A laser-induced cavitation-based sterilization technique was demonstrated to efficiently inactivate foodborne pathogenic bacteria with a low loss of nutrients. A sterilization efficiency of more than 90% (less than 5 × 105 colony-forming unit / mL) was achieved when the flow rate was no more than 40 μL / s on a chip that could mimic an industrial sterilization system. In addition, the sterilization efficiency could be enhanced if the channels of the chip were coated with Ta2O5 / SiO2 film. Moreover, the nutrient composition of the milk was well preserved. The laser-induced cavitation-based sterilization technique provides an alternative method for the inactivation of foodborne pathogenic bacteria.
Multistaircase spiral phase plates (SPPs) are more commonly used to generate an optical vortex, as compared to ideal continuous surface SPPs. However, due to the complexities and difficulties involved in the manufacturing of the multistaircase SPPs, the number of the staircases M should not be high and should be sufficient to guarantee a similarity between the M staircase situation (considering an intrinsic topological charge l) and the ideal situation. Therefore, a Fraunhofer diffraction analysis model is proposed to quantitatively and quantificationally solve the diffraction field of the vortex generated by multistaircase SPPs. A finite hypergeometric series summation is applied to solve the diffraction fields of the vortices with different parameters, under the conditions of uniform and Gaussian incident beams. The simulation results show that the summation of the first certain terms of the Fourier expansions can appropriately approximate the diffraction field, and M is positively related with l to approach the ideal situations. Thus, the proposed model can provide a reference for designing and setting the parameters of multistaircase SPPs.