Characteristics and suppression of beam distortion in a high repetition rate nanosecond stimulated Brillouin scattering phase conjugation mirror

The stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) based on liquid media is widely used in high-power laser systems due to its robust thermal load capacity, high energy conversion efficiency and improved beam quality. Nevertheless, with an increase in the pump repetition rate, thermally-induced blooming and optical breakdown can emerge, leading to distortions in the Stokes beam. In this study, we delved into the thermal effects in liquid SBS-PCMs employing hydrodynamic analysis, establishing a relationship between beam profile distortion and the thermal convection field. We calculated the temperature and convection velocity distribution based on the pump light parameters and recorded the corresponding beam profiles. The intensities of the beam profiles were modulated in alignment with the convection directions, reaching a velocity peak of 2.85 mm/s at a pump pulse repetition rate of 250 Hz. The residual sum of squares (RSS) was employed to quantify the extent of beam profile distortion relative to a Gaussian distribution. The RSS escalated to 7.8, in contrast to 0.7 of the pump light at a pump pulse repetition rate of 500 Hz. By suppressing thermal convection using a high-viscosity medium, we effectively mitigated beam distortion. The RSS was reduced to 0.7 at a pump pulse repetition rate of 500 Hz, coinciding with a twentyfold increase in viscosity, thereby enhancing the beam quality. By integrating hydrodynamic analysis, we elucidated and mitigated distortion with targeted solutions. Our research offers an interdisciplinary perspective on studying thermal effects and contributes to the application of SBS-PCMs in high-repetition-rate laser systems by unveiling the mechanism of photothermal effects.

Effects of phonon bandgap on phonon-phonon scattering in ultrahigh thermal conductivityθ-phase TaN

Phonon bandgap typically has a significant effect on phonon-phonon scattering process.In this work,the effects of mass modified phonon bandgap inθ-phase Ta N are systemically investigated by the means of first-principles calculations with linearized Boltzmann transport equation.Through detailed calculations,we find that phonon bandgap has a significant effect on three-phonon process while exhibits a much weaker effect on four-phonon process.The reason for the ultrahigh thermal conductivity ofθ-phase Ta N is the long lifetime of phonons including both three-phonon and four-phonon processes,which originates from the weak phonon anharmonicity and large phonon bandgap-induced small phonon-phonon scattering phase space.This work advances the understanding of phonon bandgap effects on phonon transport.

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper. By making use of our improved model the calculations on scattering phase matrices of hexagonal prism ice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with the model of Cai and Liou,the required computational quantity is decreased by about two orders of magni- tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangular pyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of the two forms of ice crystals is performed.

Wide-Field Vibrational Phase Contrast Imaging Based on Coherent Anti-Stokes Raman Scattering Holography

We propose and implement a wide-field vibrational phase contrast detection to obtain imaging of imaginary components of third-order nonlinear susceptibility in a coherent anti-Stokes Raman scattering （CARS） microscope with full suppression of the non-resonant background. This technique is based on the unique ability of recovering the phase of the generated CARS signal based on holographic recording. By capturing the phase distributions of the generated CARS field from the sample and from the environment under resonant illumination, we demonstrate the retrieval of imaginary components in the CARS microscope and achieve background free coherent Raman imaging.

Growth and Raman Study of Phase Transitions of the KTa0.63Nb0.37O3 Crystal

The potassium tantalate niobate KTa_（0.63）Nb_（0.37）O_3 single crystal with large size and good quality was synthesized by Czochralski method.The crystal composition and structure were determined by electric probe microanalysis（EPMA） and X-ray diffraction（XRD） technique,respectively.The sequence of phase transitions of the as-grown crystal was investigated by Raman scattering technique.What features in the phonon spectrum corresponding to each phase transition,namely cubic to tetragonal（C-T）,tetragonal to orthorhombic（T-R） and orthorhombic to rhombohedral（O-R）,is discussed.Following the features the C-T phase transition point measured is in the vicinity of –40 ℃,and the difference from theoretical value was discussed;T-O phase transition point is at around –130 ℃,while the O-R phase transition point was not obtained due to the band overlapping and experiment limit.

Temporal Spreading Effect of Oceanic Lidar System

In this paper, multipath temporal spreading distributions of laser pulses are calculated when they travel through the seawater. Individual photon is followed in Monte Carlo calculation A modified Henyey-Greenstein （HG） function is applied to represent the scattering phase function of seawater. This paper proposes a new scaling method, which uses the effective scattering thickness τd to replace the optical thickness used in the traditional scaling technique. This paper compares the temporal spreading distributions of photons on conditions of different attenuation coefficients and target depths. The experiments reveal that these mutual deviations are changing in the range from 0.5% to 5%, so long as the corresponding effective scattering thicknesses τd remains the same. Therefore, a conclusion can be obtained, that the temporal spreading distribution is only dependent on the effective diffusion thickness τd .

Asymptotic Behaviour of the Phase in Non-Smooth Obstacle Scattering

In this paper,we study the asymptotic behaviour of the scattering phase s（λ）of the Dirichlet Laplacian associated with obstacle,where Ω is a bounded open subset of IRn（n≥2） with non-smooth boundaryΩ and connected complement Ωe=IRn\.We can prove that if Ω satisfies a certain geometrical condition,then where φ（λ）=[（4π）n/2Γ(1+（n/2）]-1|Ω|nλn/2,dn】0 depending only on n,and |·|j（j=n-1,n）is a j-dimensional Lebesgue measure.

A polarized micro-Raman study of a 0.65PbMg_(1/3)Nb_(2/3)O_3-0.35PbTiO_3 single crystal

Polarized micro-Raman spectra of a 0.65PbMgl/3Nb2/303 0.35PbTiO3 （0.65PMN-0.35PT） single crystal poled in the [001] direction are obtained in a wide frequency range （50 2000 cm^-1） at different temperatures. The best fit to the Raman spectrum at 77 K is achieved using 17 Lorenzians to convolute into it, and this is proved to be a reasonable fit. According to the group theory and selection rules of overtone and combinational modes, apart from the seven Raman modes that are from first-order Raman scattering, the remaining ones are attributed to being from second-order Raman scattering. A comparison between the experimental results and theoretical predictions shows that they are in satisfactory agreement with each other. Our results indicate that at 77 K the sample belongs to the rhombohedral symmetry with the C^53v（R3m） space group （Z = 1）. In our study, on heating, the 0.65PMN 0.35PT single crystal undergoes a rhombohedral → tetragonal → cubic phase transition sequence. The two phase transitions occur at 340 and 440 K, which correspond to the disappearance of the soft mode near 106 cm-1 recorded in VV polarization and the vanishing of the band around 780 cm^-1 in VH polarization, respectively.

Study of nucleon-nucleon and alphanucleon elastic scattering by the Manning-Rosen potential

Although often used in molecular dynamics,in this work the Manning-Rosen potential is parameterized to compute the scattering phase shifts for the nucleon-nucleon and the alphanucleon systems by exploiting the standard phase function method.We obtain excellent agreement in phase shifts with the more sophisticated calculations up to partial waves l=2.

Discrete unified gas kinetic scheme for multiscale anisotropic radiative heat transfer

In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present scheme is a finite-volume discretization of the anisotropic gray radiation equation,where the anisotropic scattering phase function is approximated by the Legendre polynomial expansion.With the coupling of free transport and scattering processes in the reconstruction of the flux at cell interfaces,the present DUGKS has the nice unified preserving properties such that the cell size is not limited by the photon mean free path even in the optical thick regime.Several one-and two-dimensional numerical tests are conducted to validate the performance of the present DUGKS,and the numerical results demonstrate that the scheme is a reliable method for anisotropic radiative heat transfer problems.