Fabrication Of Photic Functional Microstructures By Femtosecond Laser In Silica Glass And Metal Film

With the developments of the laser technology, femtosecond laser technologyis also becoming more and more consummate as a novel technology in recent years.Femtosecond laser pulse is a powerful tool for microfabrication and micro-machiningof various multi-functional structures in dielectric materials through multi-photon ab-sorption because of its high-quality and damage-free processing. Up to now, manyhigh-quality material processing techniques have been achieved by using femtosec-ond laser pulses with the methods of directly writing and holographic fabrication,such as waveguide, micro-gratings, photonic crystals and diffractive optical elements(DOE). In this dissertation, we propose several methods for fabrication of the photicfunctional microstructures. we also give a full and accurate theoretic interpretation forthe interactions between the femtosecond laser pulses and the materials. The researchwork has been summarized in detail as follows.improve the theory of the interaction between the laser and the transparentglass. Different periodic structures are attained on the surface of the transparent glassby a single shot of two or three pulses. When a single shot of two pulses interferedwith each other, not only did we get the ordinary grating whose periods accordedwith the theoretic equation d =λ/[2sin(θ/2)], but also obtained the extraordinarygrating whose period is a half of the ordinary grating. The depth of the extraordinarygrating is a half of the ordinary grating's. The extraordinary grating formed at themiddle of each bulge of the ordinary grating and was attributed to the higher-ordermodulation arising from second-harmonic generation (SHG) of the femtosecond laserpulse incident to the surface of silica glass.When a single shot of three pulses interfered with each other, the two-dimensional periodic microstructure have been obtained, which distributed as a hexag-onal lattice. We also analyzed the microstructure by atomic force microscopy(AFM),and the analyzed results showed that the period accorded with the calculated result bythe equation very well. Diffraction pattern of the microstructure has been observedwith a laser beam at wavelength of 400 nm. The experimental results show that thefabricated microstructure can be utilized as a multi-beam-splitter. And the first order diffraction efficiency is up to 16.42% nearly. The morphology of the structures couldbe changed when the energy of the pulse was changed. The microvoid can be formedon the surface of the silica glass when the energy of the pulses is higher, on the otherhand, the orbicular platform of the microstructure can be observed. We propose anovel theoretic model to interpret the experimental results. The formation of the dif-ferent microstructures in our experiments can be attributed to the combined action oflight pressure to the induced plasma and the Marangoni effect to the molten liquid onthe surface of the bulk silica glass at different energy level of the pulse.Propose a novel method for generating optical vortex, and realize Super-position of orbit angular momentum of photons. We introduce a novel method togenerate the optical vortex with computer-generated hologram (CGH) fabricated in-side glass by femtosecond laser pulses. The CGH was directly written inside glass byfemtosecond laser pulses induced microexplosion without any pre- or post-treatmentof the material. We also realized the restructured optical vortex beams of both thetransmission and reflection pattern with high fidelity using a collimated He–Ne laserbeam. The total diffractive efficiency of both the transmission and reflection patternis about 4.79%.A novel method to realize the superposition of orbit angular momentum (OAM)of photons has been proposed by combined computer-generated hologram (CCGH)fabricated in silica glass with femtosecond laser pulses. Firstly, the two CGH of op-tical vortex (OV) were obtained and combined as a CCGH according to the design.Then the CCGH was directly written inside glass by femtosecond laser pulses. Thevortex beams with different vortex topological charges (including new topologicalcharges) have been restructured using a collimated He-Ne laser beam incidence to theCCGH normally. Theoretical and experimental explanations have been presented forthe generations of the new topological charges.Realize optical storage on the metal Film with the aid of the computer-generated hologram (CGH). The interaction between the femtosecond laser and themetal film has been studied in theoretic and experiment. When the femtosecond pulseinteracted with the Au film, the morphology of the ablated area is changing with theenergy of the pulse. If the energy of the pulse is large enough, we can get an ablatedvoid on the surface of the metal film. while the energy of the pulse is small enough,the nanocone could be attained on the surface of the metal film. When the femtosec- ond pulse interacted with the Al film, not only did we get the voids on the surface ofthe metal film, but we obtained the nanostructure on the surface of the substrate glass.It may offer a novel method for nanofabrication.Optical information has been stored on the metal film by femtosecond laserpulses with the aid of the computer-generated hologram (CGH). The Fourier transformof an object is performed by a computer, and then the resulted complex amplitude dis-tribution is encoded by the detour phase method. The resulted cell-oriented CGH isdirectly written on the metal film deposited on the glass substrate using near infraredfemtosecond laser by selective ablation. The object wave has also been restructuredwith high fidelity by using a collimated He-Ne laser beam.Fabricate volume grating in transparent glass by femtosecond laser pulsewriting directly. Femtosecond laser pulse with high energy could caused multiplemicroexplosion in the transparent materials, and there would be a relative long re-fracting index changing line formed in the direction of the pulse propagation. Theinteraction between the pulse with different energy or different number of the pulsesand the transparent glass have been studied, and we find different microexplosionviods array in the glass. When the energy of the pulse reaches to 20μJ, the refractingindex changing line arrive at 160μm. It could be used for fabrication of the volumegrating. The diffraction efficiency of the grating is changing with the fabricating con-dition which are different energy of pulse and different scanning velocity. We give aconcrete interpretation to the physical mechanism of the diffraction efficiency trans-formation.