1.School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China 2.Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 3.University of Chinese Academy of Sciences, Beijing 100049, China 4.Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China
Fund Project:Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB0405202, 2017YFC0110301), the Major Program of the National Natural Science Foundation of China (Grant No. 61690221), the Key Program of the National Natural Science Foundation of China (Grant Nos. 11434016, 91850209), the National Natural Science Foundation of China (Grant Nos. 11574384, 61575219, 11774277), the Instrument Developing Project of the Chinese Academy of Sciences (Grant No. YZ201658), the Frontier Science Key Research Project of the Chinese Academy of Sciences (Grant No. QYZDJ-SSW-JSC006), and the Youth Innovation Promotion Association, Chinese Academy of Sciences, China (Grant No. 2018007)
Received Date:29 July 2019
Accepted Date:20 August 2019
Available Online:01 November 2019
Published Online:05 November 2019
Abstract:With the unveiling of molecular and atomic dynamics, scientists crave finer and faster tools to communicate with the microworld. Attosecond pump-probe enjoys its reputation as the fastest camera, hinting ultrafast movements in the delay graph. To employ this camera, the stability and delay control should have very great accuracy comparable to the camera resolution. It is also of significant importance for stabilizing the carrier envelope phase (CEP) in few-cycle laser field. When dealing with a huge quantity of data, conventional Fourier transform algorism is challenging in high-speed control. Here we put forward the efficient calculation method, fast Fourier transform (FFT) algorism in Mach-Zehnder interferometer for arm length locking and f-2f for CEP locking. In the interferometer locking, 532 nm continuous wave laser is used in the Mach-Zehnder interferometer, and the phase of the FFT term corresponding to the delay between the two arms of the interferometer serves as a feedback signal on piezo transducer (PZT) in the delay line to reduce the change of the arm length. In the CEP control experiment, data to be analyzed are the f-2f spectrum interference fringes recorded by the spectrometer. The CEP values are obtained from the first order of FFT module output of the integrated spectrum interference fringes, and a labview program examines the relative phase drift and sends a feedback voltage signal to the PZT through the proportion integration differentiation module to compensate slow CEP drift after the chirped pulse amplification system by changing the insert length of a prism pair. The results show that the root mean square (RMS) of the arm length difference is 1.24 nm (4.1 attosecond for light to travel) per meter in the interferometer locking over 12 h, and the RMS of CEP is 227 mrad under 3 ms integration time in the CEP locking over 20 min. These results are able to meet the requirement of the accuracy for attosecond pulse generation and attosecond pump-probe experiments. We also use FFT to stabilize the CEP and relative time simultaneously in the waveform synthesis for 8 h (Huang P, Fang S, Gao Y, Zhao K, Hou X, Wei Z 2019 Appl. Phys. Lett.115 031102), the phase-locking system results in a CEP stability of 280 mrad and a relative time stability of 110 as at a repetition rate of 1 kHz. These results imply that the FFT is versatile and reliable in ultrafast control. Keywords:fast Fourier transform/ arm length locking/ carrier envelope phase locking
其中φCE即为CEP, 该值直接影响周期量级脉冲的实际电场形状, 如图4所示. 因此在周期量级脉冲与物质相互作用的过程[21], 如高次谐波以及阿秒脉冲的产生、阈上电离[22]、探究原子分子运动过程等研究中, CEP及其稳定性是重要参数. 图 4 在同一脉冲包络下不同CEP值所对应的实际电场(CEP对少周期脉冲电场实际形状影响显著) Figure4. Actual electric field of a few cycle laser pulse under different CEP values, which affect the electric field significantly.