Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Simplified modal method for slanted grating
No full textNational Nature Science Foundation of China [61405214]We report the simplified modal method for the slanted grating based on the accurate dispersion equation. The vividly physical insight is presented to interpret the diffraction process for slanted grating. We also present that the simplified modal method with the two-lowest mode condition is effective for a large slanted angle up to 26 degrees. By examining the eignefunction, the mode index, and the two-lowest mode condition, we provide new evidences to verify the assumption that a slanted grating with subwavelength period can be analyzed as an equivalent rectangular grating using the simplified modal method, which is right and convenient to use for a small slanted angle up to 20 degrees. Numerical simulations of the simplified modal method are coincident with rigorous coupled wave analysis for small slanted angle gratings. Thus the simplified modal method can be used for small slanted angle grating since the equivalence of slanted grating and rectangular grating is verified due to its vivid physical analysis. (C) 2016 Elsevier B.V. All rights reserved
Evaluation of femtosecond laser damage to gold pulse compression gratings fabricated by magnetron sputtering and e-beam evaporation
No full textNational Natural Science Foundation of China (NSFC) [10704079, U1430121]; Shanghai Science and Technology Committee Program [16JC1420600]In this study, two kinds of Au-coated gratings (ACGs) with a period of 1740 lines/mm were fabricated and evaluated. For these ACG samples, magnetron sputtering and e-beam evaporation were used as the gold deposition process, and the samples had a bandwidth of at least 170 nm, with the -1st-order diffraction efficiency exceeding 90% around the center wavelength of 800 nm. The one-on-one damage threshold of ACGs fabricated by magnetron sputtering and e-beam evaporation measured at a pulse width of 60 fs was 0.59 J/cm(2) and 0.43 J/cm(2) in the case of the beam normal fluence, respectively. The typical damage morphology of the former type of samples was melting of the gold film, whereas those of the latter type were blisters and peeling off of the gold film. In theory, the electromagnetic field, temperature field, and thermal stress field distribution in the ACGs were calculated using the finite element method. We demonstrated that the adhesion between the gold film and the photoresist played an important role in determining the damage behavior. Thus, the laser resistance of ACG can be improved by enhancing the adhesion between the gold film and the photoresist, and magnetron sputtering was an alternative method to obtain ACGs with much better adhesion. (C) 2017 Optical Society of Americ
High spatial resolution phase-sensitive optical time domain reflectometer with a frequency-swept pulse
No full textNational Natural Science Foundation of China (NSFC) [61377062, 61405227, 61475165, 61675216]; Science and Technology Commission of Shanghai Municipality (STCSM) [15XD1524500]A high spatial resolution phase-sensitive optical time domain reflectometer (phi-OTDR) with an optical frequency-swept pulse (FSP) is proposed, and the experimental results are presented in the Letter. The FSP f-OTDR uses optical pulses with linear frequency modulation with higher pulse energy for longer sensing fiber and uses matched filter in the receiver to compress the processed pulse width. Thus, the contradiction between spatial resolution and the working distance in ordinary f-OTDR is relaxed. A spatial resolution of 30 cm, a sensing distance of 19.8 km, and a signal-to-noise ratio of 10 dB for vibration sensing were obtained experimentally. To our best of our knowledge, this is the first time that a sub-meter spatial resolution over such a long sensing range has been reported sensors. (C) 2017 Optical Society of America
Modal analysis of 1 x 3 reflective triangular gratings under normal incidence
No full textNational Natural Science Foundation of China (NSFC) [61307064, 61405214]; Ministry of Science and Technology of China (MOST) [2012YQ170004]Modal analysis of the 1 x 3 highly efficient reflective triangular grating operating in the 800 nm wavelength under normal incidence for TE polarization is presented in this Letter. The rigorous coupled wave analysis and simulated annealing algorithm are used to design this beam splitter. The reflective grating consists of a highly reflective mirror and a transmission grating on the top. The mechanism of the reflective triangular grating is clarified by the simplified modal method. Then, gratings are fabricated by direct laser writing lithography
Astigmatism transfer phenomena in the optical parametric amplification process
No full textCAS; National Natural Science Foundation of China [61475169, 61521093, 11127901]; Youth Innovation Promotion Association CASWe numerically and experimentally investigate the astigmatism transfer phenomena in femtosecond optical parametric amplification (OPA). We model the OPA process based on the coupled second-order three-wave nonlinear propagation equations. The numerical and experimental results support that the input pump pulse astigmatism can be transferred into the idler pulse but not the signal pulse, and the idler pulse astigmatism originating from spatial walk-off is less than the idler pulse astigmatism received from the pump. Thus, we can provide a clear understanding of astigmatism transfer mechanisms in the OPA process, and make better use of broadband tunable OPA sources
Measurements of nonlinear refraction in the mid-infrared materials ZnGeP2 and AgGaS2
No full text100 Talents Program of CAS; National Natural Science Foundation of China [61475169, 61521093, 11127901]; Youth Innovation Promotion Association CASAccurate values of the nonlinear index of refraction n(2) for the nonlinear optical crystals ZnGeP2 and AgGaS2 were measured using the Z-scan technique. The results were obtained using similar to 100-fs mid-infrared pulses from an OPA-DFG system driven by the 800-nm laser. The measured values of the AGS agree well with the theoretical values based on the two-band model for a direct band gap material. We confirmed the validity of the measured values for the indirect semiconductor ZGP by comparing the results with those obtained at similar to 1300 nm in a previous study. We have proved the broadening due to GVD is negligible in our experiments. We believe these nonlinear measurements of AGS and ZGP are meaningful for the analysis and design of optical systems in the mid-infrared region
Nonlinear dynamics investigation in few-cycle laser seeding of quantum cascade lasers: role of permanent dipole moment
No full textNational Natural Science Foundation of China (NNSF) [11374318, 11674312]; Chinese Academy of Sciences and Department of Human Resources and Social Security of ChinaThe ultrafast dynamics in the few-cycle laser seeding of quantum cascade laser (QCL) is numerically investigated via the exact solution of the full-wave Maxwell-Bloch equations. It is found that, with or without taking permanent dipole moment (PDM) into account, the QCL emission is quite different: beyond the fundamental frequency band, additional high and low bands occur for that with PDM, which forms an ultra broad quasi-comb. The origin for this is closely related to the generation of second order harmonic and direct current components as a result of PDM breaking down the parity symmetry. Moreover, the carrier-envelope phase (CEP) of laser seed is locked to the QCL output, no matter with or without PDM, and this phase controlled QCL maybe has more wide and convenient applications in related fields
Persistent luminescent nanoparticles as energy mediators for enhanced photodynamic therapy with fractionated irradiation
No full textNational Natural Science Foundation of China (NSFC) [11274327, 61521093, 61527821, 11575276]; Chinese Academy of Sciences [YZ201538, QYZDB-SSW-JSC002]; Shanghai Institute of Optics and Fine Mechanics [1603051J00]; Shanghai Sailing Program [17YF1421300]The excitation wavelengths of most porphyrin-based photosensitizers are in the ultraviolet (UV) spectrum. Prolonged irradiation of living cells and tissues with UV light during the clinical application of photodynamic therapy (PDT) may cause DNA damage and cell death. Here, we report a novel persistent-luminescent nanoparticle (PLNP)-based PDT approach that uses the afterglow property of PLNPs to greatly reduce the dose of UV light while maintaining the desired cancer suppression effect. Multifunctional PLNPs coated with mesoporous silica layers and subsequently conjugated to a photosensitizer were evaluated. These nanoconjugates showed high colloidal stability and biocompatibility. Furthermore, they generated a moderate amount of O-1(2) through efficient energy transfer from the nanoparticle to the photosensitizer, which can efficiently damage cancer cells. In addition to their UV-excited luminescence, PLNPs also exhibited a long-lasting luminescence afterglow. Thus, PLNPs can serve as a persistent light source for PDT activation after excitation by an external light source is stopped. When fractionated light was used for excitation instead of continuous light at equivalent irradiation doses, confocal microscopy revealed that the photosensitizer-conjugated PLNPs showed a significantly enhanced cancer cell killing ability. Moreover, quantitative flow cytometry showed that fractionated light irradiation (60 s/100 s on/off cycle) produced up to ten times more cancer cell apoptosis/necrosis than the same dose of continuous light irradiation did. These results indicate that photosensitizer-conjugated PLNPs combined with fractionated irradiation show good potential for low-dose UV-mediated PDT activation
Varied laser induced damage phenomena of gold coated gratings for pulse compression
No full textNSAF [U1430121]; National Science Foundation of China [10704079]; Key Laboratory of Material for High Power Lasers - Chinese Academy of SciencesIn this paper, gold-coated gratings for pulse compression have been prepared and their laser damage experiments have been performed. Varied laser damage morphologies have been observed: when a 60 fs-pulsed laser with energy density slightly higher than the damage threshold was used, damage morphology with a characteristic of discrete distribution of small pits was appeared. These damage pits are linearly distributed at the junction of ridges and grooves. If the laser energy density is much higher than the damage threshold, the gold films was overall ablated and the grating structure disappeared. Besides, if the gold film has poor adhesion, it was peeled off. When a 450 ps-pulsed laser with energy density slightly higher than the damage threshold was used, part of grating ridges will be ablated and an obvious line exists between the ablated area and the unchanged area. In theory, the laser induced temperature field and stress field in gold-coated gratings were calculated based on the electromagnetic field using the finite element method. It is demonstrated that the temperature and thermal stress distribution characteristics are affected by the laser heating rate and the heat diffusion time (the calculated diffusion time ranges from 6 fs to 450 ps), which determines the laser damage characteristics. The possible damage drivers have electron hydrodynamic pressure, thermal ablation and thermal stress
Diode laser array by spectral beam combing with a transmission grating
No full textThe 38.5 W spectral combined beam of a 19-element 940 nm diode laser bar has been demonstrated in the spectral beam combining experiment by using a Beam Transformation System (BTS). The outputs had a diffraction-limited beam quality in the fast axis and M-2=10.5 in the slow axis. Spectral beam combining was achieved by using an external cavity including a transmission diffraction grating