Opt Express. 2023 Mar 13;31(6):9287-9298. doi: 10.1364/OE.482995.
The frequency-resolved terahertz (THz) beam profile characteristics of a two-color air-plasma THz source were investigated in the broadband frequency range (1-15 THz). The frequency resolution is achieved by combining THz waveform measurements and the knife-edge technique. Our results show that the THz focal spot size is strongly frequency dependent. This has important implications on nonlinear THz spectroscopy applications where accurate knowledge of the applied THz electrical field strength onto the sample is important. In addition, the transition between the solid and hollow beam profile of the air-plasma THz beam was carefully identified. Far from the focus, the features across the 1-15 THz range have also been carefully examined, revealing the characteristic conical emission patterns at all frequencies.
研究了双色空气等离子体太赫兹源在宽带频率范围内（1-15 THz）的频率分辨太赫兹光束轮廓特性。通过结合太赫兹波形测量和刀口技术实现了频率分辨率。我们的结果表明，太赫兹焦斑大小强烈依赖于频率。这对于非线性太赫兹光谱学应用具有重要意义，因为在这些应用中，准确了解施加到样品上的太赫兹电场强度非常重要。此外，还仔细地识别了空气等离子体太赫兹光束的实心和空心光束轮廓之间的过渡。在远离焦点的情况下，还仔细检查了整个 1-15 THz 范围内的特征，在所有频率下都显示出了典型的圆锥形发射模式。
