1. Use Detector Volume to calculate total absorbed power and its profile
2. The SILICON material in INFRARED catalog does not include the visible range, so you’ll have to create a custom material for your purpose.
3. Your get more power than what you inserted since the detector sees multiple zigzags on it, meaning its counting each ray multiple times

• You can use coatings to model the metal with a complex refractive index. See the Coating Group section in the Zemax helps file for more information. Note that if the spacing is within a wavelength you may need to add a Etalon coating. 
• I would make your two rectangular volumes of silicon. Then I would add a coating to the front surface of the top Silicon rectangular volume. 
• A simple way to find out how much is absorbed in the coating is to turn the imaginary index to zero in the coating material file and see this change it total energy at the output of the slab.

Sorry I can’t edit comment and submitted before I finished. I meant to say 

• I would make three rectangular volumes. Two of them with material silicon and the middle one air. Then I would add a coating to the front surface of the top air rectangular volume. Make sure to take nesting into account.