Study On Propagation Factor In Non-Kolmogoroy Turbulence And Optical Trapped Properties Of The Laser Beams

Laser beams are widely used in these major aspects which containoptical communication, polarization remote sensing, optical tracking andlaser radar. Recent years, study on propagation properties throughatmospheric turbulence and optical trapping of different beams havebecome research hotspots. The optical trapping is a great method oftrapping and controlling the particles, macromolecules and cells ofmicron or nanometer size without contact and damage by usingevanescent wave, optical tweezers and photophoresis. The opticaltweezers is the most widely applied technology for optical trapping,namely three-dimensionally capturing and manipulating micro particles(particle size changed from nm to μm) at the beam focus near usingradiation forces (radiation forces changed from fN to pN) acting onparticles by single focused laser beams. The present results indicate thatthe partially coherent beams have good propagation properties, andoptical tweezers formed after focusing are more effective for trappingparticles. In view of this, based on the extended Huygens-Fresnelprinciple and the second-order moments of the Wigner distributionfunction, we have first studied the beam propagation factor of thepartially coherent Laguerre-Gaussian beam in non-Kolmogorov turbulence. On the basis of this, combining with the Rayleigh scatteringtheory,by adjusting the beam parameters (such as beam orders, the initialspatial coherence widths and so on) and the particles refractive index, wehave further studied the optical forces of the focused partially coherentstandard Laguerre-Gaussian beam, the focused partially coherent elegantHermite-Gaussian beam, the focused partially coherent elegantLaguerre-Gaussian beam and nanosecond pulsed flat-topped beamsacting on the Rayleigh dielectric sphere and proceeded numericalcalculations and analysis. The results will provide theoretical referencefor effective trapping of particles. The main work of this paper is asfollows:(1) Based on the extended Huygens-Fresnel principle and thesecond-order moments of the Wigner distribution function, we havederived the analytical expression for the beam propagation factor of thepartially coherent Laguerre-Gaussian beam in non-Kolmogorovturbulence, calculated the influences of the beam order, the turbulenceexponential factor, the turbulence structural constant，the turbulence inneror out scale and the correlation length on the beam propagation factorof the partially coherent Laguerre-Gaussian beam in non-Kolmogorovturbulence.(2) Based on the cross-spectral density function and the Rayleighscattering theory, we have derived the analytical formulae for optical forces on Rayleigh dielectric sphere of the focused partially coherentstandard Laguerre-Gaussian beam and the focused partially coherentelegant Hermite-Gaussian beam, and made the corresponding numericalcalculations. By adjusting the beam orders, the initial spatial coherencewidths and the refractive index of particles, we have preliminarily studiedthe mechanism of interaction between the focused partially coherentbeams and Rayleigh dielectric sphere, and discussed the influence ofspectral bandwidth on the capturing characteristics of focused partiallycoherent elegant Laguerre-Gaussian beam. This work provides atheoretical method for stably trapping particles.(3) Based on the nonlinear optical theory and combined withthird-order electric susceptibilities of particles, we have derived theanalytical expressions for optical forces exerting on nanometre sphericalglass particles. We also made the numerical calculations and investigatedthe influence of three order nonlinear optical effects on the opticaltrapping.