Abstract
This study systematically investigates the influence of free carriers on the generation of THz in ZnTe crystals, over a wide range of pumping fluences. As the pumping fluence is increased (< 6.36 mJ/cm(2)), the concentration of free carriers gradually increases and the THz output power is saturated, as clearly demonstrated by the time delay in the THz temporal waveforms, the changes in the THz spectral weight and the red-shift in the PL spectra. For high pumping fluences (> 6.36 mJ/cm(2)), spectacularly, there is a significant quadratic increase in the THz output power when the pumping fluence is increased, as well as at low pumping fluences of < 0.58 mJ/cm(2), because of the saturation of free carriers.
Highlights
Terahertz (THz) science has seen significant developments over past decades and has a large number of applications in plasma physics, astronomy, medical imaging, biology and communication [1]
This study systematically investigates the influence of free carriers on the generation of THz in ZnTe crystals, over a wide range of pumping fluences
These results demonstrate that there is a potential for intense THz generation in semiconducting nonlinear materials
Summary
Terahertz (THz) science has seen significant developments over past decades and has a large number of applications in plasma physics, astronomy, medical imaging, biology and communication [1]. It has been proved that the saturated THz conversion efficiency of ZnTe crystals mainly depends on free carrier absorption, rather than the pumping power, which is attenuated by two-photon absorption [5, 6]. These studies used ultrafast laser amplifiers with high pulse energy. The red shift in the THz spectra of ZnTe crystals and other nonlinear effects due to high pumping fluences (below the damage threshold) has not been explained, because of the lack of wide range and finely tuned pumping fluences
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