Nonlinear optical properties of Ge$_7$Sb$_{93}$ chalcogenide glass as a low-melting immersion medium for femtosecond laser marking of diamonds in the near-infrared range

The possibility of the femtosecond laser structural micromodification (microlabeling) of diamond through a solid immersion layer made of Ge$_7$Sb$_{93}$ chalcogenide glass at a wavelength of $1.55$ $\mu$m has been investigated. The two-photon absorption coefficient of Ge$_7$Sb$_{93}$ has been measured to be $\beta_2=(0.09\pm0.01)$ cm/GW, which allows the propagation of intense femtosecond laser radiation in this spectral range through realistically thin ($<0.1$–$1$ mm) immersion layers. Despite the nonlinear absorption and optical damage in the immersion volume, photoluminescent microlabels have been observed in the test writing modes in the volume of diamond, which become more uniform with decreasing exposure time and pulse energy.