查看更多>>摘要：? 2021 Elsevier B.V.This study presents an optical system equivalent to a polarization element, which can be applied as a linear phase retarder with arbitrary phase retardation or a linear diattenuator with arbitrary diattenuation. The principal axis of the equivalent polarization element can be rotated by applying an electrical signal to an electro-optic modulator. The simple optical system setup is only composed of three polarization elements in a round-trip configuration. The proposed system is versatile, in that it can be applied to a variety of polarization elements that have linear anisotropy.
查看更多>>摘要：? 2021 The Author(s)We theoretically investigate the influence of a phonon bath on entangled generation between two semiconductor quantum dots coupled to a plasmonic nanocavity and coherently driven by an external optical field. Our study reveals that phonons could be useful in a certain range of system parameters where a subradian state preparation is possible. We point out that this behavior is due to the fact that phonon environment modify the radiative properties of the two-qubit inducing different decay rates between the collective states of the system. The influence of the factors characteristic of quantum dot systems and plasmonic nanocavity such as energy mismatch in different dots, different plasmonic cavity losses as well as coupling to phonons is analyzed. The entanglement can be controlled via different external parameters such as the cavity detuning, the Rabi frequency of the driving field and the resonance frequency of the QDs.
查看更多>>摘要：? 2021 Elsevier B.V.The high-order harmonic generation (HHG) by aligned molecules is the consequence of coherent summation of the complex laser-induced dipoles according to the alignment distribution of the molecules. Using the single-molecule quantitative rescattering (QRS) model with the known alignment distribution and the strong-field ionization of fixed-in-space molecules, the complex angle-dependent photorecombination transition dipoles between the ground and ionic states of molecules can be retrieved from the single-molecule HHG. However, such retrieval does not consider the real experimental conditions, such as the propagation of HHG in the medium and the inaccurate measurement of the probe intensity and the alignment degree. Here we propose a method to retrieve the complex angle-dependent molecular frame transition dipoles between the highest occupied molecular orbital (HOMO) and the ionic states of N2 molecules from the macroscopic HHG of aligned molecules. In this method, the complex transition dipole is expanded with Legendre polynomials, and the HHG is expressed as a function of the modulus and phase of the complex expansion coefficients. The complex expansion coefficients can be determined by fitting the HHG data, then the angle-dependent amplitude and phase of the complex transition dipole can be obtained. We show that the angle-dependent amplitude and phase of the transition dipoles for each individual harmonic can be successfully retrieved at both low and high probe intensity and degrees of alignment. Then we show the inaccuracy of the retrieved angular dependence amplitude and phase due to the uncertainty of the probe intensity and alignment degree. As the probe intensity increases, which is usually not measured precisely in the experiment, HOMO-1 may also contribute to HHG, we thus compare the retrieved amplitude and phase of the transition dipole with or without HOMO-1’s contribution to HHG.
查看更多>>摘要：? 2021 Elsevier B.V.Continuous-wave lasing properties of the tetragonal Yb:CaWO4 crystal were investigated with a- and c-cut crystals under 976-nm diode pumping, revealing a strong anisotropy in many output characteristics. Depending on the resonator output coupling, the laser oscillation realized with the a-cut crystal could be σ- or π-polarized; it could also consist of σ and π polarization states simultaneously. An output power of 2.01 W was generated at 1025.1–1027.8 nm in dual-polarization laser operation, with an optical-to-optical efficiency of 24.1% and a slope efficiency of 28%; the σ- and π-polarized components were measured to be 1.05 and 0.96 W, respectively. The laser emission generated with the c-cut crystal could only be unpolarized; while the maximum output power, which was limited by the output saturation behavior, amounted only to 1.61 W.
查看更多>>摘要：? 2021 Elsevier B.V.This paper reported a comparative study of molecular vibrational dynamics in different organic molecules by femtosecond time-resolved folded box-coherent anti-Stokes Raman scattering (TR-box-CARS) spectroscopy. As model system methanol and ethanol molecules are chosen, the coherence transfer between stretching vibration modes of C-H bonds in them are excited and detected at the same time. Different vibration periods and wavenumber spacing are found for the amplitudes of the coherent vibrations of C-H stretch modes in methanol and ethanol molecules. This study makes femtosecond TR-box-CARS possible as a prospective technique for detection and identification of organic molecular species in ambient environments. A simple spatial magic filter and frequency domain filter method with folded TR-box-CARS approach of suppressing the non-resonant FWM background is demonstrated.
查看更多>>摘要：? 2021 Elsevier B.V.A novel temperature (T) and relative humidity (RH) sensor based on a graphene oxide (GO)-coated Loop-Fiber that incorporates a fiber Bragg grating (FBG) is proposed in this work. The uniform waist area of the tapered area was coated with GO for RH measurement. At the same time, FBG was used to overcome the T cross-sensitivity, thereby making a T and RH sensor. Experimental results show that the structure is sensitive to T and RH, and the sensitivity in the T range of 35 °C to 60 °C and humidity range of 37.7–65.5 %RH is ?201.1 pm/°C and ?141.7 pm/%RH. Corresponding resolutions are 0.14 %RH and 0.1 °C. FBG is insensitive to RH but sensitive to T and its T sensitivity is 5.2 pm/°C. Many experiments showed the excellent reversibility and repeatability of the sensor. This sensor has the advantages of high sensitivity, simple structure, easy production and low cost. It can also be used for measuring T and RH simultaneously.
查看更多>>摘要：? 2021 Elsevier B.V.Long period grating (LPG) with a small grating period (25 μm) is inscribed with the femtosecond laser line-by-line technique. The fabricated LPG consists of 500 vertical refractive index (RI) modification lines (15μm in length), corresponding to a compact total length of 12.5 mm. With the fabricated LPG, coupling between core modes is significantly enhanced (from previously reported <0.6 dB to ～11 dB). Moreover, coupling from core mode to forward- and backward-propagating? cladding modes is also enabled. Thanks to the co-existence of forward- and backward-propagating cladding mode resonances, wide range and sensitive RI sensing is realized by the LPG, with a RI sensitivity more than 500 nm/RIU. In addition, the grating shows a low temperature cross-sensitivity, and the enhanced core mode resonance can serve as a monitor for temperature variation, allowing simultaneous measurement of RI and temperature. Note that these advantages are achieved with only one uniform grating. With a simple structure, the proposed grating will be a good choice for applications where wide RI sensing range and simultaneous temperature monitoring are required.
查看更多>>摘要：? 2021 Elsevier B.V.Linewidth is an important indicator for laser beam combining and coherent detection. The temperature of fiber Bragg gratings (FBGs) is one of the factors that affect the spectral performance of fiber lasers. In this article, we report an all-fiberized 100-W oscillator with a narrow-linewidth laser output based on the temperature control of FBGs. The effects of temperature on the reflected spectra of the FBG pair were studied. Then, a thermal electrical cooler was used to control the temperature of the HR-FBG to ensure spectral matching under high-power conditions. Compared with the case without temperature control, the -3 dB laser bandwidth can be narrowed from 226.5 pm to 137.8 pm. The corresponding laser power was as much as 100.6 W with a polarization extinction ratio of 99.8% (27 dB). This demonstrates that controlling the temperature of FBGs can suppress laser spectral broadening. This 100-W narrow-linewidth fiber oscillator has great potential for applications in FBG-based master oscillator power amplifier systems.
查看更多>>摘要：? 2021 Elsevier B.V.Lithium niobate integrated optical modulator is the core component of interferometric fiber optic gyroscope, and its performance has an important influence on the performance indicators of fiber optic gyroscope. The output light of lithium niobate integrated optical modulator are generally considered to have the same central wavelength and spectral width. In this paper, it is proved that there is a non-negligible difference in the central wavelength between the outgoing light through several groups of experiments. The temperature characteristics of spectral parameters are discussed, in which the wavelength difference changes obviously with temperature. In the temperature range of [?40,60] °C, the wavelength difference first increases, reaches the maximum at about 50 °C, and then decreases with the increase of temperature. The spectral width difference does not change significantly with temperature.
查看更多>>摘要：? 2021 Elsevier B.V.A new type of radially polarized (RP) cosine-Gaussian (CG) field is proposed. Through the analytical model, it is found that such RP CG beam exhibits completely different focusing properties from the reported RP plane waves. More importantly, a stable three-dimensional trap of Rayleigh particle accompanied by a subwavelength spin motion can be easily achieved using this RP CG beam.
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