Simpson Tanner T, Pigeon Jeremy J, Miller Kyle G, Ramsey Dillon, Froula Dustin H, Palastro John P
Laboratory for Laser Energetics, University of Rochester, Rochester, NY, 14623-1299, USA.
Present Address: Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA.
Sci Rep. 2024 Nov 4;14(1):26587. doi: 10.1038/s41598-024-75832-0.
A laser pulse composed of a fundamental and an appropriately phased second harmonic can drive a time-dependent current of photoionized electrons that generates broadband THz radiation. Over the propagation distances relevant to many experiments, dispersion causes the relative phase between the harmonics to evolve. This "dephasing" slows the accumulation of THz energy and results in a multi-cycle THz pulse with significant angular dispersion. Here, we introduce a novel optical configuration that compensates the relative phase evolution, allowing for the formation of a half-cycle THz pulse with almost no angular dispersion. The configuration uses the spherical aberration of an axilens to map a prescribed radial phase variation in the near field to a desired longitudinal phase variation in the far field. Simulations that combine this configuration with an ultrashort flying focus demonstrate the formation of a half-cycle THz pulse with a controlled emission angle and 1/4 the angular divergence of the multi-cycle pulse created by a conventional optical configuration.
由基频光和相位适当的二次谐波组成的激光脉冲可以驱动光致电离电子的随时间变化的电流，从而产生宽带太赫兹辐射。在与许多实验相关的传播距离上，色散会导致谐波之间的相对相位发生变化。这种“相位失配”会减缓太赫兹能量的积累，并导致产生具有显著角色散的多周期太赫兹脉冲。在此，我们引入了一种新颖的光学配置，该配置可补偿相对相位变化，从而能够形成几乎没有角色散的半周期太赫兹脉冲。该配置利用轴棱锥的球差将近场中规定的径向相位变化映射到远场中所需的纵向相位变化。将这种配置与超短飞行焦点相结合的模拟表明，形成了具有可控发射角且角发散为传统光学配置产生的多周期脉冲的四分之一的半周期太赫兹脉冲。
