The peak frequency of the terahertz radiation generated from the femtosecond laser-induced air plasmas is blue shifted with the increased second harmonics intensity when a high voltage is added upon the air plasmas. This blue shift is the result of the DC-biased field from the high voltage plus the AC-biased field from the second harmonics, indicating that this terahertz radiation frequency peak is tunable by varying the two field components. This tunable frequency peak is significant to various applications such as remote sensing and material characterization.

中文翻译：

---

飞秒激光诱导的空气等离子体中太赫兹辐射的频率蓝移

飞秒激光诱导的空气等离子体产生的太赫兹辐射的峰值频率随着向空气等离子体施加高电压而随着增加的二次谐波强度而蓝移。这种蓝移是来自高电压的直流偏置场加上来自二次谐波的交流偏置场的结果，表明通过改变两个场分量可以调谐此太赫兹辐射频率峰值。这个可调的峰值频率对于诸如遥感和材料表征之类的各种应用具有重要意义。