Ms. Tong Zhang Profile

Tong Zhang

at Beijing University of Technology

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Publications (3)

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Proceedings Article | 18 March 2024 Paper

Femtosecond Bessel beam-assisted wet etching for the fabrication of microhole arrays on YAG crystal

Lin Chen, Tong Zhang, Heng Yang, Mingyuan Wang, Zhiyong Wang

Proceedings Volume 13104, 131045W (2024) https://doi.org/10.1117/12.3023703

KEYWORDS: Femtosecond phenomena, YAG lasers, Crystals, Bessel beams, Wet etching, Laser crystals, Fabrication, Waveguides, Gaussian beams, Beam diameter

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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.

Proceedings Article | 18 March 2024 Paper

Ultrafast laser lift-off technology for delamination of GaN layers

Mingyuan Wang, Tong Zhang, Heng Yang, Lin Chen, Yanlei Liu

Proceedings Volume 13104, 131045X (2024) https://doi.org/10.1117/12.3023706

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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.

Proceedings Article | 29 September 2016 Presentation + Paper

Laser stabilization in atom lithography based on LIF signal from the chromium beam

Tong Zhang, Yuejin Zhao, Cong Yin

Proceedings Volume 9948, 99480S (2016) https://doi.org/10.1117/12.2237099

KEYWORDS: Chemical species, Laser stabilization, Laser induced fluorescence, Lithography, Chromium, Luminescence, Signal detection, Collimation, Optics manufacturing, Sensors

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Atom lithography has now become an important means for manufacturing Nano-scale gratings, which are indispensable instruments for Nano-scale dimensional metrology. However, the presence of laser frequency drift makes the results unsatisfactory. Using the atoms’ laser induced fluorescence (LIF) to stabilize the laser frequency provides an effective method of overcoming the drift. This paper gives an analysis with regard to our own experimentation conditions in some aspects, such as fluorescence of Cr beam, difference signal, the correlation between laser frequency and the central of fluorescence. Based on the analysis, the laser induced fluorescence frequency stabilizing equipment is built in our selfdesigned system of chromium atom lithography. The laser is detuned near the wavelength of the ⁷S₃→⁷P₄⁰ transition of 52Cr, so that the atom beam could be illuminated. The power of the laser we used is 15mW. The position of the fluorescent spot depends on detune of the laser. This spot is imaged onto a split- photodiode. Whenever the laser frequency exhibits some deviations from the desired value, the difference signal between the right and the left area of the detector is non-zero. The measured signal is used to servo-lock the laser. It is acquired by the servo-lock port of the Ti:sapphire laser. As a result, the laser frequency is stabilized in the wavelength corresponding to ⁷S₃→⁷P₄⁰ transition of 52Cr. The stability is superior

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