中国激光, 2024, 51 (7): 0701003, 网络出版: 2024-03-29  

单个阿秒脉冲表征技术研究进展

Research Progress of Isolated Attosecond Pulse Characterization
王家灿 1,2肖凡 1,2王小伟 1,2,**王力 1,2陶文凯 1,2赵零一 1,2李悉奥 1,2赵增秀 1,2,*
作者单位
1 国防科技大学理学院,湖南 长沙 410073
2 极端条件物理及应用湖南省重点实验室,湖南 长沙 410073
摘要
自本世纪初超快科学进入阿秒领域以来,阿秒脉冲以其超宽频谱和超短时间分辨,为研究阿秒时间尺度的瞬态过程提供了有力工具,推动了人们对光与物质相互作用以及微观超快动力学机制的理解。基于高次谐波的单个阿秒脉冲产生技术已日臻成熟,通过发展多种时空选通门技术,阿秒脉冲脉宽不断缩短,已达到的最短纪录为43 as。相较于阿秒脉冲的产生,对其精确测量与表征是深入研究和应用的基础,目前主流表征方法是通过阿秒条纹相机技术测量获得条纹能谱,进而从中提取阿秒脉冲的时域信息。首先简要回顾了高次谐波产生、单个阿秒脉冲选通及测量的发展,然后介绍了阿秒条纹相机技术的原理,并重点阐述了基于阿秒条纹能谱的表征算法,对其主要优缺点进行分析,最后对阿秒脉冲表征的发展进行了总结和展望。
Abstract
Significance

In 2023, Pierre Agostini, Ference Krausz and Anne L'Huillier had been awarded the Nobel Prize in Physics for their contribution in experimental methods of generating attosecond pulses of light for the study of electron dynamics in matter. Based on their pioneering work of high harmonics generation (HHG), generation and characterization of attosecond pulse trains (APTs) and isolated attosecond pulses (IAPs), a whole new physics research field named attosecond science was opened up. With the rapid development of attosecond science in the past two decades, extremely short IAPs have been generated and applied in photon spectroscopy and attosecond transient absorption spectroscopy (ATAS), providing researchers more powerful tool to study the ultrafast electron dynamics in atoms, molecules and condensed matter than ever with attosecond temporal resolution. These ultrafast processes include the photoionization time delay in atoms, ionization difference of polar and non-polar molecules, electrons migration in multi-atomic molecules, measurement of Auger decay process, inner-shell transition and probing of multielectron dynamics.

Progress

Thanks to the progress of the ultrafast laser techniques as pumping lasers, multiple methods for gating, and fine spectral chirp for compensation in the past two decades, the spectrum of the IAP has expanded from tens of electron volts to hundreds of electron volts and its pulse duration record is getting compressed. Although many research groups have succeeded in achievement of broadband spectrum and appropriate dispersion compensation, generating sub-100 as (1 as=10-18 s) IAP with world record 43 as, precise characterization is the basis of further study and applications of IAP. Firstly in 2001, the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) and model analysis method were proposed independently for characterization of half-cycle separated 250 as duration APTs and IAP with 650 as pulse duration respectively.

For the accurate measurement of such short attosecond pulses, the attosecond streaking camera scheme is adopted from the femtosecond pulses measurement in 2002. Based on the cross-correlation scheme, the IAP photoionized electrons are modulated in the presence of the delay controllable near-infrared (NIR) light field. And both the spectral phase and intensity distribution of IAP and NIR are encoded in the detected frequency and delay time two-dimensional measurement, denoted as spectrogram, which permits full reconstruction of the IAP and NIR.

Based on the attosecond streaking camera, many techniques have been proposed to retrieve the spectral phase and then reconstruct the temporal electric field of IAP and NIR. Developed by Mairesse et al., the frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) is commonly used for attosecond pulse characterization. But it uses high intensity streaking fields, resulting in the above-threshold ionized electrons that could overlap with streaked electrons. Much worse is the central momentum approximation (CMA) used to apply the iterative algorithms in femtosecond laser measurement, which limits the IAP bandwidth to few electron volts. For circumventing the CMA, Chini et al. proposed the phase retrieval by omega oscillation filtering (PROOF) for broader bandwidth and shorter IAP. PROOF applies weak field approximation (WFA) to modulate the photoelectrons and therefore focuses on the oscillation component of the dressing laser frequency, while WFA limits the streaking and retrieval application and its genetic algorithm has the problems of huge time cost and fatal shortcomings of multiple solutions in the iterative process. The quick version of PROOF (qPROOF) proposes a new error function to improve the retrieval accuracy and can be solved by the steepest descent method, improving the speed 5000 times faster than genetic algorithm. Moreover, qPROOF algorithm is numerically tested and proved to be robust against the pulse duration and intensity of streaking NIR, time-of-flight (TOF) electron detection noise, pump-probe delay jitter and large scanning step.

Multiple methods also have been proposed to avoid the CMA, WFA and slowly varying envelope approximation. The Volkov transform generalized projections algorithm (VTGPA) based on the Volkov states is developed to bypass the commonly used Fourier transform, making this method more applicable for complex IAP electric field waveform. Also, many groups have come up with novel approaches such as phase retrieval of broadband pulse (PROBP) and PROBP-autocorrelation (PROBP-AC), as well as ptychographic algorithm for attosecond reconstruction, and even the neural network and machine learning techniques are adopted to inject new solutions for attosecond measurement.

Conclusions and Prospects

Since the advent of IAP generation, extensive efforts have been devoted to IAP experimental generation, measurement and characterization algorithm research mainly based on attosecond streaking camera scheme, paving the way for further attosecond application, such as ATAS and attosecond photoelectron spectroscopy.

With the development and application of high-repetition, high pulse energy mid-infrared laser, the attosecond streaking camera faces theoretical flaws as its energy resolution and photoionization cross-section of the gas medium decrease with the increase of photon energy. Also streaking camera based characterization algorithm should be verified and developed under these novel experimental conditions. Both theoretically and experimentally, there is urgent need for a new approach to accurately characterize the spectral and temporal properties of IAP with the latest driving laser and measurement techniques. And the single shot measurement and characterization of IAP is also of vital importance in high-energy laser drive facility with relatively lower repetition rate.

王家灿, 肖凡, 王小伟, 王力, 陶文凯, 赵零一, 李悉奥, 赵增秀. 单个阿秒脉冲表征技术研究进展[J]. 中国激光, 2024, 51(7): 0701003. Jiacan Wang, Fan Xiao, Xiaowei Wang, Li Wang, Wenkai Tao, Lingyi Zhao, Xi ao Li, Zengxiu Zhao. Research Progress of Isolated Attosecond Pulse Characterization[J]. Chinese Journal of Lasers, 2024, 51(7): 0701003.

引用该论文: TXT   |   EndNote

相关论文

加载中...

关于本站 Cookie 的使用提示

中国光学期刊网使用基于 cookie 的技术来更好地为您提供各项服务,点击此处了解我们的隐私策略。 如您需继续使用本网站,请您授权我们使用本地 cookie 来保存部分信息。
全站搜索
您最值得信赖的光电行业旗舰网络服务平台!