The manipulation of high-absorptive airborne particles using doughnut-shaped laser beams is possible given the dominance of a thermo-optical force, called photophoretic force (PP-force), over the particle motion. For this reason, under the proper experimental parameters, we can improve the hit ratio of micron-sized biological particles in x-ray diffractive imaging experiments using optical-induced forces. In this project, we extend the research for the proposal of the construction of a slow-diverging optical funnel based on non-diffractive high-order Bessel-Gaussian beams (HOBBs).
The generation of Bessel-like beams requires the phase modulation of an initial laser beam, which can be achieved using diffractive optics or a spatial light modulator (SLM). However, to reach the optimal matching in the optical funnel geometry and predicted force, a model is beneficial. In the first stage of the project, we have developed a numerical modelling for free-space propagation and wavefronts modulation based on Fourier Optics. The model has been compared with the experimental construction of a first-order optical funnel Bessel-Gaussian beam using a combination of a phase plate and an axicon.
In addition, a preliminary comparison between the model and the SLM-generated HOBBs is performed and discussed. Experiments of manipulation of granulovirus (GV) bioparticles using an optical funnel have been performed by DESY, Germany. Considering the particle under the effect of friction and optically induced forces, we have developed a method to estimate the range of temperature gradients across the GV bioparticle under several laser illumination powers.
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