研究目的
Investigating the improvement of ablation capacity of sapphire by gold film-assisted femtosecond laser processing.
研究成果
The study demonstrates that the ablation capacity of sapphire can be significantly improved by coating it with a nanolayered gold film before femtosecond laser processing. The gold film enhances the laser energy absorption of sapphire, leading to better ablation morphology, lower ablation threshold, and higher material removal rate. The theoretical analysis reveals that the gold film provides more free electrons at the sapphire surface, enhancing energy transfer from incident laser to sapphire lattice phonons and causing homogenous laser energy deposition on the sapphire surface.
研究不足
The study is limited to the effects of a 12-nm-thick gold film on femtosecond laser processing of sapphire. The experiments were carried out in the atmosphere and room temperature, which may not cover all possible environmental conditions.
1：Experimental Design and Method Selection:
A commercial Ti:sapphire amplifier with a central wavelength of 800 nm was used to generate 160 femtosecond laser pulses. The repetition rate was tunable in the range from 1 Hz to 1 kHz. The maximum pulse energy was limited to 1 mJ. Laser pulse energy applied on the specimen surface was adjusted using a rotating half-wave plate and a thin film polarizer. The pulse number N incident on the specimen surface was controlled by an electronic shutter. The incident laser beam was focused on the specimen surface at normal incidence by a 2 × microscope objective lens. The beam diameter at the focal point was approximately 40 μm. The specimen was positioned on a precision motorized three-dimensional (3D) stage with a resolution of 1 μm.
2：Sample Selection and Data Sources:
The specimens used in the experiment were single crystal sapphire plates coated by a 12-nm-thick gold film. The sapphire plates were 10 mm in length, 10 mm in width and
3：5 mm in thickness, and were polished on both sides with Sa < 5 ?. List of Experimental Equipment and Materials:
Ti:sapphire amplifier (Spitfire, Spectra-Physics), rotating half-wave plate, thin film polarizer, energy meter, electronic shutter, 2 × microscope objective lens (NA =
4：055, Motic), precision motorized three-dimensional (3D) stage, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM). Experimental Procedures and Operational Workflow:
Laser-generated structures were produced on Au-coated and uncoated sapphire plates for comparison. All experiments were performed three times to ensure repeatability. The crater morphologies and crater diameters were measured with SEM. The crater depth and crater volume were measured via CLSM. The morphologies and dimensions of laser-generated ripples were evaluated with AFM.
5：Data Analysis Methods:
The squared diameter D2 of the ablation crater is related to the pulse energy Ep applied on the specimen by the equation D2 = 2ω02 ln(Ep/Eth), where Eth is the minimum pulse energy for material removal, and ω0 is the laser beam radius at which the intensity has dropped to 1/e2 of the peak value. The threshold fluences for multi-pulse ablation were calculated using the incubation model.
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