Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates

Multilayer antireflection coatings have been modeled in visible and IR (3-5μm) bands to reduce reflectance from glass, germanium (Ge), silicon (Si) and zinc selenide (ZnSe) substrates. The transmittance of bare glass substrate is around 95% whereas for Ge 64%, Si 70%, ZnSe 84%. Theses values are enh...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Datum:2003
Hauptverfasser: Asghar, M.H., Khan, M.B., Naseem, S.
Format: Artikel
Sprache:English
Veröffentlicht: Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України 2003
Schriftenreihe:Semiconductor Physics Quantum Electronics & Optoelectronics
Online Zugang:http://dspace.nbuv.gov.ua/handle/123456789/118077
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Назва журналу:Digital Library of Periodicals of National Academy of Sciences of Ukraine
Zitieren:Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates / M.H. Asghar, M.B. Khan, S. Naseem // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 508-513. — Бібліогр.: 19 назв. — англ.

Institution

Digital Library of Periodicals of National Academy of Sciences of Ukraine
id irk-123456789-118077
record_format dspace
spelling irk-123456789-1180772017-05-29T03:05:06Z Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates Asghar, M.H. Khan, M.B. Naseem, S. Multilayer antireflection coatings have been modeled in visible and IR (3-5μm) bands to reduce reflectance from glass, germanium (Ge), silicon (Si) and zinc selenide (ZnSe) substrates. The transmittance of bare glass substrate is around 95% whereas for Ge 64%, Si 70%, ZnSe 84%. Theses values are enhanced reasonably by the application of multilayers films. Starting from a single layer, the layers have been added systematically forming multilayer structures to reduce reflectance considerably with each increasing layer. The designed layers are optimized for their performance by varying their thickness and refractive indices. The analysis of these modals has shown that the proposed multilayer structures are very effective in reducing the reflectance for all the substrates in two spectra. 2003 Article Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates / M.H. Asghar, M.B. Khan, S. Naseem // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 508-513. — Бібліогр.: 19 назв. — англ. 1560-8034 PACS: 42.79.Wc, 78.20.-e http://dspace.nbuv.gov.ua/handle/123456789/118077 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
description Multilayer antireflection coatings have been modeled in visible and IR (3-5μm) bands to reduce reflectance from glass, germanium (Ge), silicon (Si) and zinc selenide (ZnSe) substrates. The transmittance of bare glass substrate is around 95% whereas for Ge 64%, Si 70%, ZnSe 84%. Theses values are enhanced reasonably by the application of multilayers films. Starting from a single layer, the layers have been added systematically forming multilayer structures to reduce reflectance considerably with each increasing layer. The designed layers are optimized for their performance by varying their thickness and refractive indices. The analysis of these modals has shown that the proposed multilayer structures are very effective in reducing the reflectance for all the substrates in two spectra.
format Article
author Asghar, M.H.
Khan, M.B.
Naseem, S.
spellingShingle Asghar, M.H.
Khan, M.B.
Naseem, S.
Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
Semiconductor Physics Quantum Electronics & Optoelectronics
author_facet Asghar, M.H.
Khan, M.B.
Naseem, S.
author_sort Asghar, M.H.
title Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
title_short Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
title_full Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
title_fullStr Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
title_full_unstemmed Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
title_sort modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates
publisher Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
publishDate 2003
url http://dspace.nbuv.gov.ua/handle/123456789/118077
citation_txt Modeling high performance multilayer antireflection coatings for visible and infrared (3-5μm) substrates / M.H. Asghar, M.B. Khan, S. Naseem // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 508-513. — Бібліогр.: 19 назв. — англ.
series Semiconductor Physics Quantum Electronics & Optoelectronics
work_keys_str_mv AT asgharmh modelinghighperformancemultilayerantireflectioncoatingsforvisibleandinfrared35mmsubstrates
AT khanmb modelinghighperformancemultilayerantireflectioncoatingsforvisibleandinfrared35mmsubstrates
AT naseems modelinghighperformancemultilayerantireflectioncoatingsforvisibleandinfrared35mmsubstrates
first_indexed 2025-07-08T13:19:34Z
last_indexed 2025-07-08T13:19:34Z
_version_ 1837084996267933696
fulltext Semiconductor Physics, Quantum Electronics & Optoelectronics. 2003. V. 6, N 4. P. 508-513. © 2003, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine508 PACS: 42.79.Wc, 78.20.�e Modeling high performance multilayer antireflection coatings for visible and infrared (3�5µµµµµm) substrates M.H. Asghar1, M.B. Khan1, and S. Naseem2 1Advanced Engineering Research Organization (AERO), Wah Cantt. Pakistan. 2Centre for Solid State Physics, Punjab University, Lahore. Pakistan. 1E-mail: mha_19@yahoo.com Abstract. Multilayer antireflection coatings have been modeled in visible and IR (3�5µm) bands to reduce reflectance from glass, germanium (Ge), silicon (Si) and zinc selenide (ZnSe) substrates. The transmittance of bare glass substrate is around 95% whereas for Ge 64%, Si 70%, ZnSe 84%. Theses values are enhanced reasonably by the application of multilayers films. Starting from a single layer, the layers have been added systematically forming multilayer structures to reduce reflectance considerably with each increasing layer. The designed layers are optimized for their performance by varying their thickness and refractive indices. The analysis of these modals has shown that the proposed multilayer structures are very effective in reducing the reflectance for all the substrates in two spectra. Keywords: antireflection coatings, multilayers. Paper received 21.07.03; revised manuscript received 02.01.04; accepted for publication 11.12.03. 1. Introduction Antireflection coatings have had the greatest impact on optics, and even today, in sheer volume of production, they still exceed all the other types of coatings. In some applications antireflection coatings are required for the reduction of surface reflections. In other not only reflec- tion is reduced but also transmittance is increased con- siderably. As it is a known fact that radiations incident upon the surface of an optical material is separated into reflected, transmitted, absorbed and scattered fractions. The fraction of available energy that is distributed amongst these is determined by the indices of refraction. Antireflection coatings can range from a single layer having virtually zero reflectance at just one wavelength, to a multilayer system of many layers having virtually zero reflectance over a wide spectral range. 2. Theory of antireflection coatings The simplest antireflection coating is a single layer de- posited on a substrate [1]. To achieve antireflection prop- erties, this layer depends on the cancellation of light at the upper and lower of the two surfaces. Assuming the refractive index of air as n0, film as n1 and that of substrate as ns, then in order to cancel the two reflected beams the intensity of the radiation reflected at the upper and lower surfaces of the coating should be equal which means that the ratios of the refractive indices at each boundary should be equal, that is: n0 / n1 = n1/ ns, with film thickness, n1t1 = λ/4 This configuration will give only one minimum in the re- flectance profile. For more minima, more layers are re- quired. The same theory is used to calculate the expres- sions for two- and three- layers antireflection coatings [2]. Similarly, multiple layers are used to achieve more minima in reflectance profile for broadband antireflection coat- ings [3, 4]. We have modeled multilayer antireflection coat- ings for glass and infrared substrates. These coatings are modeled at a design wavelength of λ0 = 0.55 µm for vis- ible and λ0 = 4µm for infrared substrates, respectively. Moreover all the designs have been optimized by varying the individual layer refractive index and thickness. 2.1 Multilayer matrix calculations Matrix calculations determine the spectral transmittance and reflectance profile for multilayer structures on a M.H. Asghar et al.: Modeling high performance multilayer antireflection coatings for... 509SQO, 6(4), 2003 substrate. Consider a loss free multilayer design, nor- mally incident radiations, and assume that films are op- tically homogenous. The electric field vector (Em�1) and magnetic field and the magnetic field vector (Hm�1) at the incident boundary of a film are related to the electric field vector Em and magnetic field vector Hm vectors at the boundary of the adjacent film by the product of the following matrices per layer. The matrix is calculated at each boundary throughout the multilayer as the magni- tude of electric and magnetic field vectors alter with the properties of the layer [5]. Application of the appropri- ate boundary conditions between each layer requires that the tangential components of E and H vectors are con- tinuous across each boundary to the equations of wave propagation. Let the electric and magnetic field vectors of the wave traveling in the direction of the incidence are denoted by symbol �+�, and those waves traveling in the opposite direction by the symbol ���. At the interface of mth layer, the tangential component of E and H are given as Em = Em + + Em � Hm/H1 = Em/E1 Hm = Em × H1/E1 (1) Neglecting the common phase factors, and where Em and Hm represent the resultants then:           +=+ m m m E E H H E 1 1 2/1 (2)           +−=− m m m E E H H E 1 1 2/1 (3)       +=+ 1 12/1 E HE HH m mm (4)       −=− 1 12/1 E HE HH m mm (5) The fields at other interfaces m�1 are similar to equa- tions 2�5 at the same instant of time and a position with identical x and y coordinates. These can be determined by multiplying by phase difference in z direction given by eiδ or e�iδ where: λ θπ δ 1 cos2 1dN = (6) And θ1 may be complex. The values of E and H at this interface are therefore: δδ η i m mi mm eE H eEE         +== + − + 1 1 2/1 (7) δδ η i m mi mm eE H eEE       +−== −− − − 1 1 2/1 (8) [ ] δδ η i mm i mm eEHeHH 11 2/1 +== + − + (9) [ ] δδ η i mm i mm eEHeHH −−− − − −== 11 2/1 (10) Where η1 is the tilted optical admittance given by η1 = H1/E1 Now Em�1= E+ m�1 + E� m�1 1 1 sin cos η δ δ i HEE mmm +=− δ η δ cos sin 1 1 mmm H i EH +=− This can be written in matrix form as:             =      − − m m m m H E i i H E δδη ηδδ cossin /)sin(cos 1 1 1 1 Solving the above given expression [6], the matrix expression for single layer is:       = DiC iBA M1 Where: cos δm = A = D, isinδm/ηm = B, isinδmηm= C For two successive layers: Layer 2 Layer 1             = 11 11 23 22 DiC iBA DiC iBA M (15) After multiplication we have:       +− + +      + − = 1212 1212 1212 1212 DDBC DiBiBA iCDAiC CBAA M (16) Let AA = A2A1 � B2C1, BB = A2iB1 + B2iD1, CC = = iÑ1A1 + D2iA1, DD = Ñ2B1 + D2D1 Therefore matrix is written as:       = DDCC BBAA M (17) Therefore, for a multilayer containing q-layers:         =      ∏ = q q q m m H E M H E 10 0 (18) 510 SQO, 6(4), 2003 M.H. Asghar et al.: Modeling high performance multilayer antireflection coatings for... The loss-free transmittance and reflectance for the multilayer assembly can be calculated from this product matrix by: ( ) ( )2 0 2 0 0 _ 4 CCBBnnDDnAAn nn T ss s q +++ = (19) ( ) ( ) ( ) ( )2 0 2 0 2 0 2 0 CCBBnnDDnAAn CCBBnnDDnAAn R ss ss q +++ −+− = (20) The reflectance, transmittance and absorptance are then related by R + T + A = 1. The solution of this ma- trix theory is a laborious job for multilayer coatings. Based on the matrix theory, we have developed a soft- ware program to design and simulate the performance of multilayer coatings [7]. 3. Modeling and analysis Thin film materials are required to have certain charac- teristics to become a potential candidate for multilayer structures. This includes high transparency, homogenei- ty, high packing density, good adhesion, low stress, hard- ness and ability to survive in different environmental and deposition conditions [8, 9]. These materials are then used to reduce reflection from the surfaces, which are basi- cally caused by the sharp variation of the refractive in- dex at the incident medium-substrate interface. Multi- layer coating structures based on those materials have wide band of applications in electronics, optoelectronics, optics and optoelectronics equipments. (A) visible region: The reflectance from the surface of bare glass substrate is 4.2%. Starting from single layer reflectance is reduced by application of five layers. The design data and reflectance values for all these designs are given in table 1. Initially single layer of MgF2 has been employed to reduce the magnitude of this reflect- ance. The maximum reflectance from the substrate has reduced from 4.2% to 2.2%, with reduction in average reflectance to 1.65%. For a single layer coating only one minimum is achievable. Two layer coating comprising MgF2 and Al2O3 (Air/MgF2/Al2O3/Glass) has been de- signed to further reduce the reflectance obtained by sing- le layer configuration. In this configuration we have two distinct minima of reflection as compared to one for sin- gle layer. Earlier we had a maximum reflectance of 2.26%, which has reduced to 1.77% by the addition of second layer. Further the average reflectance has gone down to 1.02%. The reflectance profile of three-layer coating comprising of SiO2, HfO2, and MgO (Air/SiO2/ HfO2/MgO/Glass) is more effective than the previous two designs. SiO2 is very low index material with a value of 1.46 in the visible spectrum, and HfO2 has a moderately high index of nearly 2.0 with a good environmental du- rability [9]. The maximum reflectance from the substrate has further reduced to 1.37% with average reflectance to 0.91%. Therefore, the performance of the coating is fur- ther improved by the addition of third layer. The reflect- ance is further reduced by four-layer design comprising MgF2, ZrO2, Al2O3 and MgF2 (Air/MgF2/ZrO2/Al2O3/ MgF2/Glass). A slight increase in reflectance at the edges of the band can be seen, but the important feature of this design is the zero reflectance at two spectral points. In this case maximum and average reflectance has appreci- ably reduced to 1.28% and 0.45%, respectively. On the application of the fifth layer in the model (Air/MgF2/ ZrO2/Al2O3/Cryolite/MgF2/Glass) maximum and aver- age reflectance further reduced to 1.11% and 0.42% re- spectively. The combined reflectance plot of the five con- figurations is shown in Fig. 1. This application of multi- ple layers encourages the use of multi-layers to achieve wide transmission bands. By increasing number of lay- Table 1. Design data and reflectance values for all configurations on glass. Configurations Material Refractive Index (n) Thickness (µm) Rp(%) Rave(%) Single Layer MgF2 1.38 0.099  2.26  1.65 Two-Layers MgF2 1.38 0.099  1.77  1.02 Al2 O3 1.62 0.169 Three-Layers SiO2 1.46 0.087  1.37  0.91 HfO2 1.98 0.128 MgO 1.73 0.073 Four-Layers MgF2 1.38 0.090  1.28  0.45 ZrO2 2.05 0.121 Al2O3 1.62 0.077 MgF2 1.38 0.181 Five Layers MgF2 1.38 0.094  1.11  0.42 ZrO2 2.05 0.126 Al2O3 1.62 0.080 Cryolite 1.35 0.096 MgF2 1.38 0.094 M.H. Asghar et al.: Modeling high performance multilayer antireflection coatings for... 511SQO, 6(4), 2003 ers and optimizing their index and thickness [11], the reflectance from the substrate can be reduced to a rea- sonably low value. In other words the transmittance through the substrate can be increased substantially. It should be noted from Fig. 1 that decrease is pretty sharp up to the addition of fourth layer. How ever, the magni- tude of reduction in reflectance with the addition of fifth layer is very small. This may suggest the threshold limit for multilayer configuration in which performance re- quirements are not very stringent. (B) infrared region: Ge, Si and ZnSe have been used as substrates material as they are commonly used in 3�5µm band for many optical and electro-optical applications [12�17]. All these substrates exhibit a very high reflect- ance value in the said spectrum. In most of the applica- tions, this high value of reflectance is not acceptable as it reduces the total energy reaching the detector surface with every increasing optical component in the system or device. Therefore, it is necessary to reduce their surface reflectance by appling ARC�s. The materials used as film layers are ZrO2, Si, SiO, CdTe, BaF2, ZnSe, Y2O3 and SiO2, LaF3 and YF2. All these materials are suitable for antireflection films in the desired region of wavelength [18]. The reflectance of bare germanium substrate in 3�5µm is 36%. Multilayer coatings can be used to reduce this value to an appreciably low level [19]. We have modeled such coatings on germanium substrate at a design wave- length of 4µm. The process starts from a single layer model, and the layers are increased to reduce the value of maximum and average reflectance over the desired band. Table 2 shows the model data and calculated values of maximum and average reflectance over the entire band for a single layer modal. The data shows that the maxi- mum and average value of reflectance has decreased form 36% to 12.36% and 2.97% respectively. The combined reflectance plot of all the four designs is shown in Fig. 2. We have adopted an approach of smooth transition of layer indices with every increasing layer in all models, starting from incidence medium right up to the substrate. This approach helps in avoiding sharp interfaces between the layers, helping in smooth reduction of reflectance from the surface of the substrate. The Fig. 2 clearly shows the reduction of peak and average values with increasing number of layers. The reflectance from bare silicon substrate surface is 30%. This value is lower as compared to the germanium, as it has got a lower refractive index in the given spec- trum. Similar procedure of layer addition has been em- ployed to model and analyze multilayer structures for reducing reflectance from the substrate. Table 3 shows the model data with maximum and average values of re- flectance for all configurations. Fig. 3 shows the com- bined plots for one, two, three and four layer configura- 3 0 3.4 5 10 15 20 25 30 35 40 3.8 4.2 4.6 5 Wavelength, mµ Single layer Bare substrate Two layers Three layers R e fl ec ta n ce , % Four layers Fig. 2. Combined reflectance profiles for all configurations on germanium. 3 0 3.4 5 10 15 20 25 30 35 3.8 4.2 4.6 5 Wavelength, mµ Single layer Bare substrate Two layers Three layers R ef le ct a n c e, % Four layers Fig. 3. Combined reflectance profiles for all configurations on silicon. 0.4 0.45 0.5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0.55 0.6 0.65 Wavelength, mµ Single layer Bare substrate Two layers Three layers A v e r a g e r ef le ct io n , % Four layers Five layers Fig. 1. Combined reflectance profiles for all configurations on glass. 512 SQO, 6(4), 2003 M.H. Asghar et al.: Modeling high performance multilayer antireflection coatings for... tions. The trend in the reduction of reflectance for all the configurations is similar to that for germanium. How- ever, in this case the performance for three and four layer configurations is even better and the curves are more flat and comparatively closer to the horizontal axis. Only two materials are used in four layers configuration. This shows that proper optimization not only helps in getting good performances but also tend to reduce unnecessary variety of materials which is very critical in manufactur- ing process. The reflectance of bare ZnSe substrate is 16.81%. Multilayer antireflection coatings are employed on the substrate to drastically lower this value. Table 4 shows the model data and calculated values of maximum and average reflectance for single, two, three and four layer structures to reduce the reflectance from the substrate. Fig. 4 shows the combined plots of all the configura- tions. The sharp fall in the reflectance values is observed, even with single layer coating configuration due to low index under lying surface. Table 2. Design data and reflectance values for all configurations on germanium. Configurations Material Refractive Index (n) Thickness (µm) Rp(%) Rave(%) Single Layer ZrO2 2.05 0.487  12.36  2.97 Two-Layers SiO 1.6 0.625  4.19  2.67 CdTe 2.6 0.384 Three-Layers SiO 1.6 0.625  2.37  1.15 CdTe 2.6 0.384 Si 3.42 0.292 Four-Layers BaF2 1.3 0.769  2.37  0.487 ZrO2 2.05 0.487 CdTe 2.6 0.375 Si 3.42 0.292 Table 3. Design data and reflectance values for all configurations on silicon. Configurations Material Refractive Index (n) Thickness (µm) Rp(%) Rave(%) Single Layer LaF3 1.6 0.632 11.17  4.46 Two-Layers MgF2 1.38 0.679  4.64  3.26 ZrO2 2.05 0.457 Three-Layers MgF2 1.38 0.724  2.35  1.17 ZrO2 2.05 0.487 CdTe 2.64 0.378 Four-Layers MgF2 1.38 0.679  0.419  0.150 ZnSe 2.39 0.784 MgF2 1.38 1.3587 ZnSe 2.39 0.392 3 0 3.4 4 8 12 16 20 3.8 4.2 4.6 5 Wavelength, mµ Single layer Bare substrate Two layers Three layers R ef le ct a n c e, % Four layers Fig. 4. Combined reflectance profiles for all configurations on ZnSe. M.H. Asghar et al.: Modeling high performance multilayer antireflection coatings for... 513SQO, 6(4), 2003 4. Conclusions Multilayer antireflection coatings in visible and IR (3� 5µm) have been modeled, starting from single layer up to five layer configuration. The performance of each suc- cessive configuration has been optimized in order to dem- onstrate efficient use of multiple layers for antireflection applications. The analysis of these designs reveal that by increasing number of layers in a judicious manner with suitable refractive indices and thickness, the maximum and average reflectance from the surface of the substrate can be decreased to very low magnitudes . References 1. J. D. Rancourt, Optical thin films: User�s handbook, SPIE Optical Engineering Press, p.8, (1996). 2. A. Thelen, Design of optical interference coatings, McGraw- Hill, p 91, (1989). 3. R. Willey, Optical thin films and applications // Proc. SPIE 1270, p. 36-38, (1990). 4. R. Willey, Realization of a very broad band AR coating // Proc. Soc. Vac. Coaters Techon., 33, p. 232, (1990). 5. H.M. Liddell, Computer aided techniques for the design of multilayer filters, Adam Hilger Ltd, ISBN 0-85274-233-9, p.2, (1981). 6. G.J. Hawkins, Spectral Characteristics of Infrared Optical Materials, Ph.D. Theses, University of Reading, UK. p.89, (1998) 7. M.H. Asghar, M.B. Khan and S. Naseem, Proc. 2nd Interna- tional Bhurban Conference on Applied Sciences and Tech- nology, Pakistan, (2003) In press. 8. H. Selhofer, E. Ritter and R. Linsbod // App. Opt., 41, p.756 (2002). 9. J.M. Bennett, E. Pelletier, G. Albrand, J.P. Borgogno, B. Lazarides, C.K. Carniglia, R.A. Schmell, T.A. Allen, T.T. Hart, K.H. Guenther and A. Saxer // App. Opt., 28, p.3303, (1989). 10. R. Willey, Comparison of two broad beam/ion plasma sources for optical coatings, // Vacuum Coating and Technology, 3, p.30, (2002). 11. H A. Macleod, Thin Film Optical Filters, IOP, Institute of Physics Publishing, Bristol and Philadelphia, p.126, (2001). 12. G. J. Hawkins, Spectral Characteristics of Infrared Optical Materials, Ph.D. Theses, University of Reading, UK, p.89, (1998). 13. R.R. Willey, infrared System and Components III, SPIE 1050, (1989). 14. A. Ghosh, P. Kant, P. K. Bandyopadhyay, P. Chandra, O.P. Nijihawan, // Infrared Physics & Technology, 40, p. 49, (1999). 15. J.A. Dobrowlski and F. Ho // App. Opt., 21, p.288 (1982). 16. C. Cole, �Broadband Antireflection Coatings for Spaceflight Optics, Ph.D. Theses, University of Readig, UK, p.21, (1995). 17. Y.A. Zagoruiko, O.A. Fedorenko, N.O. Kovalenko and P.V. Mateychenko, // Semiconductor Physics, Quantum Elec- tronics & Optoelectronics, 3, p.247, (2000). 18. G. Hawkins, R. Hunneman, R. Sherwood and B. M. Barrett, SPIE Proceeding �Specialized Optical Developments in As- tronomy�, 4842, p.43, (2002). 19. H.A. Macleod, Thin Film Optical Filters, IOP, Institute of Physics Publishing, Bristol and Philadelphia (2001). Table 4. Design data and reflectance values for all configurations on zinc selenide. Configurations Material Refractive Index (n) Thickness (µm) Rp(%) Rave(%) Single Layer YF2 1.4 0.714  5.47  1.99 Two-Layers BaF2 1.3 0.769  2.21  1.49 Y2O3 1.73 0.578 Three-Layers BaF2 1.3 0.769  1.23  0.54 Y2O3 1.73 0.578 ZrO2 2.05 0.487 Four-Layers SiO2 1.4 0.664  0.60  0.34 ZrO2 2.05 0.914 Y2O3 1.73 0.541 ZrO2 2.05 0.457