Optical waveguides play an important role in the fields of optical communications and optical sensing. As optical waveguide substrate materials, yttrium aluminum garnet (YAG) crystals have a high refractive index, high thermal conductivity, high optical quality, and good chemical stability. However, YAG crystals are difficult to fabricate since they are chemically inactive and have a Mohs hardness of 8.5. This article has proposed a method of rapidly preparing microhole arrays on YAG crystals using a femtosecond laser single-pulse Bessel beam combined with wet etching technology. The experiment used a titanium sapphire re-amplified femtosecond laser with a central wavelength of 800nm and a pulse width of 50fs. The femtosecond laser was modulated into femtosecond Bessel light using the axicon, and the beam was focused into the interior of the YAG crystal sample through a focusing objective. The sample was placed on a precision three-dimensional displacement platform, and the arrangement of microhole array distribution could be achieved by changing parameters such as repetition frequency, scanning speed, and scanning direction. Subsequently, phosphoric acid solution was used to corrode the samples to optimize the pore size and morphology features. By systematically studying and summarizing the effects of parameters such as power, focusing position on the morphology, depth, and aspect ratio of microholes. The optimal parameter range was integrated to regulate the microhole array structure. Large-area uniform microhole array with an aspect ratio of approximately 300:1 and good taper was finally obtained.
Most of nowadays light-emitting diodes (LEDs) based on gallium nitride (GaN) production use sapphire wafers as the growth substrate. However, sapphire exhibits limitations in terms of electrical and thermal conductivities, therefore, GaN must be transferred to more appropriate substrates to fulfill diverse requirements. At present, the transfer of GaN is mainly achieved by means of laser lift-off (LLO), which uses pulses of UV laser light in the nanosecond range. In this study, femtosecond LLO (fs-LLO) technique has been used for GaN delamination. Femtosecond pulsed laser with a wavelength of 800 nm (1.55 eV), and a pulse width of 50 fs was utilized for conducting the laser lift-off experiments, employing photon energy below the GaN band gap (3.4 eV). The reliance on multiphoton absorption and ultrashort pulses in fs-LLO minimizes structural damage compared to conventional LLO approaches. The effect of different laser power and different laser scanning speeds on the fs-LLO processing of GaN has been studied in detail. Various characterization methods, including optical microscopy, scanning electron microscopy, X-ray diffraction, and photoluminescence spectroscopy were used to observe the structural quality of the materials after fs-LLO. The results show that there is less thermal damage on the GaN surface when scanned with a smaller laser power. The scanning speed of the displacement stage affects the surface smoothness of the GaN. The outcome on the flexible tape yielded GaN with high surface quality with no noticeable degradation.
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