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Article

Experimental Investigation of the Optical Nonlinearity of Laser-Ablated Titanium Dioxide Nanoparticles Using Femtosecond Laser Light Pulses

by
Fatma Abdel Samad
1,
Mohammed Ali Jasim
2,
Alaa Mahmoud
1,
Yasmin Abd El-Salam
1,
Hamza Qayyum
3,
Retna Apsari
4 and
Tarek Mohamed
1,4,*
1
Laser Institute for Research and Applications LIRA, Beni-Suef University, Beni-Suef 62511, Egypt
2
Anbar Health Department, Ministry of Health, Ramadi 31001, Iraq
3
Laser-Matter Interaction Laboratory, Department of Physics, COMSATS University Islamabad, Park Road, Islamabad 45550, Pakistan
4
Department of Engineering, Faculty of Advanced Technology and Multidiscipline, Universitas Airlangga, Surabaya 60115, Indonesia
*
Author to whom correspondence should be addressed.
Nanomaterials 2024, 14(23), 1940; https://doi.org/10.3390/nano14231940
Submission received: 19 October 2024 / Revised: 20 November 2024 / Accepted: 1 December 2024 / Published: 3 December 2024
(This article belongs to the Topic Laser Processing of Metallic Materials)
Browse Figures
Figure 1
<p>Laser ablation setup for preparing TiO<sub>2</sub> NPs colloids via a 532-nm Nd:YAG laser.</p> "> Figure 2
<p>Z-scan experimental setup. L, convex lens; A, attenuator; I, Iris; S, TiO<sub>2</sub> NPs sample; PM, power meter.</p> "> Figure 3
<p>Spectral absorption of TiO<sub>2</sub> NP colloidal solutions as a function of wavelength at different ablation times.</p> "> Figure 4
<p>(<b>a</b>–<b>c</b>) show the energy band gaps that were obtained by extrapolating the straight line of Tauc’s plot of TiO<sub>2</sub> nanocolloids at various ablation times.</p> "> Figure 5
<p>(<b>a</b>–<b>c</b>) depict the size distributions of TiO<sub>2</sub> NPs colloids that were synthesized using various ablation times of 5 min, 10 min, and 15 min, respectively.</p> "> Figure 6
<p>EDX spectra of the TiO<sub>2</sub> NP colloid and inset ZAF Method Standardless Quantitative Analysis of TiO<sub>2</sub> NPs.</p> "> Figure 7
<p>(<b>a</b>–<b>c</b>) OA Z-scan measurements of TiO<sub>2</sub> NP colloids with different ablation times and incident powers at an 800 nm excitation wavelength. (<b>d</b>) Dependence of the NLA coefficient on the incident laser power at an 800 nm excitation wavelength.</p> "> Figure 8
<p>(<b>a</b>–<b>c</b>) OA Z-scan experimental data of TiO<sub>2</sub> NP colloidal solutions with different ablation times and excitation wavelengths at 1 W incident power. (<b>d</b>) Relationship between the excitation wavelength and NLA coefficient at 1 W incident laser power.</p> "> Figure 9
<p>(<b>a</b>) OA Z-scan experimental data of TiO<sub>2</sub> NP colloidal solutions with different ablation times and a constant excitation wavelength of 800 nm and an incident power of 1 W. (<b>b</b>) Dependence between the ablation time and the NLA coefficient.</p> "> Figure 10
<p>(<b>a</b>–<b>c</b>) CA Z-scan measurements for TiO<sub>2</sub> NP colloids at different incident powers and ablation times at an excitation wavelength of 800 nm. The symbols represent the experimental data, and the solid curves are the fits obtained via Equations (6) and (7). (<b>d</b>) Relationship between the NLR index and incident power at each ablation time.</p> "> Figure 11
<p>(<b>a</b>–<b>c</b>) CA Z-scan transmission of TiO<sub>2</sub> NP colloids at different excitation wavelengths and ablation times; (<b>d</b>) relationship values of n<sub>2</sub> for TiO<sub>2</sub> NP colloidal solutions with different ablation times at 1 W incident power. The dots represent the experimental data, and the solid curves are linear fits.</p> "> Figure 12
<p>(<b>a</b>) Plot of CA Z-scan measurements of different ablation times of 5 min, 10 min, and 15 min at 800 nm excitation wavelength and 1 W incident power. (<b>b</b>) Dependence between the measured n<sub>2</sub> and ablation time at a 1 W incident power and 800 nm excitation wavelength. The dots represent the experimental data, and the solid lines are linear fits.</p> "> Figure 13
<p>Optical limiting of the TiO<sub>2</sub> NP colloids at ablation times of 5 min, 10 min, and 15 min and an 800 nm excitation wavelength.</p> ">
Review Reports Versions Notes

Abstract

:
In this report, the nonlinear optical (NLO) properties of titanium dioxide nanoparticles (TiO2 NPs) have been explored experimentally using femtosecond laser light along with the Z-scan approach. The synthesis of TiO2 NPs was carried out in distilled water through nanosecond second harmonic Nd:YAG laser ablation. Characterization of the TiO2 NPs colloids was conducted using UV-visible absorption spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma (ICP), and energy-dispersive X-ray spectroscopy (EDX). The TEM analysis indicated that the size distribution and average particle size of the TiO2 NPs varied from 8.3 nm to 19.1 nm, depending on the laser ablation duration. The third-order NLO properties of the synthesized TiO2 NPs were examined at different excitation laser wavelengths and incident powers through both open- and closed-aperture Z-scan techniques, utilizing a laser pulse duration of 100 fs and a high repetition rate of 80 MHz. The nonlinear absorption (NLA) coefficient and nonlinear refractive (NLR) index of the TiO2 NPs colloidal solutions were found to be influenced by the incident power, excitation wavelength, average size, and concentration of TiO2 NPs. Maximum values of 4.93 × 10⁻⁹ cm/W for the NLA coefficient and 15.39 × 10⁻15 cm2/W for the NLR index were observed at an excitation wavelength of 800 nm, an incident power of 0.6 W, and an ablation time of 15 min. The optical limiting (OL) effects of the TiO2 NPs solution at different ablation times were investigated and revealed to be concentration and average size dependent. An increase in concentration results in a more limiting effect.

1. Introduction

Optical materials that exhibit low absorption and high optical nonlinearity are often considered ideal for photonic and optoelectronic technologies [1]. The exploration of nanoparticles (NPs) in optical applications has captured the attention of researchers due to their unique properties [2]. These nanostructures, with their sub-nano dimensions and exotic shapes, display significant quantum confinement effects, making them suitable for a broad array of applications, including photonics, solar cells, photocatalysis, catalytic chemistry [3], and nonlinear optics [4,5,6].
Nanostructured semiconductors, in particular, possess notable linear and nonlinear optical (NLO) characteristics, which makes them valuable in fields such as photonics, gas sensing, optoelectronics, field emission displays, and medical technology [7,8,9]. Among various nanostructured semiconductors, titanium dioxide (TiO2) NPs hold significant potential in diverse applications due to their wide band gap of approximately 3.2 eV [10]. Nanocrystalline TiO2 is one of the most thoroughly researched materials due to its unique physical and chemical characteristics. It finds applications in solar and fuel cells [11] and protective and self-cleaning coatings, catalysis, and photocatalysis [12,13]. TiO2 NPs are especially prominent in optoelectronic applications, sparking considerable interest within the research community [14,15,16]. When exposed to intense collimated laser beams, the optically induced properties of TiO2 NPs exhibit notable NLO characteristics. The linear and NLO responses of bulk TiO2 materials within their transparency range can be explained by virtual transitions between the filled O 2p valence band and the vacant Ti 3d cationic band [17]. Numerous methods are employed to study the NLO properties of materials [18,19,20,21,22], though many are hindered by inaccuracies, complexity, and the need for intricate wave propagation analysis [23]. Among these, the Z-scan technique stands out as the simplest and most effective method for measuring the nonlinear refractive (NLR) index and nonlinear absorption (NLA) coefficient of various materials [24,25,26,27,28]. Open aperture (OA) and closed aperture (CA) Z-scan techniques are commonly used in experiments to determine the NLA coefficient and NLR index [29,30,31]. Two-photon absorption (2PA) is the most prevalent NLA phenomenon [32], where two photons are absorbed simultaneously, transitioning from a lower to a higher energy state.
Various techniques are available for preparing nanoparticle colloids, but pulsed laser ablation in liquid (PLAL) offers a promising alternative to traditional chemical methods. PLAL enables the synthesis of stable metal colloids in pure solvents without the need for toxic or hazardous chemicals [33]. By adjusting laser parameters such as pulse duration, fluence, repetition rate, wavelength, and pulse width, the size of nanoparticles can be precisely controlled, making this method highly versatile and effective. Numerous studies have explored the NLO properties of TiO2 in various forms, including NPs, thin films, nanocomposites, and nanocolloidal solutions [34,35]. However, only a few have examined the NLO behavior of TiO2 nanocolloids in liquid form, particularly those synthesized using the laser ablation method [36,37]. For example, TiO2 NPs were produced via laser ablation by irradiating a titanium target in distilled water at 1064 nm [36]. The Z-scan technique, using a continuous-wave He–Ne laser at different power levels, was employed to investigate the NLO properties of these TiO2 colloids, revealing a negative NLR index (n2) and a positive NLA coefficient (β) [36]. In another study [37], TiO2 NPs were synthesized by femtosecond (fs) laser ablation at 800 nm in deionized water, and the NLO properties were analyzed using a 150 fs laser across wavelengths of 700 nm, 750 nm, 800 nm, and 850 nm. The results showed reverse saturable absorption (RSA) and negative n2 values for the TiO2 nanocolloids [37].The aim of this study is to explore the NLO properties of TiO2 nanocolloidal solutions synthesized via laser ablation in distilled water, without the use of chemical additives. Nanosecond (ns) laser pulses are employed to generate TiO2 NPs under varying laser conditions. The synthesized TiO2 NPs are characterized using techniques such as UV-Vis spectroscopy, energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and inductively coupled plasma (ICP). Femtosecond (fs) laser pulses are then used to study the NLA coefficient and NLR index of TiO2 colloids at different excitation wavelengths and power levels, utilizing OA and CA Z-scan methods. Additionally, the study examines the impact of various TiO2 nanoparticle concentrations and particle sizes on the NLO susceptibility and optical limiting behavior.

2. Experimental Setup

2.1. TiO2 Sample Preparation

Figure 1 illustrates the experimental setup for synthesizing TiO2 nanoparticle colloids through laser ablation, using a second harmonic Nd:YAG laser system (Spectra Physics-Quanta-Ray PRO 350, (Milpitas, CA, USA)) with a pulse duration of 10 ns and a repetition rate of 10 Hz. The 532 nm laser operates with a maximum pulse energy of 1500 mJ per pulse, and the beam has a Gaussian distribution with a TEM00 mode. A titanium sample (purity > 99%) was submerged in distilled water to generate the TiO2 colloids. A convex lens with a 10.5 cm focal length was used to focus the laser beam, with an average power of 150 mW and energy of 15 mJ per pulse. The focal spot size, determined via the knife-edge method, was around 1.75 mm. The titanium sample was immersed in 10 mL of distilled water inside a beaker. To ensure uniform distribution and prevent particle interference during ablation, the beaker was rotated at 177 RPM using a motorized spinner. TiO2 NPs were synthesized at varying ablation times of 5, 10, and 15 min.

2.2. Z-Scan Setup

The NLO properties of TiO2 NPs were analyzed using a Z-scan setup, as shown in Figure 2 [28,38]. This experiment employed an fs laser system (INSPIRE HF100, Spectra-Physics, (Milpitas, CA, USA)), pumped by a mode-locked fs Ti:Saphire laser (MAI TAI HP, Spectra-Physics, (Milpitas, CA, USA)), which offers tunable wavelengths from 690 to 1040 nm, an average power output of 1.5–2.9 W, and an 80 MHz repetition rate. The Inspire laser system includes four output apertures, with the first delivering fundamental infrared pump wavelengths, while the others are driven by two additional modes based on NLO fields: a second harmonic generator (SHG) and an optical parametric oscillator (OPO). These modes allow for output wavelengths spanning from 345 nm to 2500 nm. To examine the NLO properties of TiO2 colloidal solutions, 100 fs laser pulses with Gaussian distribution were applied at various excitation wavelengths ranging from 750 nm to 850 nm. The laser beam, characterized by a Gaussian spatial profile (TEM00) and an M2 value of less than 1.1, was tightly focused using a 5 cm focal length convex lens. The TiO2 colloidal solution was contained in a 1 mm path-length quartz cuvette, mounted on a micrometer translation stage to enable scanning around the focal point. The transmitted intensity of the samples was recorded using a power meter (PM, Newport 843 R) as a function of their position relative to the focus.
For the CA Z-scan measurements, the aperture was set to S = 0.3, and the transmitted intensity was recorded by PM1, allowing for the determination of both the sign and magnitude of the NLR index. In the OA Z-scan measurements, where S = 1 (fully open), the NLA coefficient of the TiO2 samples was obtained, with the transmitted intensity recorded by PM2.
The experimental error in the obtained NLO coefficients was approximately 10%, which mainly originated from the determination of the irradiance distribution utilized in the experiment, i.e., beam waist, pulse width, and laser power calibration.

3. Results and Discussion

3.1. TiO2 NP Colloidal Solution Characterization

The optical absorption of the TiO2 NP colloids was measured using UV-visible absorption spectroscopy (Peak Instruments C-7200, Inchinnan, UK) across a wavelength range of 200 to 1100 nm. Figure 3 shows the UV-Vis absorption spectra for TiO2 NP colloids formed at different ablation times of 5, 10, and 15 min. The concentrations of the TiO2 NP colloids were measured using an ICP device (Agilent 5100 Synchronous Vertical Dual View (SVDV) ICP-OES, Agilent Vapor Generation Accessory VGA 77, Merck Company (Darmstadt, Germany)). The results indicated that the colloids synthesized for 5, 10, and 15 min had concentrations of 1.9 mg/L, 2.9 mg/L, and 4.35 mg/L, respectively. Figure 3 shows how the concentration and average size of TiO2 NPs significantly affect the absorbance spectrum. A surface plasmon resonance (SPR) peak is observed around 227 nm for the colloidal TiO2 NPs, with the concentration and average size of the TiO2 NPs influencing the SPR peak’s position. The absorption peak maxima occur at 228.5 nm, 227 nm, and 225.3 nm for ablation times of 5 min, 10 min, and 15 min, respectively. This absorption peak corresponds to the excitation of electrons from the valence band to the conduction band in TiO2 NPs. As the laser ablation time increases, a shift of the peak toward shorter wavelengths is observed, indicating the formation of smaller particles. Additionally, longer ablation times result in sharper SPR peaks, particularly at 15 min of ablation.
In the visible region, the TiO2 NP samples show high optical transparency, a crucial factor for optoelectronic applications. It was also noted that increasing the ablation time led to higher absorbance in this region. The energy band gap (Eg) of the TiO2 NP colloidal solutions is calculated from the optical absorption data using Tauc’s plot equation [39].
( α h υ ) 1 2 = a ( h υ − E g )
where a is a constant, and α is the linear absorption coefficient, which is obtained via the relation α = 2.303 A t [40], where A is the absorbance, and t is the thickness of the sample. The absorption spectrum revealed that the value of α varied with the ablation time, as shown in Figure 3. Figure 4a–c depicts the Eg values for the TiO2 NP solutions obtained from the (α h υ )1/2 versus h υ plots [41]. The Eg values of the TiO2 NP colloids can be deduced by extrapolating the linear part of the plot to α h υ = 0. As shown in Figure 4, the Eg of TiO2 NP colloidal solutions depends on the sample concentration and average size of NPs and decreases from 3.06 eV to 2.84 eV as the ablation time increases from 5 min to 15 min. The transmission results were used to calculate the linear refractive index (n0) via the Swanepoel formalism [42].
n 0 = 1 T + 1 T 2 − 1 1 / 2
where T is the transmittance of the TiO2 NP colloidal solution. The linear refractive index was calculated for each concentration of TiO2 NPs and is summarized in Table 1.
The size distribution and average size of TiO2 NPs were determined using high-resolution transmission electron microscopy (HR-TEM, JEM-2100, Joel, Japan, operated at 200 kV) at various ablation times. Figure 5a–c presents the size distribution histograms and TEM images of the TiO2 NP colloids for ablation times of 5, 10, and 15 min, corresponding to concentrations of 1.9 mg/L, 2.9 mg/L, and 4.35 mg/L, respectively. At a laser fluence of 1.24 J/cm2, the TiO2 nanoparticle colloids displayed a spherical morphology. For consistency, all images were captured at the same magnification, and particle sizes were analyzed using calibrated imaging software (Image J 1.45). The average size of TiO2 NPs was determined by taking four images for each ablation time and at different sample positions. The average sizes of the TiO2 NP samples were found to be 19.11 nm, 11.96 nm, and 8.33 nm for the ablation times of 5, 10, and 15 min, respectively. The decrease in average particle size suggests that the photo-fragmentation process becomes more efficient as the ablation duration increases.
The elemental composition of the TiO2 NP samples was analyzed using EDX with a JSM6510LA Eds detector from Oxford Instruments (Halifax Road, High Wycombe Buckinghamshire, UK). The EDX measurements, performed to determine the atomic composition of the TiO2 colloidal solutions, were conducted with a 20 kV electron beam and a spectrum counting time of 35 s. Figure 6 presents the EDX spectra of the TiO2 colloidal solution. The ZAF method, which accounts for atomic number (Z), absorption (A), and fluorescence (F), was applied to determine the elemental composition of the TiO2 NPs. The spectrum clearly shows the presence of titanium (Ti) and oxygen (O), with atomic percentages of 31.51% and 68.49%, respectively, as summarized in Figure 6.

3.2. Open Aperture Z-Scan Measurements

3.2.1. The Effect of Incident Power on β

Figure 7 shows the experimental OA Z-scan of TiO2 NPs investigated using a high repetition rate (HRR, 80 MHz) fs laser. The NLO properties of TiO2 NPs at the different ablation times were studied at various incident powers ranging from 0.6 to 1.2 W at an 800 nm excitation wavelength. Figure 7a–c depicts that all curves represent RSA. The absorption effect depends on the laser intensity, and normalized transmittance is symmetric around the focus (Z = 0), with the lowest transmission at the focus (valley) [25,43]. The NLA coefficient depends on the laser intensity (I) delivered to the sample when exposed to high laser intensity, as shown by the following equation [29,30]:
∝ I = α + β I
where ꞵ is the 2PA coefficient. To obtain the NLA coefficient, the OA Z-scan measurements were theoretically fitted using the NLA model provided by [38,44,45]
T O A = 1 − β I 0 ( n − 1 ) L e f f ( m + 1 ) 3 2 1 + Z 2 Z 0 2 ( n − 1 )
where I0 is the peak intensity at the focus (Z = 0), and m = 1 for 2PA, and m = 2 for three-photon absorption (3PA). Z0 is the Rayleigh length Z 0 = n 0 π ω 0 2 λ . The Rayleigh length was greater than the sample thickness ( Z 0 > L ). L e f f = 1 − ( e − m α L / m α ), where L is the thickness of the sample, ω 0 is the beam waist at the focus (16 μm ± 1.6), and λ is the excitation wavelength. Normalized transmittance (TOA) decreases as the incident power increases, as illustrated in Figure 7a–c. Figure 7d depicts the dependence of the NLA coefficient on the incident laser power; as the incident power increases, the NLA coefficient decreases. Based on the absorption mechanism of semiconducting materials, NLA can be divided into RSA, multiphoton absorption, excited-state absorption (ESA), and free carrier absorption (FCA). The number of free electrons in the conduction band (Ti 3d) and holes in the valence band (O 2p) increases as the incident power increases. The collisions of electrons with each other in the conduction band are called “many-body interactions” [46]. As a result, collisions between free carriers increase, the scattering of photons and phonons increases, and ꞵ decreases.

3.2.2. Effect of the Excitation Wavelength on β

Figure 8a–c depicts the dependence of the NLA coefficient of TiO2 NP colloidal solutions on the excitation wavelength ranging from 750 nm to 850 nm, as well as different ablation times. The TOA decreases as the excitation wavelength increases, showing an increase in RSA [37]. TiO2 NPs exhibit an energy band gap from 3.06 eV to 2.84 eV at ablation times from 5 min to 15 min. Two-photon absorption occurs with photon energies ranging from 1.65 to 1.458 eV, which corresponds to the used wavelength range from 750 to 850 nm. Figure 8d depicts the effect of excitation wavelength on the NLA coefficient of TiO2 NP solutions at 1 W incident power. Increasing the excitation wavelength stimulates more electrons to fill the excited bands. TiO2 NP solutions exhibit a linear increase in the NLA coefficient as wavelength increases. As the laser wavelength decreases, it approaches the far tail of linear absorption (one-photon absorption).

3.2.3. Effect of Ablation Time on β of TiO2 NPs

As shown in Figure 9a, the OA Z-scan measurements of the TiO2 NP colloidal solutions were studied at different ablation times using an 800 nm excitation wavelength and 1 W incident power. The TOA decreased with increasing ablation time and exhibited a distinct reduction in transmittance when the laser focused on the TiO2 NP sample; a typical RSA response was observed. The NLA coefficient of the TiO2 NP colloidal solutions is linearly related to the ablation time, as depicted in Figure 9b. As the ablation time increases, TiO2 NP concentration increases, and the number of NP molecules involved in the laser interaction increases, which leads to an increase in the number of two-photon absorbers. The decrease in the NLA coefficient with increasing NP size is due to the larger number of NPs that can be accommodated in a given volume as particle size decreases [47,48].

3.3. CA Z-Scan Measurements: The Effect of Incident Power on n2

The experimental CA Z-scan of TiO2 NP colloids was studied via 100 fs HRR laser pulses. The HRR laser has a 12.5 ns separation time between pulses. For liquids and optical glasses, the thermal characteristic time tc = ω 2 4 D , tc is ≥ 40 μs [49], where D represents the sample’s thermal diffusion coefficient, and ω denotes the incident laser beam waist. The separation time is less than tc. Cumulative heating occurs when the sample does not return to its equilibrium temperature between pulses. This heating can lead to a temperature distribution that alters the spatial distribution of the refractive index, resulting in distorted CA Z-scan experimental data and inaccurate NLR index results. For the steady-state case and the thermal nonlinearity, the on-axis change in the NLR index Δn can be given as follows [50]:
∆ n = d n d T × I α ω o 2 4 κ
where κ represents the thermal conductivity, and d n d T represents the thermo-optic coefficient. The NLR index of TiO2 NP colloidal solutions depends on the excitation laser parameters. The repetition rate, the number of laser pulses that fall on the sample during the scan, and the sample position all have an impact on accumulative thermal lensing, which can be described as follows:
1 f ( Z ) = a L E p F l 3 2 ω z 2 1 − 1 N p
where Fl is the repetition rate; a represents the fitting parameter a = α (dn/dT)/2 κ (π3D)1/2; ω z represents the radius of the laser beam at the sample; Ep represents the energy per pulse; and Np represents the number of laser pulses incident on the sample. Np = t × Fl, where t is the time the TiO2 NP sample takes to complete the scan. In this work, t is approximately 3 min, and Fl = 80 × 106 s−1; then, the TiO2 NP sample is exposed to Np = 14 × 109 laser pulses during each scan. The normalized transmittance CA Z-scan measurements (ΔTCA) depend on the focal length of the induced lensing at f ≥ Z0 [51,52].
∆ T C A = 1 + 2 Z f ( Z )
The CA Z-scan experimental results at various incident powers, ablation times, and an excitation wavelength of 800 nm are displayed in Figure 10a–c. By using Equations (6) and (7), the experimental results are simulated via the theoretical fitting expressed as the solid lines. The on-axis nonlinear phase shift ∆φ as a function of the thermal focal length at the focus can be computed using the procedure outlined in the reference [30]. The fitting parameter (a) and value of f(0) were determined from the best simulation of the experimental results.
∆ φ = Z 0 2 f ( 0 )
where f (0) represents the focal length of the induced thermal lens when the sample is placed at focus (Z = 0). The NLO phase shift produces the NLR index (n2), which can be expressed as [51]
n 2 = λ ω 0 2 Δ φ ( 2 P p × L e f f )
where Pp represents the peak power. Figure 10 shows that the peak-to-valley normalized transmittance difference (ΔTp−v) increases as the incident power increases, which is related to the ∆ φ , thermal contribution, and electronic effect of the TiO2 NPs. At an excitation wavelength of 800 nm, when the incident power is varied from 0.6 W to 1.2 W, ∆ φ varies from 0.325 rad to 0.474 rad, from 0.386 rad to 0.569 rad, and from 0.502 rad to 0.623 rad at different ablation times from 5 min to 15 min, respectively.
The NLR index was estimated as a function of incident power from the best fit of the CA experimental data depicted in Figure 10a–c using Equations (6)–(9). Figure 10d shows the effect of incident power on the n2 of TiO2 NP colloids at different ablation times and an excitation wavelength of 800 nm.

3.4. Investigating the Effect of the Excitation Wavelength on the Nonlinear Refractive Index

Figure 11a–c illustrates the influence of various excitation wavelengths, ranging from 750 to 850 nm, on the n2 of TiO2 NPs at different ablation times and with an incident power of 1 W. The ΔTp−v varies based on the excitation wavelength. Figure 11d shows that n2, derived from Figure 11a–c, varies as a function of the excitation wavelength for ablation times of 5 min, 10 min, and 15 min. At an ablation time of 5 min, n2 exhibits a slight decrease as the excitation wavelength increases. Conversely, at 10 min, n2 shows a slight increase with higher excitation wavelengths. For the ablation time of 15 min, n2 increases with rising excitation wavelength, as depicted in Figure 11c. The dependence of n2 on the excitation wavelength is influenced by several factors, including the excitation photon energy, thermal contributions, and the band structure of the TiO2 NPs.

3.5. Effect of Various Ablation Times on the Nonlinear Refractive Index

The effect of ablation time on the NLR index was studied at an excitation wavelength of 800 nm and an incident power of 1 W. The results of the CA Z-scan for different ablation times are shown in Figure 12a. It was observed that the ΔTp−v increases with higher ablation times. Figure 12b illustrates the relationship between the n2 and ablation time. The NLR index of the TiO2 NPs was affected by both the average size and concentration of the TiO2 NP colloids. The NLR index increases with increasing concentrations and decreases with increasing TiO2 NP average sizes. This inverse relationship arises because larger NPs result in fewer particles being accommodated in the same volume, leading to a reduction in the volume fraction. Consequently, this reduction results in lower values for both the NLR index and the NLA coefficient [53].

3.6. NLO Susceptibility of TiO2 NP Colloidal Solutions

Using experimental results of the NLR index n2 and NLA coefficient ꞵ , the real R e χ 3 and imaginary I m χ 3 parts of the third-order nonlinear susceptibility χ ( 3 ) can be deduced. The nonlinear susceptibility of a material can be expressed as follows [54,55]:
χ ( 3 ) = R e χ 3 + i I m χ 3
where the R e χ 3 parameter is related to the NLR index n2, and the I m χ 3 parameter is related to the NLA coefficient ꞵ. The real nonlinear susceptibility R e χ 3 can be written as follows:
R e χ 3 = n 0 3 π n 2
The imaginary nonlinear susceptibility I m χ 3 is given as
I m χ 3 e s u = 10 − 7 c λ n 0 2 96 π 2 ꞵ
where c is the speed of light. The real and imaginary nonlinear susceptibilities were measured for TiO2 NP colloids, as summarized in Table 1. The figure of merit (FOM) can be used to characterize the third-order NLO properties of TiO2 NP colloids, which is dependent on linear absorption coefficient α and can be given as [56,57]
F O M = I m χ 3   α
The absolute value of nonlinear susceptibility is written as
χ ( 3 ) = R e χ 3 2 + I m χ 3 2
The absolute values of χ ( 3 ) are summarized in Table 1.

3.7. Optical Power Limiting Measurements

As optical technology continues to evolve, there is a growing need to regulate laser beam intensity to ensure the safety of both human eyes and optical sensors [58]. Various filters are employed for the protection of these sensors, with optical limiters playing a crucial role and gaining significant attention in recent studies [59]. The optical power limiting (OPL) effect of TiO2 NP colloids at different ablation times was investigated experimentally by varying the input power at an excitation wavelength of 800 nm, as illustrated in Figure 13. The TiO2 NP solution was positioned at the focal point of a convex lens (5 cm), and the output power was recorded across a range of input powers. The OPL effect exhibited by the TiO2 NP solution is dependent on concentration and average size of NPs; an increase in concentration leads to a stronger limiting effect. The data presented in Figure 13 indicate that the saturation input power diminishes with rising TiO2 NP concentration, as summarized in Table 1. Experimental results demonstrate that the OPL of TiO2 NP colloids effectively attenuates intense and potentially harmful laser beams, resulting in nonlinear extinction.
Table 2 summarizes the NLO properties of the TiO2 NP samples from the current and previous studies [10,34,35,36,37,60,61,62,63]. We can conclude that the NLO properties of our TiO2 NP samples were strongly dependent on the nanoparticle synthesis technique and the laser parameters, including repetition rate, pulse duration, wavelength, and peak intensity.

4. Conclusions

We investigated the optical nonlinearities of TiO2 NPs synthesized through laser ablation in distilled water. The TiO2 NPs were produced at various ablation times, maintaining a constant laser energy per pulse of 15 mJ, and characterized using TEM to determine the average nanoparticle size at different concentrations. Nonlinear optical studies were conducted on TiO2 NPs with average sizes of 19.11 nm, 11.96 nm, and 8.33 nm, corresponding to concentrations of 1.9 mg/L, 2.9 mg/L, and 4.35 mg/L, respectively, employing the Z-scan technique. OA Z-scan measurements using an fs HRR laser were performed at excitation wavelengths between 750 nm and 850 nm and power levels ranging from 0.6 W to 1.2 W. These experiments revealed RSA behavior with significant 2PA coefficients. The NLA coefficient was observed to depend on both power and wavelength. CA Z-scan results indicated negative nonlinearity at each ablation time. Variations in size and concentration have been identified as potential factors influencing the differences in the NLO properties of TiO2 NPs. Further research is necessary, particularly with higher concentrations of TiO2 NPs, to draw more definitive conclusions and unlock the advanced capabilities of these tunable optical nonlinearities. Investigation into the TiO2 NP solution’s optical limiting effects at various ablation times showed that these effects depended on the concentration and average size of NPs. A more limiting effect is produced with higher concentration.

Author Contributions

Conceptualization, F.A.S., M.A.J., A.M., Y.A.E.-S., R.A. and T.M.; Formal analysis, A.M., Y.A.E.-S. and T.M.; Investigation, F.A.S., M.A.J., A.M., Y.A.E.-S., H.Q. and T.M.; Methodology, F.A.S., Y.A.E.-S., H.Q. and T.M.; Project administration, T.M.; Software, R.A.; Supervision, A.M. and T.M.; Validation, F.A.S., M.A.J., R.A., H.Q. and T.M.; Visualization, M.A.J.; Writing—original draft, F.A.S., M.A.J., A.M. and Y.A.E.-S.; Writing—review and editing, R.A., H.Q. and T.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data that underlie the results that are presented in this paper are not publicly available at this time but can be obtained from the authors upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Zhou, W.; Liu, X.; Cui, J.; Liu, D.; Li, J.; Jiang, H.; Wang, J.; Liu, H. Control synthesis of rutile TiO2 microspheres, nanoflowers, nanotrees and nanobelts via acid-hydrothermal method and their optical properties. CrystEngComm 2011, 13, 4557–4563. [Google Scholar] [CrossRef]
  2. Zada, A.; Muhammad, P.; Ahmad, W.; Hussain, Z.; Ali, S.; Khan, M.; Khan, Q.; Maqbool, M. Surface plasmonic-assisted photocatalysis and optoelectronic devices with noble metal nanocrystals: Design, synthesis, and applications. Adv. Funct. Mater. 2020, 30, 1906744. [Google Scholar] [CrossRef]
  3. Chen, M.S.; Goodman, D.W. The structure of catalytically active gold on titania. Science 2004, 306, 252–255. [Google Scholar] [CrossRef] [PubMed]
  4. Liao, H.B.; Xiao, R.F.; Wang, H.; Wong, K.S.; Wong, G.K.L. Large third-order optical nonlinearity in Au: TiO2 composite films measured on a femtosecond time scale. Appl. Phys. Lett. 1998, 72, 1817–1819. [Google Scholar] [CrossRef]
  5. Zhang, C.; Liu, Y.; You, G.; Li, B.; Shi, J.; Qian, S. Ultrafast nonlinear optical response of Au: TiO2 composite nanoparticle films. Phys. B Condens. Matter 2005, 357, 334–339. [Google Scholar] [CrossRef]
  6. Ma, G.; He, J.; Tang, S.H. Femtosecond nonlinear birefringence and nonlinear dichroism in Au: TiO2 composite films. Phys. Lett. A 2003, 306, 348–352. [Google Scholar] [CrossRef]
  7. Hu, J.; Li, L.-s.; Yang, W.; Manna, L.; Wang, L.-w.; Alivisatos, A.P. Linearly polarized emission from colloidal semiconductor quantum rods. Science 2001, 292, 2060–2063. [Google Scholar] [CrossRef]
  8. Zhao, Y.; Li, C.; Liu, X.; Gu, F.; Jiang, H.; Shao, W.; Zhang, L.; He, Y. Synthesis and optical properties of TiO2 nanoparticles. Mater. Lett. 2007, 61, 79–83. [Google Scholar] [CrossRef]
  9. Lee, W.; Yoo, H.-I.; Lee, J.K. Template route toward a novel nanostructured superionic conductor film; AgI nanorod/γ-Al2O3. Chem. Commun. Vol. 2001, 2530–2531. [Google Scholar] [CrossRef]
  10. Tamgadge, Y.; Muley, G.; Deshmukh, K.; Pahurkar, V. Synthesis and nonlinear optical properties of Zn doped TiO2 nano-colloids. Opt. Mater. 2018, 86, 185–190. [Google Scholar] [CrossRef]
  11. O’regan, B.; Grätzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991, 353, 737–740. [Google Scholar] [CrossRef]
  12. Afzal, A.; Habib, A.; Ulhasan, I.; Shahid, M.; Rehman, A. Antireflective self-cleaning TiO2 coatings for solar energy harvesting applications. Front. Mater. 2021, 8, 687059. [Google Scholar] [CrossRef]
  13. Hashimoto, K.; Irie, H.; Fujishima, A. TiO2 photocatalysis: A historical overview and future prospects. Appl. Phys. 2005, 44, 8269. [Google Scholar] [CrossRef]
  14. Li, Z.; Li, Z.; Zuo, C.; Fang, X. Application of nanostructured TiO2 in UV photodetectors: A review. Adv. Mater. 2022, 34, 2109083. [Google Scholar] [CrossRef]
  15. Ge, S.; Sang, D.; Zou, L.; Yao, Y.; Zhou, C.; Fu, H.; Xi, H.; Fan, J.; Meng, L.; Wang, C. A review on the progress of optoelectronic devices based on TiO2 thin films and nanomaterials. Nanomaterials 2023, 13, 1141. [Google Scholar] [CrossRef]
  16. Sathyaseelan, B.; Manikandan, E.; Lakshmanan, V.; Baskaran, I.; Sivakumar, K.; Ladchumananandasivam, R.; Kennedy, J.; Maaza, M. Structural, optical and morphological properties of post-growth calcined TiO2 nanopowder for opto-electronic device application: Ex-situ studies. Alloys Compd. 2016, 671, 486–492. [Google Scholar] [CrossRef]
  17. Wang, Z.; Wen, B.; Hao, Q.; Liu, L.-M.; Zhou, C.; Mao, X.; Lang, X.; Yin, W.-J.; Dai, D.; Selloni, A. Localized excitation of Ti3+ ions in the photoabsorption and photocatalytic activity of reduced rutile TiO2. J. Am. Chem. Soc. 2015, 137, 9146–9152. [Google Scholar] [CrossRef]
  18. Moran, M.; She, C.-Y.; Carman, R.J.I.J. Interferometric measurements of the nonlinear refractive-index coefficient relative to CS 2 in laser-system-related materials. IEEE J. Quantum Electron. 1975, 11, 259–263. [Google Scholar] [CrossRef]
  19. Adair, R.; Chase, L.; Payne, S.A. Nonlinear refractive-index measurements of glasses using three-wave frequency mixing. JOSA B 1987, 4, 875–881. [Google Scholar] [CrossRef]
  20. Owyoung, A. Ellipse rotation studies in laser host materials. IEEE J. Quantum Electron. 1973, 9, 1064–1069. [Google Scholar] [CrossRef]
  21. Williams, W.E.; Soileau, M.; Van Stryland, E.W. Optical switching and n2 measurements in CS2. Opt. Commun. 1984, 50, 256–260. [Google Scholar] [CrossRef]
  22. Miguez, M.; Barbano, E.; Zilio, S.C.; Misoguti, L.J.O.E. Accurate measurement of nonlinear ellipse rotation using a phase-sensitive method. Opt. Express 2014, 22, 25530–25538. [Google Scholar] [CrossRef] [PubMed]
  23. Soileau, M.; Williams, W.E.; Van Stryland, E.W.; Boggess, T.F.; Smirl, A.L. Picosecond damage studies at 0.5 and 1 µm. Opt. Eng. 1983, 22, 424–430. [Google Scholar] [CrossRef]
  24. Lee, K.-H.; Cho, W.-R.; Park, J.-H.; Kim, J.-S.; Park, S.-H.; Kim, U. Measurement of free-carrier nonlinearities in ZnSe based on the Z-scan technique with a nanosecond laser. Opt. Lett. 1994, 19, 1116–1118. [Google Scholar] [CrossRef] [PubMed]
  25. Sheik-Bahae, M.; Said, A.A.; Van Stryland, E.W. High-sensitivity, single-beam n 2 measurements. Opt. Lett. 1989, 14, 955–957. [Google Scholar] [CrossRef] [PubMed]
  26. Kalanoor, B.S.; Gouda, L.; Gottesman, R.; Tirosh, S.; Haltzi, E.; Zaban, A.; Tischler, Y.R. Third-order optical nonlinearities in organometallic methylammonium lead iodide perovskite thin films. ACS Photonics 2016, 3, 361–370. [Google Scholar] [CrossRef]
  27. Gu, B.; Wang, H.-T. Linear and Nonlinear Optical Properties of Ferroelectric Thin Films. In Ferroelectrics-Physical Effects; IntechOpen: Rijeka, Croatia, 2011. [Google Scholar]
  28. Samad, F.A.; Abdel-wahab, M.S.; Tawfik, W.Z.; Qayyum, H.; Apsari, R.; Mohamed, T. Thickness-dependent nonlinear optical properties of ITO thin films. Opt. Quantum Electron. 2023, 55, 753. [Google Scholar] [CrossRef]
  29. Shehata, A.; Mohamed, T. Method for an accurate measurement of nonlinear refractive index in the case of high-repetition-rate femtosecond laser pulses. JOSA B 2019, 36, 1246–1251. [Google Scholar] [CrossRef]
  30. Shehata, A.; Tawfik, W.Z.; Mohamed, T. Cobalt enhanced nonlinear optical properties and optical limiting of zinc oxide irradiated by femtosecond laser pulses. JOSA B 2020, 37, A1–A8. [Google Scholar] [CrossRef]
  31. Samad, F.A.; Mohamed, T. Intensity and wavelength-dependent two-photon absorption and its saturation in ITO film. Appl. Phys. A 2023, 129, 31. [Google Scholar] [CrossRef]
  32. Reyna, A.S.; Russier-Antoine, I.; Bertorelle, F.; Benichou, E.; Dugourd, P.; Antoine, R.; Brevet, P.-F.; de Araújo, C.B. Nonlinear refraction and absorption of Ag29 nanoclusters: Evidence for two-photon absorption saturation. Phys. Chem. C 2018, 122, 18682–18689. [Google Scholar] [CrossRef]
  33. Zeng, H.; Du, X.W.; Singh, S.C.; Kulinich, S.A.; Yang, S.; He, J.; Cai, W. Nanomaterials via laser ablation/irradiation in liquid: A review. Adv. Funct. Mater. 2012, 22, 1333–1353. [Google Scholar] [CrossRef]
  34. Elim, H.; Ji, W.; Yuwono, A.H.; Xue, J.; Wang, J. Ultrafast optical nonlinearity in poly (methylmethacrylate)-TiO2 nanocomposites. Appl. Phys. Lett. 2003, 82, 2691–2693. [Google Scholar] [CrossRef]
  35. Pramodini, S.; Aravinda, L.; Nagaraja, K.; Poornesh, P. Continuous wave laser probed thermal nonlinearity in TiO2 and TiO2-dye nano colloidal. Opt. Laser Technol. 2021, 142, 107182. [Google Scholar] [CrossRef]
  36. Moslehirad, F.; Ara, M.M.; Torkamany, M.; Afsary, M.; Ghorannevis, M.; Sabbaghzadeh, J. Thermal nonlinear optical properties of TiO2 nanocrystals prepared through pulsed laser ablation. Laser Phys. 2013, 23, 055402. [Google Scholar] [CrossRef]
  37. Banerjee, D.; Moram, S.S.B.; Byram, C.; Rathod, J.; Jena, T.; Podagatlapalli, G.K.; Soma, V.R. Plasmon-enhanced ultrafast and tunable thermo-optic nonlinear optical properties of femtosecond laser ablated TiO2 and Silver-doped TiO2 nanoparticles. Appl. Surf. Sci. 2021, 569, 151070. [Google Scholar] [CrossRef]
  38. Ashour, M.; Faris, H.G.; 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. [Google Scholar] [CrossRef]
  39. Asanuma, T.; Matsutani, T.; Liu, C.; Mihara, T.; Kiuchi, M. Structural and optical properties of titanium dioxide films deposited by reactive magnetron sputtering in pure oxygen plasma. Appl. Phys. 2004, 95, 6011–6016. [Google Scholar] [CrossRef]
  40. Ovshinsky, S.R.; Adler, D. Local structure, bonding, and electronic properties of covalent amorphous semiconductors. Contemp. Phys. 1978, 19, 109–126. [Google Scholar] [CrossRef]
  41. Reddy, K.M.; Manorama, S.V.; Reddy, A.R. Bandgap studies on anatase titanium dioxide nanoparticles. Mater. Chem. Phys. 2003, 78, 239–245. [Google Scholar] [CrossRef]
  42. Georgescu, G.; Petris, A. Analysis of thickness influence on refractive index and absorption coefficient of zinc selenide thin films. Opt. Express 2019, 27, 34803–34823. [Google Scholar] [CrossRef] [PubMed]
  43. Sheik-Bahae, M.; Said, A.A.; Wei, T.-H.; Hagan, D.J.; Van Stryland, E.W. Sensitive measurement of optical nonlinearities using a single beam. IEEE J. Quantum Electron. 1990, 26, 760–769. [Google Scholar] [CrossRef]
  44. Xiao, Q.-H.; Feng, X.-Y.; Yang, W.; Lin, Y.-K.; Peng, Q.-Q.; Jiang, S.-Z.; Liu, J.; Su, L.B. Epsilon-near-zero indium tin oxide nanocolumns array as a saturable absorber for a Nd: BGO laser. Laser Phys. 2020, 30, 055802. [Google Scholar] [CrossRef]
  45. Ramakanth, S.; Hamad, S.; Venugopal Rao, S.; James Raju, K.C. Magnetic and nonlinear optical properties of batio3 nanoparticles. AIP Adv. 2015, 5, 057139. [Google Scholar] [CrossRef]
  46. Chemla, D.; Shah, J. Many-body and correlation effects in semiconductors. Nature 2001, 411, 549–557. [Google Scholar] [CrossRef]
  47. Shahriari, E.; Moradi, M.; Ghasemi Varnamkhasti, M. Investigation of nonlinear optical properties of Ag nanoparticles. Opt. Photonics 2015, 9, 107–114. [Google Scholar]
  48. Shahriari, E.; Yunus, W.; Saion, E. Effect of particle size on nonlinear refractive index of Au nanoparticle in PVA solution. Braz. J. Phys. 2010, 40, 256–260. [Google Scholar] [CrossRef]
  49. Falconieri, M. Thermo-optical effects in Z-scan measurements using high-repetition-rate lasers. Opt. A Pure Appl. Opt. 1999, 1, 662. [Google Scholar] [CrossRef]
  50. Callen, W.R.; Huth, B.G.; Pantell, R.H. Optical patterns of thermally self-defocused light. Appl. Phys. Lett. 1967, 11, 103–105. [Google Scholar] [CrossRef]
  51. Severiano-Carrillo, I.; Alvarado-Méndez, E.; Trejo-Durán, M.; Méndez-Otero, M.M. Improved Z-scan adjustment to thermal nonlinearities by including nonlinear absorption. Opt. Commun. 2017, 397, 140–146. [Google Scholar] [CrossRef]
  52. Shehata, A.; Ali, M.; Schuch, R.; Mohamed, T. Experimental investigations of nonlinear optical properties of soda-lime glasses and theoretical study of self-compression of fs laser pulses. Opt. Laser Technol. 2019, 116, 276–283. [Google Scholar] [CrossRef]
  53. Mohamed, T.; El-Motlak, M.H.; Mamdouh, S.; Ashour, M.; Ahmed, H.; Qayyum, H.; Mahmoud, A. Excitation wavelength and colloids concentration-dependent nonlinear optical properties of silver nanoparticles synthesized by laser ablation. Materials 2022, 15, 7348. [Google Scholar] [CrossRef] [PubMed]
  54. Jamshidi-Ghaleh, K.; Namdar, A.; Mansour, N. Nonlinear optical properties of soda-lime glass at 800-nm femtosecond irradiation. Laser Phys. 2005, 15, 1714–1717. [Google Scholar]
  55. Gordon, J.P.; Leite RC, C.; Moore, R.S.; Porto SP, S.; Whinnery, J.R. Long-transient effects in lasers with inserted liquid samples. Appl. Phys. 1965, 36, 3–8. [Google Scholar] [CrossRef]
  56. Christodoulides, D.N.; Khoo, I.C.; Salamo, G.J.; Stegeman, G.I.; Van Stryland, E.W. Nonlinear refraction and absorption: Mechanisms and magnitudes. Adv. Opt. Photonics 2010, 2, 60–200. [Google Scholar] [CrossRef]
  57. Kwak, C.H.; Lee, Y.L.; Kim, S.G. Analysis of asymmetric Z-scan measurement for large optical nonlinearities in an amorphous As 2 S 3 thin film. JOSA B 1999, 16, 600–604. [Google Scholar] [CrossRef]
  58. Venkatram, N.; Rao, D.N.; Akundi, M.A. Nonlinear absorption, scattering and optical limiting studies of CdS nanoparticles. Opt. Express 2005, 13, 867–872. [Google Scholar] [CrossRef]
  59. Miller, M.J.; Mott, A.G.; Ketchel, B.P. General optical limiting requirements. In Nonlinear Optical Liquids for Power Limiting and Imaging; SPIE: Cergy-Pontoise, France, 1998; pp. 24–29. [Google Scholar]
  60. Zhang, R.F.; Guo, D.Z.; Zhang, G.M. Strong saturable absorption of black titanium oxide nanoparticle films. Appl. Surf. Sci. 2017, 426, 763–769. [Google Scholar] [CrossRef]
  61. Divya, S.; Nampoori VP, N.; Radhakrishnan, P.; Mujeeb, A. Morphology dependent dispersion of third-order optical nonlinear susceptibility in TiO2. Appl. Phys. A 2014, 114, 1079–1084. [Google Scholar] [CrossRef]
  62. Long, H.; Chen, A.; Yang, G.; Li, Y.; Lu, P. Third-order optical nonlinearities in anatase and rutile TiO2 thin films. Thin Solid Film. 2009, 517, 5601–5604. [Google Scholar] [CrossRef]
  63. Irimpan, L.; Krishnan, B.; Nampoori VP, N.; Radhakrishnan, P. Luminescence tuning and enhanced nonlinear optical properties of nanocomposites of ZnO–TiO2. Colloid Interface Sci. 2008, 324, 99–104. [Google Scholar] [CrossRef]
Nanomaterials 14 01940 g001
Figure 1. Laser ablation setup for preparing TiO2 NPs colloids via a 532-nm Nd:YAG laser.
Figure 1. Laser ablation setup for preparing TiO2 NPs colloids via a 532-nm Nd:YAG laser.
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Figure 2. Z-scan experimental setup. L, convex lens; A, attenuator; I, Iris; S, TiO2 NPs sample; PM, power meter.
Figure 2. Z-scan experimental setup. L, convex lens; A, attenuator; I, Iris; S, TiO2 NPs sample; PM, power meter.
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Figure 3. Spectral absorption of TiO2 NP colloidal solutions as a function of wavelength at different ablation times.
Figure 3. Spectral absorption of TiO2 NP colloidal solutions as a function of wavelength at different ablation times.
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Figure 4. (a–c) show the energy band gaps that were obtained by extrapolating the straight line of Tauc’s plot of TiO2 nanocolloids at various ablation times.
Figure 4. (a–c) show the energy band gaps that were obtained by extrapolating the straight line of Tauc’s plot of TiO2 nanocolloids at various ablation times.
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Figure 5. (a–c) depict the size distributions of TiO2 NPs colloids that were synthesized using various ablation times of 5 min, 10 min, and 15 min, respectively.
Figure 5. (a–c) depict the size distributions of TiO2 NPs colloids that were synthesized using various ablation times of 5 min, 10 min, and 15 min, respectively.
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Figure 6. EDX spectra of the TiO2 NP colloid and inset ZAF Method Standardless Quantitative Analysis of TiO2 NPs.
Figure 6. EDX spectra of the TiO2 NP colloid and inset ZAF Method Standardless Quantitative Analysis of TiO2 NPs.
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Figure 7. (a–c) OA Z-scan measurements of TiO2 NP colloids with different ablation times and incident powers at an 800 nm excitation wavelength. (d) Dependence of the NLA coefficient on the incident laser power at an 800 nm excitation wavelength.
Figure 7. (a–c) OA Z-scan measurements of TiO2 NP colloids with different ablation times and incident powers at an 800 nm excitation wavelength. (d) Dependence of the NLA coefficient on the incident laser power at an 800 nm excitation wavelength.
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Figure 8. (a–c) OA Z-scan experimental data of TiO2 NP colloidal solutions with different ablation times and excitation wavelengths at 1 W incident power. (d) Relationship between the excitation wavelength and NLA coefficient at 1 W incident laser power.
Figure 8. (a–c) OA Z-scan experimental data of TiO2 NP colloidal solutions with different ablation times and excitation wavelengths at 1 W incident power. (d) Relationship between the excitation wavelength and NLA coefficient at 1 W incident laser power.
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Figure 9. (a) OA Z-scan experimental data of TiO2 NP colloidal solutions with different ablation times and a constant excitation wavelength of 800 nm and an incident power of 1 W. (b) Dependence between the ablation time and the NLA coefficient.
Figure 9. (a) OA Z-scan experimental data of TiO2 NP colloidal solutions with different ablation times and a constant excitation wavelength of 800 nm and an incident power of 1 W. (b) Dependence between the ablation time and the NLA coefficient.
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Figure 10. (a–c) CA Z-scan measurements for TiO2 NP colloids at different incident powers and ablation times at an excitation wavelength of 800 nm. The symbols represent the experimental data, and the solid curves are the fits obtained via Equations (6) and (7). (d) Relationship between the NLR index and incident power at each ablation time.
Figure 10. (a–c) CA Z-scan measurements for TiO2 NP colloids at different incident powers and ablation times at an excitation wavelength of 800 nm. The symbols represent the experimental data, and the solid curves are the fits obtained via Equations (6) and (7). (d) Relationship between the NLR index and incident power at each ablation time.
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Figure 11. (a–c) CA Z-scan transmission of TiO2 NP colloids at different excitation wavelengths and ablation times; (d) relationship values of n2 for TiO2 NP colloidal solutions with different ablation times at 1 W incident power. The dots represent the experimental data, and the solid curves are linear fits.
Figure 11. (a–c) CA Z-scan transmission of TiO2 NP colloids at different excitation wavelengths and ablation times; (d) relationship values of n2 for TiO2 NP colloidal solutions with different ablation times at 1 W incident power. The dots represent the experimental data, and the solid curves are linear fits.
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Figure 12. (a) Plot of CA Z-scan measurements of different ablation times of 5 min, 10 min, and 15 min at 800 nm excitation wavelength and 1 W incident power. (b) Dependence between the measured n2 and ablation time at a 1 W incident power and 800 nm excitation wavelength. The dots represent the experimental data, and the solid lines are linear fits.
Figure 12. (a) Plot of CA Z-scan measurements of different ablation times of 5 min, 10 min, and 15 min at 800 nm excitation wavelength and 1 W incident power. (b) Dependence between the measured n2 and ablation time at a 1 W incident power and 800 nm excitation wavelength. The dots represent the experimental data, and the solid lines are linear fits.
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Figure 13. Optical limiting of the TiO2 NP colloids at ablation times of 5 min, 10 min, and 15 min and an 800 nm excitation wavelength.
Figure 13. Optical limiting of the TiO2 NP colloids at ablation times of 5 min, 10 min, and 15 min and an 800 nm excitation wavelength.
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Table 1. The linear and nonlinear optical parameters of TiO2 NP colloids with different ablation times at an excitation wavelength of 800 nm and an incident power of 1 W.
Table 1. The linear and nonlinear optical parameters of TiO2 NP colloids with different ablation times at an excitation wavelength of 800 nm and an incident power of 1 W.
Ablation Time (min)TiO2 Conc. mg/LAverage Size (nm)n0α (m−1)n2 × 10−15 cm2/W ꞵ × 10−9 cm/W I m χ 3 × 10−13 esu R e χ 3 × 10−16 esu χ ( 3 ) × 10−13 esuFOM × 10−11 esu.cmSaturation Input Power (W)
51.919.111.354.385.961.727.938.537.931.81
102.911.961.61116.48213.1111.0713.111.20.9
154.358.331.538.77.882.1212.5512.7912.551.440.8
Table 2. Comparison between the current study and previous studies of TiO2 NPs.
Table 2. Comparison between the current study and previous studies of TiO2 NPs.
SamplePreparation MethodPhaseWavelength (nm)Pulse DurationRepetition Rate (Hz) ꞵ (cm/W) n2 (cm2/W)Ref.
Black TiO2Cathodic plasma electrolysisFilm53220 ps1000−4.9 × 10−6-[60]
TiO2ChemicalLiquid5327 ns102.206 × 10−83.477× 10−13[61]
TiO2Laser ablationLiquid632.8--0.34 × 10−3−4.3× 10−8[36]
TiO2ChemicalLiquid10647 ns10−1.53 × 10−62.35× 10−13[10]
TiO2Laser ablationLiquid800150 fs80 × 1066.2 × 10−8-[37]
TiO2-Film80050 fs −6.2 × 10−9−6.32 × 10−13[62]
TiO2ChemicalLiquid5327 ns1077.8 × 10−92.9 × 10−13[63]
TiO2Laser ablationLiquid800100 fs80 × 1062.12 × 10−97.88 × 10−15This work
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Abdel Samad, F.; Ali Jasim, M.; Mahmoud, A.; Abd El-Salam, Y.; Qayyum, H.; Apsari, R.; Mohamed, T. Experimental Investigation of the Optical Nonlinearity of Laser-Ablated Titanium Dioxide Nanoparticles Using Femtosecond Laser Light Pulses. Nanomaterials 2024, 14, 1940. https://doi.org/10.3390/nano14231940

AMA Style

Abdel Samad F, Ali Jasim M, Mahmoud A, Abd El-Salam Y, Qayyum H, Apsari R, Mohamed T. Experimental Investigation of the Optical Nonlinearity of Laser-Ablated Titanium Dioxide Nanoparticles Using Femtosecond Laser Light Pulses. Nanomaterials. 2024; 14(23):1940. https://doi.org/10.3390/nano14231940

Chicago/Turabian Style

Abdel Samad, Fatma, Mohammed Ali Jasim, Alaa Mahmoud, Yasmin Abd El-Salam, Hamza Qayyum, Retna Apsari, and Tarek Mohamed. 2024. "Experimental Investigation of the Optical Nonlinearity of Laser-Ablated Titanium Dioxide Nanoparticles Using Femtosecond Laser Light Pulses" Nanomaterials 14, no. 23: 1940. https://doi.org/10.3390/nano14231940

APA Style

Abdel Samad, F., Ali Jasim, M., Mahmoud, A., Abd El-Salam, Y., Qayyum, H., Apsari, R., & Mohamed, T. (2024). Experimental Investigation of the Optical Nonlinearity of Laser-Ablated Titanium Dioxide Nanoparticles Using Femtosecond Laser Light Pulses. Nanomaterials, 14(23), 1940. https://doi.org/10.3390/nano14231940

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