| Laser micro/nanofabrication, as one of promising techniques; have showed simpleprocess, high accuracy, excellent compatibility with a wide range of materials, and strongcapability for the preparation of complex micro/nanostructures. Laser micro-nanofabrication is currently widely used in micro-optics devices, micro-structure,micromachining, micro-welding, biomimetic surfaces and other areas. In this paper, basedon the interaction theory between laser and material (surface and interface), a systematicstudy of two maskless laser processing technology——multi-beam laser interferometerand laser micro-welding was demonstrated. We combined its own advantages with thematerial, and prepared high-precision large-area hydrophobic surfaces, for example,controlled anisotropic surfaces by different experimental parameters; anisotropicbiomimetic surface by low surface energy modification; reversible tunable surface betweenisotropy and anisotropy by curvature change. By take advantage of high energyfemtosecond laser pulse, we realize high efficiency glass micro-welding by using doublepulses with different delay time. Moreover, we systemically investigated the physicalmechanism of double-pulse irradiation glass, compared to traditional single-pulseirradiation. This will pave the way for its further application in industry. The main contentsare as follows：1. One simple method to control two-direction anisotropic wetting by regular micropearlarrays was demonstrated. Various micropearl arrays with large-area were rapidly fabricatedby a kind of improved laser interference lithography. Specially, we found that the parallelcontact angle (CA) θ2decreased from93oto67oas the intensity ratio of four laser beamsincreased from2:1to30:1, while the perpendicular CA θ1determined by the thickness ofthe resin kept constant. This was interpreted as the decrease of height variations△h from1100nm to200nm along the parallel direction caused by the increase of the intensity ratio. According to this rule, both of the θ1and θ2could be simultaneously controlled byadjusting the height variation△h and the resin thickness. Moreover, by combiningappropriate design and low surface-energy modification, natural anisotropic rice leafexhibiting CAs of146o±2o/153o±3ocould be mimicked by our anisotropic bio-surface withthe CAs145o±1o/150o±2o. We believe that these controlled anisotropic bio-surfaces will behelpful for designing smart, fluid-controllable interfaces that may be applied in novelmicrofluidic devices, evaporation-driven micro/nanostructures and liquid microdropletdirectional transfer.2. We reported a kind of novel smart surfaces with reversible switching between isotropyand anisotropic wetting, which was realized by one-direction curvature tune on flexiblesuperhydrophobic surfaces. Along the curvature change, the wettability of this flexible filmwas changed from isotropic state (150o/150o) into anisotropic state confirmed by itsanisotropic contact angles (150o/160o) and sliding properties (30o/65o). Furtherinvestigation revealed that the surface wettability was changed from composited pinnedstate into transitional state. This was interpreted as the increase of roughness factor and thedecrease of the contact area between water droplet and pillar arrays. Moreover, therelationship between the anisotropy and curvature was systemically investigated, by whichthe anisotropy could be precisely controlled by the curvature change. At last, wedemonstrated the wetting states between isotropy and anisotropy on this flexiblesuperhydrophobic film could be reversibly switched by curvature for many times (>10).3. We investigated the physical mechanism of high-efficiency glass microwelding bydouble-pulse ultrafast laser irradiation by measuring the dependences of the size of theheat-affected zone and the bonding strength on the delay time between the two pulses fordelay time up to80ns. The size of the heat-affected zone increases rapidly when the delaytime is increased from0to12.5ps. It then decreases dramatically when the delay time isfurther increased to30ps. It has a small peak around100ps. For delay time up to40ns,the size of the heat-affected zone exceeds that for a delay time of0ps, whereas for delaytime over60ps, it becomes smaller than that for a delay time of0ps. The bonding strengthexhibits the same tendency. The underlying physical mechanism is discussed in terms ofinitial electron excitation by the first pulse and subsequent excitation by the second pulse: specifically, the first pulse induces multiphoton ionization or tunneling ionization, whilethe second pulse induces electron heating or avalanche ionization or the second pulse isabsorbed by the localized state. Transient absorption of glass induced by the ultrafast laserpulse was analyzed by an ultrafast pump–probe technique. We found that the optimumpulse energy ratio is unity. These results provide new insights into high efficiency ultrafastlaser microwelding of glass and suggest new possibilities for further development of otherultrafast laser processing techniques.4. The absorption mechanism of the second pulse is experimentally and theoreticallyinvestigated for high-efficiency microwelding of photosensitive glass by double-pulseirradiation using a femtosecond laser. The transient absorption change during the secondpulse irradiation for various energies induced by the first pulse is measured at differentdelay times. The resulting effects depend on whether the delay time is0–30ps (timedomain I) or30–several ns (domain II). By solving rate equations for the proposedelectronic processes, the excitation and relaxation times of free electrons in time domain Iare estimated to be0.98and20.4ps, respectively, whereas the relaxation times from theconduction band to a localized state and from the localized state to the valence band indomain II are104.2and714.3ps, respectively. Single-photon absorption of the secondpulse by free electrons dominates in domain I, resulting in high bonding strength. In timedomain II, about46%of the second pulse is absorbed by a single photon due to thelocalized state, which is responsible for higher bonding strength compared with thatprepared by single-pulse irradiation.5. Since fused silica exhibited good optical performance and thus showed a wide range ofapplications in industrial and optical applications. So, we begin to study the high efficiencyfused silica micro-welding by double laser pulses. The maximum force is in the vicinity of0.5ps. After that, we found the laser welding force will decline rapidly. The welding forceat1ps is less than the traditional single-pulse welding force. At the delay time between1ps and200ps, laser welding force almost reached saturation. This physical phenomenon isdifferent from the one in photosensitive glass double pulse micro-welding, which isbeneficial for helping people better understand the physical mechanisms of glassmicro-welding of various materials. In summary, this paper mainly focused on large area biomimetic superhydrophobicsurfaces prepared by multi-beam laser interference lithography. Moreover, the surface wastuned by applying a force of an elastic surface to achieve reversible switching betweenisotropy anisotropy. Finally, we study high-efficiency micro-welding by ultrafast laserdouble-pulse, analyze the physical mechanism of welding, and study the double pulsewelding force changes in the fused silica, which lay the foundation for ultrafast laserwelding in various materials. |
PDF Full Text Request