2009) 3( 22مجلة ابن الھیثم للعلوم الصرفة والتطبیقیة المجلد رمایكرو مت )5 -3(ة لمنطقة األشعة تحت الحمراء تحضیر نوافذ بصری باستخدام مادة أوكسید األلمنیوم ، لیث ناظم عباس، سوزان علي حسن*عبد الرسول مجید بهاءإلطیف، خضیرعبد الحسین والتكنولوجیاوزارة العلوم الجامعة المستنصریة ،كلیة التربیة ، قسم الفیزیاء * الخالصة تم في هذا البحث تحضیر نوافذ بصریة تعمل ضمن الطول الموجي لمدى األشعة تحت الحمراء باستعمال طالء مایكرو ) 5- 3(بحیث یغطي النافذة الجویة (ZnSe)على قواعد من (Al2O3)غیر عاكس من مادة أوكسید األلمنیوم عند الطول % 97فباستعمال ثمان طبقات من أوكسید األلمنیوم وعلى جانبي القاعدة كانت أعظم نفاذیة بحدود . متر .مایكرومتر 4.4الموجي IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL.22 (3) 2009 Preparation of Optical Window in the Infrared Region (3- 5) µm Using Al2O3 Material A.K. Iltaif, B.A.Al-Hilli*, L.N.Abbas, S.A.Hasan Ministry of Science and Technology * Department of Phsics , College of Education, Al-Mustansiriyah University Abstract In this work optical window for infrared region was prepared by using Aluminum Oxide (Al2O3)material as antireflection coating on ZnSe substrate which covers the atmospheric window 3-5µm. the maximum transition was 97% at a wavelength 0f 4.4µm. Introduction Antireflection phenomenon was first recognized by Raleigh and Fraunhofer in the 19th century as a spontaneous process on atmospherically tarnished lenses (1). In 1934 Bauer (2) deduced that the reduction in reflectance is primarily due to interference phenomena. This phenomenon has been put in to good use in 1930 when the process of vacuum evaporation borrowed from the electronic industry, enabled the controlled industrial deposition to be introduced as what is subsequently called "antireflection coating (ARC)(3)".Nagendra and Mohan studied the antireflection coating phenomenon by the deposition of more than one of thin film layers in series(4). Grebenshchikov et al. (5) have published in 1946 the first book in antireflection coating of optical surfaces including the multilayer coating. ARC's enter new stage when characteristic matrix theory is submitted and discussed by Abeles (6) in 1950. Hrepin (7) and Epstein (8) put mathematical equations for designing optical filters. Also, Wellford (9) described a design of single layer ARC's with the aid of "Vector method". In all the optoelectronic devices and systems the optical windows can be considered as an optical filters for a specified spectral region. In order to minimize the losing power through reflection, it is useful to use the ARC technique for these windows (10). Novel design procedure of broad band multilayer ARC for optical and optoelectronic devices were deduced by (11). The aim of this work is to manufacture infrared optical windows by using multilayer ARC's (Al2O3) deposited on ZnSe substrates. Theory: When light incident from media (no) with angle (Φo) on antireflection coating film (n1) deposited on substrate of refractive index (ns). We obtain Rmax (maximum reflectivity and Rmin (minimum reflectivity) if (12): ns≥n1≥no ���� = � (�����) (�����) � � �ℎ�� ���� = � � , �, …… [1] IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL.22 (3) 2009 ���� = � ��� ������� ��� ������� � � �ℎ�� ���� = � � , �� � ,…… [2] Where: n1d1 is the optical thickness of the film λ is wavelength of the incident light � = �2� �� ����� cos� Phase difference, d1 is a film thickness Thin film calculations (TF-CALC) program package was used to calculate the percentage of transmission and reflection of coating layers. According to our calculations, the following design was used to get a high transmission on ZnSe substrate: (L8HL8) L: is a layer with a low refractive index such as Al2O3 H: is a layer with a high refractive index such as ZnSe From this design the maximum transmission was about 82.3% at the wavelength of 4.55µm for one face coating as shown in Fig. (1) And about 99.8% for both faces coating as shown in Fig. (2). It is clear from these figures that, the importance of using antireflection coating on both sides of substrate is to get a high transmission and a minimum reflection. Experiment The type and surface features of the substrate have a great influence on the properties of the deposition films into the substrate. In this work ZnSe substrate were used, the polishing machine and grinding for these substrates were performed by using a polishing machine type TF-250 from (TEANWARTZ CO., Germany), and using diamond pastes with different smooth degrees (0.25, 1, 3, 9)µm for each smooth degree has a special polishing cloth. Then, these substrates were chemically cleaned as follows: 1- Using chemical solutions such as methanol then insert it in the ultrasonic device for 15 min. 2- ZnSe were immersed in 2.5% HF then rinsed with demonized water and immersed in methanol, substrates where then dried with special smoothing papers. The Al2O3 with purity 99.999% was deposited on both sides of ZnSe substrates by using thermal evaporation machine type (Varian). The film thickness was measured by crystal monitoring which work with mechanical shutter to stop the deposition process when we reach the desired thickness. The thickness for each Al2O3 layer was 195nm. IBN AL- HAITHAM J. FOR P URE & APPL. SCI VOL.22 (3) 2009 The transmission for these ZnSe substrates without coating were measured by using Fourier Transform Infrared (FT-IR) spectrophotometer as shown in Fig. (3). the maximum transmission was 72%. After that, these ZnSe substrates and high purity Al2O3 material were placed in a vacuum coating machine having electron gun and operating voltage 6KV under vacuum of 10-5 mbar. Results 1- The maximum transmission was about 82% for ZnSe window after coating with eight layers of Al2O3 ARC's for one face of substrate (thickness of each layer = 195 nm) as shown in Fig.(4). 2- The transmission became 97% for these ZnSe substrates after coating with eight layers of Al2O3 ARC's on both faces of the substrate as shown in Fig.(5). Conclusion From the previous results it is possible to fabricate optical window with maximum transmission of 97% by using eight layers of Al2O3 ARC's on both faces of ZnSe substrate. These results are in agreement with the theoretical results deduced from (TF-CALC) program package. References 1- Macleod, H.A., (1968),"Thin Film Optical Filters", 2 nd ed. McGraw- Hill Co., N.Y. 2- Bauer, G. (1934), "Thin Film Phenomena", Ann.Phys.Lbz. 5th series 19: 434. 3- Knittl, Z. (1989), SPIE Proceeding, 401, 1. 4- Nagendra, C.L. and Mohan, S. (1989), Infra.Phys. 2:29-195. 5- Grebenshchikov, I.V.; Vlasov, L.G. and Suikovskaya,N.V. (1946), Prosvtlenye Optiki, "Antireflection Coating of Optical Surfaces", State publishers of Technical and Theoretical Literature, Moscow, Leningrad. 6- Abeles, F. (1990), Ann.D.Physique, 5: 596. 7- Herpin, J.D., (1987), "Optical Thin Film: User Handbook", McMillan, N.Y. 8- Epstein, L.I., (1992), J.Opt.Soc.Am. 42: 806. 9- Wellford ,W.T., (1984), Vacuum, 4, 3. 10- Cox ,J.T. and Hass,G. (1988), J.Opt.Soc.Am., 48: 677. 11- Schuler, A.; Boudaden, J. and Scartzzini,J.L. (2005), Sol. Energy Mater. Sol. Cells, 89, 219. 12- Jacobs, S., (2000), SPIE proceeding, 27, 196. 13- Chorpa, K.L., (1989), "Thin Film Phenomena", 3ed ed., McGraw – Hill Book Co., N.Y. IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL.22 (3) 2009 ٨٢ ٨٤ ٨٦ ٨٨ ٩٠ ٩٢ ٩٤ ٩٦ ٩٨ ١٠٠ ٤٠٠٠ ٤٥٠٠ ٥٠٠٠ ٥٥٠٠ ٦٠٠٠ Tr a n sm is si o n (% ) Wavelength (nm) Fig. (2) the relation between transmittitance and wavelength for ZnSe with coating on both sides IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL.22 (3) 2009 ٠ ١٠ ٢٠ ٣٠ ٤٠ ٥٠ ٦٠ ٧٠ ٨٠ ٠ ١ ٢ ٣ ٤ ٥ ٦ ٧ Tr an sm is si o n (% ) Wavelength (um) Fig.(3) Transmission spectrum for ZnSe substrate ٠ ١٠ ٢٠ ٣٠ ٤٠ ٥٠ ٦٠ ٧٠ ٨٠ ٩٠ ٠ ٢ ٤ ٦ ٨ Tr an sm is si on (% ) Wavelength (um) Fig. (4) Transmission spectrum for ZnSe substrate with antireflection coating (Al2O3)on one side ٠ ٢٠ ٤٠ ٦٠ ٨٠ ١٠٠ ١٢٠ ٠ ٢ ٤ ٦ ٨ Tr an sm is si on (% ) wavelength(um) Fig. (5) Transmission spectrum for ZnSe substrate with antireflection coating (Al2O3) on both side