Special Issue for Ultrafast Optics|33 Article(s)
Progress on the Ultrahigh Spatiotemporal-resolved Photoemission Electron Microscopy (Invited)
Yaolong LI, Yunquan LIU, and Qihuang GONG
Recently, new photoelectronic materials, magnetic materials and low-dimensional quantum materials, etc, are research frontiers of condensed matter physics. The nanoscale near-field optical dynamics for materials have drawn widely attention due to their rich physics and promising applications. The combination of the ultrahigh temporal resolution of femtosecond laser and the ultrahigh spatial resolution of photoemission electron microscopy is an ultrahigh spatialtemporal-resolved measurement technology, which has injected new vitality to material physics and surface physics and has provided a strong platform. In this review, the ultrahigh spatiotemporal-resolved photoemission electron microscopy is introduced. And the application and progress on the dynamics of surface plasmons, low-dimensional materials and other novel semiconductors, and heterostructure interfaces are discussed. Finally, an outlook in the investigation of surface and interface physics in fs-nm scale are given.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850201 (2021)
Research Progress of Generation and Control of Ultrafast and Coherent Electron Sources Based on Optical Fields (Invited)
Ye TIAN, Chuliang ZHOU, Xuewen FU, Shaozheng JI, Yuxin LENG, and Ruxin LI
The interaction between light and matter is one of the heart interactions in nature. The complete visualization of this kind of dynamics requires attosecond resolution in time and atomic resolution in space. Ultrashort and coherent electron pulses are central to achieve this goal. This review surveys the important efforts aimed at generation, phase-space control and characterization of ultrashort electron pulses using various optical fields such as microwave, terahertz radiation and visible light, and mainly summarizes its key breakthrough in four-dimensional ultrafast electron microscopy, which opens up the way for the establishment of “attomicroscopy” to allow the imaging of electron motion in the act. Finally, the development prospects of ultrafast electron research is presented.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850202 (2021)
Ultrafast Measurement Techniques Using High-order Harmonic Based Attosecond Light Sources (Invited)
Wei CAO, and Peixiang LU
Table-top attosecond coherent light sources have achieved rapid development in the past two decades. Its research focus has gradually migrated from the generation and characterization of attosecond pulses in early times to tracing and controlling exceedingly fast processes with unprecedented time resolution. Nowadays, attosecond time resolved spectroscopies have been developed to successfully capture transients in simple atomic and molecular systems. Extending their applications to dynamics measurement in complex systems such as chemical molecules, biomolecules and condensed matter is ongoing. This paper reviews the development of ultrafast measuremt techniques using high-order harmonic based attosecond pulses, and introduces their applications in physics, chemistry and information sciences.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850203 (2021)
Progress on the Interaction Between Intense Spatially Structured Light Fields and Atoms (Invited)
Yiqi FANG, and Yunquan LIU
With the development of ultra-fast and ultra-strong laser technology, the interaction between light and matters in the strong-field regime has been extensively studied. At the same time, the rapid development of spatial light modulation technology in classic optics provides a new degree of freedom for optical manipulation. In recent years, the combination between these two different fields, namely, driving the intense-laser-matter interaction by the spatially structured light fields, has become one of the research hotspots in strong-field science. Strong-field ionization and high-order harmonic generation are two fundamental and important physical processes in traditional strong-field community. Here, the effect of optical vortex beams in strong-field ionization and its related research progress are first introduced. Then, the latest works of gas high-order harmonic generation driven by vortex beams or cylindrical vector beams in the past decade are introduced. At last, we look ahead to the prospects of intense spatially structured laser fields in strong-field physics.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850209 (2021)
Probing Intrinsic Attosecond Electron Dynamics and Interactions in Condensed Matters (Invited)
Zhensheng TAO
As the development of attosecond sources and metrology technologies, the studies on ultrafast electron dynamics in condensed matter have entered the attosecond regime, leading to remarkable progress and breakthroughs in the past 15 years. Novel attosecond metrology has opened up new opportunities for the detection of ultrafast electron movement, resonant excitation, as well as complex electron-electron interactions on the attosecond timescale. This review surveys the important efforts aimed at probing intrinsic attosecond dynamics in condensed matters. The key technologies and status of attosecond sources enabled by high-harmonic generation, attosecond pulse measurements, and the detection of attosecond photoemission time delay on condensed matters are summarized. The development prospects are presented in the end.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850204 (2021)
Recent Advances on Experimental Study of Nucleation Process of Methane Hydrate (Invited)
Yu ZHANG, Rongda LIANG, Huijie XU, and Chuanshan TIAN
Methane hydrate has attracted great attention due to its close relationship with current energy and environmental issues. It is of great significance and application value to carry out fundamental scientific research on the problems related to exploitation of methane hydrate, storage and transportation of natural gas and hydrogen in the form of hydrate. The nucleation process is the key first step of the formation of methane hydrate. It is a microscopic process in which methane and water molecules form clusters and gradually evolve into hydrates. Little is known about how hydrates begin to nucleate and decompose at the molecular level, because of the lack of appropriate experimental probes. This article first summaries the current understanding of the structure and properties of hydrates, then follows the review on the study of nucleation process based on the molecular dynamics simulation. Finally, with the emphasis on ultrafast nonlinear optical spectroscopy, the advances on experimental study of hydrate formation process are discussed, and future research directions are proposed.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850205 (2021)
Review of High-power Kerr-lens Mode-locked Yb-doped All-solid-state Lasers (Invited)
Wenlong TIAN, Rui XU, Jiangfeng ZHU, and Zhiyi WEI
Ultrafast laser with high power and short pulse duration plays a more and more important role in basic scientific researches, precision machining and biomedicine etc. Among the various femtosecond light sources, the laser diode directly pumped Yb-doped all-solid-state bulk femtosecond laser has become one of the research hotspots in the ultrafast laser because of its advantages of compact structure, low cost, reliability and excellent output performance. In particular, the Kerr lens mode-locked Ytterbium-doped all-solid-state femtosecond laser is expected to deliver both an average power of one hundred watts and an pulse duration less than one hundred femtoseconds at the same time. This paper summarizes the research results of Kerr lens mode-locked ytterbium-doped bulky material all-solid-state lasers that generated short pulses with high average power in recent years, and looks forward to it. It also gives a prospect and plan for realizing the mode-locking operations with average power of one hundred watts, pulse energy of ten microjoules and high-power GHz repetition rate, respectively.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850207 (2021)
Exploration of PtSe2 Thin Film Based on Time-resolved Terahertz Spectroscopy (Invited)
Zijie DAI, Lixing KANG, Cheng GONG, Zheng LIU, and Weiwei LIU
Utilizing the time-resolved terahertz spectroscopy, the optical property of platinum selenide (PtSe2) thin films with different thicknesses in terahertz band are investigated experimentally. As the applied pump fluences increase from 0 to 2 540 μJ/cm2, the conductivity of 11 nm-PtSe2 film increases and further leading to the attenuation of the transmitted terahertz wave. Conversely, the conductivity of 197 nm-PtSe2 film decreases with the enhanced pump fluences that induces the increase of the transmitted terahertz wave. These characters enable PtSe2 thin film to be a photoactive terahertz modulator, which shows an ultrafast (~14 ps) and broadband (0.2~1.8 THz) modulation (15%~35%) of terahertz waves. The research provides a potential PtSe2-based platform to the active and ultrafast photonic devices at terahertz frequencies.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2021
  • Vol. 50, Issue 8, 0850206 (2021)
Dual-mode Square Microcavity Lasers with a Tunable Wavelength Interval(Invited)
Ting WANG, Jiliang WU, Chunguang MA, Yongtao HUANG, Yuede YANG, Jinlong XIAO, and Yongzhen HUANG
In recent years, dual-wavelength lasers are used in a wide variety of applications in interferometric measurement, optical communications, microwave and THz wave generations, and optical frequency combs. A variety of methods to realize dual-wavelength lasers have been proposed, including fiber lasers, Y-branch integrated lasers, and two-section Distributed Feedback (DFB) or Distributed Bragg Reflection (DBR) lasers. In addition, the whispering gallery mode microcavity laser has great application potential in photonic integration due to its small mode volume, high-quality factor, and simple manufacturing process.In this paper, we design and fabricate a square microcavity laser with a current injection window in the center and four corners to achieve tunable dual-wavelength lasing. By simply changing the injection current, we realize dual-mode lasing with a wavelength interval tuned from 0.18 nm to 0.1 nm, and an intensity ratio less than 4 dB.A two-dimensional finite-element method is used to simulate the TE modes of the square microcavity. It can be seen that along the lines connecting the midpoints of the adjacent sides, the fundamental mode and the first-order mode show the strong field and the weak field distribution, respectively. Due to the incomplete overlap of the mode field distributions, there is less mode competition between the fundamental mode and the first-order mode, and the quality factors are 6.994×104 and 1.838×104, respectively. Taking into account the vertical radiation, material absorption, and manufacturing process losses, the two modes have similar quality factors to achieve dual-mode lasing.Based on the mode field distribution, a deformed square microcavity laser is designed with a current injection window in the center and four corners, which induces a refractive index step. For a square microcavity with a side length of 30 μm, the numerical result shows that the mode wavelength interval can be reduced from 1.07 nm to 0.11 nm when the refractive index step increases from -0.005 to 0.003.Next, a dual-mode square microcavity laser with a current injection window in the center and four corners is successfully fabricated with a side length of 30 μm, and a waveguide of 3 μm. The maximum output power coupled into a multimode fiber is 1.04 mW when the injection current is 77 mA. The series resistance is 11.4 Ω, and the threshold current is about 9 mA. When the injection current is increased from 41 mA to 53 mA, the wavelength interval of the microcavity laser decreases from 0.18 nm to 0.1 nm. Meanwhile, the intensity ratio is less than 4 dB. Since the lasing wavelength of InP-based lasers changes with temperature at a rate of 0.1 nm/K, the temperature difference between the injection window and the non-injection window can be estimated to be 2.5 K when the injection current is 50 mA. Compared with the simulation results, the refractive index step corresponding to the dual-mode interval of the microcavity laser increases from 1×10-3 to 3×10-3 with the increase of the injection current. It indicates that the refractive index of the microcavity laser is mainly affected by the temperature distribution. According to the experimental and simulation results, the refractive index step and the current have a quadratic relationship. In addition, a period-one oscillation phenomenon appears due to the further reduction of the dual-mode interval.For comparison, a square microcavity laser with a square-ring-patterned contact window is also fabricated with a side length of 26 μm, and a waveguide of 2.5 μm. The dual-mode interval gradually increases with the increase of the injection current. When the injection current is increased from 62 mA to 85 mA, the dual-mode interval can be tuned from 0.202 nm to 0.284 nm. It further verifies the conclusion that the refractive index is mainly affected by the temperature distribution.In conclusion, a square microcavity laser with a non-uniform injection window in the center and four corners is designed to realize dual-mode lasing with tunable intervals. When the injection current is increased from 42 mA to 53 mA, the wavelength interval decreases from 0.18 nm to 0.1 nm. The proposed square microcavity laser with a current injection window in the center and four corners provides a light source with a tunable interval for the generation of microwaves, optical frequency combs, and the potential chaotic lasers.
Acta Photonica Sinica
  • Publication Date: Feb. 25, 2022
  • Vol. 51, Issue 2, 0251202 (2022)