Mpc 3100

To characterize the total spectral absorptions of our samples, we carried out absolute hemispherical measurements using a ultraviolet–visible–near-infrared spectrophotometer system (UV3600, Shimadzu Scientific Instruments) with a 60-mm diameter integrating sphere (MPC-3100) by scanning a monochromator coupled to a halogen lamp. The reflected (transmitted) beam including both specular and diffuse reflections (transmissions) from the sample were scattered and collected in an integrating sphere and measured using a photomultiplier tube detector. The reflection was normalized to a BaSO₄ reference. From Kirchhoff's law, the sample's total absorption can be obtained as A=1−(T+R), using the measured total reflection/transmission, including both specular and diffuse reflections/transmissions. Infrared spectra were collected by FTIR spectrometer (Bruker IFS-66/S), which combined with a × 15 cassegrain objective lens (NA=0.58). Spectra were acquired in the 4,000–600 cm⁻¹ range with a resolution of 0.1 cm⁻¹ and calibrated with a gold mirror reference (ref. 41 (link)).

To measure the transmittance and reflectance of the aerogels in the wavelength range of 300–1,000 nm, we used a ultraviolet–visble–NIR spectrometer (UV3600, Shimadzu Scientific Instruments) with a 60-mm-diameter integrating sphere (MPC-3100) by scanning a monochromator coupled to a halogen lamp. The transmitted and reflected light from the aerogels was scattered and collected in an integrating sphere and then detected with a photomultiplier tube. Using an integrating sphere, we can thoroughly measure the total reflectance R(λ) (transmittance (T(λ)) spectra of aerogels with scattering from ∼60 nm nanopores, including both diffuse and specular reflections (transmissions). For the measurement of the reflection/transmission spectra, we mounted the samples at an oblique incidence angle (8°) with respect to the normal at the rear/front of an integrating sphere.

The reflectance and absorption spectrum of the untreated surface and prepared hierarchical LIPSS were recorded by a UV-vis-NIR (Ultraviolet-Visible-Near Infrared) spectrophotometer (UV3600, Shimadzu Scientific Instruments, Kyoto, Japan) with an integrating sphere (MPC-3100) in the wavelength range from 250 to 700 nm.

To characterize the attenuation coefficient of the aerogels, we measured the total spectral transmittance of aerogels with various thicknesses as described in Supplementary Fig. 2. We used a ultraviolet–visble–NIR spectrometer (UV3600, Shimadzu Scientific Instruments) with a 60-mm-diameter integrating sphere (MPC-3100). Supplementary Fig. 2a presents the transmittance of the aerogels in the wavelength range of 400–850 nm with thicknesses of 2.4, 3.0, 4.2, 4.8, 5.9, 6.9, 7.2 and 7.6 mm. The transmittance reduction during light propagation is lower at longer wavelengths. This results in a smaller attenuation coefficient at longer wavelengths; consequently, red light can propagate for longer distances in the aerogels compared with light at shorter wavelengths (Supplementary Fig. 2b). Figure 2c shows the attenuation in the aerogels as a function of the propagation length (the thickness of aerogels) on a semi-logarithmic scale at wavelengths of 633, 589, 523 and 473 nm. The attenuation for an averaged transmittance in the visible spectrum from 400 to 700 nm is also plotted. The slope of the fit gives an estimate of the attenuation coefficient (in mm⁻¹) of each wavelength; the results are summarized in Supplementary Table 1.