Pulse echo accumulation is commonly employed in coherent Doppler wind LiDAR(light detection and ranging)under the assumption of steady wind.Here,the measured spectral data are analyzed in the time dimension and freque...Pulse echo accumulation is commonly employed in coherent Doppler wind LiDAR(light detection and ranging)under the assumption of steady wind.Here,the measured spectral data are analyzed in the time dimension and frequency dimension to cope with the temporal wind shear and achieve the optimal accumulation time.A hardware-efficient algorithm combining the interpolation and cross-correlation is used to enhance the wind retrieval accuracy by reducing the frequency sampling interval and then reduce the spectral width calculation error.Moreover,the temporal broadening effect and spatial broadening effect are decoupled according to the strategy we developed.展开更多
Photocurrent-voltage characterization is a crucial method for assessing key parameters in x-ray or y-ray semiconductor detectors,especially the carrier mobility lifetime product.However,the high biases during photocur...Photocurrent-voltage characterization is a crucial method for assessing key parameters in x-ray or y-ray semiconductor detectors,especially the carrier mobility lifetime product.However,the high biases during photocurrent measurements tend to cause severe ion migration,which can lead to the instability and inaccuracy of the test results.Given the mixed electronic-ionic charac teristics,it is imperative to devise novel methods capable of precisely measuring photocurrentvoltage characteristics under high bias conditions,free from interference caused by ion migration.In this paper,pulsed bias is employed to explore the photocurrent-voltage characteristics of MAPbBr_(3) single crystals.The method yields stable photocurrent-voltage characteristics at a pulsed bias of up to 30 V,proving to be effective in mitigating ion migration.Through fitting the modified Hecht equation,we determined the mobility lifetime products of 1.0×10^(2) cm^(2)·V^(-1)for hole and 2.78×10~(-3)cm^(2)·V^(-1)for electron.This approach offers a promising solution for accurately measuring the transport properties of carriers in perovskite.展开更多
A new type of beam called the NPEP-BG(a Bessel-Gaussian(BG)beam with a spiral phase term of a new powerexponent-phase(NPEP))is theoretically studied in this paper.The results show that the number of singularities of t...A new type of beam called the NPEP-BG(a Bessel-Gaussian(BG)beam with a spiral phase term of a new powerexponent-phase(NPEP))is theoretically studied in this paper.The results show that the number of singularities of the phase and side lobes of the intensity of this beam were equal to the topological charges(TCs)and the beam has the characteristics of self-healing during propagation.The NPEP-BG beam combined the partial characteristics of the new power-exponentphase vortex(NPEPV)and the Bessel-Gaussian beam.At the focus of the beam,the characteristic like a perfect vortex beam was present,in which the focal radius is stable and independent of the topological charge.There are multi-focal spots around a ring in the focal plane,meaning that the NPEP-BG beam has a potential for application in multi-particle manipulation.展开更多
This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intens...This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e. the roughness w, the lateral correlation length ξ and the roughness exponent α, from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with α= 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.展开更多
Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical ...Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities (T. D. ) with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at twavelength range of 300 - 800 nm.展开更多
In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode (LFM) op...In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode (LFM) optical fibres is presented. A comparison is made between the properties of a three-layer LFM structure and a standard step-index profile with the same core size. The obtained results indicate that the effective area of the LFM fibre is about twice as large as that of the standard step-index fibre, but the LFM fibre has less effective ability to filter out the higher order modes than the standard step-index fibre with the same bending radius.展开更多
Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, ...Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime of each energy levels for Er^(3+) were calculated by Judd-Ofelt theory, and stimulated emission cross-section of (()~4I_(13/2))→(()~4I_(15/2)) transition was calculated by McCumber theory. The results show that fluorescence full width at half maximum and stimulated emission cross-section of Er^(3+)-doped heavy metal oxyfluoride silicate glass are broad and large, respectively. Compared with other host glasses, the gain bandwidth property of Er^(3+)-doped heavy metal oxyfluoride silicate glass is close to those of tellurite and bismuth glasses, and has advantage over those of silicate, phosphate and germante glasses.展开更多
The rapid development of bulk β-Ga_2O_3 crystals has attracted much attention to their use as ultra-wide bandgap materials for next-generation power devices owing to its large bandgap(~ 4.9 eV) and large breakdown e...The rapid development of bulk β-Ga_2O_3 crystals has attracted much attention to their use as ultra-wide bandgap materials for next-generation power devices owing to its large bandgap(~ 4.9 eV) and large breakdown electric field of about8 MV/cm. Low cost and high quality of large β-Ga_2O_3 single-crystal substrates can be attained by melting growth techniques widely used in the industry. In this paper, we first present an overview of the properties of β-Ga_2O_3 crystals in bulk form. We then describe the various methods for producing bulk β-Ga_2O_3 crystals and their applications. Finally, we will present a future perspective of the research in the area in the area of single crystal growth.展开更多
The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd-Ofelt i...The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10^-20cm^2, Ω4 = 2.92 ×10^-20 cm^2, and Ω6 =1.71 ×10^-20cm^2, this paper calculated the fluorescence lifetime to be 6 ms for ^5I7→^5Is transition, and the integrated emission cross section to be 2.24 × 10^-18 cm^2. It investigates the room-temperature Ho:YAP laser end-pumped by a 1.91-μm Tm:YLF laser. The maximum output power was 4.1 W when the incident 1.91-μm pump power was 14.4W. The slope efficiency is 40.8%, corresponding to an optical-to-optical conversion efficiency of 28.4%. The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8nm.展开更多
This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radi...This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radiation energy of the flashlamp is obtained by a pyroelectric energy meter.Voltage and current curves are recorded to shed light on the plasma characteristics.With these diagnostic methods,typical factors influencing the evolution process of plasma channel are studied,including the external electric field and the pre-ionization.The electric potential distribution in the flashlamp influence the plasma channel characteristics the most significantly.The plasma channel pattern for the cases with grounded wires is different from that with ungrounded metal wires.When the wire is ungrounded,it is the coupling voltage between the metal wire and the flashlamp that influences the development of plasma channel.In terms of radiation efficiency,it is proven that there is an optimal interval within 200~300μs between the pre-ionization pulse and the main pulse.展开更多
Homoepitaxial growth of Si-doped β-Ga_(2)O_(3) films on semi-insulating(100) β-Ga_(2)O_(3) substrates by metalorganic chemical vapor deposition(MOCVD) is studied in this work. By appropriately optimizing the growth ...Homoepitaxial growth of Si-doped β-Ga_(2)O_(3) films on semi-insulating(100) β-Ga_(2)O_(3) substrates by metalorganic chemical vapor deposition(MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in(100) β-Ga_(2)O_(3) films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga_(2)O_(3) film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the(400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 10~(15) – 1.74 × 10~(20) cm~(-3). Hall measurements demonstrate a high electron mobility value of 51cm~2/(V·s), corresponding to a carrier concentration of 7.19 × 10~(18) cm~(-3) and a high activation efficiency of up to 61.5%. Transmission line model(TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10~(-4) Ω·cm~2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 10~(19) cm~(-3), confirming the effective Si doing in the MOCVD epitaxy.展开更多
A waveguide amplifier is fabricated by Ag^+-Na^+ two-step ion exchange on Er/Yb-doped phosphate glass. The spectroscopic performance of glass and the properties of channel waveguide are characterized. A double-pass ...A waveguide amplifier is fabricated by Ag^+-Na^+ two-step ion exchange on Er/Yb-doped phosphate glass. The spectroscopic performance of glass and the properties of channel waveguide are characterized. A double-pass configuration is adopted to measure the gain and noise figure (NF) of the waveguide amplifier, and the comparison of gain and NF for the single and double-pass configuration of the waveguide amplifier is presented. The results show that the double-pass configuration can make the gain increase from 8.8dB (net gain 2.2dB/cm) of the single-pass one to 14.6dB (net gain 3.65dB/cm) for small input power at 1534nm, and the NF are all lower than 5.5dB for both the configurations.展开更多
While ptychography is an algorithm based on coherent illumination,satisfactory reconstructions can still be generated in most experiments,even though the radiation sources that are used are not ideally coherent.The un...While ptychography is an algorithm based on coherent illumination,satisfactory reconstructions can still be generated in most experiments,even though the radiation sources that are used are not ideally coherent.The underlying physics of this phenomenon is that the diffraction patterns of partially coherent illumination can be treated as those of purely coherent illumination by altering the intensities of the diffracted beams relative to their real values.On the other hand,due to the inconsistency in the altering interference among all the diffraction beams,noise/distortion is always involved in the reconstructed images.Furthermore,for a weak object,the noise/distortion in the reconstruction can be mostly reduced by using a highly curved beam for illumination in the data recording and forcing the dark field diffraction to be zero in the reconstruction.展开更多
The influence of vacuum polarization effects on the interactions of multiple ultra-intense lasers with plasmas is discussed. The nonlinear paraxial monochromatic model of the interactions has been improved by consider...The influence of vacuum polarization effects on the interactions of multiple ultra-intense lasers with plasmas is discussed. The nonlinear paraxial monochromatic model of the interactions has been improved by considering the Heisenberg–Euler Lagrangian density of two laser processes. Comparing the corrections of vacuum polarization effects in the collision of laser beams with one generated by a single intense laser, we find that the former has a higher order of magnitude correction. The laser collision also produces variations in the propagation direction and polarization direction of the lasers propagating in the plasma. In addition, the strong-field quantum electrodynamic(QED) effects can be enhanced by increasing the laser intensity or frequency difference, or by adjusting the incident angles of the two laser beams.展开更多
Based on the Fresnel-Kirchhoff diffraction theory, we build up a Gaussian diffraction model of metal-oxide-type super-resolution near field structure (super-liENS), which can describe far field optical properties. T...Based on the Fresnel-Kirchhoff diffraction theory, we build up a Gaussian diffraction model of metal-oxide-type super-resolution near field structure (super-liENS), which can describe far field optical properties. The spectral contrast induced by refractive index and the structural changes in AgOg, PtOx and PdOz thin films, which are the key functional layers in super-RENS, are studied by using this model. Comparison results indicate that the spectral contrast depends intensively on the laser-induced distribution and change of the refractive index in the metal-oxide films. The readout mechanism of the metal-oxide-type super-RENS optical disc is further clarified. This Gaussian diffraction model can be used as a simple and effective method for choosing proper active materials in super-RENS.展开更多
Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers...Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed(TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux(I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.展开更多
γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high...γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high-resolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec and etch pits density of (0.3- 2.2)×10^4 cm^-2 throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5μm and becomes completely absorbing around 6.7μm wavelength, The optical absorption edge in near UV region is about 191 nm.展开更多
We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a 7-LiAlO2 (100) substrate. The TMGa, TMIn and NH3 are used as sources of Ga, In and N, respectively. The ...We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a 7-LiAlO2 (100) substrate. The TMGa, TMIn and NH3 are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10×10μm^2 by AFM scan area. The XRD spectra show that the materials grown on 7-LiAl02 (100) have (1 - 100) m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown on the 7-LiAlO2 substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on voltage of 1-3 V.展开更多
Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resona...Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of the grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared with each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, et al., on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.展开更多
基金Project supported by the Shanghai Science and Technology Innovation Action(Grant No.22dz1208700).
文摘Pulse echo accumulation is commonly employed in coherent Doppler wind LiDAR(light detection and ranging)under the assumption of steady wind.Here,the measured spectral data are analyzed in the time dimension and frequency dimension to cope with the temporal wind shear and achieve the optimal accumulation time.A hardware-efficient algorithm combining the interpolation and cross-correlation is used to enhance the wind retrieval accuracy by reducing the frequency sampling interval and then reduce the spectral width calculation error.Moreover,the temporal broadening effect and spatial broadening effect are decoupled according to the strategy we developed.
基金Project supported by the National Natural Science Foundation of China (Grant No.62104234)Shanghai Explorer Program (Grant No.22TS1400100)。
文摘Photocurrent-voltage characterization is a crucial method for assessing key parameters in x-ray or y-ray semiconductor detectors,especially the carrier mobility lifetime product.However,the high biases during photocurrent measurements tend to cause severe ion migration,which can lead to the instability and inaccuracy of the test results.Given the mixed electronic-ionic charac teristics,it is imperative to devise novel methods capable of precisely measuring photocurrentvoltage characteristics under high bias conditions,free from interference caused by ion migration.In this paper,pulsed bias is employed to explore the photocurrent-voltage characteristics of MAPbBr_(3) single crystals.The method yields stable photocurrent-voltage characteristics at a pulsed bias of up to 30 V,proving to be effective in mitigating ion migration.Through fitting the modified Hecht equation,we determined the mobility lifetime products of 1.0×10^(2) cm^(2)·V^(-1)for hole and 2.78×10~(-3)cm^(2)·V^(-1)for electron.This approach offers a promising solution for accurately measuring the transport properties of carriers in perovskite.
基金Project supported by the Program of Shanghai Academic/Technology Research Leader(Grant No.20SR014501)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB1603)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2019247)。
文摘A new type of beam called the NPEP-BG(a Bessel-Gaussian(BG)beam with a spiral phase term of a new powerexponent-phase(NPEP))is theoretically studied in this paper.The results show that the number of singularities of the phase and side lobes of the intensity of this beam were equal to the topological charges(TCs)and the beam has the characteristics of self-healing during propagation.The NPEP-BG beam combined the partial characteristics of the new power-exponentphase vortex(NPEPV)and the Bessel-Gaussian beam.At the focus of the beam,the characteristic like a perfect vortex beam was present,in which the focal radius is stable and independent of the topological charge.There are multi-focal spots around a ring in the focal plane,meaning that the NPEP-BG beam has a potential for application in multi-particle manipulation.
基金Project supported by the National Natural Science Foundation of China (Grant No 69978012), and by the National Key Basic Research Special Foundation (NKBRSF) of China (Grant No G1999075200).
文摘This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e. the roughness w, the lateral correlation length ξ and the roughness exponent α, from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with α= 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.
文摘Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities (T. D. ) with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at twavelength range of 300 - 800 nm.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10576012 and 60538010).
文摘In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode (LFM) optical fibres is presented. A comparison is made between the properties of a three-layer LFM structure and a standard step-index profile with the same core size. The obtained results indicate that the effective area of the LFM fibre is about twice as large as that of the standard step-index fibre, but the LFM fibre has less effective ability to filter out the higher order modes than the standard step-index fibre with the same bending radius.
文摘Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime of each energy levels for Er^(3+) were calculated by Judd-Ofelt theory, and stimulated emission cross-section of (()~4I_(13/2))→(()~4I_(15/2)) transition was calculated by McCumber theory. The results show that fluorescence full width at half maximum and stimulated emission cross-section of Er^(3+)-doped heavy metal oxyfluoride silicate glass are broad and large, respectively. Compared with other host glasses, the gain bandwidth property of Er^(3+)-doped heavy metal oxyfluoride silicate glass is close to those of tellurite and bismuth glasses, and has advantage over those of silicate, phosphate and germante glasses.
基金funded by the following grants:Chinese Academy of Sciences president’s International Fellowship Initiative(Grant No.2018PE0033)National Natural Science Foundation of China(Grant No.51802327)+1 种基金Science and Technology Commission of Shanghai Municipality(No.18511110500)Pre-research Fund Key Project(No.6140922010601)
文摘The rapid development of bulk β-Ga_2O_3 crystals has attracted much attention to their use as ultra-wide bandgap materials for next-generation power devices owing to its large bandgap(~ 4.9 eV) and large breakdown electric field of about8 MV/cm. Low cost and high quality of large β-Ga_2O_3 single-crystal substrates can be attained by melting growth techniques widely used in the industry. In this paper, we first present an overview of the properties of β-Ga_2O_3 crystals in bulk form. We then describe the various methods for producing bulk β-Ga_2O_3 crystals and their applications. Finally, we will present a future perspective of the research in the area in the area of single crystal growth.
基金supported by the Program of Excellent Team in Harbin Institute of Technology of China
文摘The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10^-20cm^2, Ω4 = 2.92 ×10^-20 cm^2, and Ω6 =1.71 ×10^-20cm^2, this paper calculated the fluorescence lifetime to be 6 ms for ^5I7→^5Is transition, and the integrated emission cross section to be 2.24 × 10^-18 cm^2. It investigates the room-temperature Ho:YAP laser end-pumped by a 1.91-μm Tm:YLF laser. The maximum output power was 4.1 W when the incident 1.91-μm pump power was 14.4W. The slope efficiency is 40.8%, corresponding to an optical-to-optical conversion efficiency of 28.4%. The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8nm.
文摘This work is devoted to experimentally study the characteristics of discharge plasma in high power xenon flashlamps.In the experiments,plasma channel profiles are captured by using a high speed CCD camera,and the radiation energy of the flashlamp is obtained by a pyroelectric energy meter.Voltage and current curves are recorded to shed light on the plasma characteristics.With these diagnostic methods,typical factors influencing the evolution process of plasma channel are studied,including the external electric field and the pre-ionization.The electric potential distribution in the flashlamp influence the plasma channel characteristics the most significantly.The plasma channel pattern for the cases with grounded wires is different from that with ungrounded metal wires.When the wire is ungrounded,it is the coupling voltage between the metal wire and the flashlamp that influences the development of plasma channel.In terms of radiation efficiency,it is proven that there is an optimal interval within 200~300μs between the pre-ionization pulse and the main pulse.
基金supported in part by the National Basic Research Program of China (Grant No. 2021YFB3600202)Key Laboratory Construction Project of Nanchang (Grant No. 2020-NCZDSY-008)Suzhou Science and Technology Foundation (Grant No. SYG202027)。
文摘Homoepitaxial growth of Si-doped β-Ga_(2)O_(3) films on semi-insulating(100) β-Ga_(2)O_(3) substrates by metalorganic chemical vapor deposition(MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in(100) β-Ga_(2)O_(3) films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga_(2)O_(3) film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the(400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 10~(15) – 1.74 × 10~(20) cm~(-3). Hall measurements demonstrate a high electron mobility value of 51cm~2/(V·s), corresponding to a carrier concentration of 7.19 × 10~(18) cm~(-3) and a high activation efficiency of up to 61.5%. Transmission line model(TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10~(-4) Ω·cm~2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 10~(19) cm~(-3), confirming the effective Si doing in the MOCVD epitaxy.
文摘A waveguide amplifier is fabricated by Ag^+-Na^+ two-step ion exchange on Er/Yb-doped phosphate glass. The spectroscopic performance of glass and the properties of channel waveguide are characterized. A double-pass configuration is adopted to measure the gain and noise figure (NF) of the waveguide amplifier, and the comparison of gain and NF for the single and double-pass configuration of the waveguide amplifier is presented. The results show that the double-pass configuration can make the gain increase from 8.8dB (net gain 2.2dB/cm) of the single-pass one to 14.6dB (net gain 3.65dB/cm) for small input power at 1534nm, and the NF are all lower than 5.5dB for both the configurations.
基金supported by the Funds from the Engineering and Physical Sciences Research Council(Grant No.EP/E034055/1)the One Hundred Talent Project of the Chinese Academy of Sciences and the Financial Support(Grant No.GFZX0205010502.12)
文摘While ptychography is an algorithm based on coherent illumination,satisfactory reconstructions can still be generated in most experiments,even though the radiation sources that are used are not ideally coherent.The underlying physics of this phenomenon is that the diffraction patterns of partially coherent illumination can be treated as those of purely coherent illumination by altering the intensities of the diffracted beams relative to their real values.On the other hand,due to the inconsistency in the altering interference among all the diffraction beams,noise/distortion is always involved in the reconstructed images.Furthermore,for a weak object,the noise/distortion in the reconstruction can be mostly reduced by using a highly curved beam for illumination in the data recording and forcing the dark field diffraction to be zero in the reconstruction.
基金supported by the National Natural Science Foundation of China (Grant No. 11805117)the Shanghai Leading Academic Discipline Project (Grant No. S30105)。
文摘The influence of vacuum polarization effects on the interactions of multiple ultra-intense lasers with plasmas is discussed. The nonlinear paraxial monochromatic model of the interactions has been improved by considering the Heisenberg–Euler Lagrangian density of two laser processes. Comparing the corrections of vacuum polarization effects in the collision of laser beams with one generated by a single intense laser, we find that the former has a higher order of magnitude correction. The laser collision also produces variations in the propagation direction and polarization direction of the lasers propagating in the plasma. In addition, the strong-field quantum electrodynamic(QED) effects can be enhanced by increasing the laser intensity or frequency difference, or by adjusting the incident angles of the two laser beams.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60207005, 60490290, 60507009, and 50672108 the Science and Technology Committee of Shanghai under Grant No 06DJ14007.
文摘Based on the Fresnel-Kirchhoff diffraction theory, we build up a Gaussian diffraction model of metal-oxide-type super-resolution near field structure (super-liENS), which can describe far field optical properties. The spectral contrast induced by refractive index and the structural changes in AgOg, PtOx and PdOz thin films, which are the key functional layers in super-RENS, are studied by using this model. Comparison results indicate that the spectral contrast depends intensively on the laser-induced distribution and change of the refractive index in the metal-oxide films. The readout mechanism of the metal-oxide-type super-RENS optical disc is further clarified. This Gaussian diffraction model can be used as a simple and effective method for choosing proper active materials in super-RENS.
基金Project supported by the Fund from China National Space Administration (CNSA) (Grant No. D050104)the Fund for Low Energy Gamma Ray Detection Research Based on SQUID Techniquethe Superconducting Electronics Facility (SELF) of Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences。
文摘Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed(TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux(I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.
基金supported by the Project of High Technology Research and Development of China(2006AA03A101 and 2006AA03A103)the National Natural Science Foundation of China(60676004)the Science Research Program of Shanghai(05PJ14100 and 06dz11402).
文摘γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high-resolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec and etch pits density of (0.3- 2.2)×10^4 cm^-2 throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5μm and becomes completely absorbing around 6.7μm wavelength, The optical absorption edge in near UV region is about 191 nm.
基金The National Basic Research Programme of China under Grant No 2006CB6049, the National High-Tech Research and Development Programme of China under Grant Nos 2006AA03A103, 2006AA03Al18, 2006AA03A142, the National Natural Science Foundation of China under Grant Nos 60390072, 60676057, 60421003, The Research Fund for the Doctoral Programme of Higher Education of China (20050284004)
文摘We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a 7-LiAlO2 (100) substrate. The TMGa, TMIn and NH3 are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10×10μm^2 by AFM scan area. The XRD spectra show that the materials grown on 7-LiAl02 (100) have (1 - 100) m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown on the 7-LiAlO2 substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on voltage of 1-3 V.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10704079)
文摘Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of the grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared with each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, et al., on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.