Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation

• 作者: Qianliang Li Walter Perrie Zhaoqing Li Stuart P Edwardson Geoff Dearden
• 来源期刊: 光电进展（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: Original Article
• 页码范围: 1-12
• 页数: 12页
• 语种: 英文
• DOI: 10.29026/oea.2022.210036

摘要

The optical nonlinearity in polycrystalline zinc selenide (ZnSe), excited with 775 nm, 1 kHz femtosecond laser pulses was investigated via the nonlinear transmission with material thickness and the Z scan technique. The measured two photon absorption coefficient β was intensity dependent, inferring that reverse saturated absorption (RSA) is also relevant dur-ing high intensity excitation in ZnSe. At low peak intensity I < 5 GW cm–2, we find β = 3.5 cm GW–1 at 775 nm. The spec-tral properties of the broad blueish two-photon induced fluorescence (460 nm-500 nm) was studied, displaying self-ab-sorption near the band edge while the upper state lifetime was measured to be τe ～ 3.3 ns. Stimulated emission was ob-served when pumping a 0.5 mm thick polycrystalline ZnSe sample within an optical cavity, confirmed by significant line narrowing from Δλ = 11 nm (cavity blocked) to Δλ = 2.8 nm at peak wavelength λp = 475 nm while the upper state life-time also decreased. These results suggest that with more optimum pumping conditions and crystal cooling, polycrystal-line ZnSe might reach lasing threshold via two-photon pumping at λ = 775 nm.