Avasphere 50

Reflectance spectra of local wing areas (size ~1 mm²) were measured with a bifurcated probe and an Avantes AvaSpec-2048-2 CCD detector array spectrometer (Avantes, Apeldoorn, The Netherlands). The reference standard was a white diffuser (Avantes WS-2). Transmittance spectra were measured with an integrating sphere (AvaSphere-50, Avantes) and the detector array spectrometer.

The specular reflection was measured by multiple angle reflectometry (Film Tek 4000, scientific computing international, Carlsbad, USA) at normal and 70° incidence. The total reflectance was measured by optical spectrometer (OE65000, Ocean Optics spectrometer, USA) with an integrating sphere of 8° incidence (AvaSphere-50, Avantes, UK). The total reflectance measurement was calibrated by a white Lambertian scatter (SRS-99-020, LabSphere, USA). The scattering distribution of the samples was measured with an angular scatterometer, where a photodetector (New Focus Model 2032, Newport, USA) was rotated in a circular arc around the sample and the scattering intensity was evaluated in steps of 0.1°. A 40 mW argon-ion laser of 488 nm (60X, American Laser Corporation, USA) was used as the incident light source. The detailed description of the setup can be found in a previous publication33 (link). Canon EOS 5D Mark II camera was used to shoot the photos of the white DTU logo on the black silicon wafer. Except for the auto white balance function, no further post processing was used on the photos. The RGB profile of the photo was extracted by ImageJ.
The silicon surface texturing, SEM characterizations, and the specular reflection measurements were carried out in a class 10–100 cleanroom (Danchip, DTU, Denmark).