Research On Parallel Processing With Femtosecond Laser Using Phase Holograms

Femtosecond micromachining is the leading technology in the field of laser processing, processing with high accuracy, small thermal effect and wide range of materials processing and other advantages, and can realize three-dimensional microfabrication, has important applications in the fabrication of optical waveguide, beam splitters and couplers and other fields, but the femtosecond laser micromachining of the biggest drawback is the low processing efficiency. The low utilization ratio of energy, microprocessing requires only traditional pulse energy u J level, laser output energy is generally m J level, the energy utilization rate of less than 0.1%. Using a spatial light modulator(Spatial Light Modulator, SLM) parallel processing method, multi-beam produced by a SLM, a high energy light beam into multiple beam micro-focus level, research on direct writing gratings inside the PMMA material using femtosecond laser, high precision grating with grating constant for 10 um is obtained, and the use and method for processing, greatly improving the processing efficiency.The main research contents of this paper are as follows:Firstly, the principle of phase modulation of spatial light modulator and the principle of simulation based on the diffraction grating are introduced in detail. Introduced and discussed based on diffraction grating and diffraction angle relationship, using multiple diffraction gratings superposition modulation principle of multi-beam, using a spatial light modulator to control of the multi-beam is carried out and studied. This paper introduces several kinds of algorithms for generating multple beams, including Dammam grating and GS and GL algorithms, and analyzes their advantages and disadvantages. And the GS algorithm to optimize the target and computer generated holograms, the computer generated hologram(CGH) was calculated by the software and spatial light modulator. CGH is loaded onto the spatial light modulator realized femtosecond multi-beam parallel processing.Secondly, the femtosecond parallel processing system is designed and set up, introduces the femtosecond parallel processing parts in details, includes femtosecond laser, spatial light modulator, 4F optical system, CCD camera, 3D mobile platform and control software and the experimental light path and principle were simple analysed.Thirdly, a brief introduction of the research significance of grating direct write femtosecond laser inside the transparent materials, expounds the femtosecond laser in the definition of the transparent material damage, and introduces the mechanism of ablation of transparent material in details, which focuses on the avalanche ionization and multiphoton absorption theory. the study of direct writing grating inside transparent materials using femtosecond laser focusing is carried out. According to the experimental materials of PMMA, find out the specific photorefractive threshold, femtosecond laser in transparent PMMA internally focused is used, the realization of the grating constant for 10 um grating preparation, multi-beam in the PMMA samples of multi-beam parallel processing experiment is realized.Finally, a summary and outlook is made in this paper, and then further study and some suggestions and prospects are put forward.