Abstract
The evidence of multi-photon absorption enhancement by the dual-wavelength double-pulse laser irradiation in transparent sapphire was demonstrated experimentally and explained theoretically for the first time. Two collinearly combined laser beams with the wavelengths of 1064 nm and 355 nm, inter-pulse delay of 0.1 ns, and pulse duration of 10 ps were used to induce intra-volume modifications in sapphire. The theoretical prediction of using a particular orientation angle of 15 degrees of the half-wave plate for the most efficient absorption of laser irradiation is in good agreement with the experimental data. The new innovative effect of multi-photon absorption enhancement by dual-wavelength double-pulse irradiation allowed utilisation of the laser energy up to four times more efficiently for initiation of internal modifications in sapphire. The new absorption enhancement effect has been used for efficient intra-volume dicing and singulation of transparent sapphire wafers. The dicing speed of 150 mm/s was achieved for the 430 μm thick sapphire wafer by using the laser power of 6.8 W at the repetition rate of 100 kHz. This method opens new opportunities for the manufacturers of the GaN-based light-emitting diodes by fast and precise separation of sapphire substrates.
Highlights
Single crystal sapphire (α-Al2O3) offers superior physical, chemical and optical properties, which make it an excellent material for wide range of applications[1,2,3,4,5], including high-speed integrated circuit chips; thin-film and GaN-based light-emitting diode substrates[6]; various electronic and mechanical components; wristwatch crystals and movement bearings for the watch industry; scratch resistant display and camera cover for luxury mobile phones; high durability optical components and windows for extreme applications etc
The pulse energy was varied by changing the orientation angle of the half-wave plate (HWP)
The modifications were induced in the volume of sapphire keeping the top and bottom surfaces undamaged. It was demonstrated for the first time experimentally and confirmed theoretically that multi-photon absorption could be enhanced by the combined dual-wavelength double-pulse irradiation in the transparent sapphire
Summary
Single crystal sapphire (α-Al2O3) offers superior physical, chemical and optical properties, which make it an excellent material for wide range of applications[1,2,3,4,5], including high-speed integrated circuit chips; thin-film and GaN-based light-emitting diode substrates[6]; various electronic and mechanical components; wristwatch crystals and movement bearings for the watch industry; scratch resistant display and camera cover for luxury mobile phones; high durability optical components and windows for extreme applications etc. It has been demonstrated that dual-wavelength double pulse laser machining is an efficient way to improve the laser processing of dielectrics by providing a better control of the energy deposition process[30]. The majority of mentioned scientific works related to the dual-wavelength double-pulse irradiation has reduced the damage threshold of transparent material and improved laser energy deposition to the material. The main idea proposed in this work was to use two-colour double-pulse irradiation for efficient dicing of sapphire wafers. That ensures the more efficient use of the laser energy and enhances the speed of the intra-volume dicing of sapphire wafers. The experimental and theoretical results of the efficient volume dicing of sapphire wafers by using the dual-wavelength double-pulse picosecond laser irradiation are presented. The new technique has been used for efficient intra-volume dicing and singulation of the transparent sapphire wafers
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