Optical Limit Research Articles

Tailoring of nonlinear optical and optical limiting performance through morphology: PbTe nanostructures in liquid and solid-state matrice

Advances in nanotechnology have provided opportunities to precisely control the morphology of nanostructures and the ability to explore their structure–property relationships. In this work, well-defined PbTe nanostructures with different morphologies were prepared by a one-step microwave synthesis process. The synthesized PbTe nanostructures were incorporated into solid-state silica gel glass matrices by a facile sol-gel approach for application as optical limiters. Nonlinear optical (NLO) and optical limiting (OL) properties were measured by 532-nm laser pulses with a pulse duration of 35 ps to understand the relationship between the NLO properties and the morphology of six PbTe nanostructures (i.e., nanosheets, nanorods, particle assemblies, hoppercubes, nanocubes, and nanoflowers). The PbTe nanostructures had notably different NLO and OL properties, which strongly correlated with the structural characteristics both in liquid and gel glass matrices. The NLO mechanism was also explored and attributed to excited state absorption, which relates to the size and morphology of the nanostructures. The PbTe particle assemblies had the strongest NLO response under laser irradiation, whereas the PbTe nanocubes had the weakest response, both in liquid and a solid-state gel glass matrices. Importantly, a large OL effect was observed for PbTe particle assemblies doped into silica gel glasses, where the OL threshold surpassed that of previously reported semiconductor nanocrystals. This result suggests these materials can be considered as potential candidate for practical applications in the fields of nonlinear optics. Our work provides insights into the morphology dependence of NLO properties and a strategy to optimize the performance of nanostructures through structural design.

Enhanced nonlinear absorption and photoluminescence properties of Zn, Fe, Cu, V and Ni doped MoO3 transition metal oxide thin films

Abstract In this study, the effect of the dopant element on the linear, nonlinear absorption and optical limiting properties of ultrasonically sprayed MoO3 thin films is presented. The linear optical results showed an increase with the density of the defect states in the bandgap with doping, in conjunction with a decrease in bandgap energy and an increase in Urbach energy. Broad photoluminescence emissions are detected in the range of 350 and 600 nm, decreasing in intensity by doping. To reveal the defect states effects’ on the nonlinear absorption (NA) behavior, OA Z-scan data were analyzed with two theoretical models considering only two photon absorption (2PA) (model 1), and one photon absorption (OPA), 2PA and free carrier absorption (model 2). The NA behavior is observed and found to get enhanced by increasing input intensity and doping atoms due to generation of new oxygen vacancies and formation of further defect states. The NA coefficient values of the thin films in model 2 are 100 times higher than that of 2PA coefficient values in model 1. This result revealed the strong effect of defect states on the NA behavior. Among the investigated dopant atoms, Cu resulted in enhanced NA due to the higher density of defect states. While the genuine 2PA is the dominant NA mechanism for V and Fe doped MoO3 thin films, OPA and 2PA are the dominant NA mechanisms for the Ni, Zn and Cu doped MoO3 thin films due to their higher concentration of defect states. Cu-doped MoO3 thin film has a lower optical limiting threshold of 0.026 mJ/cm2 due to its enhanced NA behavior. Considering the results obtained, this study opens the door to the potential of doped MoO3 thin films to be used as optical limiters in the visible wavelength region.

Compensating losses in polariton propagation with synthesized complex frequency excitation.

Surface plasmon polaritons and phonon polaritons offer a means of surpassing the diffraction limit of conventional optics and facilitate efficient energy storage, local field enhancement and highsensitivity sensing, benefiting from their subwavelength confinement of light. Unfortunately, losses severely limit the propagation decay length, thus restricting the practical use of polaritons. While optimizing the fabrication technique can help circumvent the scattering loss of imperfect structures, the intrinsic absorption channel leading to heat production cannot be eliminated. Here, we utilize synthetic optical excitation of complex frequency with virtual gain, synthesized by combining the measurements made at multiple real frequencies, to compensate losses in the propagations of phonon polaritons with dramatically enhanced propagation distance. The concept of synthetic complex frequency excitation represents a viable solution to the loss problem for various applications including photonic circuits, waveguiding and plasmonic/phononic structured illumination microscopy.

On‐Chip Optical Power Limiter for Quantum Communications

AbstractThis article presents an on‐chip optical power limiter that utilizes the thermo‐optical defocusing effect. A pair of input and output waveguides is designed to mimic emitting and receiving antennas. The waveguides are separated by a free‐space region filled with poly‐methyl‐meth‐acrylate (PMMA) material, which has a negative thermal‐optic coefficient that causes a decrease in refractive index with an increase in temperature. As the power in the input waveguide increases, the refractive index of the free‐space region decreases, which in turn increases the radiated beam's divergence angle with respect to input power. The empirical findings demonstrate that the non‐linear divergence angle can be written as , where θ0 represents the divergence angle of the equivalent Gaussian beam, k is a waveguide‐specific constant, and P is the input power. The edge of the receiving waveguide is tapered to adjust the coupling of the divergent beam to the output waveguide. The taper width is optimized to minimize insertion loss. The devices are two orders lengthwise smaller compared to the bulk demonstration, and they exhibit low loss ranging from 0.2 to 10 dB.

Nonlinear optical and photostability studies of Allamanda Cathartica extract dye

In this work, we report the linear and nonlinear optical properties of a natural dye extracted from the flowers of the tropical plant Allamanda Cathartica. PVA films containing the dye in varying concentrations were prepared using the drop-casting technique. The functional groups of the major pigment in the dye were verified using FTIR spectroscopy. UV–visible spectroscopy was carried out to confirm the presence of various carotenoid pigments in the dye. Nonlinear optical characterization was performed by employing the z-scan technique using Nd: YAG laser with a wavelength of 532 nm and 9 ns pulse duration. The dye exhibited significant optical limiting properties due to reverse saturable absorption, thus making them potential candidates for optical limiting. The photostability of the dye was studied using photodegradation rate kinetics to determine its reliability. The dye provides an environmentally friendly and economical alternative to the standard synthetic materials used as optical limiters.

Effect of rare earth doped perovskite on the structural, linear/nonlinear optical properties of the fabricated PVA/CMC polymeric blends for optical limiting applications

Poly (vinyl alcohol) and carboxy methyl cellulose, PVA/CMC doped with (1, 5,8) Wt% of Lanthanum Dysprosium aluminate (LaDyAlO3) nanoparticles were prepared via traditional solution casting method. The influence of the concentration of LaDyAlO3 nanoparticles on optical and spectroscopic properties was investigated. The molecular and the crystalline structure of PVA/CMC/LaDyAlO3 polymer nanocomposites were obtained through the Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The optical characteristics were investigated via UV–Visible spectrophotometer. For all samples, the absorption coefficient was determined. The direct and indirect allowed transitions have a multi graded bandgap structure. The thermal stability was investigated and the activation energy was determined which is found to be dependent on the concentration of LaDyAlO3 nanoparticles. Furthermore, the PVA/CMC/LaDyAlO3 (5 wt%) demonstrated excellent optical limiting threshold properties at low transmission value which is a favorable result for optoelectronic devices like optical limiters, long-lasting optical filters and photonic devices like organic/Polymer LEDs, Optical switches and perovskite solar cells. Also the Reverse saturable absorption is transformed to Saturable absorption for PVA/CMC/LaDyAlO3 (8 wt%) which makes it applicable for saturable absorbers and optical switches and many others etc.

Helicity-dependent optical control of the magnetization state emerging from the Landau-Lifshitz-Gilbert equation

It is well known that the Gilbert relaxation time of a magnetic moment scales inversely with the magnitude of the externally applied field, H, and the Gilbert damping, α. Therefore, in ultrashort optical pulses, where H can temporarily reach high amplitudes, the Gilbert relaxation time can momentarily be extremely short, reaching even picosecond timescales. Here we show that for strong enough ultrashort pulses, the magnetization can respond within the optical cycle such that the optical control of the magnetization emerges by merely considering the optical magnetic field in the Landau-Lifshitz-Gilbert (LLG) equation. Surprisingly, when circularly polarized optical pulses are introduced, an optically induced helicity-dependent torque results. We find that the strength of the interaction is determined by η=αγH/fopt, where fopt and γ are the optical frequency and gyromagnetic ratio, respectively. Our results illustrate the generality of the LLG equation to the optical limit and the pivotal role of the Gilbert damping in the general interaction between optical magnetic fields and spins in solids. Published by the American Physical Society 2024

Laser manufacturing of spatial resolution approaching quantum limit

Atomic and close-to-atom scale manufacturing is a promising avenue toward single-photon emitters, single-electron transistors, single-atom memory, and quantum-bit devices for future communication, computation, and sensing applications. Laser manufacturing is outstanding to this end for ease of beam manipulation, batch production, and no requirement for photomasks. It is, however, suffering from optical diffraction limits. Herein, we report a spatial resolution improved to the quantum limit by exploiting a threshold tracing and lock-in method, whereby the two-order gap between atomic point defect complexes and optical diffraction limit is surpassed, and a feature size of <5 nm is realized. The underlying physics is that the uncertainty of local atom thermal motion dominates electron excitation, rather than the power density slope of the incident laser. We show that the colour centre yield in hexagonal boron nitride is transformed from stochastic to deterministic, and the emission from individual sites becomes polychromatic to monochromatic. As a result, single colour centres in the regular array are deterministically created with a unity yield and high positional accuracy, serving as a step forward for integrated quantum technological applications.

Third order nonlinearity examined by pulsed and CW lasers: an organic urea barbituric acid (UBA) single crystal for optical limiting application with DFT study

Bulk size of urea barbituric acid single crystal which has not been reported earlier was successfully grown by slow evaporation solution growth method. Single-crystal XRD brought out the lattice constant and the crystal system is observed to be monoclinic with space group P. Functional group of UBA were determined by FT-IR. UBA crystal is entirely visible from 270 to 900 nm with linear optical energy gap value to be 4.50 eV. The observed HOMO–LUMO energy gap was 5.21 eV. Thermally, UBA crystal is found to be stable up to 184˚°C. The Cp value of UBA increases from 1.21 to 1.58 J g−1K−1 with the temperature difference from 30 to 100˚°C. UBA shows good photoconductive nature and it found to be positive and Laser Damage Threshold (LDT) value of UBA crystal is 0.97 GW cm−2. Hardness testing confirms that UBA crystal belongs to soft nature category. Dielectric properties of UBA crystal are studied as a function of frequency and temperature. Third order NLO properties of the UBA crystal were studied under CW and pulsed lasers (ns) regimes using Z-scan technique. Good Optical limiting (OL) response (2.2860 х 1012 W/m2) confirms the efficiency of UBA crystal to be used as optical limiters for protection towards short pulse lasers.

Clamshell-type bis-phthalocyanines as colour-changing optical limiters: TDDFT modelling of electrically induced absorption for real-time colour indication of optical limiter efficiency in nonlinear laser protection.

This paper presents an innovative method for assessing the performance of optical limiters, which are devices that protect humans against laser radiation. The essence of the process is that with increasing laser radiation intensity, the colour of nonlinear absorbers, the working components of these devices, can change in contrast to the original one, which was demonstrated by quantum-chemical linear response time-dependent density functional theory (LR-TDDFT) for molecules excited by static electric finite fields (FF) within the general DFT (density functional theory) approach. Modelling was carried out on clamshell-type bis-phthalocyanines, in which the macrocycles are strapped by a cyclotriphosphazene spacer, suitable candidates for creating nonlinear optical (NLO) dyes for laser technology. As calculations have shown, acting as a "litmus test", these incredibly stable macrocyclic compounds are not only capable of providing laser protection but also give a real-time visual indication of the protection through changes in the colour of the dye, which correlate with different levels of laser power. Such indication can visually show the current state of optical limiters in practice, allowing users to easily determine whether the limiter material provides adequate protection or already requires replacement. A modelling protocol and program code for calculating the colour of a substance based on its absorption spectrum are presented.

Nuclear reaction cross sections and the optical potentials and for the n-12C and N-12C scattering

In this talk we first discuss total cross sections for the system n-12C in the incident energy range 20-500 MeV, calculated with a phenomenological optical potential and the optical model. We compare with calculations done with the eikonal model using the same potential and a single folding potential in the optical limit. Several single folding potentials are obtained using 12C densities from different models. These potentials are sensitive to the density used and none of them reproduces the characteristics of the phenomenological potential nor the cross section results. We then discuss nucleus-nucleus potentials and reaction cross sections for some projectiles on 12C within the eikonal formalism. We find that single folded projectile-target imaginary potentials and double folded potentials can produce similar energy dependence of the reaction cross sections but the single folding results agree better with experimental data provided the radius parameter of the phenomenological n-target potential is allowed to be energy dependent. We conclude that a single folding nucleusnucleus potential build on a phenomenological nucleon-nucleus potential can constitute an interesting and useful alternative to double folding potentials.

Study of two-photon absorption and excited-state dynamics of coumarin derivatives: the effect of monomeric and dimeric structures.

Intramolecular charge transfer (ICT) and π-electron delocalization are two key factors affecting the nonlinear optical absorption of organic molecules. To clarify the different influences of ICT and π-electron delocalization on two-photon absorption (TPA) and excited-state absorption (ESA), monomeric coumarin C1 and dimeric coumarin C2 are synthesized and studied. Transient absorption spectroscopy (TAS) analysis of these coumarin derivatives in solvents of varying polarities describes the polarity-dependent excited-state dynamics and reveals the ESA signals of the charge transfer state (CTS) and local excited state (LES) with different spectral features. Femtosecond broadband Z-scan experiments indicate that dimeric coumarin C2 has a more significant TPA response than monomeric coumarin C1 in the near-infrared region. Natural transition orbital (NTO) analysis further theoretically characterizes the electron transition feature induced by TPA. Our results reveal that the TPA of these coumarin derivatives can be significantly enhanced by expanding π-electron delocalization, but their ESA is mainly dominated by ICT performance. This study indicates that coumarin derivatives will exhibit extremely broad application prospects in the field of ultrafast optical limiting (OL) through reasonable molecular design.

Breaking the optical efficiency limit of virtual reality with a nonreciprocal polarization rotator

Breaking the optical efficiency limit of virtual reality with a nonreciprocal polarization rotator

Quantification of membrane geometry and protein sorting on cell membrane protrusions using fluorescence microscopy.

Plasma membranes are flexible and can exhibit numerous shapes below the optical diffraction limit. The shape of cell periphery can either induce or be a product of local protein density changes, encoding numerous cellular functions. However, quantifying membrane curvature and the ensuing sorting of proteins in live cells remains technically demanding. Here, we demonstrate the use of simple widefield fluorescence microscopy to study the geometrical properties (i.e., radius, length, and number) of thin membrane protrusions. Importantly, the quantification of protrusion radius establishes a platform for studying the curvature preferences of membrane proteins.

Exploring the optical management and efficiency limit of luminescent solar concentrators based on advanced luminophores

This work provides new insights for predicting the efficiency limit of LSCs. The use of tandem LSCs based on luminophores of singlet-fission and CuInSe2/ZnS is considered a promising method to achieve optimal efficiency.

Reflective nonlinear optical limiter design based on coupled Tamm plasmon polaritons and optical Kerr effect

With the increasing applications of high-power lasers in fields such as laser fabrication, laser measurement, laser therapy and scientific research, there is an increasing demand for high-performance nonlinear optical limiters (NOLs) to protect human eyes and optical sensitive elements. Here we propose a brand-new approach to design a reflective NOL with an ultra-wide stop band based on coupled Tamm plasmon polaritons (TPPs) and optical Kerr effect. The NOL permits the transmission of weak signal light at the desired wavelength while effectively blocking potentially harmful or accidentally intense lasers at the same wavelength to avoid damage to sensitive optical elements or human eyes. The design can be optimized for the desired operating wavelength and threshold intensity by using different dielectric layers. In a proof-of-concept design, taking the 1064 nm laser as an example, we design a NOL capable of dynamically adjusting its transmission in response to laser intensity. The NOL has a high transmission of 85.21 % at weak light (intensity less than 0.20 MW/cm2), and the transmission can be rapidly reduced to 1.39 % when the incident light intensity increases to 60.37 MW/cm2. Furthermore, the broad stop band effectively safeguards the limiter from potential damage caused by intense light at different wavelengths. Our proposed limiter exhibits an exceptionally wide stop band range spanning from 0.5 ∼ 20 µm, nearly 30 times broader than conventional reflective NOLs. The proposed NOL design scheme provides a new promising method to design an excellent reflective NOL at the desired wavelength.

Optical Limiting Properties of DNA Biopolymer Doped with Natural Dyes.

The high-power lasers have important implications for present and future light-based technologies; therefore, the protection measures against their high-intensity radiation are extremely important. Currently, a great deal of interest is directed towards the development of new nonlinear optical materials for passive optical limiters, which are used to protect the human eye and sensitive optical and optoelectronic devices from laser-induced damage. Biopolymers doped with natural dyes are emerging as a new class of optical materials with interesting photosensitive properties. In this paper, the optical limiting capability of deoxyribonucleic acid bio-polymer functionalized with Turmeric natural dye has been demonstrated for the first time, to the best of our knowledge. The experimental investigation of the optical limit has been done by the Intensity-scan method in the NIR spectral domain at the important telecommunication wavelength of 1550 nm, using ultrashort laser pulses (~120 fs). Several optical properties of this natural dye are presented and discussed. The values of the optical transmittance in the linear regime, the saturation intensity of the nonlinear transmittance curves, and the coefficient of the nonlinear absorption have been determined. The influence of the DNA biopolymer and natural dye concentration on the optical limiting properties of the investigated biomaterials is reported and discussed. The photostability and thermal stability of the investigated solutions have also been evaluated by monitoring the temporal decay of the normalized absorption spectra under illumination with UVA light and heating, respectively. Our results evidence the positive influence of the DNA, which embeds Turmeric natural dye, on the optical limiting functionality itself and on the photostability and thermal stability of this novel material. The performed study reveals the potential of the investigated novel biomaterial for applications in nonlinear photonics, in particular in optical limiting.

Effect of π-extension and halogenation on the optical limiting properties of meso-pyrenylBODIPYdyes

The lack of suitable optical limiters that cover the entire UV-visible-NIR region has motivated research to identify novel efficient and stable optical limiting materials. There has been a strong focus on attenuating the second harmonic of Nd:YAG pulsed lasers at 532 nm on the nanosecond timescale. The photophysicochemical processes of a series of mono- and di-(4-dimethylamino)styryl-meso-pyrenylBODIPY and mono- and di-(4-dimethylamino)buta-1,3-dienyl-meso-pyrenylBODIPY dyes were studied by UV-visible absorption and fluorescence emission spectroscopy, and by determining the fluorescence and triplet state lifetimes. Z-scan measurements were carried out at a fixed concentration of 10 [Formula: see text]M so that the effective nonlinear coefficients, third-order susceptibilities, second-order hyperpolarizabilities and limiting fluences of the dyes can be compared and trends in the structure-property relationships for these optical limiting parameters can be identified.

Realization of photon correlations beyond the linear optics limit.

Linear optical transformations of multiple single-photon inputs are fundamental for the development of photonic quantum technologies. Various nonclassical correlations can already be observed directly in states generated using only single-photon inputs and linear optics transformations. However, some quantum correlations require additional operations, and states that exhibit such correlations are classified as non-Fock states. Here, we demonstrate the generation of a two-photon three-mode non-Fock state that exhibits conditional quantum coherences that can only be achieved by non-Fock states. We determine the fidelity of the non-Fock state based on experimentally observed conditional visibilities that characterize the state and compare the result to the fidelity bounds for different classes of Fock and non-Fock states. Our experimental verification of the non-Fock character of the state provides insights into the technological requirements needed to achieve nonclassical correlations in multiphoton quantum optics.

XMM-Newton-discovered Fast X-ray Transients: host galaxies and limits on contemporaneous detections of optical counterparts

ABSTRACT Extragalactic fast X-ray transients (FXTs) are a class of soft (0.3–10 keV) X-ray transients lasting a few hundred seconds to several hours. Several progenitor mechanisms have been suggested to produce FXTs, including supernova shock breakouts, binary neutron star mergers, or tidal disruptions involving an intermediate-mass black hole and a white dwarf. We present detailed host studies, including spectroscopic observations of the host galaxies of seven XMM-Newton-discovered FXTs. The candidate hosts lie at redshifts 0.0928 &amp;lt;z &amp;lt; 0.645 implying peak X-ray luminosities of 1043 erg s−1&amp;lt;LX &amp;lt; 1045 erg s−1 and physical offsets of 1 kpc &amp;lt; rproj &amp;lt; 22 kpc. These observations increase the number of FXTs with a spectroscopic redshift measurement by a factor of 2, although we note that one event is re-identified as a Galactic flare star. We infer host star formation rates and stellar masses by fitting the combined spectroscopic and archival photometric data. We also report on a contemporaneous optical counterpart search to the FXTs in Pan-STARRS and ATLAS by performing forced photometry at the position of the FXTs. We do not find any counterpart in our search. Given our constraints, including peak X-ray luminosities, optical limits, and host properties, we find that XRT 110 621 is consistent with an supernova shock breakout (SN SBO) event. Spectroscopic redshifts of likely host galaxies for four events imply peak X-ray luminosities that are too high to be consistent with SN SBOs, but we are unable to discard either the binary neutron star or white dwarf–intermediate-mass black hole tidal disruption event scenarios for these FXTs.