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The optical limiting (OL) properties of single-layer graphene dispersions at 532 and 1064 nm wavelengths were investigated using a nanosecond laser. The experimental results show that the activating threshold of the single-layer graphene dispersed in chlorobenzene (CB) is lower than that of single-walled carbon nanotubes (SWNTs) by a factor of 10....
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... In recent years, carbon-based nanomaterials, including carbon black suspensions [8], carbon dots (CD) [9], carbon nanotubes (CNTs) [10][11][12][13], and graphene [14,15] have attracted much attention as OL materials. It has been demonstrated that the OL effect of carbonbased materials originates mainly from the thermal-induced nonlinear scattering effect, and the limiting range covers wavelengths from the visible to the near-infrared region [16]. ...
... Compared with N-CD-Pt, rGO-TiO 2 , Au-graphene nanocomposites, CNT's, indium phthalocyanine/SWCNTs, MWCNTs/TiO 2 , and CNH, the porous carbon materials exhibit a more intentional OL effect. [29] In previous research, the OL effect of carbon materials mainly comes from nonlinear absorption or nonlinear scattering [13]. For example, L. Vivien et al. indicated that the OL mechanism of carbon nanotubes is mainly sourced from strong nonlinear scattering, which is caused by the growth of solvent bubbles and the sublimation of nanotubes. ...
With the wide application of intense lasers, the protection of human eyes and detectors from laser damage is becoming more and more strict. In this paper, we study the nonlinear optical limiting (OL) properties of porous carbon with a super large specific surface area (2.9 × 103 m2/g) using the nanosecond Z-scan technique. Compared to the traditional OL material C60, the porous carbon material shows an excellent broadband limiting effect, and the limiting thresholds correspond to 0.11 J/cm2 for 532 nm and 0.25 J/cm2 for 1064 nm pulses, respectively. The nonlinear scattering experiments showed that the OL behavior was mainly attributed to the nonlinear scattering effect, which is caused by the rapid growth and expansion of bubbles in the dispersion induced by laser irradiation, and the scattered light distribution is consistent with the results of Mie’s scattering. These results suggest that porous carbon materials are expected to be applied to the field of laser protection in the future to further protect the human eye and precision optical instruments.
... Subsequently, studies on optical limiting (OL) have attracted much attention because of the need for automatic protection of optical sensors and human eyes against intense laser radiations. [1][2][3][4][5][6][7][8][9] One of the primary works in this field was done by Hughes and Wherrett, who investigated the molecular properties that are important for achieving a high-fluence optical power limiter, by using a theoretical rate equation analysis. 1 Up to now, two major mechanisms, nonlinear scattering 10,11 and nonlinear absorption [e.g., two-photon, 12 multi-photon, 13 free-carrier absorption, 14 and reverse saturable absorption (RSA) [15][16][17][18] ] have been employed to generate OL devices. ...
By presenting a theoretical steady-state rate equation analysis, we demonstrate an efficient optical power limiting in a fullerene system, which can be attributed to a reverse saturable absorption mechanism. Such limiting behavior, characterized by means of the sample's transmittance, is explained via population redistribution among singlet and triplet levels. Also, the effects of intersystem crossing and reverse intersystem crossing rates on the limiting behavior are investigated. Our numerical results show how these rates alter the optical limiting performance; indeed, the intersystem crossing has a constructive role in decreasing the optical limiting threshold. In addition, a theoretical investigation of the z-scan technique, for further characterizing the limiting properties, is presented.
... The saturable absorption of graphene with fast carrier response time (~200 fs) makes graphene a nice candidate to generate ultrahigh optical modulation; this unique characteristic is also used to produce ultrashort laser pulse [13][14][15]. In addition, low incident optical intensity is sufficient to operate the graphene-based optical modulator due to the low saturation intensity of graphene [16,17], and the damage threshold of graphene is much larger than its saturation intensity [18,19]. Consequently, the graphenebased all-optical modulator becomes a robust device in practical application. ...
Using the evanescent-wave saturation effect of hydrogen-free low-temperature synthesized few-layer graphene covered on the cladding region of a side-polished single-mode fiber, a blue pump/infrared probe-based all-optical switch is demonstrated with specific wavelength-dependent probe modulation efficiency. Under the illumination of a blue laser diode at 405 nm, the few-layer graphene exhibits cross-gain modulation at different wavelengths covering the C- and L-bands. At a probe power of 0.5 mW, the L-band switching throughput power variant of 16 μW results in a probe modulation depth of 3.2%. Blue shifting the probe wavelength from 1580 to 1520 nm further enlarges the switching throughput power variant to 24 mW and enhances the probe modulation depth to 5%. Enlarging the probe power from 0.5 to 1 mW further enlarges the switching throughput power variant from 25 to 58 μW to promote its probe modulation depth of up to 5.8% at 1520 nm. In contrast, the probe modulation depth degrades from 5.1% to 1.2% as the pumping power reduces from 85 to 24 mW, which is attributed to the saturable absorption of the few-layer graphene-based evanescent-wave absorber. The modulation depth at wavelength of 1550 nm under a probe power of 1 mW increases from 1.2% to 5.1%, as more carriers can be excited when increasing the blue laser power from 24 to 85 mW, whereas it decreases from 5.1% to 3.3% by increasing the input probe power from 1 to 2 mW to show an easier saturated condition at longer wavelength.
... Although effective, these multi-photon absorptions tend to lead to highly excited molecular states that are prone to molecular breakdown, thereby limiting the lifetime (and thus usefulness) of the limiter [18]. This problem also plagues limiters based on intensity-dependent scattering, leading to use of cascaded designs [19,20]. ...
A lumped distributed Bragg reflector (DBR)-nonlinear layer-DBR system is used to explore how nonlinear optical effects (in particular, optical limiting) are modulated by the dispersive character of the (optically linear) DBR. A three-level quantum optics model of the nonlinear layer is used to find self-consistent numerical solutions to the (nonlinear) optical transport in the composite system. We find that the intensity dependence of the real part of the index can be combined with the dispersion in the (linear) DBR to cause optical limiting even for materials that have only a saturated absorber (two-level) response.
... It's noteworthy that the OL behaviors of graphene nanostructures measured in organic solvents are related to the viscosity and the polarity of the host solvent (the viscosities of the solvents follow the order: water > N,N-dimethylformamide (DMF) > tetrahydrofuran (THF) > DMF-CS 2 > acetonitrile (ACN) > CS 2 ; while their polarities (dielectric constant) follow water > DMF > ACN > DMF-CS 2 > THF > CS 2 ) [196,197]. As an example, the single layer graphene dispersed in chlorobenzene (CB) shows very low activating threshold for nanosecond laser pulses at both 532 and 1064 nm wavelengths [198]. When the input fluence is higher than 0.1 J cm À2 , the transmittance of graphene in CB is much lower than graphene in N-methyl-2pyrrolidinone (NMP), while their scattered signal intensities are almost same. ...
... Although many semiconductors such as GaAs also show saturable absorption, only those whose saturable intensity is much lower than the optical damage threshold can be used in practical devices [48]. Optical devices based on graphene with high optical damage threshold have been fabricated [49]. Moreover, in saturable absorption devices, compared with single-walled carbon nanotubes (SWNTs) [17] or semiconductor saturable absorber mirrors (SESAMs) [50], graphene is much easier to be fabricated without band gap engineering or chirality (diameter) control. ...
Optical modulators (OMs) are a key device in modern optical systems. Due to its unique optical properties, graphene has been recently utilized in the fabrication of optical modulators, which promise high performance such as broadband response, high modulation speed, and high modulation depth. In this paper, the latest experimental and theoretical demonstrations of graphene optical modulators (GOMs) with different structures and functions are reviewed. Particularly, the principles of electro-optical and all-optical modulators are illustrated. Additionally, the limitation of GOMs and possible methods to improve performance and practicability are discussed. At last, graphene terahertz modulators (GTMs) are introduced.
... Much effort has been devoted to the development of OL materials with large nonlinear responses. These materials include fullerenes [1,2], single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs [3][4][5]), graphene [6][7][8][9], carbon black suspensions [10,11], porphyrins and phthalocyanines [12][13][14][15]. ...
The optical limiting (OL) properties of carbon nanotubes (CNTs) with different lengths were investigated using a nanosecond pulse laser. Experimental results showed that the OL behaviour of CNTs dispersion with shorter tube length and smaller bundle size was much better than for those with a longer length and larger bundle size. The nonlinear scattering experiments and numerical modelling results indicated that forward scattering light played an important role in deteriorating the OL property of longer CNTs. By removing parts of the forward scattering light using an aperture placed before the detector, the OL properties of materials could be improved.
This paper provides an experimental study on development of heat transfer and pressure drop of hybrid nanofluids flow in coil
heat exchanger of the solar collector in Iraq. The two methods were utilized in this article to enhance heat transfer and pressure drop.
Firstly, spirally coiled tube heat exchange was tested in evacuated tube solar collector then the pure water was replaced with
different concentration of hybrid nanoparticles fluids ranging from (1 – 5 vol %). The hybrid nanoparticles used in this study
(copper Cu (40nm) + silver Ag (40nm)) and (Aluminum Oxide Al2O3 (80nm)+ Zirconium oxide ZrO2 (80nm)) as well as the pure
water. The effects of various factors together with hybridnanofluid temperature, concentration, hybridnanoparticle type and flow
Reynolds number, on pressure drop and heat transfer coefficient of the flow, has been studied. The results show 50.76 % increment
in heat transfer coefficient Cu + Ag – Pw and 38.56 % for Al2O3+ ZrO2 – Pw at the concentration of 5 vol% compared with the pure
water. The pressure drop and coefficient of heat transfer are increased by using hybrid nanofluids (Cu+ Ag– Pw, Al2O3+ ZrO2 –
Pw) instead of the pure water. In addition to the results indicated that using the heat exchanger with helically coiled tube and shell,
the heat transfer performance is improved moreover the pressure drop enhancement because of the curvature of the coil tube. The
most increase of 38.42% (Cu + Ag – Pw) and 25.41% (Al2O3 + ZrO2 – Pw) in Nusselt number ratio for several of Reynolds
numbers of 200 – 800. This article decided that the hybrid nanofluid behaviors are near to common Newtonian fluids through the
relationship between shear rate and viscosity. Moreover to overall performance index are used to give the corresponding heat
transfer method and flow. The type and size hybridnanoparticles, as well as synergistic impact, play an important function within
the enhancement of heat transfer rate.
PbS quantum dots with nearly monodisperse size (∼3.8 nm) were successfully fabricated via a cation-exchange method, and were investigated by the z-scan technique with 532 nm laser radiation. The PbS quantum dots exhibited high optical nonlinearity with nonlinear absorption coefficient, nonlinear refractive index, and nonlinear susceptibility of 2.93 × 10⁻⁹ m/W, 1.12×10⁻⁹ esu, and 1.90 × 10⁻¹⁰ esu, respectively, and with optical limiting threshold value of 1.5 J/ cm2 under experimental conditions.
