查看更多>>摘要：Combined laser-mechanical rock breaking drilling is an emerging technology that uses laser-assisted mechan-ical rock breaking to efficiently drill wells. A physical model of rectangular and circular laser spot scanning rock breaking is developed using the energy conservation theorem and heat transfer related theories, and the reasonableness of the model is analyzed through a combination of experiments and simulations. The effect of two kinds of scanning spots on the strength and drillability of granite was also obtained experimentally, and the effect of two kinds of laser spot scanning on rock breaking was evaluated. The results show that the uniaxial compressive strength of the rock decreases by 24% and 15%, the tensile strength by 20% and 11%, and the drillability by 16% and 10%, respectively, after scanning the granite with rectangular and circular laser spots at the stated parameters, and that the rock breaking effect of the rectangular scanning spot is better than that of the circular scanning spot.
查看更多>>摘要：The characteristics of the filaments generated by propagating a femtosecond Gaussian beam in a 2 m long gas cell with continuously varying pressures at different focal distances are numerically investigated. The simulated results indicate that the onset distance and the length of the filaments depend sensitively on the variation of pressure. These effects are enhanced with the increase of the focal length for the initial power P-in = 5P(cr). The main reason is that some parameters (the group velocity dispersion, the nonlinear refractive index, multiphoton ionization rate and the neutral atom density) are variational with the gaseous pressure. And the stability of the filament is determined by the combined effect of the pressure and the focal distance. In addition, we discuss the differences of the filament characteristics between the fixed pressure and continuously varying pressures. Through the analyses of the temporal dynamics and supercontinuum spectra, we find that maintaining a large pressure (1 atm) and changing to a large pressure (such as 0.3 similar to 1 atm) are beneficial to the propagation of the filament and the broadening of the spectra. It is interesting that, for fixing the initial energy E-in = 1 mJ, although the critical power of laser pulse is higher at the low pressure, the filament length at the continuously varying pressure p = 0.3 similar to 1 atm is still longer than that of p = 1 similar to 0.3 atm as the focal distance increases. This research is of great significance to remotely detect atmospheric pollutant components.
查看更多>>摘要：Based on the geometrical phase principle, we design an all-dielectric transmission coded metasurface in the near-infrared band. The all-dielectric unit cell is composed of silicon nanopillars and silicon dioxide substrate. We can encode design unit structures to build coded metasurface. We introduce the addition principle of encoding metasurface sequence into geometric phase metasurface. A new encoding sequence can be obtained by adding the two encoding metasurfaces through the addition rules between the numerically encoded particles, and the new encoding sequence has the scattering properties of the previous two encoding sequences. In other words, we can get the result of adding the functions by adding the sequences of two coded metasurfaces. We verify the accuracy of the addition principle of geometric phase coding metasurface by designing the addition of different coding sequences. This design method has potential applications in multifunctional photonic devices.
查看更多>>摘要：Quarter-wave plate (QWP) is one of the most important components of dynamic interferometer and its retardation can influence the measurement accuracy, which is usually manifested as periodic ripple error in the measurement results. Based on Jones matrix, the error formula is deduced in this paper, and the error correction method by rotating the half-wave plate (HWP) to change the intensity distribution in the four phase-shifted interferograms is proposed. In the experiment, the ripple error can be effectively suppressed when the background intensity of four interferograms tend to be the same. The performance of dynamic interferometer can be significantly improved through the proposed method.
查看更多>>摘要：In this paper, a polarization-insensitive reverse-ridge AlGaAs waveguide is designed for the supercontinuum generation. In the considered wavelength range from 3.4 to 8 mu m, the dispersion profiles, nonlinear coefficients, and effective mode field areas for the quasi-TE and quasi-TM modes coincide well. The simulation results show that when pump pulse with wavelength of 4.2 mu m, peak power of 4.8 kW, and width of 90 fs is launched into the anomalous dispersion region of the quasi-TE and quasi-TM modes of the 3.4-mm-long waveguide, the two generated SCs overlap well. For the quasi-TE and quasi-TM modes, the SCs generated extend from 2.17 to 8.53 mu m and 2.23 to 8.61 mu m, respectively, spanning more than 1.95 octaves. The proposed reverse-ridge AlGaAs waveguide structure is expected to provide a possible solution for alleviating the undesired polarization effect related to the nonlinear dynamics.
查看更多>>摘要：We report the measurement of one-body loss rates for magnetically trapped metastable europium atoms and the study of their loss mechanism. The loss of atoms observed in a magneto-optical trap is not fully understood because of the indivisibility of the loss regarding optical pumpings due to the presence of cooling laser beams. We magnetically trapped the atoms by directly loading from the magneto-optical trap and observed almost identical one-body loss rates of approximately 2.6 s(-1) for two isotopes: Eu-151 and Eu-153. Our rate-equation-based model, combined with loss rate measurements carried out with repumpers, shows that blackbody radiation at room temperature drives E1 transitions and induces the observed losses.
查看更多>>摘要：Propagation of ultrashort pulses at least a few tens of optical cycles in duration through a negative index material is investigated theoretically based on the generalized nonlinear Schrodinger equation with pseudoquintic nonlinearity and self-steepening effect. Novel periodic waves of different forms are shown to exist in the system in the presence of higher-order effects. It is found that such periodic structures exhibit an interesting chirping property which depends on the light field intensity. The nonlinearity in pulse chirp is found to be caused by the presence of self-steepening effect in the negative index medium. The solutions also comprise dark, bright, and kink solitary waves. Stability of the solitary wave solutions are proved analytically using the theory of nonlinear dispersive waves. The stability of the solutions is numerically studied under finite initial perturbations.
查看更多>>摘要：Low-cost tunable lasers have broad application prospects in optoelectronics. In this paper, a laser device based on fingerprint-textured cholesteric liquid crystal (CLC) was designed and fabricated, in which a narrow linewidth single-mode laser output on the side of the device was realized. The planar helical structure of the "fingerprint-texture"of CLC was obtained by the combined effect of externally applied electric field and substrate surface anchoring. Under the pumping light of a Nd:YAG solid-state pulsed second harmonic laser with the wavelength of 532 nm, the lasing emission wavelength of our CLC device changes non-monotonically with gradually increasing electric field, which first shifting from 568.5 nm to 609.2 nm and then shifting from 609.2 nm to 586.2 nm. And the observed spectral tuning of the lasing emission was reproducible and reversible. The analysis shows that the output laser radiation was the result of the Bragg reflection feedback provided by the fingerprint-texture.
查看更多>>摘要：In the field of microscopic imaging, the double-helix point spread function (DH-PSF) based on the Fresnel zones is often used to locate the three-dimensional position of particles. The lower transfer function efficiency makes it difficult to track the trajectory of moving particles in real-time, especially when the particles are far from the initial focal plane. We proposed a method based on the iterative Fourier transform algorithm and the Fresnel approximate imaging to optimize the phase which is used to generate the DH-PSF. The optimized DH-PSF has been significantly improved throughout the rotation process, and the maximum peak intensities of some positions have been increased by 82.31%. The main lobe strength of the optimized DH-PSF has been significantly improved, which was proved in vector diffraction simulation and practical experiments. After that, the optimized DH-PSF was used to track the 3D motion trajectories of nanoparticles with different shapes, and their diffusion coefficients were calculated. Experiments show that the optimized DH-PSF can quickly and accurately obtain the 3D motion trajectories of nanoparticles of various shapes and accurately calculate their diffusion coefficients in various solutions, which is important for the development of nanomedicine.
查看更多>>摘要：A seven-core fiber torsion sensor with microcavity structure based on intensity measurement is proposed. It is composed of a seven-core fiber (SCF) and two multi-mode fibers (MMF). The first end of the SCF has a microcavity structure. Because the mode fields between the MMF and SCF do not match at the splicing point, the phenomenon of mode interference will be formed between cladding modes and core modes. Experimental results show that in a clockwise situation, the intensity of transmission spectrum increases in the torsion range of 0 similar to 70 degrees, the torsion sensitivity is 0.098 dB/degrees. And in a counterclockwise situation, the intensity of transmission spectrum decreases, the torsion sensitivity is 0.103 dB/degrees. The sensor has a simple structure and easy to fabricate, so it has wide application prospects in the field of torsion sensing.
NSTL
Elsevier