Abstract
Polycrystalline zinc selenide (ZnSe) has been the subject of many nonlinear optics studies for wavelengths under 4.0 µm including sum/difference frequency generation, harmonic generation, and filamentation. In this report, the conversion efficiency of high harmonic generation (HHG) in ZnSe is quantified for mid-infrared wavelengths ranging from 2.7 µm to 8.0 µm. By increasing the fundamental wavelength, we demonstrate that HHG in thick ZnSe targets is limited by the band gap. The high conversion efficiency of mid-infrared to near-infrared light in ZnSe raises concerns of a nonlinear retinal hazard. We contrast the HHG behavior of ZnSe against the observed harmonic generation of calcium fluoride, BK7, and fused silica over the same wavelengths.
Highlights
Polycrystalline zinc selenide (ZnSe) is utilized for applications ranging from harmonic generation [1] to broadband frequency conversion [2] due to its unusually strong nonlinear properties
We performed a systematic study of high harmonic generation (HHG) in ZnSe using excitation pulses from 2.7 μm to 8.0 μm resulting in HHG at wavelengths not previously studied and the generation of HHG up to twelfth order
We demonstrate that the band gap wavelength acts as an upper limit of efficient harmonic generation in polycrystalline ZnSe
Summary
Polycrystalline zinc selenide (ZnSe) is utilized for applications ranging from harmonic generation [1] to broadband frequency conversion [2] due to its unusually strong nonlinear properties. The nonlinear behavior of three common optical materials (calcium fluoride (CaF2), BK7 and UV-Vis grade fused silica) are contrasted against ZnSe. Prior studies of CaF2 have reported a measurable third order susceptibility resulting in third harmonic generation, with fifth harmonic generation in CaF2 believed to be a result of four wave mixing and not a fifth order susceptibility [9]. BK7 can generate second harmonic signals only from its surface due to its amorphous composition and has been observed to undergo third harmonic generation in the bulk media [10,11]. Like BK7, fused silica can undergo second harmonic generation at its surface [10] and third harmonic generation in the bulk media [12]. Higher odd harmonics up to 33rd order have been observed in fused silica when using a vacuum chamber [13]
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