This paper discusses the transmission spectra of a nanocomposite created by a new electron-ion technology-low-temperature laser surface modification of a layer of nanoporous silicon in a medium of a strong gaseous oxidant. A selective-absorption effect has been detected in the IR range. It is shown that the transmission spectrum of laser-oxidized nanoporous silicon has the form of a complex curve with four local minima, lying in the wavenumber ranges 4000-2750 cm-1, 2400-2100 cm-1, 1900-1600 cm-1, and 1300-1000 cm-1. A comparison of the transmission spectra of thermally oxidized nanoporous silicon and laser-modified nanoporous silicon in a strong oxidant atmosphere made it possible to explain the selective absorption of optical radiation in the nanocomposite thus created.