Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the in...Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the instantaneous bloodflow velocity distribution.This is mainly due to the lack of measurement technology with high spatial and temporal resolution.Here,we tackle this problem with our recently developed dual-wavelength line-scan third-harmonic generation(THG)imaging technology.Simultaneous acquisition of dual-wavelength THG line-scanning signals enables measurement of bloodflow velocities at two radially symmetric positions in both venules and arterioles in mouse brain in vivo.Our results clearly show that the instantaneous bloodflow velocity is not symmetric under general conditions.展开更多
The influence of electron-phonon interactions on third-harmonic generation in a square quantum well is investigated. The first- and third-harmonic generation coefficient is obtained by using compact-density-matrix app...The influence of electron-phonon interactions on third-harmonic generation in a square quantum well is investigated. The first- and third-harmonic generation coefficient is obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for a GaAs square quantum well. The results show that the third-harmonic generation coefficient is obviously enhanced after considering the influence of electron-phonon interactions.展开更多
Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compare...Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compared to metasurfaces composed of the periodic arrangement of nanoparticles,inverse,so-called,membrane metasurfaces offer unique possibilities for supporting multipolar resonances,while maintaining small unit cell size,large mode volume and high field enhancement for enhancing nonlinear frequency conversion.Here,we theoretically and experimentally investigate the formation of bound states in the continuum(BICs)from silicon dimer-hole membrane metasurfaces.We demonstrate that our BIC-formed resonance features a strong and tailorable electric near-field confinement inside the silicon membrane films.Furthermore,we show that by tuning the gap between the holes,one can open a leaky channel to transform these regular BICs into quasi-BICs,which can be excited directly under normal plane wave incidence.To prove the capabilities of such metasurfaces,we demonstrate the conversion of an infrared image to the visible range,based on the Third-harmonic generation(THG)process with the resonant membrane metasurfaces.Our results suggest a new paradigm for realising efficient nonlinear photonics metadevices and hold promise for extending the applications of nonlinear structuring surfaces to new types of all-optical near-infrared imaging technologies.展开更多
The skin is heterogeneous and exerts strong scattering and aberration onto excitation light in multiphoton microscopy(MPM).Shifting to longer excitation wavelengths may help reduce skin scattering and aberration,poten...The skin is heterogeneous and exerts strong scattering and aberration onto excitation light in multiphoton microscopy(MPM).Shifting to longer excitation wavelengths may help reduce skin scattering and aberration,potentially enabling larger imaging depths.However,previous demonstrations of skin MPM employ excitation wavelengths only up to the 1700 nm window,leaving an open question as to whether longer excitation wavelengths are suitable for deep-skin MPM.Here,in order to explore the longer-wavelength territory,first,we demonstrate characterization of the broadband transmittance of excised mouse skin,revealing a high transmittance window at 2200nm.Then,we demonstrate third-harmonic generation(THG)imaging in mouse skin in vivo excited at this window.With 9mW optical power on the skin surface operating at 1MHz repetition rate,we can get THG signals of 250m below the skin surface.Comparative THG imaging excited at the 1700nm window shows that as imaging depth increases,THG signals decay even faster than those excited at 2200 nm.Our results thus uncover the 2200 nm window as a new,promising excitation window potential for deep-skin MPM.展开更多
We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating ...We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament.展开更多
Broadband frequency-tripling pulses with high energy are attractive for scientific research,such as inertial confinement fusion,but are difficult to scale up.Third-harmonic generation via nonlinear frequency conversio...Broadband frequency-tripling pulses with high energy are attractive for scientific research,such as inertial confinement fusion,but are difficult to scale up.Third-harmonic generation via nonlinear frequency conversion,however,remains a trade-off between bandwidth and conversion efficiency.Based on gradient deuterium deuterated potassium dihydrogen phosphate(KD_(x)H_(2-x)PO_(4),DKDP)crystal,here we report the generation of frequency-tripling pulses by rapid adiabatic passage with a low-coherence laser driver facility.The efficiency dependence on the phase-matching angle in a Type-II configuration is studied.We attained an output at 352 nm with a bandwidth of 4.4 THz and an efficiency of 36%.These results,to the best of our knowledge,represent the first experimental demonstration of gradient deuterium DKDP crystal in obtaining frequency-tripling pulses.Our research paves a new way for developing high-efficiency,large-bandwidth frequency-tripling technology.展开更多
Nonlinear dielectric metasurfaces provide a promising approach to control and manipulate frequency conversion optical processes at the nanoscale,thus facilitating both advances in fundamental research and the developm...Nonlinear dielectric metasurfaces provide a promising approach to control and manipulate frequency conversion optical processes at the nanoscale,thus facilitating both advances in fundamental research and the development of new practical applications in photonics,lasing,and sensing.Here,we employ symmetry-broken metasurfaces made of centrosymmetric amorphous silicon for resonantly enhanced second-and third-order nonlinear optical response.Exploiting the rich physics of optical quasi-bound states in the continuum and guided mode resonances,we comprehensively study through rigorous numerical calculations the relative contribution of surface and bulk effects to second-harmonic generation(SHG)and the bulk contribution to third-harmonic generation(THG) from the meta-atoms.Next,we experimentally achieve optical resonances with high quality factors,which greatly boosts light-matter interaction,resulting in about 550 times SHG enhancement and nearly 5000-fold increase of THG.A good agreement between theoretical predictions and experimental measurements is observed.To gain deeper insights into the physics of the investigated nonlinear optical processes,we further numerically study the relation between nonlinear emission and the structural asymmetry of the metasurface and reveal that the generated harmonic signals arising from linear sharp resonances are highly dependent on the asymmetry of the meta-atoms.Our work suggests a fruitful strategy to enhance the harmonic generation and effectively control different orders of harmonics in all-dielectric metasurfaces,enabling the development of efficient active photonic nanodevices.展开更多
The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion.This paper presents the intracavity frequency t...The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion.This paper presents the intracavity frequency tripling in a self-mode-locked semiconductor disk laser,and a picosecond pulse train at 327 nm wavelength is achieved.The pulse repetition rate is 0.49 GHz,and the pulse width is 5.0 ps.The obtained maximum ultraviolet output power under mode locking is 30.5 m W,and the corresponding conversion efficiency is obviously larger than that of continuous-wave operation.These ultraviolet picosecond pulses have high spatial and temporal resolution and can be applied in some emerging fields.展开更多
In this manuscript,a new axial-flux permanentmagnet machine(AFPMM)is designed,analyzed,improved,and successfully tested.A double-sided AFPM generator with four layers of stator winding is initially designed using a we...In this manuscript,a new axial-flux permanentmagnet machine(AFPMM)is designed,analyzed,improved,and successfully tested.A double-sided AFPM generator with four layers of stator winding is initially designed using a well-known quasi-3D analytical method.Then,the designed machine is simulated using commercial software.It is shown that modification techniques are required to improve the performance of both the torque ripple and the ratio of the third to the fundamental harmonics of the induced voltage.Therefore,a new improvement technique is proposed,in which the layers of the stator winding are shifted relative to each other.While this new technique significantly improves the third harmonic problem,the design still has a high torque ripple and,thus,it is suggested to combine the proposed method with the conventional magnet shifting technique.It is revealed numerically that the resulting combination properly resolves both third harmonic and torque ripple problems.Therefore,this design is considered the main design of the present manuscript.In the end,a prototype of the main design is manufactured and tested.It is shown that the measurement results are in good agreement with those of numerical software.展开更多
Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region.Howeve...Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region.However,the generated high-harmonic emissions are subject to a resonance shift with a change in temperature.We present a comprehensive study of the thermal behavior induced phase mismatch that shows this resonance shift can be compensated by a combination of the linear and nonlinear thermo-optics effects.Using this model,we predict and experimentally demonstrate visible third harmonic modes having temperature dependent wavelength shifts between−2.84 pm/ºC and 2.35 pm/ºC when pumped at the L-band.Besides providing a new way to achieve athermal operation,this also allows one to measure the thermal coefficients and Q-factor of the visible modes.Through steady state analysis,we have also identified the existence of stable athermal third harmonic generation and experimentally demonstrated orthogonally pumped visible third harmonic modes with a temperature dependent wavelength shift of 0.05 pm/ºC over a temperature range of 12ºC.Our findings promise a configurable and active temperature dependent wavelength shift compensation scheme for highly efficient and precise visible emission generation for potential 2f–3f self-referencing in metrology,biological and chemical sensing applications.展开更多
The critical current density Jc is one of the most important parameters of high temperature superconducting films in superconducting applications, such as superconducting filter and superconducting Josephson devices. ...The critical current density Jc is one of the most important parameters of high temperature superconducting films in superconducting applications, such as superconducting filter and superconducting Josephson devices. This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation. Using this model, it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for Jc. The theoretic curve is consistent with the experimental results about measuring superconducting film, especially when the third-harmonic voltage just exceeds zero. The Jc value of superconducting films determined by the inductive method is also compared with results raeasured by four-probe transport method. The agreements between inductive method and transport method are very good.展开更多
To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,...To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness.By rotating the plate up to 35°along the beam direction,we reduced the walk-off angle up to ~ 13%.The same phenomenon is predicted by the model,confirming the performance of the model.It is found that,due to the walk-off effect,the intensity profile of the thirdharmonic generation beam is slightly degraded.To compensate for the observed phenomena and further reduce the walkoff,we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form.As a result,the walk-off is decreased to~ 48.81 mrad,providing ~ 30%relative reduction.By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction,the walk-off angle is further reduced to 38.9 mrad.Moreover,it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.展开更多
A detailed procedure for the calculation of the third-harmonic-generation susceptibility tensor is given in special asymmetric quantum wells, and an analytic formula for the third-harmonic-generation susceptibility is...A detailed procedure for the calculation of the third-harmonic-generation susceptibility tensor is given in special asymmetric quantum wells, and an analytic formula for the third-harmonic-generation susceptibility is obtained by the compact density matrix approach and the iterative procedure. Finally, the numerical results are presented for typical GaAs/AlGaAs asymmetric quantum wells. The calculated results show that the origin of the large thirdharmonic-generation susceptibility is due to the increase in asymmetry of the quantum well.展开更多
Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics,chemistry and materials science to information communications and processing.Here we present the d...Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics,chemistry and materials science to information communications and processing.Here we present the design and fabrication of a chirped periodically poled lithium niobate(CPPLN)nonlinear photonic crystal that supports multiple orders of quasiphase matching with finite bandwidth and allows for the simultaneous broadband generation of second and third harmonics with high conversion efficiency.Moreover,the chirp rate has a significant influence on the conversion efficiency and bandwidth.The CPPLN scheme offers a promising approach for the construction of short-wavelength laser sources and enables the generation of the three primary colors—red,green and blue—from a single crystal,which may have potential applications in large-screen laser displays.展开更多
A key concept underlying the specific functionalities of metasurfaces is the use of constituent components to shape the wavefront of the light on demand.Metasurfaces are versatile,novel platforms for manipulating the ...A key concept underlying the specific functionalities of metasurfaces is the use of constituent components to shape the wavefront of the light on demand.Metasurfaces are versatile,novel platforms for manipulating the scattering,color,phase,or intensity of light.Currently,one of the typical approaches for designing a metasurface is to optimize one or two variables among a vast number of fixed parameters,such as various materials’properties and coupling effects,as well as the geometrical parameters.Ideally,this would require multidimensional space optimization through direct numerical simulations.Recently,an alternative,popular approach allows for reducing the computational cost significantly based on a deep-learning-assisted method.We utilize a deep-learning approach for obtaining high-quality factor(high-Q)resonances with desired characteristics,such as linewidth,amplitude,and spectral position.We exploit such high-Q resonances for enhancedlight–matter interaction in nonlinearoptical metasurfaces and optomechanical vibrations,simultaneously.We demonstrate that optimized metasurfaces achieve up to 400-fold enhancement of the third-harmonic generation;at the same time,they also contribute to 100-fold enhancement of the amplitude of optomechanical vibrations.This approach can be further used to realize structures with unconventional scattering responses.展开更多
Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet(UV) laser based on a micro-lens array(MLA) is presente...Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet(UV) laser based on a micro-lens array(MLA) is presented in this Letter. It is worth noting that the MLA is employed to act as the spatial splitter as well as the coupling lens. With assistance of the MLA,the 1064 nm laser and 532 nm laser are divided into four sub-beams and focused at different areas of the third-harmonic generation(THG) crystal. As a result, the multi-beam pulsed 355 nm UV laser is successfully generated inside the THG crystal. The measured pulse widths of four sub-beams are shorter than 9 ns. Especially, the generated four sub-beams have good long-term power stability benefitting from the employed MLA. We believe that the generated stable multi-beam355 nm UV laser can meet the requirement of high-efficiency laser processing, and the presented method can also pave the way to generate stable and long-lived multi-beam UV lasers.展开更多
Nowadays,realizing miniaturized nonlinear optical(NLO)device is crucial to meet the growing needs in on-chip nanophotonics as well as compact integrated devices.The strong optical nonlinearities,ultrafast photoexcitat...Nowadays,realizing miniaturized nonlinear optical(NLO)device is crucial to meet the growing needs in on-chip nanophotonics as well as compact integrated devices.The strong optical nonlinearities,ultrafast photoexcitation dynamics,available exciton effects as well as without lattice matching make two-dimensional(2D)layered materials potential candidates for integrated and nano-scale NLO devices.Herein,a novel and inversion symmetry broken 2D layered SnP_(2)S_(6)with strong second-harmonic and third-harmonic response has been reported for the first time.The second-order susceptibility(χ^(2))of SnP_(2)S_(6)flakes can reach up to 4.06×10^(−9)m·V^(−1)under 810 nm excitation wavelength,which is around 1–2 orders of magnitude higher than that of most reported 2D materials.In addition,the NLO response of 2D SnP_(2)S_(6)can break through the limitation of odd/even layers and exhibit broadband spectral response.Moreover,since the second-harmonic signal is closely related to structure variation,the second-harmonic response in 2D SnP_(2)S_(6)is extremely sensitive to polarization angle and temperature,which is beneficial to some specific applications.The excellent NLO response in 2D SnP_(2)S_(6)provides a new arena for realizing miniaturized NLO devices in the future.展开更多
Preparation of a metallic diffuse-fringe film system and its electrical properties are reported.The anomalous R-I characteristics,third-harmonic coefficient and critical behavior are observed in the film system.Analys...Preparation of a metallic diffuse-fringe film system and its electrical properties are reported.The anomalous R-I characteristics,third-harmonic coefficient and critical behavior are observed in the film system.Analysis shows that this behavior is caused by the location-dependent tunneling and hopping effects,which result from the continuous variation of the diffuse fringe structure of the film due to the increase of the current.展开更多
We experimentally demonstrate third-harmonic generation(THG)in gases ionized by a femtosecond laser pulse superimposed on its second-harmonic(SH).The mechanism of THG has been investigated,and it demonstrates that a t...We experimentally demonstrate third-harmonic generation(THG)in gases ionized by a femtosecond laser pulse superimposed on its second-harmonic(SH).The mechanism of THG has been investigated,and it demonstrates that a third-order nonlinear process dominates at low pump intensity.Asymmetric third-harmonic(TH)spectra are observed at different time delays in two color fields,which are attributed to the process of the four-wave mixing(FWM)of the broad spectrum of pump pulses.A joint measurement on the terahertz(THz)and the TH is performed.It reveals that the optimized phase for the THG jumps from 0 to 0.5πas the pump intensity increases,which is different from the THz being a constant,and indicates that the THG arises from the nonlinearity of the third-order bound electrons to the tunnel-ionization current.展开更多
基金funded by the National Natural Science Foundation of China(Grant/Award Numbers 62075135 and 61975126)the Science and Technology Innovation Commission of Shenzhen(Grant/Award Numbers JCYJ20190808174819083 and JCYJ20190808175201640)Shenzhen Science and Technology Planning Project(ZDSYS 20210623092006020).
文摘Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the instantaneous bloodflow velocity distribution.This is mainly due to the lack of measurement technology with high spatial and temporal resolution.Here,we tackle this problem with our recently developed dual-wavelength line-scan third-harmonic generation(THG)imaging technology.Simultaneous acquisition of dual-wavelength THG line-scanning signals enables measurement of bloodflow velocities at two radially symmetric positions in both venules and arterioles in mouse brain in vivo.Our results clearly show that the instantaneous bloodflow velocity is not symmetric under general conditions.
基金The project supported by National Natural Science Foundation of China under Grant No. 60478010, the Science and Technology Committee of Guangdong Province of China under Grant Nos. 2004B10301014 and 04105406, Science and Technology Bureau of Guangzhou under Grant Nos. 200J1-C0031 and 2004J1-C0226, and Education Bureau of Guangzhou under Grant No. 2024
文摘The influence of electron-phonon interactions on third-harmonic generation in a square quantum well is investigated. The first- and third-harmonic generation coefficient is obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for a GaAs square quantum well. The results show that the third-harmonic generation coefficient is obviously enhanced after considering the influence of electron-phonon interactions.
基金the support from the Royal Society scholarshipsupport from the UK Research and Innovation Future Leaders Fellowship (MR/T040513/1).
文摘Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compared to metasurfaces composed of the periodic arrangement of nanoparticles,inverse,so-called,membrane metasurfaces offer unique possibilities for supporting multipolar resonances,while maintaining small unit cell size,large mode volume and high field enhancement for enhancing nonlinear frequency conversion.Here,we theoretically and experimentally investigate the formation of bound states in the continuum(BICs)from silicon dimer-hole membrane metasurfaces.We demonstrate that our BIC-formed resonance features a strong and tailorable electric near-field confinement inside the silicon membrane films.Furthermore,we show that by tuning the gap between the holes,one can open a leaky channel to transform these regular BICs into quasi-BICs,which can be excited directly under normal plane wave incidence.To prove the capabilities of such metasurfaces,we demonstrate the conversion of an infrared image to the visible range,based on the Third-harmonic generation(THG)process with the resonant membrane metasurfaces.Our results suggest a new paradigm for realising efficient nonlinear photonics metadevices and hold promise for extending the applications of nonlinear structuring surfaces to new types of all-optical near-infrared imaging technologies.
基金supported by National Natural Science Foundation of China (NSFC) (Nos.61775143,61975126 and 62075135)the Science and Technology Innovation Commission of Shenzhen under Nos.JCYJ20190808174819083,JCYJ20190808175201640 and KQTD20150710165601017China Postdoctoral Science Foundation (No.2021M702241).
文摘The skin is heterogeneous and exerts strong scattering and aberration onto excitation light in multiphoton microscopy(MPM).Shifting to longer excitation wavelengths may help reduce skin scattering and aberration,potentially enabling larger imaging depths.However,previous demonstrations of skin MPM employ excitation wavelengths only up to the 1700 nm window,leaving an open question as to whether longer excitation wavelengths are suitable for deep-skin MPM.Here,in order to explore the longer-wavelength territory,first,we demonstrate characterization of the broadband transmittance of excised mouse skin,revealing a high transmittance window at 2200nm.Then,we demonstrate third-harmonic generation(THG)imaging in mouse skin in vivo excited at this window.With 9mW optical power on the skin surface operating at 1MHz repetition rate,we can get THG signals of 250m below the skin surface.Comparative THG imaging excited at the 1700nm window shows that as imaging depth increases,THG signals decay even faster than those excited at 2200 nm.Our results thus uncover the 2200 nm window as a new,promising excitation window potential for deep-skin MPM.
基金supported by the National Key Scientific Instrument Project,China(Grant No.2012YQ150092)the National Basic Research Program of China(Grant No.2011CB808105)+3 种基金the National Natural Science Foundation of China(Grant No.11434005)China Postdoctoral Science Foundation(Grant No.2014M560348)the National Natural Science Foundation of China(Grant No.11504237)the Shanghai Municipal Science and Technology Commission,China(Grant No.14JC1401600)
文摘We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament.
基金supported by the President Funding Independent Project of the China Academy of Engineering Physics(No.YZJJZL2024200)the National Natural Science Foundation of China(No.62405298)the National Key Research and Development Program of China(No.2023YFA1608503).
文摘Broadband frequency-tripling pulses with high energy are attractive for scientific research,such as inertial confinement fusion,but are difficult to scale up.Third-harmonic generation via nonlinear frequency conversion,however,remains a trade-off between bandwidth and conversion efficiency.Based on gradient deuterium deuterated potassium dihydrogen phosphate(KD_(x)H_(2-x)PO_(4),DKDP)crystal,here we report the generation of frequency-tripling pulses by rapid adiabatic passage with a low-coherence laser driver facility.The efficiency dependence on the phase-matching angle in a Type-II configuration is studied.We attained an output at 352 nm with a bandwidth of 4.4 THz and an efficiency of 36%.These results,to the best of our knowledge,represent the first experimental demonstration of gradient deuterium DKDP crystal in obtaining frequency-tripling pulses.Our research paves a new way for developing high-efficiency,large-bandwidth frequency-tripling technology.
基金supported by the Australian Research Council(Grant No.DP210101292)the International Technology Center Indo-Pacific (ITC IPAC) via Army Research Office (contract FA520923C0023)。
文摘Nonlinear dielectric metasurfaces provide a promising approach to control and manipulate frequency conversion optical processes at the nanoscale,thus facilitating both advances in fundamental research and the development of new practical applications in photonics,lasing,and sensing.Here,we employ symmetry-broken metasurfaces made of centrosymmetric amorphous silicon for resonantly enhanced second-and third-order nonlinear optical response.Exploiting the rich physics of optical quasi-bound states in the continuum and guided mode resonances,we comprehensively study through rigorous numerical calculations the relative contribution of surface and bulk effects to second-harmonic generation(SHG)and the bulk contribution to third-harmonic generation(THG) from the meta-atoms.Next,we experimentally achieve optical resonances with high quality factors,which greatly boosts light-matter interaction,resulting in about 550 times SHG enhancement and nearly 5000-fold increase of THG.A good agreement between theoretical predictions and experimental measurements is observed.To gain deeper insights into the physics of the investigated nonlinear optical processes,we further numerically study the relation between nonlinear emission and the structural asymmetry of the metasurface and reveal that the generated harmonic signals arising from linear sharp resonances are highly dependent on the asymmetry of the meta-atoms.Our work suggests a fruitful strategy to enhance the harmonic generation and effectively control different orders of harmonics in all-dielectric metasurfaces,enabling the development of efficient active photonic nanodevices.
基金supported by the Cooperation Project between Chongqing Local Universities and Institutions of Chinese Academy of Sciences,Chongqing Municipal Education Commission(No.HZ2021007)the National Natural Science Foundation of China(Nos.61904024,61975003,61790584,and 62025506)the Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJZD-M201900502)。
文摘The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion.This paper presents the intracavity frequency tripling in a self-mode-locked semiconductor disk laser,and a picosecond pulse train at 327 nm wavelength is achieved.The pulse repetition rate is 0.49 GHz,and the pulse width is 5.0 ps.The obtained maximum ultraviolet output power under mode locking is 30.5 m W,and the corresponding conversion efficiency is obviously larger than that of continuous-wave operation.These ultraviolet picosecond pulses have high spatial and temporal resolution and can be applied in some emerging fields.
文摘In this manuscript,a new axial-flux permanentmagnet machine(AFPMM)is designed,analyzed,improved,and successfully tested.A double-sided AFPM generator with four layers of stator winding is initially designed using a well-known quasi-3D analytical method.Then,the designed machine is simulated using commercial software.It is shown that modification techniques are required to improve the performance of both the torque ripple and the ratio of the third to the fundamental harmonics of the induced voltage.Therefore,a new improvement technique is proposed,in which the layers of the stator winding are shifted relative to each other.While this new technique significantly improves the third harmonic problem,the design still has a high torque ripple and,thus,it is suggested to combine the proposed method with the conventional magnet shifting technique.It is revealed numerically that the resulting combination properly resolves both third harmonic and torque ripple problems.Therefore,this design is considered the main design of the present manuscript.In the end,a prototype of the main design is manufactured and tested.It is shown that the measurement results are in good agreement with those of numerical software.
基金We are grateful for financial supports from the Natural Science Foundation of Fujian Province(Grant No.2017J01756)National Natural Science Foundation of China(Grant No.R-IND12101,No.61675231)Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB24030300).
文摘Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region.However,the generated high-harmonic emissions are subject to a resonance shift with a change in temperature.We present a comprehensive study of the thermal behavior induced phase mismatch that shows this resonance shift can be compensated by a combination of the linear and nonlinear thermo-optics effects.Using this model,we predict and experimentally demonstrate visible third harmonic modes having temperature dependent wavelength shifts between−2.84 pm/ºC and 2.35 pm/ºC when pumped at the L-band.Besides providing a new way to achieve athermal operation,this also allows one to measure the thermal coefficients and Q-factor of the visible modes.Through steady state analysis,we have also identified the existence of stable athermal third harmonic generation and experimentally demonstrated orthogonally pumped visible third harmonic modes with a temperature dependent wavelength shift of 0.05 pm/ºC over a temperature range of 12ºC.Our findings promise a configurable and active temperature dependent wavelength shift compensation scheme for highly efficient and precise visible emission generation for potential 2f–3f self-referencing in metrology,biological and chemical sensing applications.
基金supported by the National High Technology Research and Development Program ('863' Program) of China (Grant No. 2006AA03Z213)
文摘The critical current density Jc is one of the most important parameters of high temperature superconducting films in superconducting applications, such as superconducting filter and superconducting Josephson devices. This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation. Using this model, it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for Jc. The theoretic curve is consistent with the experimental results about measuring superconducting film, especially when the third-harmonic voltage just exceeds zero. The Jc value of superconducting films determined by the inductive method is also compared with results raeasured by four-probe transport method. The agreements between inductive method and transport method are very good.
文摘To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness.By rotating the plate up to 35°along the beam direction,we reduced the walk-off angle up to ~ 13%.The same phenomenon is predicted by the model,confirming the performance of the model.It is found that,due to the walk-off effect,the intensity profile of the thirdharmonic generation beam is slightly degraded.To compensate for the observed phenomena and further reduce the walkoff,we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form.As a result,the walk-off is decreased to~ 48.81 mrad,providing ~ 30%relative reduction.By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction,the walk-off angle is further reduced to 38.9 mrad.Moreover,it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.
文摘A detailed procedure for the calculation of the third-harmonic-generation susceptibility tensor is given in special asymmetric quantum wells, and an analytic formula for the third-harmonic-generation susceptibility is obtained by the compact density matrix approach and the iterative procedure. Finally, the numerical results are presented for typical GaAs/AlGaAs asymmetric quantum wells. The calculated results show that the origin of the large thirdharmonic-generation susceptibility is due to the increase in asymmetry of the quantum well.
基金This work was supported by the 973 Program of China(No.2011CB922002 and No.2013CB632704)the Knowledge Innovation Program of the Chinese Academy of Sciences(No.Y1 V2013 L11).
文摘Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics,chemistry and materials science to information communications and processing.Here we present the design and fabrication of a chirped periodically poled lithium niobate(CPPLN)nonlinear photonic crystal that supports multiple orders of quasiphase matching with finite bandwidth and allows for the simultaneous broadband generation of second and third harmonics with high conversion efficiency.Moreover,the chirp rate has a significant influence on the conversion efficiency and bandwidth.The CPPLN scheme offers a promising approach for the construction of short-wavelength laser sources and enables the generation of the three primary colors—red,green and blue—from a single crystal,which may have potential applications in large-screen laser displays.
基金supported by UNSW Scientia Fellowship and ARC Discovery Project(DP170103778)funding from ARC Discovery Early Career Research Fellowship(DE170100250)+1 种基金financial support from the Russian Foundation for Basic Research(Grants Nos.18-02-00381 and 19-02-00261)the Australian Research Council(DE19010043).
文摘A key concept underlying the specific functionalities of metasurfaces is the use of constituent components to shape the wavefront of the light on demand.Metasurfaces are versatile,novel platforms for manipulating the scattering,color,phase,or intensity of light.Currently,one of the typical approaches for designing a metasurface is to optimize one or two variables among a vast number of fixed parameters,such as various materials’properties and coupling effects,as well as the geometrical parameters.Ideally,this would require multidimensional space optimization through direct numerical simulations.Recently,an alternative,popular approach allows for reducing the computational cost significantly based on a deep-learning-assisted method.We utilize a deep-learning approach for obtaining high-quality factor(high-Q)resonances with desired characteristics,such as linewidth,amplitude,and spectral position.We exploit such high-Q resonances for enhancedlight–matter interaction in nonlinearoptical metasurfaces and optomechanical vibrations,simultaneously.We demonstrate that optimized metasurfaces achieve up to 400-fold enhancement of the third-harmonic generation;at the same time,they also contribute to 100-fold enhancement of the amplitude of optomechanical vibrations.This approach can be further used to realize structures with unconventional scattering responses.
基金supported by the National Natural Science Foundation of China (Nos. 61975100 and 62027821)Program for the Innovative Talents of High Education Institutions of ShanxiFund for Shanxi “1331 Project” Key Subjects Construction
文摘Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet(UV) laser based on a micro-lens array(MLA) is presented in this Letter. It is worth noting that the MLA is employed to act as the spatial splitter as well as the coupling lens. With assistance of the MLA,the 1064 nm laser and 532 nm laser are divided into four sub-beams and focused at different areas of the third-harmonic generation(THG) crystal. As a result, the multi-beam pulsed 355 nm UV laser is successfully generated inside the THG crystal. The measured pulse widths of four sub-beams are shorter than 9 ns. Especially, the generated four sub-beams have good long-term power stability benefitting from the employed MLA. We believe that the generated stable multi-beam355 nm UV laser can meet the requirement of high-efficiency laser processing, and the presented method can also pave the way to generate stable and long-lived multi-beam UV lasers.
基金the National Natural Science Foundation of China(Nos.21825103 and 51727809)Hubei Provincial Nature Science Foundation of China(No.2019CFA002)+1 种基金the Fundamental Research Funds for the Central Universities(No.2019kfyXMBZ018)China Postdoctoral Science Foundation(No.2020M682338).
文摘Nowadays,realizing miniaturized nonlinear optical(NLO)device is crucial to meet the growing needs in on-chip nanophotonics as well as compact integrated devices.The strong optical nonlinearities,ultrafast photoexcitation dynamics,available exciton effects as well as without lattice matching make two-dimensional(2D)layered materials potential candidates for integrated and nano-scale NLO devices.Herein,a novel and inversion symmetry broken 2D layered SnP_(2)S_(6)with strong second-harmonic and third-harmonic response has been reported for the first time.The second-order susceptibility(χ^(2))of SnP_(2)S_(6)flakes can reach up to 4.06×10^(−9)m·V^(−1)under 810 nm excitation wavelength,which is around 1–2 orders of magnitude higher than that of most reported 2D materials.In addition,the NLO response of 2D SnP_(2)S_(6)can break through the limitation of odd/even layers and exhibit broadband spectral response.Moreover,since the second-harmonic signal is closely related to structure variation,the second-harmonic response in 2D SnP_(2)S_(6)is extremely sensitive to polarization angle and temperature,which is beneficial to some specific applications.The excellent NLO response in 2D SnP_(2)S_(6)provides a new arena for realizing miniaturized NLO devices in the future.
基金Project supported by the National Natural Science Foundation of China and Zhejinag Provincial Natural Science Foundation of China.
文摘Preparation of a metallic diffuse-fringe film system and its electrical properties are reported.The anomalous R-I characteristics,third-harmonic coefficient and critical behavior are observed in the film system.Analysis shows that this behavior is caused by the location-dependent tunneling and hopping effects,which result from the continuous variation of the diffuse fringe structure of the film due to the increase of the current.
基金supported by the National Key Research and Development Program of China(No.2019YFA0307704)the National Natural Science Foundation of China(Nos.11974425 and 11974426)the National Safety Academic Fund(No.U1830206)。
文摘We experimentally demonstrate third-harmonic generation(THG)in gases ionized by a femtosecond laser pulse superimposed on its second-harmonic(SH).The mechanism of THG has been investigated,and it demonstrates that a third-order nonlinear process dominates at low pump intensity.Asymmetric third-harmonic(TH)spectra are observed at different time delays in two color fields,which are attributed to the process of the four-wave mixing(FWM)of the broad spectrum of pump pulses.A joint measurement on the terahertz(THz)and the TH is performed.It reveals that the optimized phase for the THG jumps from 0 to 0.5πas the pump intensity increases,which is different from the THz being a constant,and indicates that the THG arises from the nonlinearity of the third-order bound electrons to the tunnel-ionization current.
