7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Unraveling the Physics of Laser-Sustained Plasma: Insights into the Influence ofLaser Conditions
Dongheyu Zhang1, Jinbao Liu1, Yangyang Fu1
1
Department of Electrical Engineering, Tsinghua University
e-mail (speaker): z_d_h_y@163.com

The utilization of laser-sustained plasma (LSP) as a point
light source has garnered attention due to its desirable
characteristics, such as high light intensity, wide spectral
range, and stable luminescence, which has beensuccessfully applied in semiconductor wafer defectdetection technology. LSP refers to the plasma generated
by the interaction of laser and ionized gas, where theplasma can absorb energy from the laser radiation,
thereby maintaining a stable high-temperature state.[1]Despite the development and practical implementation ofcommercial LSP-based light sources, the fundamental
physical mechanisms of LSP remain unclear due to thesystem's complexity and susceptibility to multiple
influencing factors.
Recent advancements in high-power continuous-wave(CW) laser manufacturing have expanded the range of
CW lasers employed for LSP generation, including CO2laser (centered at ~10 μm) and fiber laser (centered at ~1μm), among others. Existing experimental results haverevealed notable differences in the conditions requiredfor LSP generation using various types of lasers.[2]However, corresponding phenomena have not been
observed in the simulation models yet, hindering theinvestigation of the underlying causes for thesedifferences in temporal evolution.

Figure 1. Absorption coefficients of Xe LSP generated
by lasers whose central wavelengths are 10.6 μm, 1070nm, and 1080 nm, respectively. The solid lines represents
the absorption coefficients at the pressure of 18 atm,
while the dotted lines represents the ones at 10 atm.

In this work, we present a two-dimensional
time-dependent laser-thermal-hydrodynamically coupled
fluid model of LSP, which can capture the temporal
evolution of LSP in the computational domain. Using Xe
LSP as an example, we initially calculated the absorption
coefficients, as a function of LSP temperature, fordifferent laser types respectively. Subsequently, weobtained the temporal evolution and steady state of LSP
generated by distinct lasers. Generally, the power
absorption coefficients of LSP exhibit significant
variations depending on the lasers’ central wavelengthand profile, resulting in entirely different steady-state
temperature distributions of LSP. Figure 1 illustrates that
the LSP absorption coefficient under conditions of lasers
with central wavelength of 10.6 μm, 1070 nm, and 1080nm, respectively. Furthermore, steady-state temperature
distributions of LSP in the corresponding conditions canbe seen in Figure 2. As a result, the characteristics of
LSP are significantly influenced by the laser types
employed for plasma sustenance.
References[1] Yuri P Raizer, Sov. Phys. Usp. 23, 789 (1980)[2] M. Matsui et al, Vacuum 167, 490–494 (2019)

Figure 2. The steady-state temperature distributions of
LSP generated by lasers whose central wavelengths are10.6 μm, 1070 nm, and 1080 nm, respectively. Here, Xe
LSP is selected, and the pressure is set as 10 atm. The
dash lines represent the radius of the focused laser beam.