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    Journals > > Topics > Ultrafast Optics

    Contents
    Ultrafast Optics|65 Article(s)
    Influence of Magnetic Field on Space Charge Effect in Pulse-Dilation Framing Camera
    Yanli Bai, Mingcheng Song, and Wangchun Zhu
    ObjectiveIn the inertial confinement fusion (ICF) experiment, the microchannel plate (MCP) framing camera is an important two-dimensional ultrafast diagnostic device that is used to acquire the duration and dynamic image of plasma at the stage of implosion compression. However, due to limitations of the electronic transmission time and its dispersion in the channel of the MCP, the temporal resolution is restricted to 60-100 ps for a long time. In order to further improve temporal resolution, a pulse-dilation framing camera (PDFC) is developed, which couples the MCP framing camera with the temporal dilation technique of the electron beam. With an ultrafast temporal resolution of better than 10 ps, it is easier to meet the detection requirements of the shorter duration states in the ICF. Therefore, the relevant ways and techniques of the PDFC are gradually focused on the field of ultrafast diagnosis. The PDFC is a new kind of framing camera with a long drift region using the imaging of magnetic focusing technique. Due to its similar structure to the streak camera, the improvement of its spatio-temporal performance to a higher order is restricted by the space charge effect (SCE). Moreover, the temporal width and radius of the electronic pulses (EPs) are dynamically changed by the dilating pulse and magnetic focusing in the PDFC. Therefore, building the model of the SCE that meets the dynamic parameters of the EPs and analyzing the influence of the dynamic radius caused by magnetic focusing on the spatio-temporal dispersions will be an important theoretical significance for systemically studying the SCE of the PDFC.MethodsIn the research, to analyze the influence of magnetic field on the spatio-temporal dispersions of the SCE, first of all, the model of the PDFC using magnetic focusing is built, and the dynamic characteristics of EPs during transmission are analyzed by the working principle of the PDFC. Then, the spatio-temporal dispersion model of the SCE is deduced by solving the equation of the electric field force based on the two-dimensional potential distribution of the EPs. To build a relationship between magnetic field and imaging area, while ensuring consistent imaging magnification, the different imaging magnetic fields are reasonably calibrated through the analysis procedure of optimal spatial performance of the PDFC based on the method of regional imaging. Finally, the dynamic temporal width and radius of the EPs are applied to the model of the SCE in different magnetic fields, and the spatio-temporal dispersions of different off-axis positions are analyzed.Results and DiscussionsThe innovative and significant research results are mainly summarized in three aspects. First, the dynamic variation of the electronic density during transmission is analyzed in the PDFC, on which the dynamic temporal width and radius of the EPs are based [Fig. 2 (d)]. Second, under consistent imaging magnification, the optimal spatial performance of the PDFC is analyzed, and different imaging magnetic fields are reasonably calibrated by regional imaging (Fig. 3). Third, the dynamic temporal width and radius of the EPs are applied to the model of the SCE. When the radius of the imaging region is 1 mm, as the off-axis position increases from 0 mm to 15 mm, the magnetic field intensity is enlarged from 4.585×10-3 T to 4.763×10-3 T. The defocusing and dynamic radius of EPs of the off-axis are much larger than those of the on-axis. Therefore, as the electronic density of the EPs reduces, the temporal dispersion of the SCE is reduced from 2.94 ps to 483 fs, and the spatial dispersion is reduced from 668 μm to 22 μm (Fig. 4). When the radius of imaging region is gradually enlarged to 20 mm, the magnetic field intensity of the on-axis is reduced from 4.585×10-3 T to 3.359×10-3 T, and the spatio-temporal dispersions of the SCE are optimum value in the range of 3.4×10-3-3.5×10-3 T. The range of temporal dispersions of different positions is 256-392 fs, and spatial dispersions is 3.1-15.4 μm (Fig. 5).ConclusionsIn the PDFC, the temporal width, radius, and electronic density of the EPs during the transmission process are dynamically changed by the effect of the dilating pulse and the imaging system of magnetic focusing. Moreover, the spatio-temporal dispersions of the SCE are significantly affected by the defocusing of the EPs and the fluctuation of radius caused by a magnetic field. According to the research methods and results, on the one hand, the different magnetic field is reasonably calibrated through the analysis of the optimal spatial performance of the PDFC; on the other hand, it also provides a theoretical basis for analyzing the relationship between the magnetic field and the SCE. In the next stage, to provide a theoretical basis for achieving faster temporal resolution of the PDFC, the spatio-temporal dispersions of the SCE are systematically studied from different types of magnetic focusing imaging systems and the long drift regions.
    Acta Optica Sinica
    • Publication Date: Mar. 10, 2024
    • Vol. 44, Issue 5, 0532001 (2024)
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    Improvement of Temporal Uniformity of Pulse-Dilation Framing Camera Using Pulse Superposition Technique
    Siqi Wu, Yanli Bai, Haiying Gao, Rongbin Yao, and Dajian Liu
    ObjectiveThe framing camera is a two-dimensional (2D) ultrafast diagnostic device with high spatio-temporal resolution. In inertial confinement fusion (ICF) experiments, it can effectively acquire the duration and dynamic images at the stage of implosion compression. The pulse dilation framing camera is a new ultrafast diagnostic device with temporal resolution better than 10 ps. Firstly, this paper loads the dilating pulse between the photocathode (PC) and grid to achieve greater acceleration energy of the front edge of electron beams. Then, the temporal width of the electron beam is dilated through long-distance transmission. Finally, the dilated electron beam signal is measured by the microchannel plate (MCP) framing camera, and the temporal resolution is exponentially improved. However, in the pulse-dilation framing camera, with the transmission of dilating pulse along the PC, the voltage at different positions on the PC is changed, which results in temporal non-uniformity. This is one of the main factors restricting the development of framing cameras with large detection areas. To improve the restriction of temporal non-uniformity of the pulse-dilation framing camera, the gating pulse with picoseconds is designed, and the improvement of the temporal uniformity is studied by simultaneously loading the falling edge of the gating pulse and dilating pulse on the PC, which is based on the variational phenomenon of voltage during the transmission of dilating pulse along the PC.MethodsThis paper first deduces the computational equation of the dynamic dilating ratio of the electron beam along the PC by analyzing the causes of temporal non-uniformity and combines the principle of temporal dilation and the transmission characteristics of the electric pulse along the PC. Then, the high-voltage gating pulse with picoseconds is designed by the three-stage Marx pulse generator and the pulse shaping circuit. The Marx pulse generator is realized by the series and parallel of avalanche triodes, and the pulse shaping circuit is made up of the avalanche diode and the two-stage high pass filter with LC. In addition, based on the electric pulse superposition technology and the voltage variation characteristics of dilating pulse transmission along the PC, the improvement of temporal non-uniformity is studied with the optimization of the PC voltage distribution by simultaneously loading the falling edge of the gating pulse and the dilating pulse on the PC. Finally, when the falling edge of the gating pulse is loaded or not loaded on the PC, the temporal uniformity is numerically compared by calculating the dilating ratio of electron beams along the PC, and the temporal uniformity improvement is quantized via the difference percentage between the sampling points.Results and DiscussionsThe picosecond pulse generator [Fig. 2(a)] is designed by the series and parallel of avalanche triodes, the series of avalanche diodes, and the two-stage high pass filter with LC. The gating pulse with an amplitude of -2.59 kV and full width at half maximum of 236 ps is obtained, and its rising and falling edges are 217 ps and 204 ps respectively [Fig. 2 (b)]. Temporal uniformity improvement is analyzed when the falling edge of the gating pulse is loaded or not loaded on the PC and then quantized by the difference percentage between the sampling points [Fig. 4 (d)]. While the falling edge of the gating pulse is not loaded on the PC, the dilating ratio of the electron beam along the PC increases from 11.74 to 39.04, and the difference percentage is 232.5%. When the falling edge is loaded, the dilating ratio rises from 11.28 to 14.23, and the difference percentage is descended to 40.21%. The temporal uniformity of the pulse-dilation framing camera is improved by loading the falling edge of the gating pulse.ConclusionsThe Marx pulse generator is designed by series and parallel of avalanche triodes. The high-voltage picosecond circuit is designed with avalanche diodes and high pass filters, and the high-voltage picosecond gating pulse is generated. Based on the pulse superposition technology, the temporal uniformity of the pulse dilation framing camera is improved by the falling edge of the gating pulse. The results show that when the PC voltage is -2 kV, the initial width of the electron beam is 5 ps, and the gradient of dilating pulse is 11.9 V/ps, with the transmission of the dilating pulse along the PC, the voltage is changed from -4.48 kV to -2.47 kV, and the dilating ratio of the electron beam grows from 11.74 to 39.04 with the difference percentage of 232.5%. When the falling edge of the gating pulse with the gradient of 12.7 V/ps is simultaneously loaded on the PC, the voltage along the PC is changed from -4.62 kV to -4.97 kV, and the dilating ratio of the electron beam rises from 11.28 to 14.23. The difference percentage is descended to 40.21%, and the temporal uniformity is improved. This study can provide an effective method for improving the temporal non-uniformity of pulse-dilation framing cameras, and a theoretical reference for the development of 10 ps framing cameras with large detection areas.
    Acta Optica Sinica
    • Publication Date: Mar. 10, 2023
    • Vol. 43, Issue 5, 0532001 (2023)
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    Modulation of Ultrashort Pulse Width in Optical Moiré Lattices
    Xueqian Zhao, Zhinan Liu, and Hui Liu
    ObjectiveUltrashort pulses, with a pulse duration of tens of picoseconds (10–12 ps) or less, are timing tools with the highest precision available currently. Their narrow pulse width and high peak power characteristics have considerably advanced the development of nonlinear optics. However, ultrashort pulse lasers unavoidably suffer from the dispersion introduced by various optical elements during their operation, resulting in pulse deformation and power attenuation, which adversely affect the performance of ultrashort pulses. Therefore, extensive research has been conducted on pulse width regulation. The current solution is primarily based on the utilization of dispersion-compensation devices, which suffer from low integration characteristics and nonactive regulation. Recently, the optical Moiré structure has become a widely discussed topic due to its high potential in the modulation of light field by changing Moiré angles. However, most published works introduce physical twisted angles, and optical Moiré structures combined with the concept of synthetic dimensions have rarely been reported. Therefore, we propose an optical Moiré lattice with artificially synthesized Moiré angles to achieve ultrashort pulse width modulation.MethodsA method of constructing optical Moiré lattices with artificially synthesized Moiré angles (nonphysical twisted angles) is proposed herein. Moiré lattices comprise two simple photonic lattices with different periods, and the ratio of the arctangents of their periods represents the Moiré angle of the optical Moiré lattice. Three optical Moiré lattices with gradually increasing Moiré angles are theoretically designed, and the band structure of the optical Moiré lattices is determined by the transfer matrix method; we observe that the increase in Moiré angles leads to the flattening of the band structure. The band dispersion is further analyzed, following which the group velocity and pulse width changes introduced by an ultrashort pulse through the Moiré lattices are computed. The theoretical calculations demonstrate the effect of Moiré lattices on the width of ultrashort pulses. Subsequently, an optical path based on an autocorrelator is built to experimentally verify the theoretical results. Further, we define the variation rate of pulse width to effectively illustrate the modulation of ultrashort pulses.Results and DiscussionsFirst, the effects of artificially synthesized Moiré angles on the band structure are analyzed: the increase in the Moiré angles results in higher band compression coefficients (Fig.2), which indicates a decrease in the bandwidth (Fig.3). Meanwhile, a narrow band leads to a decreased group velocity (Fig.4) and considerable second- and third-order group velocity dispersion (Fig.5). We demonstrate a theoretical model to explain the effect of group velocity dispersion on the width of ultrashort pulses (Equations 3-8). The equations imply that Moiré lattices with high group velocity dispersion lead to intense pulse broadening and pulse compression of ultrashort pulses. The results of pulse width measurements before and after passing through the three Moiré lattices were obtained using the autocorrelator (Table 1). As seen from Table 1, the variation in pulse width increases with the increase in the Moiré angle. The accurate modulation of the ultrashort pulse width by the optical Moiré lattice is confirmed by the comparison of the theoretical and experimental values of the pulse width ratio (Fig.7).ConclusionsThe construction method for the optical Moiré lattices in the synthetic space proposed herein can effectively realize the analogy of traditional optical Moiré lattices with physical twisted angles. The regularity of the artificially synthesized Moiré angles affecting band structures has been clearly confirmed. Theoretical calculations show the following: a larger artificially synthesized Moiré angle leads to lower group velocity and more considerable second- and third-order group velocity dispersion, which results in larger variations in pulse widths. Moreover, the accurate modulation achieved by the optical Moiré lattice indicates that the lattices can be predesigned to satisfy universal requirements such as a wide range of pulse width adjustments. In theory, we can design a series of Moiré lattices with different artificially synthesized Moiré angles, resulting in rich and more predictable pulse width variations. In summary, first, we state that the optical Moiré lattice in the synthetic dimension considerably simplifies the complexity of structural processing: traditional optical Moiré lattices require precise control of the physical twisted angles of the two sublattices, while the optical Moiré lattice in the synthetic space depends on strategic parameter definitions. The one-dimensional structure in the geometric space renders its processing highly convenient. Second, the optical Moiré lattice provides a new degree of light field modulation, which means that a flattened band structure can be obtained by changing the Moiré angle. Finally, the overall thickness of our optical Moiré lattice is at the micrometer level, which has the advantage of high integration. Our structure can become the key component in the manufacturing of laser pulse width compressors.
    Acta Optica Sinica
    • Publication Date: Oct. 25, 2023
    • Vol. 43, Issue 20, 2032001 (2023)
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    Research Progress on Intense, Broadband, Terahertz Wave Radiation
    Hang Zhao, Yuejin Zhao, Liangliang Zhang, and Cunlin Zhang
    SignificanceThe terahertz (THz) range (0.1-10 THz) lies between the microwave and infrared region in the electromagnetic spectrum and is characterized by low photon energy and strong penetration. The THz range covers the spectra attributed to the intermolecular vibrations and rotational energy levels of various organic and biological macromolecules. Terahertz technology realizes the integration of electronics and photonics, offering tremendous development potential in fields such as military applications, biomedical applications, and future communications. However, before mid-1980s, research on the nature of terahertz radiation could not be conducted owing to the absence of effective generation and detection methods with respect to electromagnetic radiation in the terahertz frequency range.The subsequent rapid advancement in ultrafast laser pulse technology offered a stable and effective excitation source for generating terahertz pulses. However, owing to the low output power of existing terahertz-radiation sources and the high thermal-radiation background in the terahertz frequency range, new sources need to be developed to meet high requirements in terms of energy, bandwidth, and other performance characteristics.Terahertz radiation can be generated through several methods, including optical methods, terahertz quantum cascade lasers, and solid electronic devices. This study primarily focuses on optical devices used for generating terahertz radiation. The femtosecond laser pulse, characterized by low repetition rates and high energy, can serve as the pump source, triggering strong nonlinear effects in various targets, thus generating strong terahertz radiation. This radiation affords manipulation and control over complex condensed-matter systems. Moreover, this method of generating terahertz radiation has been studied extensively, and the material state covers solid, gas, and liquid.However, sources that can emit terahertz radiation having high energy and a broad frequency spectrum are still lacking. If a broadband strong terahertz source with stable output can be realized, it can greatly promote the development and practical process of terahertz technology in various fields. This study summarizes recent research progresses in generating intense broadband terahertz radiation using various materials excited via ultrafast femtosecond lasers, including studies on laser-induced terahertz radiation from nanometal films, gas plasma, and liquid plasma. The inherent physical mechanisms of each method are analyzed and discussed herein, affording numerous important exploration directions for research on terahertz-radiation sources.ProgressPhotoconductive antennas and nonlinear electro-optic crystals, which are routinely used as terahertz-radiation sources in laboratories, generate stable terahertz radiation when excited via ultrashort laser pulses. Terahertz radiation can be employed in research applications such as terahertz time-domain spectral imaging. Although the signal-to-noise ratio of terahertz radiation is considerably higher than that of the radiation in the traditional far-infrared Fourier spectrum, the detection and observed spectrum range of terahertz radiation is constrained, only covering a range of 0-3 THz. Recently, researchers have focused on generating terahertz waves from metal films. In 2007, Gregor et al. reported in Physical Review Letters that terahertz waves ranging from 0.2 to 2.5 THz could be generated using metal gratings with nanostructures. They postulated that these terahertz waves were generated owing to incoherent optical rectification, which was caused by the acceleration of photoelectrons by surface plasma evanescent waves. In 2011, Polyushkin et al. reported in Nano Letters the use of silver nanoparticle arrays to generate a terahertz pulse with a bandwidth of 0-1.5 THz. They suggested that terahertz waves were generated when photoelectrons were accelerated by the driving force created by the inhomogeneous plasma electric field. In 2014, Dai et al. reported in Optics Letters the generation of a terahertz wave with a bandwidth of 0-2.5 THz by exciting a gold film deposited on a titanium sapphire substrate using a two-color laser field. They attributed this generation process to the third-order nonlinear effect of metal, namely the four-wave mixing mechanism. We reported that femtosecond laser pulses can excite thin metal films to emit high-energy, broadband terahertz waves and studied the physical mechanism of this emission process from various aspects such as energy, material, frequency, and gas environment (Figs. 1-7).In contrast to the abovementioned solid-medium generation methods, generating terahertz radiation using the femtosecond laser-excited air plasma provides several advantages, including ultrawideband, high intensity, remote detection feasibility, and no laser damage threshold. Using different pump lasers to excite plasma presents a novel research approach. Clerici et al. proposed a model in Physical Review Letters that could effectively predict the wavelength dependence of terahertz emission through experimental research. They demonstrated that the plasma current increases proportionally with the square of the pump wavelength, and the terahertz emission at 1800 nm is 30 times higher than that at 800 nm owing to the wavelength combination effect. We explored the characteristics of terahertz waves radiated from plasma excited using long-wavelength lasers (Figs. 8-12) and observed that the radiation ability of the terahertz waves is enhanced by pre-modulating the plasma, changing the excitation medium, and altering the ratio of the two-color light frequency (Figs. 13-19).Reports on liquids being used as terahertz-radiation sources are scarce. In 2017, in Applied Physics Letters, Jin et al. reported the possibility of a terahertz wave being generated using a liquid water film. Simultaneously, Dey et al. reported in Nature Communications that ultrashort laser filaments in liquids could generate terahertz wave radiation. They discovered that the terahertz energy radiated by a liquid excited by the monochromatic field is an order of magnitude higher than that of the terahertz wave obtained by the two-color field scheme in the air. In 2018, Yiwen E et al. reported in Applied Physics Letters the mechanism of terahertz radiation generated by a water film based on the simulation they performed using a dynamic dipole that demonstrated the dependence of terahertz intensity on incident laser angle. Moreover, we conducted research on terahertz waves generated by exciting a liquid water film. We explored the characteristics of a terahertz wave generated via the laser excitation of a water film and water line (Figs. 20-25), and further increased the radiation efficiency of the terahertz wave.Conclusions and ProspectsHerein, we report that materials such as metal films, air, and liquid water films excited using ultrafast femtosecond lasers provide a novel approach for obtaining powerful terahertz radiation. The development of robust terahertz sources allows the exploration of the nonlinear characteristics of materials in the terahertz range and provides the experimental basis for observing the dynamic evolution of materials on the picosecond scale. The increasing development of terahertz technology and the practical application demand also constantly put forward new expectations for terahertz sources. Improving the understanding related to the terahertz-radiation mechanism in materials excited by laser pulses and identifying excellent terahertz sources will remain a long-term objective for many researchers.
    Acta Optica Sinica
    • Publication Date: Aug. 10, 2023
    • Vol. 43, Issue 15, 1532001 (2023)
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    Generation of Isolated Attosecond Pulse Using Orthogonally Polarized Two-Color Fields
    Jianan Sun, Yanben Yin, and Gao Chen
    ObjectiveAttosecond pulses are currently the shortest radiation pulses that can be obtained, and their ultra-fine temporal and spatial resolution has become an important tool to study ultra-fast electron dynamics in atoms and molecules. At present, the high-order harmonic generation from the interaction of femtosecond pulses with atoms or molecules is the only effective means to produce desktop attosecond pulse radiation sources. Thus, researchers have proposed many advanced techniques for generating isolated attosecond pulses in experiments and theories, such as few-cycle laser pulses, dual-color or multi-color fields, and polarization gating schemes. The orthogonally polarized dual-color fields, composed of two linearly polarized pulses with different wavelengths and perpendicular polarization directions, have become an effective way to control electron motion with the characteristics of polarization modulation and two-color field. By numerically simulating the interaction between helium atoms and orthogonally polarized dual-color fields composed of 4 fs/800 nm driving pulses and 8 fs/400 nm gating pulses, we obtain a 54 as high-intensity isolated attosecond pulse. The advantage of this scheme is that a single quantum trajectory (short trajectory) can be selected during a single atomic response. Additionally, the isolated attosecond pulse is less affected by the relative phase between the two pulses and by the change in the electric field intensity of the gating pulse.MethodsThe high-order harmonic generation from the interaction of the orthogonally polarized two-color field with helium atom is studied numerically by the strong field approximation theory. Attosecond pulses are synthesized by superimposing the super-continuum harmonic spectra. The ionization rate of helium atoms is calculated through the ADK tunneling ionization theory model, and the classical trajectory of electrons is calculated using the semi-classical three-step model theory proposed by Corkum.Results and DiscussionsAn orthogonally polarized bichromatic field consisting of a 4 fs/800 nm driving pulse and an 8 fs/400 nm gating pulse interacting with helium atoms is employed to obtain a super-continuous harmonic spectrum with high intensity and small oscillation amplitude. The supercontinuum harmonic range extends from 120th to 180 th order (Fig. 1), which is fully consistent with the calculation results of the semi-classical three-step model theory [Figs. 2(a) and (b)]. The electron trajectory shows that the platform harmonics mainly come from the contribution of short-orbit electrons. Due to its short motion time, less wave packet diffusion, and no interference with the harmonics generated by long-orbit electrons, the high-order harmonic spectrum in the direction of the driving pulsed electric field presents the characteristics of a super-continuous platform region with higher intensity and smaller modulation amplitude [Fig. 2(c) and (d)]. To further verify the rationality of the classic analysis, we adopt the wavelet transform method to calculate the time-frequency analysis diagram of the high-order harmonic emission when the orthogonally polarized two-color field irradiates the helium atom. The obtained results are consistent with the above supercontinuum harmonic spectrum range (Fig. 3). By superimposing the entire supercontinuum band in the spectrum, an isolated attosecond pulse with a duration of 54 as and an intensity of 3.2×10-6 is generated [Fig. 4(b)]. The results are three orders of magnitude stronger and shorter than the isolated attosecond pulse with a duration of 126 as and an intensity of 1.9×10-9 generated in a single 800 nm titanium sapphire laser pulse [Fig. 4(a)]. In addition, we find that under the current selected pulse laser parameters, the selection requirements of the relative phase among the combined pulses are not strict, and isolated attosecond pulses with shorter pulse widths can be obtained in the range of 0.3π. Additionally, controlling the change of pulse electric field intensity exerts little effect on the above numerical simulation results (Fig. 5). Furthermore, in terms of the cutoff position of the harmonic emission spectrum and harmonic conversion efficiency, the proposed orthogonally polarized bichromatic field scheme has obvious advantages over the parallel polarized bichromatic field scheme with the same parameters.ConclusionsWe obtain the broadband super-continuous harmonic spectrum with small oscillation amplitude through the orthogonally polarized bichromatic field synthesized by a titanium gemstone pulse and its second harmonic pulse interacting with helium atoms. The origin of the super-continuous harmonic spectrum is explained based on analyzing the electronic motion orbit, and it is attributed to a single contribution of short-track electrons with a short motion time and less wave packet dispersion. By performing Fourier transformation on the supercontinuum harmonic, a high-intensity isolated attosecond pulse with a duration of 54 as is obtained. The isolated attosecond pulse is less affected by the relative phase between the two pulses and by the change in the electric field intensity of the gating pulse.
    Acta Optica Sinica
    • Publication Date: Jul. 10, 2023
    • Vol. 43, Issue 13, 1332001 (2023)
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    Chirped Airy Pulse Modulated by Gaussian Pulse
    Hao Zhang, Zhenming Song, Lujia Zhou, Zhaoqi Li, and Qian Ma
    Airy pulse, especially chirped Airy pulse, has attracted more and more attention and research because of its unique properties. However, due to the complexity of chirped Airy pulses, there are few experimental reports about chirped Airy pulses. In view of this, the chirped Airy pulse can be obtained by modulating the chirped Gaussian pulse in theory, and the modulation mechanism and the transmission properties of the modulated pulse are studied. The results show that the like chirped Airy pulse obtained after modulation is basically the same as the chirped Airy pulse, and has the transmission property of the chirped Airy pulse, which proves the feasibility of the chirped Airy pulse obtained by modulating the chirped Gaussian pulse.
    Acta Optica Sinica
    • Publication Date: Mar. 29, 2022
    • Vol. 42, Issue 8, 0832001 (2022)
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    Research Progress of Ultrafast Laser Regulated Nucleation and Growth of Nanocrystals
    Ke Sun, Haiyi Jiang, Kaiyi Xiong, Bo Zhang, Dezhi Tan, and Jianrong Qiu
    Ultrafast laser has features of ultrafast speed, ultra-high intensity, and ultra-wide spectrum. Focused ultrafast laser can instantaneously generate extremely high temperature and pressure within transparent materials. Under such local extreme conditions, many new changes in the internal structures of the materials take place. Taking all-inorganic halide perovskite nanocrystals (PNCs) as an example, the basic principle of ultrafast laser-induced nucleation and nanocrystal precipitation in glass is expounded. Researches conducted in recent years on the precipitation of all-inorganic PNCs in glass by ultrafast laser are summarized, and the applications of this technology in the fields of optical storage and color display are analyzed.
    Acta Optica Sinica
    • Publication Date: Sep. 10, 2022
    • Vol. 42, Issue 17, 1732001 (2022)
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    Study on Field Curvature Characteristics of Pulse-Dilation Framing Tube
    Yunfei Lei, Jinyuan Liu, Houzhi Cai, Junkun Huang, Yong Wang, and Pokun Deng
    In this paper, a pulse-dilation framing tube is developed, and the field curvature characteristics and off-axis spatial resolution of this tube are analyzed. Multiple short magnetic lenses are used in this tube to image the photoelectrons from the cathode onto the receiving surface of the microchannel plate. The field curvature characteristics of lenses number imaging are studied by simulations and verified by experiments. The simulation results show that the field curvature of the imaging system can be reduced by multiple lenses and the spatial resolution is improved. When the imaging ratio is 1∶1, the axial deviations of simple lens, bilens, triplet lens, and four lenses from Gaussian image plane are 13 cm, 4.7 cm, 2.5 cm, and 1.7 cm, respectively. The experimental results show that the off-axis modulation of the four lenses system is 40% higher than that of the single lens.
    Acta Optica Sinica
    • Publication Date: Nov. 17, 2021
    • Vol. 41, Issue 21, 2132001 (2021)
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    All-Optical Framing Imaging Technology Based on Diffractive Optical Elements
    Yanjin Li, Lang Zhou, Zhuo Li, Rui Shi, Xin Wang, and Suhui Yang
    Ultrafast imaging is an important method for studying ultrafast phenomena such as explosions and high-voltage discharges. All-optical framing imaging has great development prospects because it can overcome the time limitation of optical-to-electric signal conversion. In this study, an all-optical spatial framing imaging system is constructed using a diffractive optical element and a band pass filter, the array framing imaging is successfully realized, and the results of different bands are analyzed. The experimental results show that the designed all-optical spatial framing imaging system can realize 16-framing imaging in a 4×4 array in different wavelength bands. The relative standard deviation of the non-uniformity between the image frames is 7.4%, and the average deviation of the non-uniformity within a frame is 2.83%. Further, the modulation transfer function of the all-optical framing imaging system is 0.991 at resolution of 35 lp/mm.
    Acta Optica Sinica
    • Publication Date: Feb. 26, 2021
    • Vol. 41, Issue 2, 0232001 (2021)
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    Raman Shift Temperature Effect and New Temperature Measurement Method
    Yan Wang, Ling Zhu, Xuexian Yang, Xiaoyun Wang, and Jinzhang Peng
    The existing distributed optical fiber Raman temperature measuring principle is to use the relationship between Stokes and anti-Stokes intensity ratio and temperature to obtain the temperature. However, it is difficult to process the light intensity signal, since the Raman scattering peak intensity is relatively weak. According to the bond relaxation theory and the relationship between Raman frequency shift and bond parameters, a linear relationship between Raman frequency shift and temperature is established. And a new method for measuring Raman frequency shift temperature is proposed. The Raman frequency shift high temperature effects of diamond, graphite, CdS, Bi2Se3 and Sb2Te3 are calculated. These calculation results match well with the experimental ones and the Raman reference frequency and the atomic cohesive energy are obtained. The proposed method effectively avoids the influence of Raman peak strength on temperature measurement and provides a new theoretical method for the rapid development of distributed optical fiber Raman temperature measuring techniques.
    Acta Optica Sinica
    • Publication Date: Sep. 01, 2021
    • Vol. 41, Issue 17, 1732001 (2021)
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