Energy penetrated and inverse bremsstrahlung absorption co-efficient in laser ablated germanium plasma

Journal Pre-proof Energy Penetrated and Inverse Bremsstrahlung absorption co-efficient in laser ablated Germanium Plasma

Muhammad Ashraf, Nek Muhammad Shaikh, Ghulam Abbas Kandhro, Ghulam Murtaza, Javed Iqbal, Azhar Iqbal, Shafqat Ali Lashari PII:

S0022-2860(19)31521-2

DOI:

https://doi.org/10.1016/j.molstruc.2019.127412

Reference:

MOLSTR 127412

To appear in:

Journal of Molecular Structure

Received Date:

06 October 2019

Accepted Date:

11 November 2019

Please cite this article as: Muhammad Ashraf, Nek Muhammad Shaikh, Ghulam Abbas Kandhro, Ghulam Murtaza, Javed Iqbal, Azhar Iqbal, Shafqat Ali Lashari, Energy Penetrated and Inverse Bremsstrahlung absorption co-efficient in laser ablated Germanium Plasma, Journal of Molecular Structure (2019), https://doi.org/10.1016/j.molstruc.2019.127412

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Energy Penetrated and Inverse Bremsstrahlung absorption co-efficient in laser ablated Germanium Plasma Muhammad Ashraf a,b *, Nek Muhammad Shaikh b, Ghulam Abbas Kandhro a, Ghulam Murtaza b, Javed Iqbal c, Azhar Iqbal a, Shafqat Ali Lashari a a Department

of Basic Sciences, Mathematics and Humanities, Dawood University of Engineering

and Technology, Karachi, Sindh, Pakistan b Institute

of Physics, University of Sindh, Jamshoro, Sindh, Pakistan

c Department

of Physics, University of Azad Jammu and Kashmir, Muzafeabad, AJK, Pakistan

*Corresponding

author

*Muhammad Ashraf (M.S), e-mail: [email protected], Department of Basic Sciences, Mathematics and Humanities, Dawood University of Engineering and Technology, Karachi, Sindh, Pakistan, Tel: + 92-334-3123415; fax: + 90 21 99230710. Institute of Physics, University of Sindh, Jamshoro, Sindh, Pakistan, Tel: + 92-334-3123415; fax: + 90 21 99230710. Nek Muhammad Shaikh (Ph.D), e-mail: [email protected], Institute of Physics, University of Sindh, Jamshoro, Sindh, Pakistan, Tel: +92-333-5354464. Ghulam Abbas Kandhro (Ph.D.), e-mail [email protected], Department of Basic Sciences, Mathematics and Humanities, Dawood University of Engineering and Technology, Karachi, Sindh, Pakistan, Tel: + 92- 21 232644; fax: + 90 21 99230710. Ghulam Murtaza (M.S), e-mail: [email protected], Institute of Physics, University of Sindh, Jamshoro, Sindh, Pakistan, Tel: +92-333-1337685. Javed Iqbal (Ph.D.), e-mail [email protected], Department of Physics, University of Azad Jammu and Kashmir, Muzafeabad, AJK, Pakistan, , Mob: + 92-3125253279. Azhar Iqbal (Ph.D.), e-mail [email protected] Department of Basic Sciences, Mathematics and Humanities, Dawood University of Engineering and Technology, Karachi, Sindh, Pakistan, Tel: + 92- 21 232644; fax: + 90 21 99230710. Shafqat Ali Lashari (M.Phil), e-mail [email protected] Department of Basic Sciences, Mathematics and Humanities, Dawood University of Engineering and Technology, Karachi, Sindh, Pakistan, Tel: + 92- 21 232644; fax: + 90 21 99230710.

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Energy Penetrated and Inverse Bremsstrahlung absorption co-efficient in laser ablated Germanium Plasma Muhammad Ashraf a,b *, Nek Muhammad Shaikh b, Ghulam Abbas Kandhro a, Ghulam Murtaza b, Javed Iqbal c, Azhar Iqbal a, Shafqat Ali Lashari a

Abstract In the present experimental conditions, at Nd:YAG laser in fundamental (1064) nm, at laser irradiance 1.0  1011 Wcm-2 the (IB) absorption  ib is approximately equal to (0.0204 cm-1.). In present work irradiance is varied from 1.01011 to 1.81011Wcm-2 and inverse bremsstrahlung varies from 2.010-3 to 1.210-2 cm-1. The power absorbed by germanium target surface is found to be Pabs= 2.07108 Wcm-2 and 1.04103 Wcm-2 is reflected back from germanium surface. Whereas at highest laser irradiance 1.81011 Wcm-2 the power absorbed by surface is found to be Pabs= 3.67108 Wcm-2 and 1.84103Wcm-2 is reflected back from germanium surface. In present work we have calculated laser absorbance and percentage which is estimated by absorbed light throughout the original irradiance I0 at target surface, in present work absorbance at germanium surface is 0.2 where as reflectivity R of germanium sample which is found to be 0.39 for 1064 nm wavelength. At irradiance I0 1.01011 Wcm-2 the energy penetrated is E~5.051010 Wcm-2 and for high laser irradiance at I0 1.81011 Wcm-2 the energy penetrated is E~8.951010 Wcm-2 respectively. Keywords: Spectroscopy, plasma, germanium, LIBS, laser.

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1. Introduction In recent era the laser spectroscopy is a main source for optical emission analysis which is known as Laser induced breakdown spectroscopy (LIBS), deals with the interaction of laser with materials. The LIBS is counted in the category of fast multi-elemental analysis technique than any other spectral analysis techniques [1-4]. The laser based analysis technique is widely used for chemical analysis, environmental monitoring, agricultural analysis such as different crops soils and fertilizers, and bio-medical analysis such as calcium based body parts (tooth, bones, nail and hair) [5-8] and number of literature has been published about LIBS fundamentals [9-12]. LIBS and laser ablation have found applications in field of thin film and pulsed laser deposition on substrate. Laser fluence responsible to overcome the material threshold, and generates the heating and vaporization of the material [13-14]. The ablation from the surface is a complex process achieved by excitation, ionization and absorbing laser fluence on the sample surface. The wavelength, energy, laser spot size and along with pulse duration is the main parameters of laser ablation [15-16]. Plasma comprises on species such as charged particles which attains the dynamic property, which leads to generate energy and transferred wave propagation to the medium. These charged species of plasma are responsible for generation of electric and magnetic field in local environment of plasma that shows the interaction with electrons and positive ions [17-18]. The light emitted due to relaxation between electrons and ions, and this transient plasma which readily converts into gas in the environment and emitted light that gives the characteristics spectral structure regarding plasma and sample composition [19]. Laboratory produced laser plasma is widely affected by laser parameters such as wavelength, pulse duration and laser energy. This creates immense pressure at target surface, shock waves are blown at surface and that also effects on mass removal at sample surface [20]. Sophisticated light collection system for plasma plume gives well resolved spectral lines. This shows possible shifts in atomic and ionic lines for subsequent analysis of the sample. Whereas detectors and delay time for light collection from plasma plume after laser shots, that gives value able effects for data collection of resolved light captured through detectors. That is helpful to avoid the strong continuum emission from plasma plume at early stage of plasma plume after the plasma evolution [21-22]. To investigate the laser produced plasma, spectroscopy is a widely used experimental technique, which helps in

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analysis of laser plasma which gives the spectrum of plasma plume. This spectrum analysis can be used for inspection of plasma temperature, electron number density and stark width broadening [23]. In laser induced plasma we are interested in LTE plasma, this is generally achieved after few μs of laser sample interaction and the system is considered in local thermodynamic equilibrium (LTE). McWhirter criterion is readily used for verification of LTE conditions, this assumptions has been widely discussed in several literature [24]. This work which is based on germanium as a semiconductor to estimate McWhirter criterion, and the excitation temperature of germanium plasma through Boltzmann plot method and electron density was estimated by using the 265.11 nm wavelength (4p5s 3p2 → 4p2 3p2). We present the temporally resolved germanium plasma parameters such as Te and Ne. Further we present effect of laser irradiance on germanium plasma features and absorbance of laser irradiance and energy transmitted into the germanium sample. Some past study about germanium has been reported by several research groups [25-27]. They study surface morphology and ablation of germanium at ambient conditions and also studied the effect of germanium plasma in presence of magnetic field [28-29]. These research groups have worked on laser irradiance, spatially resolved and time integrated germanium plasma. Some literature about germanium alloy and laser ablated photo acoustic technique have been studied by researches [30-31]. 2. Material and Methods Laser produced plasma can be generated by creating irradiance at target surface, by decreasing in pulse duration which transfer all its energy in small fragment of time, i.e power mainly effects on sample target surface. Which enables LIBS as a deep analysis technique, this work is continuity of our past work [32] and same method has been employed which is given Fig. 1. In which we have used Nd:YAG laser system as a projectile on the germanium target surface using the IR (infra-red) 1064 nm wavelength. The laser light emitted from Nd:YAG Laser is capable of delivering power of 1.8x1011 W/cm-2 at pulse duration of 5~ns with 10 Hz repitation rate and laser was fired for duration of 5~ns. Two main lenses used one of them a quartz crystal with 20 cm focal length for collecting laser light on the germanium sample, so the focusing lens distance and germanium target was managed in manner that no ambient gas breakdown could happen before target surface. Sample was mounted into 3d rotating holder which prevents from laser-material interaction on same surface. By rotation of sample stage each time fresh surface was provided and

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to avoid from statistical error in data. To minimize the error concern the output of data was the average of three laser shots, the emitted light collected from plasma plume by setting the focusing lens, through the LIBS2000 spectrometer, OOLIBS2000 software was utilized for correction of emission signal by filtering the dark signal that is comprised on five spectrometers each one has slit width of 5 m, this configuration which enable the capturing power of spectrum that has range of 200-720 nm wavelengths. The company calibrated value for optical resolution  0.06 nm and that has 2048 element linear CCD array. The Nd: YAG laser was operated in Q-switch mode and that was synchronized with detector LIBS 2000 spectrometer. For variation in pulse energy of laser system OOILIBS software was used and the spectrum recorded was resultant of 3 laser shots. The spectrum captured by 5 sub spectrometers this is the internal configuration of LIBS 2000 spectrometer and subsequent analysis of spectrum was performed by storing through the OOI LIBS software. 3. Results and Discussion In this set of experiment we used laser irradiance at germanium target surface, which changes from 1.01011 to 1.81011 Wcm-2 and excitation temperature, electron density of germanium plasma has been estimated through Boltzmann plot method and stark broadening of germanium atom line of 265.11 nm wavelength as shown in Fig. 2 and Fig. 3 respectively. NIST data base was used to calculate plasma parameter as given in table 1. Excitation temperature and electron density of germanium plasma changes from 9546 to 15690 k, and ne changes from 1.041017 to 3.471017cm-3 as given in Fig. 4 and Fig. 5. Both parameters Te and Ne density of germanium plasma are seems to be highest at laser irradiance of 1.81011 Wcm-2 with the increase of further laser irradiance at germanium target surface, no noticeable change is observed because of plasma shielding for incoming laser irradiance which does not allow laser irradiance to reach at the germanium sample surface. Because formation of plasma and absorbing of laser irradiance by plasma takes place simultaneously so remaining laser irradiance is absorbed in the plasma plume. 3.1. Effect of laser irradiance on germanium plasma: The laser effect on plasma parameter is also highlighted in the Fig. 4 and Fig. 5 respectively; laser irradiance effect increases the Te and Ne exponentially at fixed target distance. The electron temperature and electron number density of plasma plume increases as soon as high laser

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irradiance effect is created at the germanium target surface. Similar behavior of plasma parameter such Te and Ne varying at high irradiance was reported by Zhang et al [34]. They reported the change in Te and Ne of magnese sulfate plasma with the change of irradiance from 21010 to 71010 Wcm-2 using 1064 nm wavelength and Te varied from 9367 to 9835 K and Ne varies from 5.301016 to 2.221017 cm-3 respectively. Same relation was also discussed by Santos et al [33] at germane (GeH4) plasma and found density (0.7–6.2) 1017 cm−3 at laser fluence from 1.81 to 352 J/cm-2 and plasma produced at different pressure ranging from 20 to 10 kPa . 3.2. Inverse bremsstrahlung and laser absorbance in germanium plasma: Plasma parameters changes with different laser irradiance both highest Te and peak Ne density of germanium plasma found to be at irradiance of 1.81011 Wcm-2. This satisfies the past reported work and shows the similar behavior in the related work that has been reported in the articles [33, 34]. The variation in plasma parameters such as Te and Ne is observed through the absorption of laser irradiance at germanium surface. This laser matter interaction also takes place simultaneously and other physical process also takes place which is known to be the reflection of laser irradiance at germanium target surface. These constant parameters used for calculation of absorbance and reflection of laser irradiance depend upon the laser frequency and wavelength which is given in table 2. Table shows the constant parameters for IR 1064 nm wavelength. The laser frequency according to reference [35] Hohreiteret al and [36] J. Chang and B. E. Warner, for fundamental (1064 nm) Nd:YAG laser is 2.81014 Hz, where as plasma frequency is υp= 8.9  103 Ne 0.5. In present research work for electron density Ne ≈ 3.641017 cm-3, and whereas plasma frequency is ~ 5.341012 Hz, germanium plasma frequency seems to be quiet less than laser frequency. As a result, energy loss from the reflection of the Nd: YAG laser at the plasma surface is neglected. On increasing the further laser irradiance at germanium target surface, a huge amount of excited constituents, included as free electrons and ions are excited into the higher state. Interaction between laser pulse and these excited species, which leads to heating and ionization through laser plume interaction and there by absorbance of laser into plasma plume takes place. At this stage two dominant phenomenon takes place namely inverse bremsstrahlung absorption (IB) and photo

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ionization. Inverse bremsstrahlung absorption via free electrons under the influence of field of an ion can be estimated from the relation  ib (cm 1 )  1.37  10 35 3 N e2Te1 / 2

(1)

From above relation λ (µm) stands for the wavelength of used laser photon, Te (K) and Ne (cm-3) is the electron temperature and electron density respectively. The IB process takes place with absorption of photon by free electrons near the vicinity of an ion as consequence energy of free electrons is increased by laser. This IB process seems to be dominant at λ ~ 1064 nm (IR) than the visible due to behavior of longer wavelength and this wavelength dependent behavior of λ3which leads to absorbance through process of electron-ion inverse bremsstrahlung can be estimated from the above relation. The second mechanism is photo ionization in germanium the first excited state above the ground state is 0.69 eV and ionization potential is 7.90 eV. At 1064 nm wavelength the energy of photon is 1.16 eV these values shows that photon ionization process does not seems to be dominant in IR (1064) nm where as inverse bremsstrahlung is dominant in IR (1064) nm wavelength the photoionization absorption co-efficient αPI (cm-1) and Inverse bremsstrahlung absorption via free electrons by relation Harilal et al [37].

 PI   PI N n   2.9  10 17 n

(En ) 5 / 2 Nn , (h ) 3

(2)

From above relation the symbol Nn and En are used for number density of excited state n; and for the ionization of energy respectively whereas h stands for Plank’s constant and υl stands for laser frequency. In present work we have estimated the inverse bremsstrahlung by using variable laser irradiance this was given in Fig. 6, that gives the detail information about laser absorbance through inverse bremsstrahlung Shaikh et al [38] calculated the inverse bremsstrahlung of aluminum plasma using Nd:YAG laser with fundamental second and third harmonics. In present work irradiance is varied from 1.01011 to 1.81011Wcm-2 and inverse bremsstrahlung varies from 2.010-3 to 1.210-2 cm-1 this inverse bremsstrahlung was estimated using equation 1 as given above. Irradiance absorbed by germanium plasma at surface in given by relation in the given reference [39]

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Pabs  P(1  e  P X )

(3)

In the given equation αp stands for absorption co-efficient of plasma plume P is laser irradiance power and X stands for dimension for plasma, in the dimension which is perpendicular to the germanium target surface. In this experiment at irradiance of 1.01011 Wcm-2 by using (1064 nm), of Nd:YAG laser the (IB) absorption is approximately = (0.0204 cm-1). The power absorbed by germanium target surface is found to be Pabs= 2.07108 Wcm-2 and 1.04103 Wcm-2 is reflected back from germanium surface. Whereas at highest laser irradiance 1.81011 Wcm-2 the power absorbed by surface is found to be Pabs= 3.67108 Wcm-2 and 1.84103Wcm-2 is reflected back from germanium surface. Laser irradiance penetrating at germanium target surface can be estimated using relation given in above reference [39]. E ~ I 0 (1  R )(1  A)

(4)

In the above relation I0 stands for laser irradiance where R and A stands for sample target surface reflectivity and absorbance percentage by target. 3.2. Energy penetrated in germanium plasma: In present work we have calculated laser absorbance and percentage which is estimated by absorbed light throughout the original irradiance I0 at target surface, in present work absorbance at germanium surface is 0.2 where as reflectivity R of germanium sample can be taken from reference date [40] which is found to be 0.39 for 1064 nm wavelength. At irradiance I0 1.01011 Wcm-2 the energy penetrated is E~5.051010 Wcm-2 and for high laser irradiance at I0 1.81011 Wcm-2 the energy penetrated is E~8.951010 Wcm-2. 3.3. Electron impact excitation rate in germanium plasma: The rate of electron impact excitation τex-1can be approximated by reference Hafeezet al [41] and calculated the electron impact excitation of calcium plasma 2



1 EI

 2  10

10

 I H  0.5  I Al   *     N  T exp e *    T  I Al      *

(5)

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In present research work for Ne~3.471017cm-3, Te= 1.35 eV and germanium first excited state above ground state ε*=0.69 eV. Considering these parameters τexcomes out to be ~0.9 ns this is clearly very short time to enhance the ionization during pulse duration of order of (~5 ns) the calculated value for electron impact excitation rate in germanium is close agreement with literature [41]. 3.4. Temporal behavior of germanium plasma: The temporal behavior of electron temperature ranges 13,460 K to 7,692 K, from 1 μs to 30 μs delay time which is show in the Fig. 8 this temperature was estimated from Boltzmann plot method shown in Fig. 7. The origin of becoming smaller value in temperature is readily changing of thermal energy in the form of kinetic energy of a plasma species obtaining the maximum velocities, this is resulted in expansion and cooling process of plasma plume is achieved. At different time delays electron number density has been evaluated by using 256.11 nm Ge – I atomic line Fig. 9 shows the broadening of this spectral line at delay time of 1μ at early time of plasma formation this figure shows the stark broadening of 265.11 nm wavelength. When laser is irradiated with germanium surface removal of target material takes place Whereas Ne at the vicinity of target surface is consequence of laser energy absorption and the observed Ne nearer to the surface is 3.171017 cm-3 and value becomes smaller to 1.981017 cm-3 with the change of time delay from 1μs to 30 μs which is given in Fig. 10. Consequently at nearer to surface of target higher number density is resulted, which becomes smaller as the time delay of observation is increased, the lower value of density is resulted at large delay time, which is the main cause resulted between electrons and ions recombination process. Aragόn et al [42] worked on the temporal variations of Te and Ne at delay time (0.4 to 3.4) μs of the plasma plume and observed that Te changes from 12000 K to 17600 K and density changes (0.8-10)´1017 cm-3 respectively. Camacho et al [43] worked on time related optical emission measurements of the germanium plasma produced by the CO2 pulsed-laser having 10.6 m wavelength 64 ns pulse duration. The stark broadening of Ge – I line 303.90 nm line at 2.5 μs have been used.

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4. Conclusions In present research work excitation temperature and electron density of Ge plasma changes from 9546 to 15690 k and 1.041017 to 3.471017cm-3 respectively. Both parameters Te and Ne of Ge plasma seems to be highest at laser irradiance of 1.81011 Wcm-2 with the increase of further laser irradiance at germanium target surface and we have found the values of Ne~3.471017cm-3, Te= 1.35 eV and Ge first excited state was ε*=0.69 eV. Considering these parameters τex comes out to be ~0.9 ns this is clearly very short time to enhance the ionization during pulse duration of order of (~5 ns). Calculated value of electron impact excitation rate in Ge and fundamental (1064 nm) Nd:YAG laser was 2.81014 Hz, where as plasma frequency was υp= 8.9  103 Ne

0.5.

In our

current study results of electron density and plasma frequency were found to be Ne ≈ 3.641017 cm-3 and ~ 5.341012 Hz respectively, which shows the Ge plasma frequency seems to be quiet less than laser frequency. 5. Acknowledgment We are thankful to QAU Islamabad for providing the necessary experimental facilities in atomic and molecular physics laboratory.

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[33] M. Santos, L. Díaz, J.J. Camacho, J.M.L. Poyato, J. Pola, T. Krenek, Laser induced breakdown spectroscopy of germane plasma induced by IR CO2 pulsed laser, Appl. Phys. A 99 (2010) 811–821. [34] M. Salik, M.Hanif, J. Wang, X.Q. Zhang, and Spectroscopic characterization of laserablated Magnese sulfate plasma, Laser Beams. 320 (2014) 137-144. [35] V. Hohreiter, J.E. Carranza, D.W. Hahn, Temporal analysis of laser-induced plasma properties as related to laser-induced breakdown spectroscopy, Spectrochim. Acta B 59 (2004) 327-333. [36] J.J. Chang and B.E. Warner, Laser plasma interaction during visible laser ablation of methods, J. Appl. Phys. Lett. 69 (1996) 473-477. [37] S.S. Harilal, C.V. Bindhu, Riju C. Issac, Electron density and temperature measurement in a laser produced carbon plasma, J. Appl. Phys. 82 (1997) 2140-2146. [38] N.M. Shaikh, S. Hafeez, B. Rashid, M.A. Baig, Spectroscopic studies of laser induced aluminum plasma using fundamental, second and third harmonics of a Nd: YAG laser, Eur. Phys. 44 (2007) 371-379. [39] R.K. Singh, O.W. Holland, T. Narayan, Theoretical model for deposition of superconducting thin films using pulsed laser evaporation technique, J. Appl. Phy. 68 (1990) 223-226. [40] D.R. Lide, H.P.R. Frederikse, Hand book of chemistry and physics, 8thedn. CRC Press, Boca Raton, FL, (2003-2004). [41] S. Hafeez, N.M. Shaikh, M.A. Baig, Spectroscopic studies of Ca plasma generated by the Fundamental, Second and third harmonics of a Nd: YAg laser, Laser Part. Beams. 26 (2008) 4150. [42] C. Aragόn, J.A. Aguilera, J. Manrique, Measurement of Stark broadening parameters of Fe II and Ni II Spectral lines by laser induced breakdown spectroscopy using fused glass sample, J. Quant. Spectrosc. Ra. 134 (2014) 39-45. [43] J.J. Camacho, L. Diaz, J.M.L. Poyato, Time-resolved spectroscopic diagnostic of laserinduced plasma on germanium targets, J. Appl. Phys. 109 (2011) 103304.

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Muhammad Ashraf (MA), Nek Muhammad Shaikh (NMS), Ghulam Abbas Kandhro (GAK), Ghulam Murtaza (GM), Javed Iqbal (JI), Azhar Iqbal (AI), Shafqat Ali Lashari (SAL)

NMS supervised the research NMS supervised the findings of this work MA, GM and JI Designed and performed experiments NMS and MA wrote the manuscript with support of GAK MA, AI and SAL conducted all statistical analyses MA, GM, AI and SAL performed the analytic calculations and performed the numerical simulations All authors discussed the results and contributed to the final manuscript NMK and GAK Critical revision of the article All authors contributed to the final version of the manuscript

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Authors Agreement:All authors agreed to participate in the research work.

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Fig. 1 Schematic diagram of LIBS experimental setup which comprises on necessary equipment to generate germanium plasma Fig. 2 Boltzmann plot at laser irradiance of 1.81011 Wcm-2 Fig. 3 Stark broadening of 265.11 nm at laser irradiance Fig. 4 Variation of electron temperature with laser irradiance for germanium plasma Fig. 5 Variation of electron density with laser irradiance for germanium plasma Fig. 6 Variation of inverse bremsstrahlung with laser irradiance Fig. 7 Boltzmann plot at 1 μs delay time of germanium plasma Fig.8 Temporal behavior of electron temperature of germanium plasma Fig. 9 Stark broadening of 265.11 nm at 1 μs delay time of germanium plasma Fig. 10 Temporal behavior of electron number density of germanium plasma

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Fig. 1

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Fig. 2

19.2

T = 15690 K

18.8

ln(I/gA)

18.4 18.0 17.6 17.2 16.8 16.4 16.0 37500

40000

42500

45000

Energy (cm-1)

47500

50000

Fig. 3

2200

4p 5s 3p2

2000 1800

4p2 3p2

265.11 nm

Intensity (a.u)

1600 1400

FWHM=0.181

1200 1000 800 600 400 200 0 264.0

264.5

265.0

265.5

266.0

wavelength (nm)

266.5

267.0

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Fig. 4

15000

Electron Temperature (K)

Electron Temperature 9546 to 15690 K

14000

13000

12000

11000

10000

9000

11

1.0x10

11

11

11

1.2x10 1.4x10 1.6x10 -2 Irradiance (W cm )

11

1.8x10

Fig. 5

17

-3 Electron number density (cm )

3.0x10

17

2.8x10

17

Electron number density 17 17 -3 1.04x10 to 3.47x10 cm

2.6x10

17

2.4x10

17

2.2x10

17

2.0x10

17

1.8x10

17

1.6x10

17

1.4x10

17

1.2x10

17

1.0x10

11

1.0x10

11

1.2x10

11

1.4x10

11

1.6x10

-2 Irradiance (W cm )

11

1.8x10

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Fig. 6

-2

1.2x10

Inverbremsthlung -2

1.0x10

1.2x10- 2 to 2.0x10- 3 cm -1

-1

 iB (cm )

-3

8.0x10

-3

6.0x10

-3

4.0x10

-3

2.0x10

11

1.0x10

11

11

11

1.2x10 1.4x10 1.6x10 -2 Irradiance (W cm )

11

1.8x10

Fig. 7

20.5

T = 13460 K

20.0

ln(I/gA)

19.5 19.0 18.5 18.0 17.5 17.0 16.5 50000

55000

60000

65000

Energy (cm-1)

70000

75000

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Fig. 8

Electron Temperature (K)

14000

Electron Temperature 13460 to 7690 K

13000 12000 11000 10000 9000 8000 0

4

8

12

16

20

24

28

32

Time delay (s)

Fig. 9

2000

4p5s 3p2

1800

Intensity (a.u)

1600

4p2 3p2

265.11 nm

1400 1200

FWHM= 0.178

1000 800 600 400 200 0 264.0

264.5

265.0

265.5

266.0

wavelength (nm)

266.5

267.0

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Fig. 10

Electron number Density

17

Electron number density (cm-3)

3.2x10

3.17x1017 to 1.98x1017 cm- 3

17

3.0x10

17

2.8x10

17

2.6x10

17

2.4x10

17

2.2x10

17

2.0x10

0

4

8

12

16

Time delay (s)

20

24

28

32

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Highlights 

LIBS technique is used for the analysis of germanium plasma



Laser absorption in plasma and surface reflectivity



Ambient conditions play significant role for pulsed laser deposition



Energy penetrated and laser threshold for germanium sample surface



Laser plasma spectrum is used for weight percentage of different elements

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Table 1: Spectroscopic data for germanium spectral lines

Wavelength(nm)

gk

Aik (s-1)

Ek(cm-1)

241.7

5

9.6E+07

48480.048

259.3

5

7.1E+07

39117.902

270.9

1

2.8E+08

37451.689

275.5

3

1.1E+08

37702.305

269.1

3

1.8E+08

37702.305

Table 2. Constant used for calculation of laser reflection and laser absorbance at germanium sample Wavelength (nm)

Energy

1064

Reflection

(ev)

Index of refraction (n)

Excitation coefficient (K)

(R=at o degree)

Absorption (α) coefficient(1/m)

1.16

4.385

0.103

0.39

1.2 × 106𝑚 -1