IHJPAS. 36 (4) 2023 

188 

This work is licensed under a Creative Commons Attribution 4.0 International License 

 

   

 

 
 

 

 

 

 

 

 

 

 

*Corresponding Author: halhelfy@yahoo.com 

 

 
  

 

 

Abstract  

      The sample's physical characteristics and laser parameters impact the generation and 

characterization of Laser-Induced Plasma (LIP), which is a relevant phenomenon in many 

applications. We investigated the effect of laser energy on laser-induced Zn plasma 

characterization in this study. A Zn plasma with a repeating frequency of 5 Hz, a first laser 

wavelength of 1064 nm, a pulse duration of 9 ns, and a laser energy range of 300 mJ to 500 mJ 

was created using a Q-switched ND: YAG laser. The basic plasma properties, such as electron 

temperature and density, were estimated using optical emission spectroscopy (OES). The 

electrons temperature was measured by the Boltzmann plot method, and the electrons temperature 

ranged from 1.6 eV to 2.051 eV in the laser energy range (300-500) mJ. In electron density value 

estimation using the Stark broadening methods, the density value ranges from 12.75×1017 cm-3 to 

19.50×1017 cm-3, in the laser energy range (300-500 ) mJ. In addition, various plasma 

characteristics such as plasma frequency (fp), the number of particles in the Debye sphere (ND), 

and Debye length (λD) were estimated. We found that laser energy affects every plasma 

parameter. 

Keywords :  Emission spectroscopy, Zn Plasma, Spectroscopic, ND: YAG laser. 

1. Introduction 

         The term "laser-induced plasma spectroscopy" (abbreviated as "LIBS") refers to an 

application of atomic emission spectroscopy that utilizes high-energy laser pulses to excite 

doi.org/10.30526/36.4.3255 

Article history: Received 4 February 2023, Accepted 27 Februray 2023, Published in October 2023 

 

 

Ibn Al-Haitham Journal for Pure and Applied Sciences 

Journal homepage: jih.uobaghdad.edu.iq 

 

Spectroscopic Diagnostic of Laser-Induced Zn Plasma 

Hayim Chasib Magid*  

Department of Physics, College of Education, 

Al-Mustanseriyah University, Baghdad,Iraq. 

 

  Waleed Jabbar Mhana  

Department of Physics, Colleg of Sciences, 

Al-Mustansiriya University-Iraq. 

  Hanaa Salih Sabaa  

Department of Physics, College of Science, 

Al-Mustansiriya University, Baghdad, Iraq. 

https://creativecommons.org/licenses/by/4.0/
mailto:halhelfy@yahoo.com
mailto:dr.waleed1967@uomustansiriyah.edu.iq
mailto:dr.hanaa.salah@uomstansiriyah.edu.iq


IHJPAS. 36 (4) 2023 

189 
 

optical materials (LIPS). Plasma is created when strong laser pulses strike a metal surface, and it 

is well recognized to be a source of incredibly pure metal spectra [1]. The production of plasma 

may be separated into many steps. In the initial step of the process, the laser light interacts with 

a solid, producing plasma products and rapid surface ionization in comparison to the pulse period. 

The second stage's plasma absorbs the laser light as it expands consistently and efficiently [2]. 

After step three, plasma is produced, which may occur as soon as the laser pulse energy heats the 

particular material (sample), causing the material's atoms to receive more energy and plasma to 

develop. For this, large samples of solids, liquids, and gases can be employed [3]. It is critical to 

understand that the generated plasma's spectral line emission intensity is determined by the 

characteristics of the plasma itself as well as the concentration of the element in the sample, which 

are determined by elements such as the physical and chemical properties of the sample under 

study, including density, the boiling point of the target, specific heat, and surface reflectance, 

laser parameters (pulse duration, energy, wavelength), as well as ambient conditions of the 

surrounding atmosphere in terms of electric field composition, pressure, and temperature [4, 5]. 

The temperature, density, and variety of emission types of electrons are the fundamental 

characteristics of plasma [6]. The importance of plasma temperature in plasma parameters is well 

established. Evaluating other plasma features, such as particle velocity dispersion and relative 

energy concentrations, depends on having a solid understanding of the plasma temperature [5,  

6]. The spectrum of plasma light is detected using the spectrophotometer. Analyzing the plasma 

spectrum emissions, such as the target components, can yield quantitative and qualitative 

information. The breadth, forms, and transitions of emission lines can provide information on the 

temperature and density of electrons in the plasma [4]. It is also difficult to assess the influence 

of energy on its own. Increased laser energy usually increases the incised mass and ablation rate 

[7]. This work aims to utilize OES methods to analyze the influence of laser energy on Zn plasma 

properties. 

Experimental Setup 

The LIPS experiments, depicted in Fig. 1 as a schematic, were carried out at atmospheric 

pressure. Plasma was created using a sample of the element Zinc. A Q-switched ND; YAG 

nanosecond laser source with a pulse duration of 9 ns, a first wavelength of 1064 nm, a repeating 

frequency of 5 Hz, and laser energy of 300, 400, and 500 m J was used to create plasma. A 

spectrometer was used to collect and evaluate the light emission. The spectrometer is nearly 30 

cm away from the laser target, at a 45o angle from the laser beam path. An optical fiber with a 

core diameter of 50 m and a location of 1 cm was used to receive plasma light emissions induced 

by lasers from the surface of the Zn target. The optical emission line results were compared to 

NIST database software [8].  



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Figure 1. Schematic depiction of the experimental setup for laser-induced Zn plasma. 

2. Results and discussion 

2.1. Spectroscopy diagnostics of plasma optical emission (OES) 

The composition of the material is determined by utilizing optical emission spectroscopy to 

simulate the decay of excited species in plasma. The investigation of optical emission by excited 

species helps in the identification of pure constituents in a substance. Throughout this method, 

assume that a bound electron relaxes from an excited state to a lower energy level, or ground 

level. In this case, a spectral line emission produces photons with a certain wavelength. The Zn 

plasma emission spectrum, which is restricted to the spectral region (300–700 nm) for distinct 

pulsed laser energies of 400, 500, and 300 mJ, is shown in Figure 2. This spectrum contains the 

emission of six spectral lines as a result of 1064 nm laser excitation at various laser energies. The 

spectral lines for Zn II are three ionic lines at 481.9, 491.1, and 636.2 nm, whereas for Zn I are 

three atomic lines at 328.2, 334.5, and 472.2 nm. Figure (2) shows that when laser energy rises, 

plasma absorbs more laser light, increasing both the ablation rate and the spectral lines' intensity 

[9]. 



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191 
 

 

 Figure 2. The spectra of the Zn plasma emission from a 1064 nm laser at different laser energies. 

 

2.2. Characterization of laser induced Zn plasma 

The electron temperature and density are two important plasma parameters inferred from 

emission characteristics unique to atomic and ionic species of Zn spectrum intensities and line 

width. The temperature and density of plasma electrons were then estimated as a function of laser 

energy. 

Equation (1) [10] illustrates the Boltzmann plot technique for determining the electron 

temperature of the Zn plasma: 

ln (
𝐼𝑗𝑖 𝜆𝑗𝑖

𝑔𝑗 𝐴𝑗𝑖
) = −

𝐸𝑗

𝑘𝐵 𝑇𝑒
+ ln (

ℎ𝑐𝑁𝑗 

4𝜋𝑄(𝑇)
)          (1)   

Where, 𝐼𝑗𝑖 the light emitted intensity, 𝜆𝑗𝑖 the emitted line wavelength, gj is the statistical weight 

of the state concerned, 𝐴𝑗𝑖 is the transition probability, 𝐸𝑗 the excited state energy, 𝑘𝐵 is the  

Boltzmann constant, the number density is 𝑁𝑗 (particle / cm3), Q(T) is a plasma-temperature 

partition function for the emitting species of atoms that emit each species. Once the plasma 

temperature is known, the partition function for each element may be determined using 

spectroscopic data. By plotting ln (
𝐼𝑗𝑖 𝜆𝑗𝑖

𝑔𝑗 𝐴𝑗𝑖
) versus 𝐸𝑘, as appears in Figure (3). The straight line is 

used to measure the plasma temperature, which is equal to −1/𝑘𝑇𝑒.  

According to Table (1), the values for the electrons' temperature (Te) values were 12672.06, 

15814.59, 19359.15, 19774.97, and 20874.57 K. The temperature of electrons at various laser 

intensities is depicted in Figure (4). According to Figure (3), the electron temperature rises as the 

energy of the laser pulse increases. In contrast to more collisions in other media, charged 

secondary particles originate from higher electron temperatures (Te), which are proportional to 

0

5000

10000

15000

20000

25000

30000

35000

40000

300 400 500 600 700

In
te

n
si

ty
 (

a
.u

)

Wavelength (nm)

300mJ

400 mJ

500 mJ

Z
n
 I

  
3

2
8

.2
 n

m

Z
n
 I

  
3

3
4

.5
 n

m

Z
n
 I

  
4

7
2

.2
 n

m Z
n
 I

I 
 4

8
1

.0
 n

m

Z
n
 I

I 
 4

9
1

.1
 n

m Z
n
 I

I 
6

3
6

.2
 n

m



IHJPAS. 36 (4) 2023 

192 
 

the top kinetic energy of free plasma electrons. This is because plasma may absorb laser photons 

while still enabling the laser beam to travel through it [11]. 

 

 

 

 

 

 

 

Figure 3. Boltzmann plot methods to measure electron temperature Zn plasma for different laser energy. 

 

Figure 4. Zn plasma electron temperature for various laser energies. 

 

When fast-moving electrons and relatively slow-moving ions combine to affect the ions or atoms 

in the plasma, electrical fields are formed. The electrical field's effect on atoms or ions to create 



IHJPAS. 36 (4) 2023 

193 
 

energy shift levels results in a sharp expansion of plasma emission lines. The density of electrons 

caused by the line width-broadening of Stark's line emission spectrum might be the culprit. At 

half-maximum, the entire width of the Stark-broadened line is equal to the number of free 

electrons per unit volume, also known as an electron density (ne) (FWHM). Equation (2) contains 

a formula for calculating electron density  [12] 

𝛥𝜆1

2

=  2𝜔 (
𝑛𝑒

1016)   (2) 

Where: ∆λ1/2 is the full-width at half-maximum (FHWM), ne is the electron density, and 𝜔 is the 

electron impact parameter.   

At wavelength 481 nm for spectral lines of Zn II, the electron density was calculated for various 

laser energies. The value range of electron density starts from 12.75×1017  to 19.50×1017 cm-3, as 

reported in Table (1). As appears in Figure (5), as the laser energy increases, the electron density 

increases. The outcomes demonstrated that the electron density (ne), a feature of the plasma 

shielding effect, fluctuates slowly (i.e., plasma reflection of laser light). The plasma shielding 

effect of the air decreases the ionization process and the laser energy's mass ablation efficiency 

since the experiment was carried out at atmospheric pressure [9]. 

 

 

 

 

 

 

 

 

 

Figure 5.  Zn plasma electron density at different laser intensity  

 

The electron temperature (Te) and density (ne) were used to assess the impact of laser energy on 

other basic plasma properties, such as plasma frequency (fp), sphere (ND), (λD), and particles in 

Debye length (λD) to characterize the Zn plasma better. Equations 3, 4, and 56 represent fp, ND, 

and λD, respectively [13]. 

𝑓𝑝 =  (
𝑛𝑒𝑒2

ԑ0𝑚𝑒
)

1/2

   … . . (3) 

𝑁𝐷 =
4𝜋

3
𝜆3

𝐷𝑛𝑒       … . . (4) 



IHJPAS. 36 (4) 2023 

194 
 

𝜆𝐷 = (
ԑ0𝑘𝐵𝑇𝑒

𝑛𝑒𝑒2
)

1/2

 … . . (5) 

Where: ne: the density of the electron, ԑ0: the permittivity, e: the charge of the electron, 𝑘𝐵 : the 

Boltzmann constant, and 𝑚𝑒: the electron mass. 

According to the findings and information in Table 1, it seems that the electron temperature and 

density affect the plasma frequency (fp), Debye sphere (ND), and Debye length (λD). With 

increasing laser energy, it was possible to observe changes in the plasma frequency (fp), Debye 

length, and particle in the Debye's sphere (ND), as seen in Figures (6), (7), and (8), respectively. 

Electron-ion collisions play a crucial part in this. Because of the rising electron density and rising 

plasma frequency in this case, the plasma is more able to absorb laser light. The troublesome 

zone becomes more prominent as the temperature rises because the Debye length grows, and the 

dependence λD on density λD ∝ ne
−1 2⁄  . It suggests that a greater quantity of shielding particles 

offers more efficient defense and minimizes the area of the troublesome zone. 

Table 1: Plasma parameters of laser-induced Zn plasma at various laser energy. 

 
Laser energy (mJ) Te (eV) ne ×1017 (cm-3) λD (cm) ND (cm-3) fp (Hz) 

300 1.600 12.75 0.366 2.621 10.140 

400 1.722 15.75 0.293 1.664 11.270 

500 2.051 19.50 0.266 1.535 12.540 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6. Zn plasma frequency at different laser energy 

 

 



IHJPAS. 36 (4) 2023 

195 
 

 

 

 

 

 

 

 

 

 

Figure 7. Debye length of Zn plasma at different laser energy 

 

 

 

 

 

  

 

 

 

 

 

 

 

Figure 8. Debye number of Zn plasma at different laser energy 

 

4. Conclusion 

We have investigated how laser energy affects the characteristics of Zn plasma. Optically emitted 

spectra, electron temperature, electron density, and other fundamental plasma characteristics have 

been shown to be significantly impacted by changes in laser energy. With laser energy, the 

electron temperature of Zn plasma changes linearly. The Stark widening, which results from 

collisions between the liberated atom and charged particles, causes the spectral lines to widen 

and is inversely proportional to the electron density. All plasma characteristics, however, increase 

linearly with rising laser energy. 

 



IHJPAS. 36 (4) 2023 

196 
 

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