Sapphire is an important material for fabricating photonic devices such as light emitting diode (LED). The matter is
strongly resistant to wet and dry chemical etching because of its unique physical property. Moreover, there also exist
some problems like chipping and edge crack by diamond dicing. Thereby, lots of emerging laser-based techniques have
been invented, including various lasers at different wavelength and different technologies, which have gradually become
the alternative powerful and efficient methods to dicing this material. Most of investigations on laser dicing sapphire are
conducted by UV and ultra-short pulse laser, few by green laser with wavelength of 532nm. So a green laser with
wavelength of 532nm and high repetition frequency is employed to dice sapphire substrate. The effects of machining
parameters as laser power, repetition frequency, scanning velocity and number of scans on kerf width, kerf depth and
aspect ratio are analyzed. Kerf width and depth are measured by optical microscope (OM) and micro-morphology of
sapphire is observed by scanning electron microscopy (SEM). Results indicate that narrower kerf, higher aspect ratio and
better surface quality can be obtained under the combined processing parameters of medium laser power, lower
repetition frequency, medium scanning velocity and multiple scans, which proves green laser to be an effective tool to
dice sapphire substrate.
A three-dimensional energy coupling model for evaporative laser cutting nonmetallic material is established
through theoretical analysis and the reflective transmission and energy absorption of laser against real bended cutting
front and both two walls are analyzed. The front and wall's energy absorption is mainly determined by the first three
incident beams, that is two reflections. The multiple reflections from the front will increase the power intensity of the
bottom and the multiple reflections from the wall will increase the power intensity from the center to the bottom. Due to
the multiple reflections, the power intensity distributes over the total front. Due to the cutting speed, the laser axis moves
toward the front. The differences of absorptive power intensity among the three polarizations light are much smaller than
those of metal. Both two walls will have waveguide effects on the incident light which will mutual reflect against both
walls and transmit toward the bottom of the cut, which is so-called "wall focusing effects".
In this paper, attenuation of laser power by coaxial powder flow was studied. Given that the distribution of laser power as well as that of powder concentration was defined as a Gaussian function and no grain was shielded from laser by other grains, resolution model of laser power attenuated by coaxial powder flow was established. The attenuation of laser power by powder flow was a function of process parameters such as powder feed rate, moving velocity of grains, spraying angles and waist positions and diameters of laser beam and powder flow, grain diameter and run of laser beam through powder flow. The attenuation coefficient increased with powder feed rate or run of laser beam through powder flow and decreased with rise in grain diameter or moving velocity. The impacts of spraying angles and waist positions and diameters of laser beam and powder flow on attenuation coefficient were complicated. In practice, powder feed rate and run of laser beam through powder flow were both often adjusted, and other parameters were usually constant under certain conditions. In the presented experiment, the experimental results agreed well with the calculation results, and it was demonstrated that attenuation of laser power by coaxial powder flow rose with powder feed rate or run of laser beam through powder flow.