^{1,a)}, Davide Bleiner

^{1}and Annemie Bogaerts

^{1}

### Abstract

A comprehensive numerical model is applied to the study of the effect of ambient pressure in laser ablation, more specifically on the copper target heating, melting and vaporization, and the resulting plume expansion in the helium gas, as well as on plasma formation in the plume. Under the laser pulse condition investigated [ full width at half maximum (FWHM) and peak irradiance], the calculated results show that the characteristics of the surface temperature and the evaporation depth are very similar even when the ambient pressure varies greatly. The influence of the ambient pressure on the fraction of absorbed laser energy is also small. The maximum ablated material vapor density in the plume is influenced slightly by the different pressures. Before , the maximum plume temperature for various ambient pressures is in the order of a few . However, the effect of ambient pressure on the plume length is quite large. A specific calculation for a Gaussian-shaped laser pulse with FWHM and peak irradiance is made. The calculated evaporation depth agrees well with the experimental data. Therefore, the model can be useful to predict trends in target and plume (plasma) characteristics, which are difficult to obtain experimentally for various ambient pressures.

One of the authors (Z.C.) is financed by a bilateral project between Flanders and China. The authors thank A. Vertes for supplying the original code for laser ablation in vacuum and A. Vertes and R. Gijbels for the interesting discussions. Swiss Federal Laboratory for Material Testing (EMPA) is acknowledged for the laser ablation facility, which was redesigned and run by one of the authors (D.B.). Olga Guseva (EMPA) is acknowledged for assistance during the profilometry measurement. Christian Bottali and Francisco Alvarez (EMPA) are acknowledged for preparation of the metallic targets.

I. INTRODUCTION

II. DESCRIPTION OF THE MODEL

III. NUMERICAL RESULTS AND DISCUSSIONS

IV. CONCLUSION

### Key Topics

- Copper
- 36.0
- Vapor pressure
- 26.0
- High pressure
- 23.0
- Laser ablation
- 23.0
- Plasma expansion
- 21.0

## Figures

Laser intensity-time profile assumed in the model. It is a Gaussian-shaped pulse with full width at half maximum and peak irradiance of . The solid line represents the original laser pulse and the dashed line represents the calculated laser irradiance arriving at the target, after passing through the plume (plasma).

Laser intensity-time profile assumed in the model. It is a Gaussian-shaped pulse with full width at half maximum and peak irradiance of . The solid line represents the original laser pulse and the dashed line represents the calculated laser irradiance arriving at the target, after passing through the plume (plasma).

Calculated fraction of laser energy absorbed by the plume as a function of ambient pressure. The original laser pulse is given in Fig. 1.

Calculated fraction of laser energy absorbed by the plume as a function of ambient pressure. The original laser pulse is given in Fig. 1.

Calculated maximum surface temperature as a function of ambient pressure for the condition shown in Fig. 1.

Calculated maximum surface temperature as a function of ambient pressure for the condition shown in Fig. 1.

Calculated maximum evaporation rate as a function of ambient pressure for the condition shown in Fig. 1.

Calculated maximum evaporation rate as a function of ambient pressure for the condition shown in Fig. 1.

Calculated evaporation depth as a function of ambient pressure for the condition shown in Fig. 1.

Calculated evaporation depth as a function of ambient pressure for the condition shown in Fig. 1.

Spatial distribution of (a) calculated Cu vapor density and (b) calculated ambient He gas density, at different times: 8 (1), 16 (2), 24 (3), 32 (4), and (5), for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated Cu vapor density and (b) calculated ambient He gas density, at different times: 8 (1), 16 (2), 24 (3), 32 (4), and (5), for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated plume velocity and (b) calculated plume temperature, at different times: 8 (1), 16 (2), 24 (3), 32 (4), and (5), for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated plume velocity and (b) calculated plume temperature, at different times: 8 (1), 16 (2), 24 (3), 32 (4), and (5), for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated Cu vapor density (solid line), calculated ambient gas density (dash-dotted line), and calculated electron density (dashed line) and (b) calculated plume temperature at , for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated Cu vapor density (solid line), calculated ambient gas density (dash-dotted line), and calculated electron density (dashed line) and (b) calculated plume temperature at , for the laser condition shown in Fig. 1 and ambient pressure at .

Spatial distribution of (a) calculated Cu vapor density (solid line), calculated ambient gas density (dash-dotted line), and calculated electron density (dashed line) and (b) calculated plume temperature at , for the laser condition shown in Fig. 1 and ambient pressure at .

(Color online) Calculated plume length at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated plume length at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum plume temperature at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum plume temperature at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum Cu vapor density at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum Cu vapor density at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum electron density in the plume at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(Color online) Calculated maximum electron density in the plume at different times: 10 (●), 20 (▴), and (▾), as a function of ambient pressure, for the condition shown in Fig. 1.

(a) Laser intensity-time profile. It is a Gaussian-shaped pulse with full width at half maximum and peak irradiance of . The solid line represents the original laser pulse and the dashed line represents the calculated laser irradiance arriving at the target, after passing through the plume (plasma). (b) Calculated evaporation depth vs time for the laser condition given in (a). (c) Measured target surface depth profile after 200 laser pulses.

(a) Laser intensity-time profile. It is a Gaussian-shaped pulse with full width at half maximum and peak irradiance of . The solid line represents the original laser pulse and the dashed line represents the calculated laser irradiance arriving at the target, after passing through the plume (plasma). (b) Calculated evaporation depth vs time for the laser condition given in (a). (c) Measured target surface depth profile after 200 laser pulses.

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