Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Two-Photon, Three-Photon, Four-Photon Near-Infrared Quantum Cutting Luminescence of Er3+ Activator in Oxyfluoride Vitroceramics
No full textNational Natural Science Foundation of China [51472028]; Fundamental Research Funds for the Central Universities of China [2017TZ01]Two-photon, three-photon, and four-photon near-infrared quantum cutting luminescence of Er3+: oxyfluoride vitroceramics are studied. X-ray diffraction, absorption, visible to near infrared luminescence and excitation spectra of Er3+-doped oxyfluoride vitroceramics have been measured. We found that when the concentration of the Er3+ ion increased from 0.5% to 2., the infrared excitation spectra intensities of the Er3+ ion enhanced by approximately 5.64, 4.26, 2.77, 7.31, 6.76, 4.75, 2.40, 11.14, 2. 88, and 4.61 times for the I-4(15/2)->(2)G(7/2), I-4(15/2)->(4)G(9/2), I-4(15/2)->(4)G(11/2), I-4(15/2)-> H-2(9/2), I-4(15/2)->(F-4(3/2), F-4(5/2)) I-4(15/2)-> F-4(7/2), I-4(15/2)-> H-2(11/2), I-4(15/2)-> S-4(3/2), I-4(15/2)-> F-4(9/2), and I-4(15/2)-> I-4(9/2) transitions. Meanwhile, it can also be found that the visible excitation spectra intensity of the Er3+ ion decreased by approximately 1. 36, 1.93, 3.43, 1.01, 2.24, and 2.28 times for the I-4(15/2)->(2)G(7/2), I-4(15/2)->(4)G(9/2), I-4(15/2)->(4)G(11/2), I-4(15/2)-> H-2(9/2), I-4(15/2)->(F-4(3/2), F-4(5/2)) and I-4(15/2)-> F-7/2 absorption transitions of the Er3+ ion, respectively. That is to say, the samples exhibited a 2 to 11 times enhancement in both infrared luminescence and excitation intensities, with a concomitant one to three times decreasing of both visible luminescence and excitation intensities. Moreover, the excitation spectra of 1 543. 0 and 550. 0 nm luminescence were very similar both in shape and peak wavelength, confirming that the multiphoton near-infrared quantum cutting luminescence phenomena were found. In order to analyze the process and mechanism of quantum cutting better, we measured the variation of main visible and infrared luminescence intensity based on the excitation intensity. It found that all visible and infrared luminescence intensity was linear depended on the excitation intensity basically. In which, the variation of the visible luminescence intensity depended on the excitation intensity was slightly larger than linear. It is resulted from the very small absorption of excited state. The variation of the infrared 1 543. 0 nm luminescence intensity depended on the excitation intensity was slightly smaller than linear. It is the characteristic phenomena of quantum cutting luminescence. It found that two-photon quantum cutting luminescence of I-4(9/2) state mainly resulted from the {I-4(9/2)-> I-4(13/2), I-4(15/2)-> I-4(13/2)} ETr31-ETa01 cross-energy transfer process. Three-photon quantum cutting luminescence of the S-4(3/2) state mainly result from the {S-4(3/2)-> I-4(9/2), I-4(15/2)-> I-4(13/2)} ETr31-ETa01 and {I-4(9/2)-> I-4(13/2), I-4(15/2)-> I-4(13/2)} ETr31-ETa01 cross-energy transfer process. Four-photon quantum cutting of H-2(9/2) mainly results from the {H-2(9/2)-> I-4(13/2), I-4(15/2), S-4(3/2)}ETr91-ETa05 {S-4(3/2)-> I-4(9/2), I-4(15/2)-> I-4(13/2)} ETr53-ETa05 and {I-4(9/2)-> I-4(13/2), I-4(15/2)-> I-4(13/2)} ETr31-ETa01 cross-energy transfer process. These measured results are useful for the next-generation of quantum cutting solar cells, a current hot point globally
Low beam quality degradation, high-efficiency pump and signal combiner by built- in mode field adapter
No full textNational Key Research and Development Program of China [2016YFB0402201]; National Natural Science Foundation of China (NSFC) [6130824, 61377062, U1330134]; Natural Science Foundation of Shanghai [16ZR1440100, 16ZR1440200]; Primary Research & Development Plan of Jiangsu [BE2016005-4]; Key Project of Science and Technology of Jiangsu [BE2014001-2]A low beam quality degradation, high-efficiency (6 + 1) x 1 pump and signal combiner based on an end-pumping technique was realized by a built-in mode field adapter. A 2D simulation model to calculate the taper ratios of signal input and output fibers for matching the mode field profile in the coupling region was established. Based on the simulation results, we fabricated a combiner, achieving a signal coupling ratio of 87.52% and an average pump coupling ratio of 98.56%. The beam quality degradation caused by the signal feed-through of the combiner was theoretically determined in terms of the well-known M-2 parameter and experimentally measured to be only Delta M-2 = 0.15 (1.05 to 1.2). Theoretical results are in good agreement with the experimental results. (C) 2017 Optical Society of Americ
Polarization multiplexed dual-loop optoelectronic oscillator based on stimulated Brillouin scattering
No full textInternational Science & Technology Cooperation Program of China [2014DFG32590]; Natural Science Foundation of Liaoning Province [201402002]; Opening Project of Shanghai Key Laboratory of All Solid-state Laser and Applied Techniques [2013ADL04]; Fundamental Research Funds for the Central Universities [DUT15ZD231, DUT2015TD47]A polarization multiplexed dual-loop optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is theoretically analyzed and experimentally demonstrated. The narrow bandwidth of SBS gain spectrum is utilized to implement the phase modulation to intensity modulation conversion and select the oscillation mode of the OEO. The polarization multiplexed dual-loop is constructed to suppress the side modes with Vernier effect. The output frequency of the OEO can be tuned by changing the frequency of the signal or the pump light wave. With the polarization multiplexed dual-loop the side mode suppression ratio (SMSR) of 45 dB is achieved at 10 GHz. The generated oscillation frequency is tuned from 4 GHz to 16 GHz by changing the frequency of the signal light wave. The phase noise decreases with the power increase of the signal light wave when it is under the threshold of SBS. By adjusting the polarization state of the light wave, the influence of the power distribution between the long loop and the short loop on the phase noise of the OEO is investigated. The results show that more power in the long loop is helpful to suppress the near end phase noise. (C) 2016 Elsevier B.V. All rights reserved
Automatic spectral calibration for polarization-sensitive optical coherence tomography
No full textInnovation Action Plan of Science and Technology Commission of Shanghai Municipality [15441905600]; Open Fund of Key Laboratory of Optoelectronic Information Processing of University in Guangxi [KFJJ2016-04]Accurate wavelength assignment is important for Fourier domain polarization-sensitive optical coherence tomography. Incorrect wavelength mapping between the orthogonal horizontal (H) and vertical (V) polarization channels leads to broadening the axial point spread function and generating polarization artifacts. To solve the problem, we propose an automatic spectral calibration method by seeking the optimal calibration coefficient between wavenumber k(H) and k(V). The method first performs a rough calibration to get the relationship between the wavelength. and the pixel number x of the CCD for each channel. And then a precise calibration is taken to bring both polarization interferograms in the same k range through the optimal calibration coefficient. The optimal coefficient is automatically obtained by evaluating the cross-correlation of A-line signals. Simulations and experiments are implemented to demonstrate the performance of the proposed method. The results show that, compared to the peaks method, the proposed method is suitable in both Gaussian and non-Gaussian spectrums with a higher calibration accuracy
Fast modal decomposition for optical fibers using digital holography
No full textNational Natural Science Foundation of China [61377005]; Chinese Academy of Sciences [QYZDB-SSW-JSC002]Eigenmode decomposition of the light field at the output end of optical fibers can provide fundamental insights into the nature of electromagnetic-wave propagation through the fibers. Here we present a fast and complete modal decomposition technique for step-index optical fibers. The proposed technique employs digital holography to measure the light field at the output end of the multimode optical fiber, and utilizes the modal orthonormal property of the basis modes to calculate the modal coefficients of each mode. Optical experiments were carried out to demonstrate the proposed decomposition technique, showing that this approach is fast, accurate and cost-effective
Dynamics of electron injection in a laser-wakefield accelerator
No full textDFG [Transregio TR18]; Euratom research and training program of the EUROfusion Consortium [633053]; Munich Centre for Advanced Photonics (MAP); Swedish Research Council [2016-05409]; Max Planck Society (MPS)-Chinese Academy of Sciences (CAS) Joint Doctoral Promotion Program; National Natural Science Foundation of China [11505264]The detailed temporal evolution of the laser-wakefield acceleration process with controlled injection, producing reproducible high-quality electron bunches, has been investigated. The localized injection of electrons into the wakefield has been realized in a simple way-called shock-front injection-utilizing a sharp drop in plasma density. Both experimental and numerical results reveal the electron injection and acceleration process as well as the electron bunch's temporal properties. The possibility to visualize the plasma wave gives invaluable spatially resolved information about the local background electron density, which in turn allows for an efficient suppression of electron self-injection before the controlled process of injection at the sharp density jump. Upper limits for the electron bunch duration of 6.6 fs FWHM, or 2.8 fs (r. m. s.) were found. These results indicate that shock-front injection not only provides stable and tunable, but also few-femtosecond short electron pulses for applications such as ultrashort radiation sources, time-resolved electron diffraction or for the seeding of further acceleration stages. Published by AIP Publishing
Laser-driven fast electron ionization wave propagation in a dielectric target
No full textNational Natural Science Foundation of China [11425418, 11405244, 11127901, 61521093]; Shanghai Natural Science Funds [14ZR1444800]; Strategic Priority Research Program [XDB16]; Open Foundation of the National Key Laboratory of Shock Wave and Detonation PhysicsUltrafast shadowgraphy with sub-picosecond resolution is applied to investigate the propagation of laser-driven fast electron beams inside a dielectric target. Time-resolved expansion of an ionization sphere caused by hot electron transportation in the target is observed. An abnormal absorption area with a width of approximately 10 mu m is observed near the ionization front and is consistent with the one-dimensional electron transport model. The observed distortions of the edge diffraction fringes near the surface of the target are analyzed to qualitatively retrieve the phase shift caused by the ionization front. A simplified three-dimensional model is proposed to analyze the underlying physics and indicates that the valley in the ionization front appears due to the unstable propagation of hot electrons in a self-induced fountain electric field, which is induced by the collective effect of the free electrons and the ions. Published by AIP Publishing
Self-compression of 1.8-mu m pulses in gas-filled hollow-core fibers
No full textNational Natural Science Foundation of China [61475169, 61521093, 11127901]; Chinese Academy of Sciences [XDB16]; International Science and Technology Cooperation Program of China [2016YFE0119300]We numerically study the self-compression of the optical pulses centered at 1.8-mu m in a hollow-core fiber (HCF) filled with argon. It is found that the pulse can be self-compressed to 2 optical cycles when the input pulse energy is 0.2-mJ and the gas pressure is 500-mbar (1 bar = 10(5) Pa). Inducing a proper positive chirp into the input pulse can lead to a shorter temporal duration after self-compression. These results will benefit the generation of energetic few-cycle mid-infrared pulses
Wavefront-sensing-based autofocusing in microscopy
No full textNational Natural Science Foundation of China [61705092, 11647144, 31522056]; National Natural Science Foundation of Jiangsu Province of China [BK20130162, BK20170194]; Shanghai Sailing Program [17YF1407000]; Fundamental Research Funds for the Central Universities [JUSRP115A14, JUSRP51721B]; Local Colleges and Universities Capacity Building Program [15110500900, 14110500900]Massive image acquisition is required along the optical axis in the classical image-analysis-based autofocus method, which significantly decreases autofocus efficiency. A wavefront-sensing-based autofocus technique is proposed to increase the speed of autofocusing and obtain high localization accuracy. Intensities at different planes along the optical axis can be computed numerically after extracting the wavefront at defocus position with the help of the transport-of-intensity equation method. According to the focus criterion, the focal plane can then be determined, and after sample shifting to this plane, the in-focus image can be recorded. The proposed approach allows for fast, precise focus detection with fewer image acquisitions compared to classical image-analysis-based autofocus techniques, and it can be applied in commercial microscopes only with an extra illumination filter. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License
Compact transient-grating self-referenced spectral interferometry for sub-nanojoule femtosecond pulse characterization
No full textNational Natural Science Foundation of China (NSFC) [11274327, 61521093, 61527821]; Instrument Developing Project of the Chinese Academy of Sciences (CAS) [YZ201538]; Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) [XDB16]The self-referenced spectral interferometry (SRSI) technique, which is usually used for microjoule-level femtosecond pulse characterization, is improved to characterize weak femtosecond pulses with nanojoule based on the transient-grating effect. Both femtosecond pulses from an amplifier with 3 nJ per pulse at 1 kHz repetition rates and femtosecond pulses from an oscillator with less than 0.5 nJ per pulse at 84 MHz repetition rates are successfully characterized. Furthermore, through a special design, the optical setup of the device is even smaller than a palm, which will make it simple and convenient during the application. These improvements extend the application of the SRSI technique to the characterization of femtosecond pulses in a broad range. Not only pulses from an amplifier but also pulses from an oscillator or weak pulses used in ultrafast spectroscopy can be monitored with this SRSI method right now. (C) 2017 Optical Society of Americ