Investigation of optical limiting in iron oxide nanoparticles

Nonlinear optical properties in chiral copper oxide nanosheets

Chiral transition metal oxides (TMOs) are in the forefront of research as potential active materials in various optoelectronic applications. However, the nonlinear optical (NLO) properties of the chiral TMOs have not been fully understood. Here, several kinds of copper oxide nanosheets capped with different chiral amino acids are synthesized. Notably, we investigate the NLO activities of these materials, including broadband second harmonic generation and transformation of nonlinear optical properties from saturable absorption to reverse saturable absorption. This work will broaden the use of chiral TMO materials in nonlinear photonic devices.

Femtosecond laser ablation in liquid synthesis of iron-oxidation nanoparticles with saturable absorption performance

"Naked" ferroferric-oxide nanoparticles (FONPs) synthesized by a femtosecond laser ablation on a bulk stainless steel in liquid were applied to the Nd: YVO₄ laser to achieve passive Q-switched pulse laser output. Without the pollution of ligand, the inherent light characteristic of "naked" FONPs was unaffected. The analysis of the morphological characteristics, dominant chemical elements, and phase composition of the FONPs showed that they were mainly composed of Fe₃O₄, which was spherical with an average diameter of 40 nm. The electron transition and orbital splitting of the iron element's octahedral center position under the laser-driven were considered the primary mechanisms of saturable absorption of Fe₃O₄ nanoparticles.

Dark Field and Coherent Anti-Stokes Raman (DF-CARS) Imaging of Cell Uptake of Core-Shell, Magnetic-Plasmonic Nanoparticles

Magnetic-plasmonic, Fe₃O₄-Au, core-shell nanoparticles are popular in many applications, most notably in therapeutics and diagnostics, and thus, the imaging of these nanostructures in biological samples is of high importance. These nanostructures are typically imaged in biological material by dark field scatter imaging, which requires an even distribution of nanostructures in the sample and, therefore, high nanoparticle doses, potentially leading to toxicology issues. Herein, we explore the nonlinear optical properties of magnetic nanoparticles coated with various thicknesses of gold using the open aperture z-scan technique to determine the nonlinear optical properties and moreover, predict the efficacy of the nanostructures in nonlinear imaging. We find that the magnetic nanoparticles coated with gold nanoseeds and thinner gold shells (ca. 4 nm) show the largest nonlinear absorption coefficient β and imaginary part of the third-order susceptibility Im χ⁽³⁾, suggesting that these nanostructures would be suitable contrast agents. Next, we combine laser dark field microscopy and epi-detected coherent anti-Stokes Raman (CARS) microscopy to image the uptake of magnetic-plasmonic nanoparticles in human pancreatic cancer cells. We show the epi-detected CARS technique is suitable for imaging of the magnetic-plasmonic nanoparticles without requiring a dense distribution of nanoparticles. This technique achieves superior nanoparticle contrasting over both epi-detected backscatter imaging and transmission dark field imaging, while also attaining label-free chemical contrasting of the cell. Lastly, we show the high biocompatibility of the Fe₃O₄ nanoparticles with ca. 4-nm thick Au shell at concentrations of 10-100 µg/mL.

Multiangle Long-Axis Lateral Illumination Photoacoustic Imaging Using Linear Array Transducer

Photoacoustic imaging (PAI) combines optical contrast with ultrasound spatial resolution and can be obtained up to a depth of a few centimeters. Hand-held PAI systems using linear array usually operate in reflection mode using a dark-field illumination scheme, where the optical fiber output is attached to both sides of the elevation plane (short-axis) of the transducer. More recently, bright-field strategies where the optical illumination is coaxial with acoustic detection have been proposed to overcome some limitations of the standard dark-field approach. In this paper, a novel multiangle long-axis lateral illumination is proposed. Monte Carlo simulations were conducted to evaluate light delivery for three different illumination schemes: bright-field, standard dark-field, and long-axis lateral illumination. Long-axis lateral illumination showed remarkable improvement in light delivery for targets with a width smaller than the transducer lateral dimension. A prototype was developed to experimentally demonstrate the feasibility of the proposed approach. In this device, the fiber bundle terminal ends are attached to both sides of the transducer’s long-axis and the illumination angle of each fiber bundle can be independently controlled. The final PA image is obtained by the coherent sum of subframes acquired using different angles. The prototype was experimentally evaluated by taking images from a phantom, a mouse abdomen, forearm, and index finger of a volunteer. The system provided light delivery enhancement taking advantage of the geometry of the target, achieving sufficient signal-to-noise ratio at clinically relevant depths.

Evolution of Nonlinear Optical Characteristics of Magnetic Nanoparticle Colloidal Suspensions after Laser-Induced Clusters

In this paper, the nonlinear optical properties of magnetic nanoparticle colloidal solutions were studied by the Z-scan technique using 25 ps laser pulses at a wavelength of 1064 nm. Our results reveal that the formed magnetic nanoparticle clusters under high incident laser intensity will greatly affect the nonlinear optical characteristics of the solution. As the intensity of the pulsed laser decreases, the reverse saturable absorption coefficient and nonlinear refractive index of the sample tend to increase. The evolution of this nonlinear characteristic only occurs in liquid suspension. This is confirmed by fixing particles on a substrate upon which the responses observed in the liquid medium are no longer present. Besides, the possibility of generating optical trapping in the focus of the laser pulses is proposed to explain our experimental results.

Mode-locked and Q-switched mode-locked fiber laser based on a ferroferric-oxide nanoparticles saturable absorber

We demonstrated an ultrafast erbium-doped fiber laser (EDFL) based on ferroferric-oxide (Fe₃O₄) nanoparticles as a saturable absorber (SA). The investigated SA was based on magnetic fluid deposited on the end face of a fiber ferrule connector. When the SA was inserted into an EDFL cavity, a stable 2.93 ps mode-locked pulse can be achieved by adjusting the intra-cavity polarization controller. The pulse had a central wavelength of 1572.39 nm and a 3 dB bandwidth of 1.39 nm. We also obtained Q-switched mode-locked pulses at 1593.4 nm. The repetition frequency and the temporal width of the Q-switched pulse envelope varied with the pump power. When the pump power reached 225 mW, the maximum average output power and the pulse envelope energy were up to 4.51 mW and 235.5 nJ. To the best of our knowledge, this is the first time that mode-locked and Q-switched mode-locked pulses have been obtained in a fiber laser based on Fe₃O₄ nanoparticles.

Design of photonic crystal nonlinear laser power limiter based on topological edge states and optical Kerr effect

We propose a novel topological photonic crystal nonlinear laser power limiter based on topological edge states and optical Kerr effect. In the proposed laser power limiter, a one-dimensional photonic crystal in topological edge state allows the relatively weak signal light with a certain wavelength to pass through with high transmission, but blocks most of the intense hostile or accidental laser with the same wavelength due to the change of topological edge state generated from optical Kerr effect. Taking a 1064 nm wavelength as an example, we have designed such a nonlinear laser power limiter corresponding to the wavelength. When the optical power density is low (less than 0.12 MW/cm²), the light transmission can reach 82.54%, and the transmission can be reduced to 1.04% when the optical power density is increased to 11.66 MW/cm². Therefore, this method provides a new promising approach to realize laser protection at the desired wavelength.

Preparation of different shaped α-Fe2O3 nanoparticles with large particles of iron oxide red

Using anions (OH⁻, Cl⁻, SO₄²⁻, NO₃⁻ and CH₃COOH⁻) as structure and surface directing agents, α-Fe₂O₃ nanoparticles with quasi cube, parallel hexahedron, irregular sphere, nanosheet and hexagon shapes were successfully prepared by utilizing larger particles of iron oxide red.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Nonlinear optical behaviour of indium-phthalocyanine tethered to magnetite or silica nanoparticles

Enhanced nonlinear optical properties (NLO) were observed for an indium phthalocyanine–magnetite nanocomposite at 532 nm compared to the performance of the bare phthalocyanine and its silica nanoparticle dyad.

Far-field Imaging of Non-fluorescent Species with Sub-diffraction Resolution

Super-resolution optical microscopy is opening a new window to unveil the unseen details on the nanoscopic scale. Current far-field super-resolution techniques rely on fluorescence as the read-out^1-5. Here, we demonstrate a scheme for breaking the diffraction limit in far-field imaging of non-fluorescent species by using spatially controlled saturation of electronic absorption. Our method is based on a pump-probe process where a modulated pump field perturbs the charge-carrier density in a sample, thus modulating the transmission of a probe field. A doughnut shape laser beam is then added to transiently saturate the electronic transition in the periphery of the focal volume, thus the induced modulation in the sequential probe pulse only occurs at the focal center. By raster scanning the three collinearly aligned beams, high-speed sub-diffraction-limited imaging of graphite nano-platelets was performed. This technique potentially enables super-resolution imaging of nano-materials and non-fluorescent chromophores, which may remain out of reach for fluorescence-based methods.

Synthesis, growth, optical, mechanical, dielectric and thermal properties of 4-chloro-4'-chlorobenzylidene aniline single crystal

The organic material 4-chloro-4'-chlorobenzylidene aniline (CCBA) was synthesized and confirmed by NMR and FTIR spectral analyses. CCBA crystal was grown from chloroform by slow evaporation at room temperature and the single crystal cell parameters were determined by single crystal X-ray diffraction method. The perfection of the grown crystal was analyzed by high resolution X-ray diffraction rocking curve analysis. Fluorescence spectrum indicated violet emission at 428 nm. The range of optical absorbance was ascertained by recording UV-vis-NIR spectrum. Load dependant microhardness measurements on this crystal revealed the mechanical behavior of the material. Stiffness constant, Meyer index and yield strength of CCBA crystal were calculated. Dielectric studies were carried out to estimate the dielectric parameters of the grown crystal in the frequency range from 100 Hz to 100 kHz. The thermal behavior of CCBA was investigated using differential scanning calorimetry (DSC) and no phase transition was identified in the temperature region 30-100°C. Further, the CCBA crystal was subjected to open aperture Z-scan studies in order to investigate the third order nonlinear optical (NLO) properties of CCBA crystal.

Facile assembly of cadmium sulfide quantum dots on titanate nanobelts for enhanced nonlinear optical properties

A facile route to assemble cadmium sulfide (CdS) quantum dots (QDs) uniformly on the surface of titanate nanobelts (TNBs) through electrostatic interactions is demonstrated. The photophysical properties of the resulting TNB-CdS nanostructured composite, including optical limiting properties, were studied using ultraviolet-visible absorption spectroscopy, photoluminescence spectroscopy, and the open aperture Z-scan technique in the nanosecond regime using a laser with a wavelength of 532 nm. The linear and nonlinear optical properties of this composite nanostructure were strongly influenced by a possible charge/energy transfer process between the QDs and TNBs. The as-prepared TNB-CdS composite offers an optical limiting effect that is superior to that of unmodified CdS QDs and TNBs. The main contributors to the enhanced optical limiting effect in the TNB-CdS composite were a combination of nonlinear scattering and increased nonlinear absorption resulting from efficient charge/energy transfer at the CdS/TNB interface.

Fe(3)O(4)-Ag nanocomposites for optical limiting:broad temporal response and low threshold

We report the observation of optical limiting in Fe(3)O(4)-Ag nanocomposites in solution. With these nanocomposites, we demonstrate that broad temporal optical limiting can be accomplished with low limiting threshold. Due to the presence of Ag nanoparticles, nonlinear scattering gives rise to enhanced optical limiting responses to 532-nm nanosecond laser pulses, with a limiting threshold comparable to carbon nanotubes. As exposed to 780-nm femtosecond laser pulses, the largest value (approximately 10(-44) cm(4)s photon(-1) or 10(6) GM) for two-photon absorption cross-sections reported to date results in superior limiting responses with a limiting threshold as low as 0.04 J/cm(2) or 100 GW/cm(2) for Fe(3)O(4)-Ag (7nm) solution in 1 cm quartz cell. The limiting threshold can be further reduced by increasing Ag particle size through plasmon enhancement or taking advantage of self-defocusing.