Study On Process Of Polishing Sapphire With Ultraviolet Laser

Sapphire is a kind of monocrystal withα-Al2O3, the material with good light transmission,heat travels,insulating and holds good mechanics.It is widely applied to field of industrial,medical, national defence,space air,and so on.While the process of polishing with laser have some critical drawbacks with traditional methods. The laser polishing have vast potential for future development.The ultraviolet laser is used to investigations of the mechanism of polishing sapphire in the theoretical and experimental in this paper. From the research,the author on the basis of summarized up laser micro-machining technology and mechanisms,analysis the photochemical mechanism and thermal mechanism in the process of laser etching in theory;though experimentals investigated the photochemical and thermal effect in laser etching of sapphire with wavelength of 355nm.Experimental investigated the mechanisms and the effect of polished surface roughness of laser polishing in different parameters,included laser fluence,frequency, scanning speed,scann-ing ways and angle of incidence,adopted orthogonal test method to optimize the technological parameters.1.Theory derived that the threshold of sapphire is 16.23J/cm2.According to SSB model,analysis photochemical and thermal mechanism were coexisted in UV laser etching sapphire,combined the characteristic of gauss spot of laser,derived the photochemical and thermal model of depth of laser etching sapphire.2.Through the experiment of pulses etching sapphire and arrived:laser etching sapphire with 355nm,sapphire damage threshold is 14.8J/cm2,get close to theoretical value.The etching experiment demonstrated that photochemical and thermal effect are coexist in laser etching sapphire with 355nm,and thermal is dominate.Analysis influence of laser fluence to etched mechanism:when laser fluence at the range of 18.7J/cm2 to 40.3J/cm2,the proportion of photochemical is greater in laser etching,on the condition of laser fluence from 25.9J/cm2 to 35.5J/cm2,the proportion of photochemical etching is highest.The Raman spectrum analysis demonstrated that:under the low laser fluence,laser thermal effection are slightly and destroy organizational structure finely,the photochemical etching destroyed sapphire finely;when laser fluence overtop,the thermal effection intensively and sapphire damaged obviously and badly, further more,the etched surface will became amorphously.When laser fluence or pulses increasing,the depth and diameter of etched concave are extended,the section shape of concave were changed from "V" to "U",the depth of experimental greater than theoretical value.3.According to one-factor polishing experiments arrived that:with increasing of laser fluence,frequency, scanning speed,angle of incidence,the surface roughness of polished sapphire decreased.when laser fluence in the range of 25.9 J/cm2to 35.5J/cm2,the proportion of photochemical effection in polishing is maximum,we get the best surface roughness;when laser frequency within of 25kHz to 30kHz.the surface roughness of sapphire lowest;when scanning speed in the range of 80mm/s to 120mm/s, the surface roughness after polishing decreased to minimum;when in the range of 20°to 40°,we achieved the lowest surface roughness.Scanning ways more complicated,the polished surfaceness acquired were more lower,in the intersection angle of 60°we get the best surface roughness.According to the experiment of optimize the technological parameters:the scanning speed is the most significant factor which influence the polished surface roughness,we obtained the polished surface of sapphire with lowest surface roughness at the best processing parameter:laser fluence of 30.2J/cm2,repetitive frequency with 25kHz,scanning speed of 120mm/s, the angle of incidence with 35°,and scanning ways of the two intersection and intersection angle for 75°.Polished sapphire in the best processing parameter,polished surface more neatness,smoothness and thermal effection weaker comparatively,less broken pieces on microscopic surface；the polished surface were uniformity.