I'm working on research into the feasibility of separating out the infrared rays above 1200 nm in sunlight for solar power generation. Since silicon cells do not effectively harness these wavelengths, we are experimenting with using interference coatings and a wave guide to separate these waves out. Since we'll need to measure the impact that this separation will have on the available power, I'm wondering how we could measure the power that is separated out? The visible light can simply be measured with the silicon cell, but how can the infrared light be measured? Given our dimensions, I'd expect ~25 W of infrared light leaving through a 40 cm^2 opening. This would mean getting an output 6250 W/m^2. Ideally I'd be looking to measure either the irradiance or the total power of the infrared light exiting the waveguide. I'd rather measure this directly if possible. I looked at using a pyranometer for this, but our irradiance seems to be too high for this and I'm not very familiar with optics in general. Anyone have any ideas for measuring devices?