Abstract
InP@ZnS core-shell colloidal quantum dots (CQDs) were synthesized and characterized using the z-scan technique. The nonlinear refraction and nonlinear absorption coefficients (γ = −2 × 10−12 cm2 W−1, β = 4 × 10−8 cm W−1) of these CQDs were determined using 10 ns, 532 nm pulses. The saturable absorption (β = −1.4 × 10−9 cm W−1, Isat = 3.7 × 108 W cm−2) in the 3.5 nm CQDs dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2) followed by reverse saturable absorption at higher laser intensities. We report the optical limiting studies using these CQDs showing the suppression of propagated nanosecond radiation in the intensity range of 8 × 107–2 × 109 W cm−2. The role of nonlinear scattering is considered using off-axis z-scan scheme, which demonstrated the insignificant role of this process along the whole range of used intensities of 532 nm pulses. We discuss the thermal nature of the negative nonlinear refraction in the studied species.
Highlights
The novelty of this study is related with broader consideration of the thermal-related nonlinear refractive processes, analysis of the influence of particles concentration and pulse energy on the nonlinear optical response, distinction of the role of acoustic and accumulative processes in formation of thermal lens, analysis of optical limiting and nonlinear scattering in studied quantum dots, and determination of various nonlinear optical parameters of InP@ZnS core-shell colloidal quantum dots
We have reported the studies of the low-order optical nonlinearities of InP@ZnS
The saturable absorption in the 3.5-nm-sized colloidal quantum dots (CQDs) dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2 ) followed by reverse saturable absorption at higher laser intensities
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. We report the synthesis of 3.5 nm InP@ZnS core-shell QDs and characterize them using the z-scan technique allowing the analysis of the low-order optical nonlinearities using long pulses We demonstrate that this core-shell structure possesses strong nonlinear absorption and thermal-lens-related nonlinear refraction at the wavelength of λ = 532 nm in the case of 10 ns laser pulses. These energy-dependent measurements of OA and CA z-scans determine the most suitable parameters of probe pulses (0.01–0.02 mJ) at which the saturation of studied nonlinear optical processes caused by the influence of additional effect does not prevent the accurate determination of the nonlinear refraction indices, nonlinear absorption coefficients, and saturated intensities of studied QDs using the theoretical relations of z-scans. Our further analysis of OA and CA curves using the fitting procedures of experimental data and theoretical approaches was carried out using the moderate energies of probe pulses (0.01–0.02 mJ)
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