Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation
飞秒激光激发多晶硒化锌中的双光子吸收和受激发射
フェムト秒レーザー励起による多結晶セレン化亜鉛の2光子吸収と誘導放出
펨토초 레이저 여기를 사용하는 다결정 셀렌화 아연의 2광자 흡수 및 자극 방출
Absorción de dos fotones y emisión estimulada en seleniuro de zinc policristalino con excitación láser de femtosegundo
Absorption à deux photons et émission stimulée dans du séléniure de zinc polycristallin avec excitation laser femtoseconde
Двухфотонное поглощение и стимулированное излучение в поликристаллическом селениде цинка с фемтосекундным лазерным возбуждением
Qianliang Li ¹, Walter Perrie ¹, Zhaoqing Li ², Stuart P Edwardson ¹, Geoff Dearden ¹
¹ Laser Engineering Group, School of Engineering, University of Liverpool, Liverpool, L69 3GQ, United Kingdom
² Laser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M13 9PL, United Kingdom
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 during 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 spectral properties of the broad blueish two-photon induced fluorescence (460 nm-500 nm) was studied, displaying self-absorption near the band edge while the upper state lifetime was measured to be τe ~ 3.3 ns. Stimulated emission was observed 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 lifetime also decreased.
These results suggest that with more optimum pumping conditions and crystal cooling, polycrystalline ZnSe might reach lasing threshold via two-photon pumping at λ = 775 nm.
