A thin film of cryolite ( n c = 1.33 ) is applied to a camera lens ( n g = 1.61

Question

A thin film of cryolite ( n c = 1.33 ) is applied to a camera lens ( n g = 1.61 ). The coating is designed to reflect wavelengths at the blue end of the spectrum and transmit wavelengths in the near infrared. What minimum thickness gives high reflec- tivity at 512 nm? Answer in units of nm. A thin film of cryolite ( n c = 1.33 ) is applied to a camera lens ( n g = 1.61 ). The coating is designed to reflect wavelengths at the blue end of the spectrum and transmit wavelengths in the near infrared. What minimum thickness gives high reflec- tivity at 512 nm? Answer in units of nm.

Explanation / Answer

Hi,   Given c = 1.33,            g = 1.61,               = 512 nm. For high reflectivity we have the equation to besatisfied  2ct =(m).   where and m an integer.    (Here we have taken into account that highreflectivity is achieved for constructive interference. The phasechanges at both air-cryolite and the cryolite-glass surfaces is = 180o for  air = 1<  c<  g ).       for minimum thickness,m = 1.   i.e., 2ct =.          => t= /2c  = 512 / (2 * 1.33)= 192.48 nm. Hope this helps you.   

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