Yer gözlem uydularında yansıtıcı ve yansıma engelleyici optik kaplamalar

Abstract

Bu tez yer gozlem uydu sistemlerinin optik elemanlarindan, ayna ve mercek yuzeylerine yapilacak olan sirasi ile yansitici ve yansima engelleyici kaplamalarin tasarim ve uygulama surecini anlatmaktadir. Bu kaplamalar, sistemin istenilen tayfsal alanda iyi bir optik performansla calisabilmesi icin gereklidir. 400-900nm tayfsal alanda mercekler uzerine kaplanmasi icin yansima engelleyici kaplamalarda yuksek kiricilik indisli ve dusuk kiricilik indisli malzeme olarak, uzay uygulamalarinda sikca kullanildigi bilinen TiO2/SiO2, alternatif malzeme olarak MgF2 kullanilmistir. Yansitici kaplamalarda Ag, koruma katmani olarak ise TiO2/SiO2 malzemeleri kullanilmistir. Bu tezde oncelikle kavramsal altyapi bilgisi ve kullanilan kaplama teknikleri gozden gecirilmistir. Kaplamalarin uretiminde TiO2, SiO2 ve MgF2 malzemeleri icin elektron demetli buharlastirma teknigi, Ag icin isisal buharlastirma teknigi kullanilmistir. Yapilan kaplamalarin yansiticilik olcumleri spektrofotometre ile alinmistir. ‘Opti-Layer’ programi kullanilarak yansima engelleyici kaplamalarda ortalama yansiticiligi %0,21, yansitici kaplamalar icin ortalama yansiticiligi %98,5 olan iki ayri kaplama tasarimi elde edilmistir. Uretim asamasinda her tasarimdan, uretimde tekrarlanabilirligi saglamak icin iki ayri ornek uretilmistir. Hazirlanan tasarimlara kiyasla yansima engelleyici kaplamalarda ortalama %0.05 farkla, yansitici kaplamalarda ortalama %0.3 farkla uretimler gerceklestirilmistir. Yapilan kaplamalarin zaman asiminda nasil degisiklikler gosterecegini anlamak icin 7 ay sonra tekrar olcumleri alinmis ve 400-900nm tayfsal araligin yuksek enerjili kisminda yansiticiliginda, yansima engelleyici kaplamalarda ortalama %0.1, yansitici kaplamalarda ortalama %0.3 artis saptanmistir. Ayrica kaplamalarin sicaklik farkliliklarinda nasil degisiklik gosterdigini incelemek icin ornekler once 70 °C’de iki saat firinlanmis, ardindan da -20°C’de tutulmustur. Bu islemler sonucunda optik performansin bozulmadigi gozlenmistir. Abstract The main scope of this thesis is to investigate the design and implementation process of reflective and antireflective coatings applied on the optical components of earth observational satellites such as mirrors and lens surfaces. These coatings play an important role on the optical performance of the system at a desired spectral range. For coating the lenses to be worked in 400-900nm spectral range, antireflective coatings of TiO2/SiO2 were used as high and low refractive index materials which are known to be widely integrated in space applications. MgF2 was used as an alternative material. Ag was used in the reflective coatings and TiO2/SiO2 were used as protective layers. As a first goal, the basic background information and the coating techniques used up to date were investigated in this thesis. During the fabrication, TiO2, SiO2 and MgF2 were deposited by using e-beam evaporation technique, and Ag was deposited with thermal evaporation technique. The reflectivity properties of the coatings were probed via spectrophotometer. Modeling of the reflective and antireflective layers was performed with “Opti-Layer” software. By using this software, the average reflectivity of 0.21% and 98.5% were modeled for antireflective and reflective coatings, respectively. All the samples related to a specific model were fabricated two times to show the reproductively of the same properties of the coatings. When the experimental results were compared with the theoretical modeling, an average difference of 0.05% was found for antireflective coatings and 0.3% an average difference was found for reflective coatings. To see the effect of time, ageing experiments were performed after seven months and the samples were re-measured in spectrophotometer. The results of the ageing experiments showed an increase in reflectivity at the higher energy part of 400-900nm spectral region, namely 0.1% for antireflective coatings and 0.3% for reflective coatings. Moreover, for the investigation of the effect of temperature on the optical coatings the samples were first heated up to 70°C for two hours and then kept under -20°C to see the stability. After these experiments, it was shown that, there were no changes in the performance of the coatings.