Phys.org  September 9, 2022 The THz generation efficiency and the plasma density generated by a filament in air have been found anti-correlated when pumped by two-color laser field. The plasma density near zero delay of two laser pulses has a minimum value, which is opposite to the trend of THz generation efficiency and contradicts common sense. The lower plasma density cannot be explained by the static tunneling model according to the conventional photocurrent model, but it might be attributed to the electron trapping by the excited states of nitrogen molecule. An international team of researchers (China, Japan) clarified the dominant […]