Growth of dyed KAP crystals and their third-order nonlinear optical properties†

Dyed crystals belong to the family of mixed or composite crystals, which are usually studied for solid-state laser devices. However, there have been few studies on their third-order nonlinear optical properties under nanosecond pulsed laser irradiation. In this work, potassium acid phthalate (KAP) was chosen as the matrix crystal. KAP crystals were doped with different functional dyes, such as basic fuchsin (BF), acid fuchsin (AF) and neutral red (NR), through evaporation technology. The third-order nonlinear optical properties of dyed KAP crystals were studied using the Z-scan technique. KAP crystals doped with BF, AF and NR exhibited saturable absorption at 532 nm. Compared with the property of dyes in solution, the saturated absorption performance of dye-doped KAP crystals was improved significantly. For example, the nonlinear absorption coefficient (β) and the imaginary part of the third-order NLO susceptibility (Imχ⁽³⁾) of AF increased from −13.11 cm GW⁻¹ to −247.44 cm GW⁻¹ and from −6.54 × 10⁻²⁰ to −1.23 × 10⁻¹⁸ esu after the incorporation of KAP crystals. These results indicate that dyed KAP crystals are promising third-order nonlinear optical crystal composites.