Citation: Ashour, M.; G. Faris, H.;
Ahmed, H.; Mamdouh, S.;
Thambiratnam, K.; Mohamed, T.
Using Femtosecond Laser Pulses to
Explore the Nonlinear Optical
Properties of Au NP Colloids That
Were Synthesized by Laser Ablation.
Nanomaterials 2022, 12, 2980. https://
doi.org/10.3390/nano12172980
Academic Editors: Ki-Hyun Kim,
Deepak Kukkar and Marco Cannas
Received: 7 August 2022
Accepted: 25 August 2022
Published: 28 August 2022
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Article
Using Femtosecond Laser Pulses to Explore the Nonlinear
Optical Properties of Au NP Colloids That Were Synthesized by
Laser Ablation
Mohamed Ashour
1,2
, Hameed G. Faris
3
, Hanan Ahmed
1
, Samar Mamdouh
1
, Kavintheran Thambiratnam
4
and Tarek Mohamed
1,5,
*
1
Laser Institute for Research and Applications LIRA, Beni-Suef University, Beni-Suef 62511, Egypt
2
High Institute of Optics Technology HIOT, Sheraton Heliopolis, Cairo 11799, Egypt
3
Al Anbar Health Directorate, Training and Human Development Center, Ramadi 31001, Iraq
4
Photonics Research Centre, University of Malaya, Kuala Lumpur 50603, Malaysia
5
Department of Engineering, Faculty of Advanced Technology and Multidiscipline, Universitas Airlangga,
Surabaya 60115, Indonesia
* Correspondence: tarek_mohamed1969@lira.bsu.edu.eg
Abstract:
In this study, we experimentally investigated the nonlinear optical properties of Au nanopar-
ticles (Au NPs) that were prepared in pure distilled water using the laser ablation method. The Au
NPs were prepared using a nanosecond Nd:YAG laser with an ablation time of 5 or 10 min at a
constant laser energy of 100 mJ. The structure and the linear optical properties of the Au NPs were
investigated using a transmission electron microscope (TEM) and UV-visible spectrophotometer anal-
ysis, respectively. The TEM measurements showed that the average size of the Au NPs varied from
20.3 to 14.1 nm, depending on the laser ablation time. The z-scan technique was used to investigate
the nonlinear refractive index (
n
2
) and nonlinear absorption coefficient (
γ
) of the Au NPs, which were
irradiated at different excitation wavelengths that ranged from 740 to 820 nm and at different average
powers that ranged from 0.8 to 1.6 W. The Au NP samples exhibited a reverse saturable absorption
(RSA) behavior that increased when the excitation wavelength and/or incident laser power increased.
In addition, the Au NPs acted as a self-defocusing material whenever the excitation wavelength or
incident power were modified.
Keywords: nonlinear optics; nanoparticles; femtosecond laser; high repetition rate; gold nanoparticles;
nonlinear absorption; nonlinear refraction
1. Introduction
The plethora of recently developed and potential future applications for new non-
linear optical (NLO) materials in optics and photonics has attracted the interest of many
researchers, particularly nanosized NLOs. This is because nanostructured NLO mate-
rials inherently have various unique and highly desirable characteristics, such as high
surface/volume ratios, unique structures, and better optical and electrical properties than
their bulkier counterparts [1–3].
Among the different nanostructure materials, metal nanoparticles (MNPs) have been
found to have substantial uses in a very wide range of applications, such as biosensors [
4
],
cancer therapy [
5
], waveguiding [
6
], data storage [
7
], all-optical switching devices [
8
],
and many more. Moreover, noble metallic nanoparticles (NMNPs) offer easy chemical
synthesis, high stability, and tunable surface functionalization [
9
]. In particular, silver (Ag)
and gold (Au) NPs are among the most useful nanomaterials out of the NMNPs, especially
for optoelectronic and nonlinear optical applications [10].
Gold nanoparticles (Au NPs) have attracted a great deal of interest in many fields
over the past few years due to their strong surface plasmon resonance (SPR) in the visible
Nanomaterials 2022, 12, 2980. https://doi.org/10.3390/nano12172980 https://www.mdpi.com/journal/nanomaterials
