**7. The effect of light absorption with nanoparticles in laser ablation method**

The absorption of laser beam with nanoparticles is the effective factor of the laser ablation process at high laser fluence to prepare the nanoparticles in an aqueous solution. When the prepared nanoparticles have not high mobility in liquid, they are aggregated near the target. Hence, they can absorb the energy of laser beam. This effect increases with increasing laser fluence because of the increase in the number of produced nanoparticles. Therefore, the intensity of laser beam that can reach the metal target is decreased. In addition, the size of the nanoparticles that absorb the incident laser beam decreases because of the laser-induced fragmentation occurs [68, 69]. This phenomenon was reported by Prochazka et al. [9]. They achieved the size of nanoparticles decreased when the laser beam interacted with the colloids during ablation of the metal target [70]. Consequently, the colloidal absorption causes the decreasing of the formation efficiency and the size of nanoparticles. This phenomenon called secondary effect. It can produce the high concentration nanoparticles and can control the formation process, and the size of nanoparticles and especially suppression of the ablation efficiency are undesired. Another considerable parameter is a flow-cell system, which is necessary for suppressing the colloidal absorption. Two colloidal absorption processes can be considered for preparation of metal nanoparticles. One is "interpulse" absorption and other is "intrapulse" absorption. The interpulse absorption related to the generation of nanoparticles by the earlier pulses stays in the laser beam path and absorbs the latterly coming pulses. The intrapulse absorption related to particles produced by the earlier part of one pulse immediately absorbs the later part of the same pulse.

silver nanoparticles, and nanoparticles grow in the unique form of organic and inorganic solutions without any agglomeration and collapsing. Silver nanoparticles were prepared in water, methanol, palm oil [22], coconut oil [71], pomegranate seed oil [72], polyvinyl alcohol (PVA) [28], and graphene oxide solution [73]. Silver nanoparticles were capped by chain fatty acid of oils, and the particle size was about 10 nm. When the ablation time increases, the size of particles decreases. Nanoparticles formed in the spherical shape that was obtained using transmission electron microscope image (**Figure 2a**). The efficiency of the colloidal absorption by silver nanoparticles for 355, 532, and 1064 nm laser beam depends on localized surface plasmon resonance or the plasmon band around 400 nm (**Figure 2b**). Hence, the maximum and minimum efficiency occurred in 355 and 1064 nm. Thus, the influence of the colloidal absorption was more prominent for shorter wavelength laser beam, leading to the conclusion that the formation efficiency and the size of nanoparticles decrease with decreasing laser

Laser Ablation Technique for Synthesis of Metal Nanoparticle in Liquid

http://dx.doi.org/10.5772/intechopen.80374

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Gold nanoparticles (Au-NPs) have more applications for electronics [74], photodynamic therapy [75], therapeutic agent delivery [76], tumor therapy [77], sensors [78], drugs carriers [79], and medical diagnoses [80]. High activity and high sensitivity of Au-NPs have been fabricated using laser ablation in water [81]. The final product was used to reclaim the area of glassy graphite electrode for detection of Hg, Pb, Cu, and Co in the low concentration [81]. Gold nanoparticles can absorb and interact with the electrical field of laser beam [79], and Au-NPs generate localized surface plasmon absorption in the range of 400–900 nm [82]. The coherent excitation of free electrons causes the surface plasmon band in a colloidal nanoparticle [83]. The response of the Au-NPs to an interaction of laser beam depends on particle size, the surrounding material, and nanoparticle concentration [84]. Hence, the investigation and consideration of green synthesis of gold nanoparticles are intense interest subject in nanomedicine and nanotechnology area. Laser ablation technique is an alternative method for preparation of gold nanoparticles in an aqueous solution. Recently, gold nanoparticles were prepared in graphene oxide and vegetable oils such as pomegranate seed oil [25]. When gold nanoparticles were fabricated using laser ablation of the gold target, the nanoparticles were formed in the spherical shape (**Figure 3a**) that was investigated using transmission electron microscopy. The particle size was in the range of 20–5 nm, and the UV-visible absorption peak appeared about 530 nm (**Figure 3b**). In accordance with Mie theory, when the particle size decreases, the blue shift (∆*λ*) occurs in the localized surface plasmon absorption peak as

\_\_\_\_\_\_\_ −*s*

, *s,* and *D* are central wavelength, interparticle gap, and particle size in the central

0.23 <sup>×</sup> *<sup>D</sup>*) (5)

wavelength.

follows:

where *λ*<sup>0</sup>

wavelength [85, 86].

**9. Laser ablation of gold nanoparticles in liquid**

∆*λ* = *λ*<sup>0</sup> × 0.18 × *exp*(
