Study Of Femtosecond Laser Fabrication Of Micro-Optical Components Based On SLM

With properties of small volume,light weight and ease of integration,micro-optical components have been widely concerned.A high-efficiency method with combination of single time femtosecond laser ablation and wet etching has been proposed for fabrication of microlens array.However,this method is usually suitable for uniform structure array,due to its serial processing mode.Liquid crystal spatial light modulator?LC-SLM?can modulate the phase of incident light and any spot array can be achieved through lens or objective.It can be used for parallel processing.On the other hand,the energy of each light spot can be adjusted independently.An ablation spot array can be generated with single pulse.This paper combines LC-SLM and wet etching innovatively for fabrication of several micro-optical components with special surface profile.This method can improve the fabrication efficiency,since it requires single laser ablation and single wet etching.At first,we present the principle of LC-SLM in brief and describe the property of Fourier transform of lens with mathematical method.We adjust the phase of LC-SLM and make it work at wavelength of 515nm.Four methods of Computer-Generated Hologram are described in detail and compared with each other.We choose the ORA method in this paper.This part provides the basic theory in the whole experiments.Sapphire?Al₂O₃?is useful for fabrication of micro-optical components due to its perfect optical performance.A microlens array is fabricated on sapphire with combination of femtosecond laser and wet etching.The forming process of sapphire microlens is studied.The curvature radius increases with etching time and decreases with increase of pulse energy.According to the size of microlens,two microlens arrays with spacing of 25 and 40?m are fabricated with multi-spot parallel ablation,which shows perfect imaging performance.Secondly,a femtosecond pulse is modulated into two spots in the propagation direction.These two spots are focused on the surface and inside the silica,respectively,to form two ablation regions.The ablation regions are involved into a microlens with two focuses with once wet etching,named bifocal microlens.The formation is studied detailed and the optical performance is test,which shows excellent experimental results.Utilizing the imprinting technology,bifocal microlens array is fabricated efficiently on PDMS.At last,we introduce two methods for fabrication of three dimensional microlens array.a)Referring to the relation between the size of microlens and the pulse energy of laser,a specific spot array is designed.The spot array is consisting of a mass of spot with different pulse energies and applied for parallel ablation to generate ablation spot with different sizes.A three dimensional microlens array is generated with wet etching of HF solution.b)Referring to the surface profile,a three-dimensional spot array is designed specially.All the spots are focused on the surface parallelly to generate three-dimensional ablation spot array.A three dimensional microlens array is generated with wet etching of HF solution.The arrangement of microlenses can be adjusted by the surface profile.Three kinds of three dimensional microlens arrays are fabricated,their microlenses are on the spherical surface with radius of 100,95.6 and 55.1?m,respectively.These three dimensional microlens arrays show perfect imaging performance.Utilizing the imprinting technology,the array of three dimensional microlens array are fabricated on PDMS successfully.Uniform and ununiform,two and three dimensional microlens array and micro-optical components with special surface profile can be fabricated with combination of LC-SLM and wet etching.This method expends the fabrication of micro-optical components,which is expected to promote the application of micro-optical components.