Single crystalline Holmium doped InSe for optical limiting operation in Near-IR region

Abstract

Single crystals possessing nonlinear absorption (NA) character are favorable optical limiter in near infrared region (NIR). The NA features of pure and 0.005%, 0.05%, 0.1% Holmium (Ho) doped single crystals of InSe were analyzed at 1200 nm wavelength within 120 fs and 1 kHz repetition rate. The open-aperture Z-scan technique was employed to determine the NA performance and optical limiting-(OL) threshold. In an attempt to determine the NA coefficients, two types of theoretical models were used. The first model takes into account only the two photon absorption-(TPA), while the second model considers one photon absorption, TPA and free carrier absorption. Based on the experimental results, the main NA mechanism of the studied single crystals is determined as sequential TPA. TPA coefficient value of the pure InSe single crystal increased from 1.41 × 10−10 to 10.7 × 10−10 cm W−1 with increasing Ho doping concentration at 398.1 GW cm−2 input intensity. The NA coefficients increased from 0.84 × 10−9 to 1.62 × 10−9 cm W−1 at the same input intensity. On the other hand, the OL threshold values were found to be 0.027, 0.025, 0.022 and 0.020 J cm−2 at 1200 nm wavelength for pure InSe and the increasing Ho concentration, respectively. The robust NA characteristics and the low OL threshold establish the Ho-doped InSe single crystal as a favorable candidate for OL applications in the NIR spectral region.