AU2021100257A4

AU2021100257A4 - An All-Dielectric Ultraviolet Filter Film

Info

Publication number: AU2021100257A4
Application number: AU2021100257A
Authority: AU
Inventors: Ruixin CHOU; Jianxin HAN; Yahui SHI; Guoquan YANG; Yali Zhao
Original assignee: Jinzhong University
Current assignee: Jinzhong University
Priority date: 2020-07-15
Filing date: 2021-01-15
Publication date: 2021-04-15
Anticipated expiration: 2029-01-15
Also published as: CN111856639A; CN111856639B

Abstract

The present invention relates to an all-dielectric ultraviolet filter film, the filter film is composed of a glass serving as a substrate, and two types of profile materials with different refractive indexes which are layered sequentially and alternately; wherein said two types of profile materials with different refractive indexes are a high-refractive-index profile material with both wide bandgap and high dielectric and a low-refractive-index material with good polarization. Based on the research results of thin-film theory, the all-dielectric ultraviolet filter film of the present invention is obtained through analyzing and correcting the number and thickness of layers of the filter film in the film structure using a simplex method, and the filter film obtained has high reflectivity to 210-260 nm and high transmittance to 280-700 nm. El I Fig. 1 low-refractive-index profile material high-refractive-index profile material substrate Fig. 2 EEE E +N E Ell \E+ El/ /1 d, E1E E N, y E+2 E 2 E N2 Fig. 3 E*4 E-* Ni di N 2d N E-i d j+1 k N E-' d' I+1 Ek+ k+1

Description

El I

Fig. 1

low-refractive-index profile material

high-refractive-index profile material

substrate

Fig. 2 EEE E

+N E Ell \E+ El/ /1 d, E1E E N, y E+2 E 2 E

N2

Fig. 3

E*4 E-*

Ni di

N 2d

N E-i d j+1 k N E-' d'

I+1 Ek+ k+1

An All-Dielectric Ultraviolet Filter Film

TECHNICAL FIELD The present invention relates to the field of thin-film preparation, and in particular to an all-dielectric ultraviolet filter film.

BACKGROUND OF THE INVENTION With the rapid development of optical technology, UV communication has attracted much more attention due to its unique advantages of small in size and light in weight. Various ultraviolet components and products have been introduced into people's lives and widely used in living, production and the like. In recent years, UV optical thin-films have also been extensively studied by scientists in order to meet the demands for developing the optical components.

The study found that the use of filter lens in the ultraviolet communication system can achieve the purpose of reducing signal attenuation and eliminating other nuclear magnetic interference to enhance the ultraviolet signal. It can be seen that the UV filters plays an important and key role in the communication system, and the quality thereof will directly determines whether the UV communication system can work normally. Even, to a certain extent, the development level of the UV filters directly determines the development level of the UV communication system. Therefore, the research on UV filters is particularly important.

Earlier UV reflectors were mainly obtained by depositing a protective film on the metal surface, which however had seriously deficiency of high UV absorption and low reflectivity. Subsequent studies found that, the dielectric films had significantly reduced UV absorption and wider transparent region compared to metal. It can be seen that the requirements for high reflection to the ultraviolet band and high transmission to other bands required for ultraviolet communication cannot be met.

Currently, UV reflection film has a structure of metal - dielectric film, in which the metal film is more active in chemical properties, and has strong absorption and oxidation ability, resulting that the reflectivity of the UV reflection film will be greatly affected. Although the absorption can be reduced in some extend by coating a protective film onto the metal film, the protective film itself also has disadvantages of serious absorption and scattering, and insufficient reflectivity. What's more, the protective film is also prone to scratches, rust and other conditions that affect reflection. Therefore, the dielectric films, which have excellent performances of wider transparent region and little absorption is considered.

SUMMARY OF THE INVENTION In view of the technical problems in the prior art, the present invention provides an all-dielectric ultraviolet filter film.

Technical solutions provided by the present invention are as follows. An all-dielectric ultraviolet filter film is constructed, the all-dielectric ultraviolet filter film is composed of a glass serving as a substrate, and two types of profile materials with different refractive indexes which are layered sequentially and alternately; wherein said two types of profile materials with different refractive indexes are a high-refractive-index profile material with both wide bandgap and high dielectric and a low-refractive-index profile material with good polarization.

wherein said high-refractive-index profile material is hafnium dioxide, and said low-refractive-index profile material is magnesium fluoride.

wherein the number of layers of high-refractive-index profile material and low-refractive-index profile material that alternately layered is set to 13, of which 7 are layers of hafnium dioxide, and a layer of magnesium fluoride is layered between every two layers of hafnium dioxide.

wherein thickness of the thin-film of hafnium dioxide is set to 25 nm, and thickness of the thin-film of magnesium fluoride is set to 40 nm.

Different from the prior art, the present invention provides an all-dielectric ultraviolet filter film, the filter film is composed of a glass serving as a substrate, and two types of profile materials with different refractive indexes which are layered sequentially and alternately; wherein said two types of profile materials with different refractive indexes are a high-refractive-index profile material with both wide bandgap and high dielectric and a low-refractive-index material with good polarization. Based on the research results of thin-film theory, the all-dielectric ultraviolet filter film of the present invention is obtained through analyzing and correcting the number and thickness of thin-film in the film system structure using a simplex method, and the filter film obtained has high reflectivity to 210-260 nm and high transmittance to 280-700 nm.

BRIEF DESCRIPTION OF THE DRAWINGS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a structural diagram of an all-dielectric ultraviolet filter film provided by the present invention.

Figure 2 shows an equivalent interface diagram of monolayer thin-film in the all-dielectric ultraviolet filter film provided by the present invention.

Figure 3 shows an equivalent interface diagram of multilayer thin-film in the all-dielectric ultraviolet filter film provided by the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS In order to have a clearer understanding of the technical features, objectives and effects of the invention, particular embodiments of the invention will now be described with reference to the accompanying drawings.

See Figure 1, the present invention provides an all-dielectric ultraviolet filter film is constructed, the all-dielectric ultraviolet filter film is composed of a glass serving as a substrate, and two types of profile materials with different refractive indexes which are layered sequentially and alternately; wherein said two types of profile materials with different refractive indexes are a high-refractive-index profile material with both wide bandgap and high dielectric and a low-refractive-index profile material with good polarization.

Currently UV reflection film has a structure of metal - dielectric film, in which the metal film is more active in chemical properties, and has strong absorption and oxidation ability, resulting that the reflectivity of the UV reflection film will be greatly affected. Although the absorption can be reduced in some extend by coating a protective film onto the metal film, the protective film itself also has disadvantages of serious absorption and scattering, and insufficient reflectivity. What's more, the protective film is also prone to scratches, rust and other conditions that affect reflection. In view of that the dielectric films have wider transparent region and little absorption, the present invention aims to design an all-dielectric ultraviolet filter film with high reflectivity to UV and high transmittance to visible light.

Firstly, the reflectivity of a monolayer dielectric film is derived according to Maxwell's equations, and the derivation process is as follows:

As shown in Figure 2, the two interfaces of the (monolayer) thin-film can be displayed as equivalent interfaces on the mathematical plane. The combined admittance coefficient of the thin-film and the substrate is Y, thus:

HO = Y(koxEo) (1)

in the equation,=H+H0 E =E +0E

The amplitude reflection coefficient of the monolayer is: 1/O r

+Y (2)

wherein, 77 is admittance of incident medium. Theoretically, the transmittance and reflectivity of the monolayer can be deduced by calculating the combined admittance coefficient Y.

At interface 1, following can be obtained by applying the boundary conditions for electromagnetic fields thereto: Eo=E++E=E+ +Ej (3)

ko x EO = ko x E + ko x El (4) HO=H +H_ = H++H_ (5)

HO= 1 (kox E -kox EJ) (6)

Taking several points from the inner side of the interface 1 and interface 2 for analysis, it is easy to find that when the abscissa is fixed, there is a certain relationship between the complex amplitude intensity and the phase difference introduced by the spatial distance of the electromagnetic field of two points with different ordinates, namely:

E*2 = Ee-, E- = Ej-e , = N dcos 0

thus, k x EO = (ko x El '"' + (k. x E- (8)

HO = (ko x E+ )ueI5 - (ko x E- )71 e- (9)

which can be written as a matrix:

kFx E1 e ig e-i1i k. x E I He j r/qeis1 - 1 ea5ko x E12 (10)

At interface 2, follows can be obtained:

E2 + EI= E2 , ko x E + ko x E- = ko x E2

Hl+2HI2=H 2, rI(koxE- kOxE-=H2 (12)

thus:

ko x E1 = -(ko x E2 )+ H2 (13) 2 2q,

ko x E- = I (k x E2 )- H2 (14) 2 2r7,

which can be written as a matrix:

ko x EJ 2 29,1 ko x E2 (15) ko x E-) I H2 -2 2r7,11

Follows can be obtained by substituting equation (15) into equation (10):

LkxE_Ho 1

[e'g' e'gl e' 8 ' _ - gf 1 2 1

1 I I 2q 17 k H2 II F

ino i

cs sin Ij H2 2koxE

1 H2 2q] qsin3, cos3 1 ] (16)

and on the basis that: Ho = Y(ko x EO), H 2 = 7 2 (ko x E2 ) (17), equation (16) can be written as

(kox Eo \17 Fcoso 1 1sino i,5 1 1Fi (ko x E 2

) L qlsin 5 cos 3 1 2 (18)

let B coso sino (19), C] iqlsin, 1 cos3 1 j 2

then (k0 xEOfI LB (ko x E2) (20),

Y= (21) is solved; B

cos,5 1 7 sin,51

wherein the matrix -iqsin 1 cos5 1 jis uniquely determined by the parameters

of the film, and is called the characteristic matrix of the film, and the matrix is C] a second-order matrix completely determined by parameters of the film system and the substrate. Obviously, follows can be obtained from Y = C B

Y= 7 2 cos o1 iq 1sin 1 cos5 +i 1 2 sin(1 7o (22)

Accordingly, the reflection coefficient r of the monolayer dielectric film can be calculated as:

(ro -97 2 )cos C i +i 7o2 _7i in (3 r = 77o - Y _771 (23) 7 0 +Y (7o+772 )COS+i o72+ 7inoi /71)

and then the reflectivity R of the monolayer dielectric film can be calculated as:

2 ( -72)2 cos 2 1 + 077o2 - sin 285 R =|r2 0 - _71

) °o+Y (G0+7 )2 cos2 + o772+7, 2 1 sin 2 9

, K'771 (24)

On the basis of study on calculation for the characteristics of the monolayer dielectric film, the matrix of the multilayer dielectric film can be calculated recursively, and the derivation diagram is shown in Figure 3.

At interfaces 1 and 2, and interfaces 2 and 3, following can be obtained by applying the boundary conditions thereto:

E0 COSuo sin 1 [ E2 2 ) (25) Lo iqisin( 1 cos3 1 H2

E12 cos5 sino2 [E33) 2 (26) Hg) q2sin 52 Cos I2Hs

Keep repeating the whole process until to interface K and K+1, following can be obtained:

E coso, sin5 Ekiki7

H iqkCsin3 os3kk (27)

Since the tangential components of each interfaces are continuous, then[2]:

2I. = (28) H12 H22 H23 H33 Hk-~ Hk and follows can be obtained through continuous linear transformation:

E0y kCO 5|-icoso~

[Eo7h 5 k (29) sind EF i -H0 iqjsino cos -5HIj

On the basis that Y=H 0 /E 0 and no backward wave in the substrate

77k-l -Hk IlEk l then

1 cs s 1I E0[I k COS (5 -sifl5 E H 7 EklI (30) L iqjsin 5 COS 5, J,+I

thus a characteristic matrix of the film system is as follows:

Bc _sind F1 FBr H osd1 (31) LC' L' iqjsin 5 cos 5jL qkl+ (1

After studying the combined admittance of the monolayer dielectric film, it can be concluded that the general formula for combined admittance of the multilayer dielectric film is: Y=C/B, and then R (reflectivity) and T (transmittance) for k-layers film are

R= °qOYqO - Y°B-C 1OB-C 7 0 +Y ri0 +Y ) r 0 B+C r 0B+C (32)

T _ 4909,+1 (q0B+ C(0B+C33)

Interferometric cut-off filters refer to that has a high-transmission to a certain wavelength range, and a sudden change to a high reflection for the light beams deviating from said wavelength range. Long wave-pass filters refer to that suppresses the short-wave region and transmits to the long-wave region; similarly, short wave-pass filters refer to that transmits to the short-wave region, and suppresses the long-wave region.

Basic film system for the cut-off filter (Interferometric) is X /4 periodic stack (LH)s, wherein L and H represent low-refractive-index and high-refractive-index materials respectively. With the film system having the above structure, a series of high transmission bands with high reflection band intervals can be realized. Furthermore, the independent design of reflection band and transmission band can be realized through the film structure design of (LH)s.

When selecting materials, it is necessary to comprehensively consider the physical and chemical characteristics of materials, such as refractive index, transparent region, the purity, density and melting point per se., and the like, as well as the chemical reaction and matching degree with other materials, such as matching stress, thermal stability, solidity and the like. Of course, for the materials used as UV thin-films, the problem of absorption is that not only requires special attention but also is an extremely important part.

In actual production, the number of materials that can be used to prepare UV thin-film is limited. Commonly used materials are selecting from hafnium dioxide, aluminum oxide, gadolinium fluoride, magnesium fluoride, lanthanum fluoride, neodymium fluoride, and aluminum fluoride. To have an integrative consideration of material properties such as the matching between the materials, conditions for the preparation process, stability and the like, hafnium dioxide is selected as the high-refractive-index profile material, and magnesium fluoride is used as the low-refractive-index profile material.

Hafnium dioxide (HfO2 ), which is essentially a kind of ceramic material and appears like white powder, has a density of 9.68 g/cm 2 , a melting point of 2812 °C, and a molecular weight of 210.49. HfO2 is often widely used in the fields of anti-radiation, fire resistance, and catalysis because of its excellent properties such as wide band gap, high dielectric constant, corrosion resistance and high physical and chemical stability, etc. Moreover, HfO2 , which also has a high refractive index, a low extinction coefficient, high laser induced damage threshold and is thus a good material with high refractive index, is widely used in the optical industry. However, among the thousands of things in nature, there is zirconium that is born accompanied with hafnium dioxide. Further, zirconium has similar chemical properties with HfO2 , and is prone to chemical reactions. Therefore, zirc affects the performance of HfO2 , to some extent, for example, zirc will affect the purity of HfO 2

, and will strongly interfere with the absorption of HfO 2 to the ultraviolet band, especially when the wavelength of the UV band is less than 250 nm (the transparent band of zinc oxide starts at 250 nm). In addition, as an impurity, zinc oxide also indirectly or directly affects the optical properties and film quality of hafnium oxide to some extent, especially when the hafnium oxide is intended to be used in the ultraviolet band, zinc oxide has a greater impact on it. Therefore, the impurity proportion of zinc oxide in hafnium dioxide materials used in the ultraviolet band must be less than 0.5%.

Magnesium fluoride (MgF 2), which has a boiling point of 2239 °C, a melting point of 1395 °C and a transparent area of 0.21-10, is hardly soluble in water and is especially suitable for ultraviolet and infrared spectrum due to its excellent properties of crystal polarization. Reflection of incident light on lens interface can be reduced by coating the optical components with a film of magnesium fluoride (thin-film interference). Furthermore, the film of magnesium fluoride has high transmittance to ultraviolet and infrared, and the refractive index and extinction coefficient thereof are relatively low. All of the above excellent characteristics make magnesium fluoride a commonly used optical material in the ultraviolet region.

From the perspective of the difficulty of preparation, the first thing to consider when designing a film system is to simplify the structure of the film system, that is, to satisfy the optical performance requirements the filter required by minimizing the number of film layers as much as possible. And it is necessary to pay attention to maintain the films in uniform thickness when minimizing the number of the film layers. The main purpose of doing this is to prevent the monolayer film from being too thick or too thin. If the monolayer film is too thin, it may difficult to control the thickness of it accurately, which in turn increases the difficulty in its manufacturing process. While, a monolayer with high thickness may has high stress, which is easy to cause demoulding.

The basic film system G(LH)AsAIR of the interference filter is adopted by the present invention to serve as the basic film structure, wherein H represents hafnium dioxide (HfO2 ), which is a high-refractive-index profile material with both wide bandgap and high dielectric; L represents magnesium fluoride (MgF 2), which is a low-refractive-index material with good polarization; G (K9 glass) represents substrate; s represents number of cycles; and AIR represents air. The basic film system designed based on the coefficients listed above cannot fully meet the requirements of use in terms of transmittance and reflectivity. On the basis of that, the TFCalc film system design software is introduced and the simplex method is used to optimize the basic film system to obtain a more ideal design for the curve of spectrum.

It can be seen by analyzing the reflectivity formula of the monolayer dielectric film that the reflectivity of a substrate can be increased by coating the substrate which has a refractive index of nG with a high-refractive-index (n,) film in an optical thickness of With regard to central wavelength A0, the combined admittance of the monolayer film and the substrate is Y = nIns , and the reflectivity for normal incidence is:

no - 1f R ns (34) no+ n ns

It can be seen obviously that the higher the ni/ns is, the higher the reflectivity is. However, in practice, the refractive index ( nj ) of a film is limited, and the theoretically achievable maximum reflectivity of a monolayer film is less than 50%.

A higher reflectivity can be obtained by using a multilayer dielectric film which comprises a high-refractive-index layer and a low-refractive-index layer that are layered sequentially and alternately and has a thickness d for each layer ofA 0 /4 This is mainly because the light beam reflected by a film interface will return to the same place on the phase of the previous interface , thus resulting in relatively long interference. Theoretically, the reflectivity of such dielectric film system may approach 100% infinitely.

If nH represents high refractive index, nL represents low refractive index, the two

outermost layers in the dielectric film system are high-refractive-index layers, and S 2 Y = n. n, the thickness d for each layer is 4', i.e. G|H(LH)AsIA, and nL s can

be obtained for a center wavelength '0 , and thus the reflectivity and transmittance

to a light beam with the central wavelength A0 and at normal incidence are:

R = '-nL f S (35) 2's H 1+ nH

_ nL nS

>2S

T=4 nL S(36) n n

It can be seen that the greater the nu L or the more layers (2S+1), the greater the value of R and the smaller the value of T. After analysis, following can be concluded: when the number of layers in the film system is greater than 12, the reflectivity of it to the band of 210-260 nm reaches 95%, and when the number of layers therein is increased to 16, the reflectivity cannot be improved significantly by further increasing the number of layers. In theory, the more layers there are in the film system, the closer the reflectivity thereof will be to the value of 1. However, with the increase in the number of layers in the film system, the ripple number of oscillation to the band of 280-700 nm is increasing, resulting that the transmittance to this band is getting lower and lower. Therefore, a dielectric film system with 13 layers of film is selected after comprehensive consideration, and the structure thereof is G|H(LH)A6AIR.

In actual preparation for a film system, in addition to the influence of the number of layers on the film-forming performance, influence of the thickness of the film thereon should also be considered. If the total thickness of the film system is too thick, the sensitivity of some the film layer therein will also increase, resulting in greater overall fluctuations in the film system, and the error generated during the preparation will increase exponentially as the number of layers increases. In order to minimize the influence described above, a physical thickness satisfying the demand is found out through studying the influence of changing the physical thickness of the high-refractive-index profile material or the low-refractive-index profile material on the reflectivity to UV and the transmission to visible light under the condition of normal incidence of light and based on the structure of the film system of G|H(LH)A6AIR.

Based on the structure of the film system of G|H(LH)A^6AIR and without changing the physical thickness (dL =47 nm) of the low-refractive-index profile material of magnesium fluoride and using TFCalc film system design software, the reflectivity and the transmittance of the film system to the band of 200-800nm are calculated by designing the high-refractive-index profile material of hafnium dioxide to have a minimum physical thickness of 20nm and an interval thickness of 5 nm. The results are shown in table 1:

Thickness of the film (nm) 20 25 30 35 40 Mean reflectivity (210-260 nm) 56.90% 93.82% 91.30% 64.18% 32.57% Mean transmittance (280-700 94.27% 92.30% 90.10% 84.87% 79.24% nm) Table 1: Comparison of mean reflectivity to 210-260 nm and mean transmittance to 280-700

nm of the film system having different thicknesses of hafnium dioxide.

It is found that, in the band of 210-260 nm, the central wavelength of the reflection band gradually shifts to the long-wave direction along with the increase of the thickness of the film. Moreover, it is shown in table 1 that the mean reflectivity increases firstly and then decreases, and the mean reflectivity for the thickness of 25 nm and 30 nm is much higher than that for other thicknesses, which reaches 90%. However, in the band of 280-700 nm, much more ripple number of oscillation is observed for the thickness of 30 nm than that for the thickness of 25 nm, and as also shown in table 1, the mean transmittance for the thickness of 30 nm decreases obviously. Therefore, 25nm is selected as the physical thickness for high-refractive-index profile material of hafnium dioxide.

Based on the structure of the film system of G|H(LH)A^6AIR and without changing the physical thickness (dL=33 nm) of the high-refractive-index profile material of hafnium dioxide and using TFCalc film system design software, the reflectivity and the transmittance of the film system to the band of 200-800nm are calculated by designing the low-refractive-index profile material of magnesium fluoride to have a minimum physical thickness of 35nm and an interval thickness of 5 nm. The results are shown in table 2:

Thickness of the film (nm) 35 40 45 50 55 Mean reflectivity (210-260 nm) 92.20% 96.18% 84.05% 66.97% 47.32% Mean transmittance (280-700 nm) 90.15% 90.45% 88.58% 85.80% 82.73%

Table 2: Comparison of mean reflectivity to 210-260 nm and mean transmittance to 280-700

nm of the film system having different thicknesses of magnesium fluoride.

It can be seen from table 2 that the central wavelength of the reflection band gradually shifts to the long-wave direction along with the increase of the thickness of the film. In the band of 210-260 nm, the mean reflectivity shown by the two curves of spectrum for the thickness of 25 nm and 30 nm reaches 92%. However, in the band of 280-700 nm, much more ripple number of oscillation is observed for the thickness of 35 nm than that for the thickness of 40 nm, and as also shown in table 2, the mean transmittance for the thickness of 40 nm, which is higher than that for the thickness of 35 nm, is 90.45%. Therefore, 40 nm is selected as the physical thickness of low-refractive-index profile material of magnesium fluoride.

The structure of the film system can be determined to G|H(LH)A^6AIR through the above research, wherein the thickness of H is 25 nm and the thickness of L is 40 nm. Furthermore, the film system is input into TFCalc film system design software and optimized using simplex method, and table 3 is finally obtained through making comparison with the reflectivity, the transmittance and the thickness of each layer of film before and after the optimization.

Structure of the film HfO2/MgF2/HfO2/MgF2/HfO2/MgF2/HfO2/MgF2/HfO2/MgF2/HfO2/MgF2/HfO2 system

orti izathon 20.00/40.00/20.00/40.00/20.00/40.00/20.00/40.00/20.00/40.00/20.00/40.00/20.00

opimizat ion 23.00/39.00/31.00/40.00/30.00/45.00/29.00/44.00/32.00/40. 00/30.00/50.00/17.00

Table 3: Comparison of thicknesses of films (nm) before and after the optimization

After optimization, the structure of the film system is (G0.69H 0.83L 0.96H 0.86L 0.93H 0.96L 0.89H 0.95L 0.97H 0.86L 0.94H 1.07L 0.52HIAIR). It is a non-periodic film having a total physical thickness of 450nm and a total of 13 layers. And with regard to the theoretical reflectivity and transmittance finally obtained, the mean reflectivity to the band range of 210-260 nm is 95.23%, and the mean transmittance to the band of 280 - 700 nm is 96.68%.

For the all-dielectric ultraviolet filter film of the present invention, the reflectivity of it increases gradually, while the transmittance decreases gradually with the increase of the number of layers therein. It is also found that the reflectivity of the film system with an odd number of layers is always greater than that with an even number of layers. And the reflectivity of the film system to the band of 210-260 nm reaches 95% when the number of layers therein is greater than 12. Considering comprehensively, a structure with 13 layers of films is finally selected as the dielectric film system, and structure of this film system is GH(LH)A^6AIR.

In the band of 210-260 nm, the center wavelength of the reflection band gradually shifts to the long wave direction with the increase of film thickness; and in the band range of 280-700 nm, the transmittance of the high-refractive-index profile material (hafnium dioxide) decreases gradually and that of the low-refractive-index profile material (magnesium fluoride) increases gradually along with the increase of film thickness. Through investigation and analysis, 25 nm is finally selected as the physical thickness for the high-refractive-index profile material of hafnium dioxide and 40 nm is finally selected as the physical thickness for the low-refractive-index profile material of magnesium fluoride.

Finally, an all-dielectric ultraviolet filter film is designed after making optimization by the simplex method of the TFCalc film system design software, and the mean reflectivity of the all-dielectric ultraviolet filter film to the band range of 210-260 nm is 95.23%, and the mean transmittance to the band of 280 - 700 nm is 96.68%. The structure of the film system in the all-dielectric ultraviolet filter film is (G|0.68H 0.82L 0.97H 0.85L 0.93H 0.97L 0.88H 0.95L 0.98H 0.84L 0.94H 1.11L 0.47HIAIR), which is a non-periodic film having a total physical thickness of 450nm.

The above embodiments of the present invention are described in detail in combination with the drawings. It will be appreciated by those skilled in the art that the embodiments provided are only used to illustrate the present invention, rather than limiting the scope of the present invention in any way. Those skilled in the art can make various changes and variations according to the present invention, which are within the protection scope of the present invention without departing from the spirit of the same.

Claims

What is claimed is: 1. An all-dielectric ultraviolet filter film, which is characterized in that the all-dielectric ultraviolet filter film is composed of a glass serving as a substrate, and two types of profile materials with different refractive indexes which are layered sequentially and alternately; wherein said two types of profile materials with different refractive indexes are a high-refractive-index profile material with both wide bandgap and high dielectric and a low-refractive-index profile material with good polarization.
2. The all-dielectric ultraviolet filter film according to Claim 1, which is characterized in that said high-refractive-index profile material is hafnium dioxide, and said low-refractive-index profile material is magnesium fluoride.
3. The all-dielectric ultraviolet filter film according to Claim 2, which is characterized in that the number of layers of high-refractive-index profile material and low-refractive-index profile material that alternately layered is set to 13, of which 7 are layers of hafnium dioxide, and a layer of magnesium fluoride is layered between every two layers of hafnium dioxide.
4. The all-dielectric ultraviolet filter film according to Claim 2, which is characterized in that thickness of the thin-film of hafnium dioxide is set to 25 nm, and thickness of the thin-film of magnesium fluoride is set to 40 nm.