectively suppressed when the Al/Yb/Al filter is introduced. However, the higher harmonics closest to the zero order are still partially transmitted through the filter. By fitting the test data according to the angle relationship, the wavelengths of the higher harmonics of the transmittance sheet can be calculated to be less than 10 nm.
Results of filter transmittance test
In order to obtain the real absorption edge position of the Al/Yb/Al filter, a transmittance test was performed on the Al/Yb/Al filter, and fig. 8 is a transmittance curve obtained by actually measuring, theoretically calculating, and removing the harmonic influence from the actually measured result of the Al/Yb/Al filter. According to FIG. 8, the Yb absorption edge is at 47.8 nm. It can be seen that the transmission obtained from the test is lower than the theoretical value. The reason that the transmittance obtained by actual test is low may be: 1. the harmonic content of the test wave band is very high, so that the test transmittance is reduced; 2. yb thin film anddiffusion between Al film layers and oxidation of filter disc, Yb will generate AlYb at interface with Al3A compound is provided.
The transmittance is represented by the formula T ═ I/I0Obtaining: wherein I is the transmitted signal intensity, I0Is the source intensity signal strength. From the results of the spectroscopic measurements, I and I obtained in the measurement0The signals all contain components of harmonics, and the harmonic ratio is shown in fig. 6. To obtain more real transmittance, the transmission signal I and the source intensity signal I are required0The removal of the medium and high harmonic components can be performed according to the following formula:
T=I×(1/((IH/IF)with filter+1))/Ia×(1/((IH/IF)withoutfilter+1))
as can be seen from fig. 8, the transmittance after treatment is still lower than the theoretical value. And fitting the transmittance of the Al/Yb/Al filter disc after correction. Because the filter disc is prepared by an evaporation coating method, and a film prepared by the evaporation coating method is generally loose and porous, an Al protective layer with the thickness of 15nm is difficult to play a better protection role. Therefore, to investigate whether Yb is oxidized, two film systems were used in the fitting, namely a Yb-containing oxide layer and a Yb-free oxide layer: al (Al)2O3/Al/Yb2O3/YbAl3/Yb/YbAl3/Yb2O3/Al/Al2O3And Al2O3/Al/YbAl3/Yb/YbAl3/Al/Al2O3The two membrane systems were fitted and the fitting results are shown in fig. 9, with the fitting parameters shown in table 1. From the fitting results, it can be concluded that diffusion did occur for both materials in the filter disc. Using a catalyst containing Yb2O3The correlation coefficient between the fitting result obtained by the model and the test result is 0.989. Use of a catalyst containing no Yb2O3The correlation coefficient between the fitting result obtained by the model and the test result is 0.982. The fitting results of the two models show that the Yb is contained2O3The fitting result obtained by the model is well matched with the actually measured data. It is inferred that Yb is also oxidized to some extent.
FIG. 10 shows Yb and its oxide Yb2O3Al and its oxide Al2O3And YbAl compound formed by diffusion of Yb and Al3And Yb and Al in the wavelength range of 40 to 80 nm. From the figure, Yb can be seen2O3And Al2O3The linear absorption coefficient in the designed wave band is much higher than that of Yb and Al, while YbAl3The linear absorption coefficient was not very different from the Yb or Al ratio, and it was concluded that the decrease in transmittance observed for the Al/Yb/Al filter was mainly due to oxidation of Al and Yb.
TABLE 1 transmittance test results fitting parameters
Figure BDA0002536418800000061
Figure BDA0002536418800000071
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims (8)

1. A higher harmonic suppression filter sheet for a 50-100 nm waveband is characterized by comprising a first Al film, a Yb thin film and a second Al film which are sequentially stacked.
2. The harmonic suppression filter according to claim 1, wherein the Yb thin film has a thickness of 100 to 500 nm.
3. The higher harmonic suppression filter of claim 2, wherein the Yb thin film has a thickness of 300 nm.
4. The higher harmonic suppression filter according to any one of claims 1 to 3, wherein the first Al film and the second Al film each have a thickness of 15 nm.
5. The higher harmonic suppression filter according to claim 1, wherein the Yb thin film has a circular structure, and the diameter of the circular structure is 8 to 20 mm.
6. The method for producing a higher harmonic suppression filter according to any one of claims 1 to 4, comprising the steps of:
and sequentially coating a first Al film, a Yb thin film and a second Al film to obtain the higher harmonic suppression filter disc.
7. The production method according to claim 6, wherein the coating film is an evaporation coating film or a magnetron sputtering coating film.
8. The method according to claim 7, wherein the background gas pressure of the evaporation coating film is less than 2 × 10- 5Pa。
CN202010534058.XA 2020-06-12 2020-06-12 Higher harmonic suppression filter disc for 50-100 nm wave band and preparation method thereof Pending CN111580207A (en)

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