Spectrum NIR reflectance spectrum of the non-irradiated Mighei pellet Spectrum NIR reflectance spectrum of the Mighei pellet irradiated by $He^+$ ions at 40 keV and a total fluence of $5.10^{15} ions.cm^{-2}$ Spectrum NIR reflectance spectrum of the Mighei pellet irradiated by $He^+$ ions at 40 keV and a total fluence of $1.10^{16} ions.cm^{-2}$ Spectrum NIR reflectance spectrum of the Mighei pellet irradiated by $He^+$ ions at 40 keV and a total fluence of $3.10^{16} ions.cm^{-2}$ Spectrum NIR reflectance spectrum of the Mighei pellet irradiated by $He^+$ ions at 40 keV and a total fluence of $6.10^{16} ions.cm^{-2}$