Research On Polishing Process Of Fused Silica Optical Components Based On Laser

Fused silica is an important optical element in optoelectronics,microelectronics,optics and optical fiber technology.Advanced functional optoelectronic devices?including laser gyros,soft X-rays,free electron lasers?and laser fusion systems have an urgent demand for fused silica components with super-smooth surfaces.The preparation process of a super-smooth surface typically includes grinding,polishing,and other optical processing steps;however,to achieve a super-smooth surface,the most important process is the ultra-precision polishing technique.Traditional super-smooth polishing techniques,such as float polishing,plasma polishing and micro-fluid jet polishing still have certain limitations.For instance,there are still scratches and micro defects on the optical surface produced by them;in addition,the processing efficiency is low and the operation is difficult.Laser polishing,as a new ultra-smooth polishing process,has been widely used in surface treatment and crack control of metals,ceramics and other materials in recent years due to its non-contact,high flexibility,high efficiency and local repair.In this paper,the process of smoothing the fused silica surface with CW CO₂ laser is studied by means of simulation combined with experiment.The effects of laser power,laser beam radius,laser scanning velocity and initial surface roughness of fused silica elements on laser polishing are analyzed.The main research contents are as follows:?1?The research of the temperature field in laser polishing process.The temperature field of laser interacting with fused silica in two types?fixed-point and scanning type?is simulated by finite element software COMSOL.The temperature field under the action of different laser parameters?laser power,laser beam radius?and process parameters?scanning speed,scanning distance,interaction time?is obtained.The effects of each parameters on the temperature field are also summarized.The maximum temperature at the laser action point is proportional to the laser power and interaction time,and inversely proportional to the scanning speed and laser beam radius.?2?Research on surface micro-flow during laser polishing.A multi-physics model coupled with solid heat transfer and fluid mechanics is established by using COMSOL.The process of phase transformation and flow behavior of fused silica is simulated when laser shines on fused silica surface.It is found that the surface tension is crucial in laser polishing,which avoids the accumulation of material on the boundary of the molten pool under the Marangoni effect,and the Marangoni effect effectively eliminated the bulge in the middle of the molten pool.In addition,by setting different parameters?such as laser power,surface characteristic shape,surface characteristic amplitude,surface characteristic frequency,laser energy distribution form?Gaussian type,Flat-top type??,and the influence of parameters on polishing surface roughness is analyzed.?3?The experiment of laser polishing fused silica is carried out using a CW CO₂ laser.The influence of laser power and laser scanning speed on polishing effect is studied by single factor experiment.After laser polishing experiment,the best combination of laser power and laser scanning speed is found.At a laser power of 28 W and a scanning speed of 0.1 mm/s,the surface of the fused silica with an initial roughness of about 150 nm was successfully smoothed to 1.5 nm.