Ultrafast Optics|5 Article(s)
ALL-SOLID-STATE MULTI-WAVELENGTH FEMTOSECOND PULSE LASER SYSTEM
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Acta Photonica Sinica
  • Publication Date: Sep. 01, 2002
  • Vol. 31, Issue 9, 1112 (2002)
Research Progress of Attosecond Pulse Generation and Characterization (Invited)
Hushan WANG, Huabao CAO, Liangwen PI, Pei HUANG, Xianglin WANG, Peng XU, Hao YUAN, Xin LIU, Yishan WANG, Wei ZHAO, and Yuxi FU
Attosecond pulse light source, born at the turn of 21st centruy, is a fully coherent light source with attosecond-temporal and nano-spatial resolution, leading to the remarkable progress and breakthroughs in attosecond science in the past two decades. New research methods and important innovation opportunities in physics, chemistry, biology, materials, information and other fields have emerged with the advent of attoseond pulse. This review surveys the important efforts aimed at developing attosecond pulses, mainly summarizes the key technologies and status of high-order harmonics, attosecond pulse generation and attosecond pulse measurement, and presents the development prospects of attosecond pulse research in the end.
Acta Photonica Sinica
  • Publication Date: Jan. 25, 2021
  • Vol. 50, Issue 1, 1 (2021)
All-optically Measuring Mechanical Parameters of Bio-surface/interface with Femtosecond Laser Spectroscopy(Invited)
He ZHANG, Wenxiong XU, Qiwei LI, Chuansheng XIA, Xiaoxuan WANG, Haibo DING, Chunxiang XU, and Qiannan CUI
The mechanical properties and parameters of bio-surface/interface are very important in fundamental researches and applications, such as constructing organ-on-a-chip in order to realize vitro culture of human cells and tissues. To acquire mechanical parameters of bio-surface/interface for real human cells, Atomic Force Microscopy (AFM) is usually employed. The young's modulus of human cells' surface/interface can be obtained by measuring the stress and strain of human cells induced by AFM tip. Obviously, this conventional method is invasive, which might not only cause damage of bio-surface/interface such as cell membrane, but also accompany a low speed for sensing and imaging applications. Besides, ultrasound elastography imaging has been developed to obtain three-dimensional distribution of mechanical parameters for bio-tissues. Unfortunately, the MHz ultrasound waves emitted by conventional ultrasound transducer limit its spatial resolution to micrometer. Hence, developing an accurate, in-situ, noninvasive and quantitative measuring method with high spatiotemporal resolutions to evaluate the mechanical performances has been highly desired. In recent years, layered Two-dimensional (2D) semiconductors, such as Transition Metal Dichalcogenides (TMDs) have presented extraordinary fundamental physical properties as well as good biocompatibility. Van der Waals bondings facilitate their facile integrations with other materials, including bio-materials, to form hetero-interfaces. Most importantly, previous studies have shown that GHz Coherent Acoustic Phonon (CAP) oscillations can be generated under femtosecond laser excitations. Although TMDs show great potential as novel optoacoustic transducers, the effective generation of CAP pulse and experimental measurements of mechanical parameters of bio-surface/interface still need further investigations.In this paper, employing layered 2D semiconductors as GHz optoacoustic transducer, we report a new all-optical technique to noninvasively, accurately, and swiftly measure mechanical parameters of bio-surface/interface based on femtosecond laser pump-probe. To demonstrate our technique, 2D optoacoustic transducer/bio-material hetero-interface formed by integrating multilayer MoS2 samples with PEGDA hydrogels are comprehensively investigated. Initially, through deformation potential mechanism, one femosecond pump pulse absorbed by multilayer MoS2 can induce GHz CAP oscillations, which is usually called interlayer breathing mode. Then, MoS2 lattice will periodically strike the surface of the PEGDA hydrogel and a CAP pulse can be emitted into PEGDA hydrogels by interfacial coupling of mechanical energy. Emitted CAP pulse will propagate in PEGDA at the speed of acoustic velocity. Since light speed is about five order of magnitude larger than acoustic velocity, to track the spatiotemproal propagations of emitted CAP pulse, another femtosecond probe pulse is employed. As the propagation of the emitted CAP pulse can induce a strain of PEDGA hydrogel, optical refractive index of PEGDA hydrogel will be changed so that by monitoring the differential reflection of probe laser as function of time delay with respect to the pump pulse, one can record the spatiotemporal propagation of emitted CAP pulse. As a result, the differential reflection signal of the probe laser contains exponential decay component originating from photocarrier relaxation of MoS2 and the damped oscillation components originating from CAP oscillation of MoS2 lattice as well as CAP pulse propagation in PEGDA hydrogel. To decouple the signal of CAP pulse propagation in PEGDA hydrogel, a curve fitting procedure is performed. At last, from frequency spectra obtained by fast Fourier transformations of the fitted time-resolved damped oscillation components, two different resonant frequency peaks are obtained. The higher resonant peak centered around 30.0 GHz is corresponding to CAP oscillations of MoS2 lattice, while the lower resonant peak below 10.0 GHz is caused by spatiotemporal propagation of the emitted CAP pulse in PEGDA hydrogel. Based on the model of Brillouin oscillation for CAP, mechanical parameters, such as acoustic velocity and Young's modulus of PEGDA hydrogel, are calculated. Last but not the least, we investigate five different positions of MoS2/PEGDA hydrogel interface. The spatial dependence of the mechanical properties of PEGDA hydrogel is discussed. In brief, physical principles, theoretical models, experimental systems, data analysis and calculation methods of the reported all-optical technique have been clearly demonstrated. Our results set a solid foundation for understanding CAP dynamics of hetero-interface, developing novel optoacoustic transducers for bio-surface/interface and realizing interfacial imaging of mechanical parameters with ultrahigh spatiotemporal resolutions.
Acta Photonica Sinica
  • Publication Date: Oct. 25, 2022
  • Vol. 51, Issue 10, 1032001 (2022)
Optimal Control of Isolated Attosecond Pulse Generation in an Ar Crystal(Invited)
Suna PANG, and Feng WANG
The ultrafast motion of electrons in atoms, molecules, and condensed matter can generally involve attosecond timescales. Attosecond light pulse can provide unusual functionalities for probing, initiating, driving, and controlling the ultrafast electronic dynamics with unprecedented high temporal and spatial resolutions simultaneously. The progress of attosecond science is closely linked to the improvement of attosecond light sources in terms of shorter and more intense attosecond pulses. Indeed, following its first synthesis and characterization, with the tendency towards reducing the pulse durations and increasing the pulse intensities, attosecond light pulses have and will continue to open up new venues for studying both fundamental and applied sciences, enabling a number of exciting possibilities.Over the last decade, people have conducted a lot of explorations on new methods of generating single attosecond pulses both experimentally and theoretically. In principle, an isolated attosecond light pulse can be generated via HHG originating from coherent electron motion in atoms, molecules, clusters and bulk crystals exposed to intense few-cycle femtosecond laser pulses. Theoretically, HHG in the atomic case can be well understood in the framework of a semi-classical model consisting of three steps. First, an electron is ionized into the continuum by tunneling through the potential barrier formed by the atomic Coulomb field and the driving laser field. Then, the ionized electron gains energy while being accelerated by the driving laser field. Finally, the electron recombines to the parent ion with an energy release in the form of harmonic photons. The generated harmonic radiation that occurs on successive half-cycles of the driving laser is coherent, leading to the emission of odd harmonics. Ultrashort attosecond pulse can be obtained only when the low-harmonic orders are filtered out. In the last two decades, almost all advances in isolated attosecond laser sources were based on HHG from atoms exposed to intense driving laser pulses. The main problem of isolated attosecond pulse generated by HHG in atoms is its weak intensity and low generation efficiency. To increase the strength of isolated pulses, laser-crystal interaction may be an alternative method worth investigating because in bulk crystals the existence of multiple ionization and recombination sites, the high density and periodic structure makes for richer dynamics allowing the possibility of higher conversion efficiency. At present, it is safe to say that while HHG in atomic gases has been explored extensively, much less has been done for bulk crystals. Interestingly enough, NDABASHIMIYE G et al. reported a direct comparison of HHG in the solid and gas phases of Ar. They found that the HHG spectra of the noble gas solids exhibit multiple platforms, well beyond the atomic limits of the corresponding gas phase harmonics measured under similar conditions, implying that shorter attosecond pulses could be realized in solids. What is most interesting to us is that the dependence of HHG on the laser polarization direction with respect to the Ar crystal, which are currently little studied. We theoretically investigated optimal control of isolated attosecond pulse generation in an Ar crystal irradiated by few-cycle femtosecond pulse, employing quantum time-dependent density-functional theory method. We explored systematically the effect of different laser polarization directions on isolated attosecond pulses generation, showing that the laser polarization direction with respect to the crystal is a sensitive control parameter for producing isolated attosecond pulses. The results indicate that for an Ar crystal, the intensity of isolated attosecond pulses is maximal at an optimal laser polarization direction with respect to the crystal, demonstrating about 11-fold intensity enhancement compared with that generated in an Ar atom under the same driving laser pulses. Our results also suggest opportunities for future investigations for the optimal control of isolated attosecond pulse generation in bulk crystal solids.
Acta Photonica Sinica
  • Publication Date: Oct. 25, 2022
  • Vol. 51, Issue 10, 1032002 (2022)
High-gain Ultra-small Streak Camera and Its Integrated Control System
Yuchi ZHANG, Jinshou TIAN, Yanhua XUE, Zhibing LI, Shaohui LI, Junfeng WANG, Baiyu LIU, Guilong GAO, Ping CHEN, Xing WANG, and Wei ZHAO
As a diagnostic instrument with ultra-high temporal and spatial resolution and spectral resolution, the streak camera is widely used in basic research fields such as physics, life sciences, and materials science, as well as in national strategic fields such as detonation physics, lidar, and inertial confinement fusion. Aiming at the requirements of airborne lidar for miniaturized, high-sensitivity, high-gain, and high spatiotemporal resolution streak camera, a high-brightness-gain compact streak camera and its new integrated control system are developed.Compared with the general picosecond visible light streak camera, the volume and weight of the camera are reduced by more than 2/3. The selected streak camera adopts the theoretical simulation research of cathode semiconductor and the method of optimizing the process to greatly improve the sensitivity of the cathode. Using a slit acceleration grid improves the photoelectron transmittance, enhances the photoelectron energy to give the fluorescent screen higher luminous efficiency, and optimizes the cathode process to improve the brightness gain. The streak image tube has the characteristics of high sensitivity, large detection field, high brightness gain, and high temporal and spatial resolution.Starting from the principle and control requirements, combined with the theoretical analysis of the defects of the active control system, a new type of high-integration control system is developed for the camera, which fully eliminates the low integration, poor reliability and compatibility of the previous version. defect. The hardware of the new control system adopts the design method of modularization and function reuse, and the PCB adopts the multi-layer board design. Compared with the current version, the degree of integration is increased by 2.36 times to achieve multi-device compatibility. The bottom layer of the system hardware is divided into main control module, power supply module, A/D module, D/A module, digital I/O and extended scan switching module: the main control module takes STM32F107VCT6 as the core and is responsible for the information between each module and the host computer Interaction; the power supply module is divided into a high-voltage power supply part and a low-voltage power supply part, which provide corresponding voltages for the stripe tube and each element of the circuit; the A/D module takes ADS1256 as the core, adds anti-static protection and digital-analog isolation to entirely eliminate noise interference, and uses SPI The protocol communicates with the host computer; the D/A module takes DAC8534 as the core to control the output of analog devices such as MCP and high-voltage power supply; the digital I/O and expansion scan switching module use the microcontroller GPIO as the control, and the 24 pins programmable interface supports function multiplexing. The PC-side visualization system realizes human-computer interaction and has functions such as camera control, instant feedback of collected images and data, and operation logs. The interface is concise and optimized, which greatly enhances the operability and maintainability of the camera.Finally, the streak tube static test system is used to test the parameters of the streak image tube: the cathode integral sensitivity is 268 μA/lm, the brightness gain is 20.1, and the time resolution is 36 ps; femtosecond laser, F-P etalon, DG645 delayer, oscilloscope, etc. built a dynamic test system for streak camera, and tested the static/dynamic spatial resolution, time resolution, control system function, etc. of the whole machine. The static spatial resolution is higher than 26 lp/mm, the full-screen scanning time is 600 ps, and the functions of control, monitoring and information exchange of the control system are normal. The developed streak camera works well in the laser radar and Inertial Confinement Fusion (ICF) picosecond laser targeting experiments.
Acta Photonica Sinica
  • Publication Date: Oct. 25, 2022
  • Vol. 51, Issue 10, 1032003 (2022)