Investigation On Ring-shape Laser Induced Forward Transfer Technology

Laser induced forward transfer(LIFT)is a kind of technology that promotes the separation of materials by laser-induced cavitation to form pulse pressure.At present,the technology has broad prospects in the field of biological cell printing technology.However,due to the interaction of fluid dynamics in the separation material,the traditional laser-induced technology may lead to excessive transfer of the solution.In order to improve the printing accuracy of biological cells,a new method of laser-induced forward transfer using ring-shape facula is proposed.The following is the specific research content.First of all,the incident laser beam with a diameter of 6 mm in the experiment is adjusted,and two conical lenses with the same curvature radius are placed opposite to each other.The incident laser beam is refracted into a parallel circular beam,and the circular spot is obtained by combining the flat convex lens and focusing the beam.The adjustable range of the inner diameter of the ring-shape spot is 5-300?m,and the adjustable range of the outer diameter is 60-1000?m.several important forming parameters are calibrated.Secondly,high speed photography and finite element simulation were used to analyze and verify the pushing effect of ring-shape cavitation bubble on the solution outside the ring at the initial stage of expansion and the energy center convergence effect from expansion to collapse.It is found that the growth process of ring-shape cavitation bubbles in a single cycle can be divided into three stages,namely,expansion stage to the outside of the ring,convergence and contraction stage to the center of the ring,and the generation and continuous pulsation of cavitation groups.In the velocity field of numerical simulation results,it is found that in the initial stage of cavitation bubble expansion,the horizontal velocity of the solution outside the ring increases rapidly and then decreases slowly,while in the later stage of cavitation bubble expansion,the vertical velocity gradually converges and increases.Thirdly,the mechanism of jet transport induced by ring-shape cavitating bubble under solid wall is analyzed.Under different laser energy and different ratio of inner diameter to outer diameter of ring-shape facula,the formation conditions of stable jet are analyzed and discussed by high-speed photography and finite element simulation analysis at different angles.Under the condition of laser energy of 2 m J and the ratio of inner diameter to outer diameter of ring-shape spot of 0.45,the formation process of ideal jet was photographed.Compared with the finite element simulation results,it can be seen that the target transfer solution in the center of ring-shape spot was pushed out in the expansion stage of cavitation bubble,and the solution was completely disconnected until the later stage of expansion(the beginning of contraction stage),which realized the accurate transmission of target transfer solution.Then,the ring laser-induced separation technology was studied by using polyethylene microspheres with a diameter of 17?m instead of biological cells.Through the orthogonal analysis experiment,the order of the influence on the parameters of the average droplet diameter is: the thickness of the sacrificial layer,the laser energy,the ratio of the inner and outer diameter of the spot,and the mass fraction of the solution.Under the condition of stable jet formation,the transmission parameters of the induced minimum droplet are obtained as follows: laser energy 0.8m J,ratio of inner diameter to outer diameter of ring-shape spot 0.25,mass fraction of sodium alginate solution 4%,thickness of sacrificial layer titanium 240 nm.Finally,a novel Triazene sacrificial layer material with no regeneration pollution was prepared by controlling the interfacial polycondensation reaction using N,N'-diethyl-1.3-propanediamine and 4,4'-diaminobenzophenone as raw materials.The main functional groups of the materials were detected by Fourier transform infrared spectrometer and the synthesis accuracy was verified.In addition,the NMR spectra of the materials irradiated by blue violet light were tested.It was concluded that nitrogen was released from the new materials irradiated by blue violet light.The results show that the new material is effective in reducing the ablation residue.