Numerical model and experimental demonstration of high precision ablation of pulse CO<sub>2</sub> laser

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

doi:10.3788/COL201816.041401

Chinese Optics Letters, Volume. 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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Figures & Tables(11)

Fig. 1. Schematic of the computation model.

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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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Table 1. Governing Equations and Boundary Condition

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Table 1. Governing Equations and Boundary Condition

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 2. Material Properties of Fused Silica and Laser Ablation Parameters

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

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 3. The Detected Maximum Velocity, Pressure, and Surface Temperature of the Fluid Field at Different Timesa

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Table 3. The Detected Maximum Velocity, Pressure, and Surface Temperature of the Fluid Field at Different Timesa

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	$5.18 \times 10^{- 6}$	$5.5 \times 10^{6}$	$2.05 \times 10^{3}$

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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," Chin. Opt. Lett. 16, 041401 (2018)

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Paper Information

Category: Lasers and Laser Optics

Received: Nov. 2, 2017

Accepted: Feb. 9, 2018

Published Online: Jul. 12, 2018

The Author Email: Jianda Shao (jdshao@siom.ac.cn)

DOI:10.3788/COL201816.041401

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology