Lin Yu-Chieh, Midorikawa Katsumi, Nabekawa Yasuo
Attosecond Science Research Team, RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan.
Light Sci Appl. 2023 Nov 24;12(1):279. doi: 10.1038/s41377-023-01328-7.
The carrier-envelope phase (CEP) of an ultrashort laser pulse is becoming more crucial to specify the temporal characteristic of the pulse's electric field when the pulse duration becomes shorter and attains the subcycle regime; here, the pulse duration of the intensity envelope is shorter than one cycle period of the carrier field oscillation. When this subcycle pulse involves a structured wavefront as is contained in an optical vortex (OV) pulse, the CEP has an impact on not only the temporal but also the spatial characteristics owing to the spatiotemporal coupling in the structured optical pulse. However, the direct observation of the spatial effect of the CEP control has not yet been demonstrated. In this study, we report on the measurement and control of the spatial wavefront of a subcycle OV pulse by adjusting the CEP. To generate subcycle OV pulses, an optical parametric amplifier delivering subcycle Gaussian pulses and a Sagnac interferometer as a mode converter were integrated and provided an adequate spectral adaptability. The pulse duration of the generated OV pulse was 4.7 fs at a carrier wavelength of 1.54 µm. To confirm the wavefront control with the alteration of the CEP, we developed a novel [Formula: see text]-2[Formula: see text] interferometer that exhibited spiral fringes originating from the spatial interference between the subcycle OV pulse and the second harmonic of the subcycle Gaussian pulse producing a parabolic wavefront as a reference; this resulted in the successful observation of the rotation of spiral interference fringes during CEP manipulation.
当超短激光脉冲的脉宽变得更短并进入亚周期状态时，其载波包络相位（CEP）对于确定脉冲电场的时间特性变得愈发关键；在此情况下，强度包络的脉宽短于载波场振荡的一个周期。当这种亚周期脉冲包含如光学涡旋（OV）脉冲中那样的结构化波前时，由于结构化光脉冲中的时空耦合，CEP不仅会影响时间特性，还会影响空间特性。然而，CEP控制的空间效应尚未得到直接观测。在本研究中，我们报告了通过调整CEP对亚周期OV脉冲的空间波前进行测量和控制的情况。为了产生亚周期OV脉冲，将一个能产生亚周期高斯脉冲的光学参量放大器和一个作为模式转换器的萨格纳克干涉仪集成在一起，并提供了足够的光谱适应性。所产生的OV脉冲在载波波长为1.54 µm时的脉宽为4.7 fs。为了证实随着CEP的改变对波前的控制，我们开发了一种新型的[公式：见原文]-2[公式：见原文]干涉仪，它呈现出源于亚周期OV脉冲与产生抛物面波前作为参考的亚周期高斯脉冲的二次谐波之间空间干涉的螺旋条纹；这使得在CEP操纵过程中成功观测到了螺旋干涉条纹的旋转。
