Numerical model and experimental demonstration of high precision ablation of pulse CO2 laser

Ting He; Chaoyang Wei; Zhigang Jiang; Zhen Yu; Zhen Cao; Jianda Shao

doi:10.3788/COL201816.041401

Journals >Chinese Optics Letters >Volume 16 >Issue 4 >Page 041401 > Article

Chinese Optics Letters
Vol. 16, Issue 4, 041401 (2018)

Numerical model and experimental demonstration of high precision ablation of pulse CO₂ laser

Ting He^1、2, Chaoyang Wei¹, Zhigang Jiang¹, Zhen Yu^1、2, Zhen Cao^1、2, and Jianda Shao^1、*

Author Affiliations

¹Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

²University of Chinese Academy of Sciences, Beijing 100049, China

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DOI: 10.3788/COL201816.041401 Cite this Article Set citation alerts

Ting He, Chaoyang Wei, Zhigang Jiang, Zhen Yu, Zhen Cao, Jianda Shao. Numerical model and experimental demonstration of high precision ablation of pulse CO₂ laser[J]. Chinese Optics Letters, 2018, 16(4): 041401 Copy Citation Text

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Fig. 1. Schematic of the computation model.

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Temperature dependent material properties of fused silica. (a) Specific heat capacity and heat conductivity coefficient, (b) dynamic viscosity.

Fig. 2. Temperature dependent material properties of fused silica. (a) Specific heat capacity and heat conductivity coefficient, (b) dynamic viscosity.

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Fig. 3. Phase distribution, special velocity field, and surface profile at (a) 25 μs, (b) 35.5 μs, (c) 40 μs, and (d) 40.5 μs with laser intensity 66.52 kW/cm2 and pulse duration tp=40 μs.

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Fig. 4. (a) Axial ablation depth depending on laser pulse duration with laser intensity of 66.52 kW/cm2 and 66.94 kW/cm2. (b) Axial ablation depth depending on laser power with laser pulse duration of 34 μs and 30 μs. (c) The ablation radius and pile-up height dependent on ablation depth.

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Fig. 5. Experimental setup (left) and scanning method (right).

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Fig. 6. Single pulse ablation depths as a function of laser intensity.

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Fig. 7. Profiler images of ablated areas with varied overlap rates of (a) 25%, (b) 50%, and (c) 70%. (d) Ablation depths and roughness rms of ablated area as a function of the overlap rates with P=2.2 W and frep=1.25 kHz.

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Fig. 8. Profiler images of ablated areas with laser energy density of (a) 15.00 kW/cm2, (b) 15.63 kW/cm2, and (c) 18.722 kW/cm2. (d) Ablation depth and roughness rms of ablated area as a function of laser intensity with overlap rate of Ox=60% and frep=1.25 kHz.

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Model	Boundary No.	Boundary Condition	Equations
	Whole geometry	Governing equation	$ρ C_{p} (T) \frac{\partial T}{\partial t} + ρ C_{p} (T) u \frac{\partial T}{\partial t} = \nabla \cdot [- K (T) \nabla T] + Q$ (1)
Heat transfer model	2, 3	Heat flux, nature convection, and radiation	$- K (T) \nabla T = Q_{0} + h (T - T_{a}) + ε σ (T^{4} - T_{a}^{4})$ (2) $Q_{0} = \frac{2 A P}{π r_{0}^{2}} \exp (- \frac{r^{2}}{r_{0}^{2}})$ (3)
	4	Nature convection	$\nabla [- K (T) \nabla T] = h (T - T_{a})$ (4)
	5	Insulation	$\nabla [- K (T) \nabla T] = 0$ (5)
Fluid flow coupled with heat transfer model	Whole geometry	Governing equation	$\nabla \cdot u = 0$ (6) $ρ \frac{\partial μ}{\partial t} = - \nabla p + η (T) \nabla^{2} u + F_{v}$ (7)
	2, 3	Marangoni convention, capillary force, and recoil pressure	$σ_{t} = \frac{\partial γ}{\partial T} \nabla T \cdot t$ (8) $σ_{n} = k γ \cdot n$ (9) $R_{p} = 0.54 P_{0} \exp [\frac{L_{v} (T - T_{v})}{R T T_{v}}] \exp (- \frac{r^{2}}{r_{0}^{2}}), T > T_{v}$ (10)
	1	Axisymmetry
Deformed geometry	2, 3	Free deformation	$V = u$ (11)
	4, 5	Fixed boundary	$V = 0$ (12)

Table 1. Governing Equations and Boundary Condition

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Parameter (units)	Nomenclature	Value
Melting temperature (K)	$T_{m}$	1875^[19]
Vaporization temperature (K)	$T_{v}$	2500^[23]
Latent heat of evaporation (MJ/kg)	$L_{v}$	11.4^[18]
Absorptivity	$A$	0.8^[18]
Initial temperature (K)	$T_{0}$	298.15
Density ( $kg / m^{3}$ )	$ρ$	2201^[23]
Radiation emissivity	$ε$	0.8^[23]
Stefan Bolzmann constant [ $W / (m^{2} \cdot K^{4})$ ]	$σ$	$5.67 \times 10^{- 8}$
Universal gas constant [ $J / (mol \cdot K)$ ]	$R$	8.314
Surface tension coefficient ( $N / m$ )	$γ$	0.38
Temperature derivative of surface $[N / (m \cdot K)]$	$ə γ / ə T$	$- 6 \times 10^{- 5}$
Pressure (Pa)	$P_{0}$	$10^{5}$

Table 2. Material Properties of Fused Silica and Laser Ablation Parameters

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Time (μs)	Maximum Velocity (m/s)	Maximum Pressure (Pa)	Maximum Temperature (K)
25.0	$4.98 \times 10^{- 9}$	$4.8 \times 10^{6}$	$2.01 \times 10^{3}$
35.5	$5.42 \times 10^{- 3}$	$15 \times 10^{6}$	$2.50 \times 10^{3}$
40.0	0.074	$523 \times 10^{6}$	$2.55 \times 10^{3}$
40.5	$5.18 \times 10^{- 6}$	$5.5 \times 10^{6}$	$2.05 \times 10^{3}$