It was published that titanium dioxide (TiO
2) anti-reflection coatings with 25 nm of thickness were effective for high visible transmittance of solar energy control window consisting of thermochromic vanadium dioxide (VO
2) film. It is also known that photo-catalytic TiO
2 film should have the thickness of several hundreds nanometers. Increasing of the thickness of the anti-reflection coating enough for photo-catalytic properties the solar energy control window would also be a photo-catalytic window. In this report, we determined the optical constants of VO
2 film by spectro-ellipsometory and calculated the spectral transmittance of solar energy control window with various thickness of TiO
2 layer by thin film optics. In the results, solar energy control window with around 1 micrometer thickness of TiO
2 layer shows high visible transmittance and high controllability of solar transmittance, simultaneously.
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