Photon Absorption Coefficient Research Articles

Correlation between non-linear optical parameter and structure of Li2B4O7 glasses doped with [formula omitted]ions

The glass system 90Li2B4O7+xEr2O3+(10−x)BiCl3, where 0.1 ≤ x ≤ 0.5 mol%, has been synthesized by melt quenching technique. The Judd-Ofelt (JO) theory has been initiated for the precise analysis of the peak intensities. The JO parameter Ω2, which represents asymmetry and covalency of the emission environment increases with increase in Er3+ ions, while Ω4 and Ω6 reveal the rigidity of the host medium. Radiative parameters such as τR, AR, βR, FOM, and σR have been calculated. The photometric studies, CIE & CCT studies confirm that, for all the investigated glasses CIE coordinated diagram is found to be white light. CCT graph which gives white light emission around 10000K. Two photon absorption coefficient (TPA) of Er3+ doped glasses lie in the range of 7.491 to 8.868. Glasses with highest TPA shows low Eg values indicating a large density of states of O2− in highest occupied molecular orbitals.

Effect of sodium oxide and sodium fluoride in gadolinium phosphate glasses doped with Eu2O3 content

Sodium gadolinium phosphate oxide and sodium gadolinium oxyfluoride glasses doped with europium oxide were synthesized by melt-quenching method. The density, molar volume and refractive index of the glass samples were carried out. Density and molar volume of oxide glass is more than oxyfluoride glass. The average phosphate to phosphate distance for oxide glass seems to be more than oxyfluoride glass. Polaron radius, inter-ionic radius shows 1.181 nm, 2.88 nm and 1.174 nm, 2.86 nm for oxide glass and oxyfluoride glasses respectively. Oxide electronic Polarizability and optical basicity of the oxide glass are lower than oxy-fluoride glass. Theoretical optical basicity shows higher for oxide glass than oxyfluoride suggesting increase in covalency of the cation to oxygen bonds in oxide glass. Optical band gap was estimated and found to be 3.061eV and 3.204 eV for oxide and oxyfluoride glass. Theoretical two photon absorption coefficient β were evaluated and found to be 11.96 and 10.80 for oxide and oxyfluoride glasses respectively. Electron-phonon coupling strength were evaluated from the phonon side band spectra for the oxide and oxy-fluoride glasses. The asymmetry ratio (R) show higher for NaF doped glass than Na2O confirming their role in elevated ionicity for oxyfluoride glass than oxide glass. Furthermore, the glasses were subjected to study for their luminescence properties of the oxide and oxyfluoride glass samples.

Mid-infrared supercontinuum generation in chalcogenide fibers with high laser damage threshold.

Laser damage thresholds (Ith) at 1.03 µm, as well as third-order nonlinear refractive indices (n2) and two photon absorption coefficients (β) at 1.55 µm of a number of Ge-As-S glasses were measured and systematically studied. The glass with the composition Ge0.12As0.24S0.64 showed a high Ith and the maximum figure of merit (fm= n2/(β·λ)), and therefore was selected as the core material for the fabrication of a step-index fiber. A compatible glass with the composition Ge0.18As0.1S0.72 was chosen as the cladding material. Based on the dispersion calculations, the fiber with a core diameter of ∼7-10 µm was designed. The designed fiber was fabricated by a multiple step rod-in-tube method. When the fiber with a core diameter of ∼9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, the mid-infrared supercontinuum (SC) covering 1.3-8.1 µm was generated. These results demonstrate the good potential of Ge-As-S chalcogenide fibers for producing high-brightness broadband mid-infrared SC light sources.

Numerical Simulation of a UV-PCO Plate Reactor

Ultraviolet photocatalytic oxidation (UV-PCO) system has gained increasing attention in indoor air treatments, of which the PCO reaction kinetics mainly depend on the radiation and airflow (contaminants) fields. It is recognized that the airflow rate has a significant influence on the PCO kinetics with the balance of the VOC mass transfer process. However, there are few discussion for the airflow rate dependency in the PCO kinetic reaction model. In addition, most of the studies in the literature assumed the incident surface irradiance was the energy participating in PCO reactions, which is not accurate. Hence, a 3D Computational Fluid Dynamics (CFD) model, including catalyst photon absorption coefficient, the conservation of mass, momentum, energy, and species, as well as PCO reaction kinetics, was introduced in this study. The determined model parameters were verified by the experimental data for a plate reactor challenged with 10 ppm acetone. The airflow rate dependency was examined in conjunction with CFD providing local flow field information, and the catalyst absorbed light intensity was quantified by a validated radiation model. It was found that the PCO removal efficiency predictions from the developed mathematical model agree with experimental data.

Comprehensive study on the nonlinear optical properties of few-layered MoSe2 nanosheets at 1 μm

The few-layered molybdenum diselenide (MoSe2) nanosheets were synthesized by the simple and low-cost ultrasonic-assisted liquid phase exfoliation (UALPE) method. The high quality of the two-dimensional nanostructures was verified by comprehensive characterization. The nonlinear optical properties including nonlinear absorption and refraction of the MoSe2 nanosheets were investigated by utilizing the open- and closed-aperture Z-scan technique. The MoSe2 nanosheets exhibits excellent nonlinear saturable and reverse saturable absorption for nanosecond laser pulses at 1 μm. The two photon absorption (TPA) coefficient, nonlinear refractive index n2, real and imaginary parts of the third-order nonlinear optical susceptibility were determined as 2.7 cm/MW, 2 × 10−4 cm2/GW, 8.2 × 10−12 esu and 1.61 × 10−12 esu, respectively. Finally, the passively Q-switched Nd:CNGG laser with MoSe2 saturable absorber at 1.06 μm was realized for the first time, showing the excellent satuable absorption properties.

Electron Diffusion Model Based on I-V Data Fitting as the Calculation Method for DSSC Internal Parameters

Dye-sensitized solar cells (DSSC) made of TiO2 have received considerable attention from many researchers for the last three decades. Rapid theoretical and experimental studies have been conducted to improve the performance of DSSC. To understand the DSSC internal parameters, we need to fine-tune each component and identify the suitable conditions in optimizing the performance of assembled devices. In this work, we analyzed and calculated of several parameters the DSSC photoanode, e.g. electron diffusion and photon absorption coefficients. The experimental I-V data from solar simulator measurements were fitted base on electron diffusion model using Microcal Origin software. We compared the photon absorption coefficient values from this calculation method with the result of UV-Vis measurement and compared the electron diffusion coefficient values with the result of the SEM image data fitting calculation method. It was apparent that the results of I-V data fitting calculation method were comparable with the results of two other techniques.

Physical, structural, and radiation shielding properties of B2O3–MgO–K2O–Sm2O3 glass network modified with TeO2

A new series of Sm3+ doped Telluroborate glasses with varying TeO2 content have been prepared following the melt quenching technique. The physical properties like density, refractive index, average molecular weight, molar volume, optical dielectric constant, and metallization criterion were calculated. Structural properties like boron-boron separation (<dB–B>), molar volume of oxygen (Vo), oxygen packing density (OPD), average coordination number (m), bond density (nb), Poisson ratio (µcal), optical electronegativity (χopt), basicity (Λth), two photon absorption (TPA) coefficient (β), ionic character (Ic), and covalent character (Cc) were calculated. In addition to that, optical bandgap and urbach energy (ΔE) values of the titled glasses have been calculated from Tauc's plot using the absorption spectra. It is observed that boron-boron separation (<dB–B>) and OPD increases with the decrease in molar volume of oxygen (Vo). Also, the increasing density and refractive index values with the progressive decrease of molar volume with increasing TeO2 content implies the formation of bridging oxygen (BO) along with nonbridging oxygen (NBO), which is later proved by the Poisson ratio values and basicity values. Further, ionic nature of the Sm3+ doped telluroborate glasses are identified from the measured optical basicity (Λth), covalent, and ionic characteristic factors. The observed variations in the optical electronegativity, basicity, metallization criterion, and optical bandgap energy (Eg) values have been discussed in terms of the structural changes that take place due to the addition of TeO2 into the B2O3 network. The gamma photon shielding properties for the prepared samples were studied using MCNPX code in the energy range of 0.356–1.33 MeV. The obtained mass attenuation coefficient exhibit an increasing trend as the TeO2 content vary from 0 to 40 mol%, especially at the energy 0.356 MeV. Of all the glasses, 4TBS glass sample shows lowest half-value layer value. The study confirms that the replacement of B2O3 by TeO2 enhances the capability of the prepared glass samples to reduce the gamma photons.

Non-linear optics study of the samples which strongly diffuse the Gaussian beam

The Z-scan experiment is the fastest method to determine non-linear optical (NLO) coefficients of materials. Classic Z-scan technique described by Sheik-Bahae et al. (1989) and Wang et al. (1994) uses pulsed or CW lasers with the Gaussian beam profile. As long as the Gaussian profile is not diffused by the examined materials, this method can be used. However, by extending the classic Z-scan technique using a CCD beam profiler and analyzing the beam deviation from the Z axis, the NLO coefficients can be estimated even for a highly diffused Gaussian beam. The method proposed in this paper tracks the centroid position of the diffused beam and on this basis the two photon absorption coefficient β and the nonlinear refractive index n2 are obtained. The accuracy depends on the samples geometry and the CCD detector used. The new approach presented in this paper can be used in substitution to the classic technique for the materials which strongly diffuse the Gaussian beam.

Correlation of theory with experimental photon absorption and photon emission of quasitype II CdS/ZnS QDs

Predictions for the photon absorption coefficient (α) and photoluminescence (PL) of quasitype II CdS/ZnS core/shell nanocrystals [quantum dots (QDs)] have been obtained using a straightforward developed procedure. The developed procedure begins by solving the three-dimensional (3-D) Schrodinger equation written in spherical coordinates. Then, α is obtained by solving an equation based on the strict k-selection approach, and PL is derived by solving the Kubo–Martin–Schwinger relationship. This formulation allows the prediction of fundamental QD energy properties as a function of the QD radius. The predicted properties include quantized energy levels, effective bandgap, effective photon absorption wavelength, and effective photon emission wavelength. In addition, CdS/ZnS QDs were synthetized and stabilized based on previously reported procedures. Experimental measurements of α and PL were found to be very well matched to the calculated results. Hence, the developed procedures can be of great interest for designers who correlate theoretical results with experimental measurements to predict next generation QD performance for nanophotonics applications.

Controlling of two photon absorption properties by altering composition ratio of GaSxSe1−x crystals

Linear and nonlinear optical properties of mixed GaSxSe1−x crystals grown by Bridgeman were investigated. Two photon absorption properties of the studied crystals were investigated by using open aperture Z-scan technique with 4 ns pulse duration at 1064 nm wavelength. Linear absorption measurement results showed that the band gap energies of the mixed crystals increase with increasing the S ratio in crystals and oppositely, two photon absorption coefficients decrease with increasing the S ratio in mixed crystals exposed to nanosecond pulse duration. The increasing of two photon absorption coefficients can be attributed to lower energy band gap values. At the same input intensities, the highest two photon absorption coefficient is found as 3.56 × 10−6 cm/W for GaSe and the lowest one is obtained as 2.42 × 10−6 cm/W for GaS crystals. In this study, the experimental results indicate that two photon absorption properties and optical band gap energies are related with each other and can be controlled by altering the S/Se ratio of the mixed GaSxSe1−x crystals.

Z-scan measurements of the third-order optical nonlinearities and linear optical properties of 70TeO2 - 5MxOy - 10P2O5 - 10ZnO - 5PbF2 glasses doped with Er3+ ions modified by transition metals

The two photon absorption (TPA) coefficient (β), the nonlinear refractive index (n2 ), and the third order nonlinear optical susceptibility (χ<3> ) of tellurium dioxide glasses were investigated using the absorption spectra, normalized transmission, and Z-scan methods. We studied the influence of different transition metals, with and without the rare earth ion Er3+, on the nonlinear properties of these glasses. The experimental results show that (n2 ) and (β) are the highest for the glass consisting of cadmium oxide doped with rare earth ions. Consequently, the real and imaginary part of the third-order nonlinear optical susceptibility (χ<3>) is the highest for these materials. Moreover, the presence of Er3+ increased the NLO coefficients the all the examined samples. The Z-scan result confirms, the glasses exhibit self-focusing effects and the sign of the refractive nonlinearity is positive.

Nonlinear optical properties of chalcogenide hybrid inorganic/organic polymers (CHIPs) using the Z-scan technique

The linear and nonlinear optical behavior of novel sulfur based polymer materials are evaluated at the optical communication wavelength, 1550 nm. These polymers are attractive for near-IR (NIR) and mid-IR applications. The two photon absorption (TPA) coefficient (β) and second order refractive index (n2) of chalcogenide hybrid inorganic/organic polymers (CHIPs) from poly(sulfur-random-(1,3-diisopropenylbenzen) (poly(S-r-DIB)) are measured via the Z-scan technique. In this study, we investigated the linear and nonlinear optical behavior of two types of CHIPs where the weight percentage of sulfur is varied (poly(S50%-r-DIB50%) and poly(S70%-r-DIB30%)). The TPA coefficients for poly(S50%-r-DIB50%) and poly(S70%-r-DIB30%) obtained were 0.11 cm/GW and 0.063 cm/GW, respectively. The n2 for poly(S50%-r-DIB50%) and poly(S70%-r-DIB30%) was measured and determined to be 2.45 × 10−15 cm2/W and 3.06 × 10−15 cm2/W, respectively, and are in good agreement with Miller’s rule prediction. These materials exhibit low cost, low temperature processing, high transparency in the near to mid-IR range (except a few interval ranges) and relatively high refractive index, providing a unique set of properties for optics and photonics device applications.

Unsupervised classification of tissues composition for Monte Carlo dose calculation

The purpose of this study is to investigate the potential of k-means clustering to efficiently reduce the variety of materials needed in Monte Carlo (MC) dose calculation. A numerical phantom with 31 human tissues surrounded by water is created. K-means clustering is used to group the tissues in clusters of constant elemental composition. Four different distance measures are used to perform the clustering technique: Euclidean, Standardized Euclidean, Chi-Squared and Cityblock. Dose distributions are calculated with MC simulations for both low-kV photons and MeV protons using the clustered and reference elemental composition. Comparison between the dose distributions in the clustered and non-clustered phantom are made to assess the impact of clustering with each distance measure. The statistical significance of the differences observed between the four different metrics is determined by comparing the accuracy of energy absorption coefficients (EAC) of low-kV photons and proton stopping powers relative to water (SPR) for repeated clustering procedures. The performance of the proposed approach for a larger number of original materials is evaluated similarly by using a population of 62 000 statistically generated materials grouped into classes defined with supervised and unsupervised classification. In the phantom geometry, the Chi-Squared distance is the one introducing the smallest error on dose distribution and significant differences are observed between the EAC and SPR values predicted by each distance metric. The proposed approach is also shown to be equivalent to a state-of-the-art supervised classification method for proton therapy, but beneficial for low-kV photons applications. In conclusion, k-means clustering successfully reduces the variety of materials needed for accurate MC dose calculation. Based on the performance of four distance measures, we conclude that k-means clustering using the Chi-Squared distance introduces the smallest errors on dose distribution. The method is shown to yield similar or improved accuracy on key physical parameters compared to supervised classification.

(Invited) III-Nitride UV-Visible Integrated Photonics for Quantum and Biomedical Applications

III-nitride semiconductors have drawn considerable attentions for its wide success in photonic devices including light-emitting diodes, laser diodes, solar cells, and photodetectors. In addition to discrete devices, recent studies on III-nitride waveguides have now opened up new opportunities in integrated photonics for biochemical sensing, beam steering, nonlinear optics, and quantum photonics applications in the UV and visible spectral region. For example, due to their wide bandgap, low material dispersion, and active integration capability, III-nitride materials are particularly attractive for integrated nonlinear optics applications, including second harmonic generation, comb generation, and parametric down conversion. In this talk, I will first present our recent studies on the fundamental nonlinear optical properties of GaN, namely, two photon absorption coefficient, three photon absorption coefficient, and Kerr nonlinear refractive index, and discuss their impacts on the device performance. I will also discuss on-going research at ASU on AlN nanophotonic ring resonators for second order harmonic generation of picosecond UV coherence light, as well as supercontinuum generation from UV to IR. The presented III-nitride integrated photonics platform would enable a wide rangeof applications in biochemical sensing, quantum information, and optical communications.

Synthesis of stable ZnO nanocolloids with enhanced optical limiting properties via simple solution method

In present work, we report the synthesis of stable ZnO nanocolloids through a simple solution method which exhibit enhanced optical limiting threshold. The influences of reaction temperature on the crystal structure as well as linear and nonlinear optical properties of prepared ZnO nanoparticles were carried out. The XRD and Raman analysis reveal that the prepared ZnO nanoparticles retain the hexagonal wurtzite crystal structure. HRTEM analysis confirms the effect of reaction temperature, solvent effect on crystallinity as well as nanostructure of ZnO nanoparticles. It has been found that crystallinity and average diameter increase with reaction temperature where ethylene glycol act as both solvent and growth inhibiter. EDS spectra shows formation of pure ZnO nanoparticles. The direct energy band gap of the nanoparticles increases with decrease in particle size due to quantum confinement effect. The third order nonlinear optical properties of ZnO nanoparticles were investigated by z scan technique using a frequency doubled Nd-YAG nanosecond laser at 532 nm wavelength. The z-scan result reveals that the prepared ZnO nanoparticles exhibit self - defocusing nonlinearity. The two photon absorption coefficient and third - order nonlinear optical susceptibility increases with increasing particle size. The third-order susceptibility of the ZnO nanoparticles is found to be in the order of 10−10 esu, which is at least three order magnitude greater than the bulk ZnO. The optical limiting threshold of the nanoparticles varies in the range of 54 to 17 MW/cm2. The results suggest that ZnO nanoparticles considered as a promising candidates for the future photonic devices.

Third-order nonlinear optical properties of ADP crystal

By using the Z-scan method, we investigated the third-order nonlinear optical (NLO) properties of ADP crystal at different wavelengths (355, 532, and 1064 nm) and different orientations ([001], [100], [110], I and II). The experimental data were fitted by NLO theory, to give out the two photon absorption (TPA) coefficient β2 and the nonlinear refractive index n2. When the light source changed from a 40 ps, 1064 nm fundamental laser to a 30 ps, 355 nm third-harmonic-generation (THG) laser, the β2 value increased about 5 times (0.2 × 10−2 → 1 × 10−2 cm GW−1), and the n2 value increased about 1.5 times (1.5 × 10−16 → 2.2 × 10−16 cm2 W−1). Among all of the orientations, the [110] sample exhibits the smallest β2, and the second smallest n2. It indicates that this orientation and its surroundings will be the preferred directions for high-power laser applications of ADP crystal.

Plasmon augmented two photon absorption in a strongly coupled nano-molecular hybrid

A long-standing goal in optical sciences has been to strengthen nonlinear optical effects at lower light powers or pulse energies. In this perspective, strongly-coupled hybrids which offer significant third order optical nonlinearities at low powers are currently a topic of global research. Herein, we report a detailed analysis of third order nonlinear photonic characteristics of the fabricated nanohybrid system. The far field and near field optical coupling between the constituents of the hybrid were investigated using Near field scanning optical microscopy and Raman spectroscopy respectively. While the optical nonlinearity (i.e. two photon absorption in this case) has been elucidated using Z-scan spectroscopy. The experimental outcomes reveal in the linear as well as the nonlinear regime the dye and the Au nanoislands represent a strongly interacting system. A 400% enhancement in the two photon absorption coefficients of an organic dye Eosin Yellow is observed when hybridized with Au nanoislands. The results are explained in terms of the energy transfer from the dye to the hybridized Au nanoislands film. The investigations of such mechanisms, may bring forth exciting advances, not only in terms of strongly interacting photons, but also shed light on the impact of energy transfer mechanisms on third order nonlinearity of nano-molecular hybrids.

Energy redistribution between layers in multi-layered target heated by x-ray pulse

Multi-layered systems with alternated layers of different materials (laminates) with thickness of the order of tens nanometers are widely used in modern technologies, e.g., as x-ray mirrors. It is important to study effect of the x-ray free electron lasers on such targets. Highenergy photons penetrate deeply into material with an attenuation depth much larger than the thickness of a single layer of a laminate. Modern hard x-rays lasers may be focused to tiny focal spots in the direction approaching diffraction limit: record today is ≈ 50 nm; ∼ 1 μm diameters are now rather easily achieved. These lasers may be used for machining of laminates. We show that thermal evolution of illuminated laminates depends on not only photon absorption in the individual materials, but also on fast redistribution of absorbed energy within a nonequilibrium stage connected with electron–ion relaxation (two-temperature stage) between hot electrons heated by absorption and much colder ions. Because of the high heat conductivity of metal layers, especially at the two-temperature stage, energy redistribution must be considered with taking into account the energy transfer from electrons to ions with different electron–ion coupling parameters α for different metals. Thus, a higher energy can be localized in a material with higher α rather than in a material with higher photon absorption coefficient.

Optical features of novel fluorotellurite glasses based on TeO2- LiNbO3- BaF2- La2O3- (Nb2O5 or TiO2)

New families from fluorotellurite glasses with composition 7.53 TeO2-7.31 LiNbO3-4.16 Nb2O5-10 BaF2-1.0La2O3, 72.53 TeO2-7.31 LiNbO3-10 Nb2O5-10 BaF2-1.0La2O3 and 77.53 TeO2-7.31 LiNbO3-5 TiO2-10 BaF2-1.0La2O3 in mol% were prepared. The thermal characterization and optical properties of these glasses were estimated by using differential scanning calorimetric, DSC, and UV–vis-NIR spectroscopy respectively. The results of thermal analysis indicate that 77.53 TeO2-7.31 LiNbO3-5 TiO2-10 BaF2-1.0La2O3 glasses has high thermal stability and high factor against crystallization. The density and linear refractive index, n, of present glasses were measured. Also, the physical parameters such as; oxygen packing density, molar volumes, oxygen molar volume, molar refraction, metallization criterion, molar polarizability, third-order non-linear susceptibility and two photon absorption coefficients were calculated. It was found that, the linear refractive index increases otherwise decrease in the optical energy gap with increase Nb2O5 concentration. On the basis on thermal and optical results of these glasses it can be concluded that fluorotellurite glasses tested can be used in optical application.

Effect of Microemulsion Structure on Fluorescence and Nonlinear Optical Properties of Rhodamine 6G.

This study is conducted to investigate the effect of nano-droplets concentration and size on linear and nonlinear optical properties of Rhodamine 6G by UV-Vis, spectrofluorometer and Z-Scan techniques. Nano-droplets were prepared by mixture of AOT, n-Decane and Water at three different water to surfactant molar ratios (W = 3, 6.7 and 40) and two dye to water mass ratios (R). At high enough dye concentration, the fluorescence intensity and its red shift depend on the concentration of dye in water nano-droplets (R). Moreover, the fluorescence spectra of R6G can be enhanced by confined water nano-droplets (microemulsion) at higher dye to water mass ratios. The Raman Spectra reveal no dependence of R6G local polarity in the AOT reversed micelles to nano-droplet size. From the Bakhshiev equation, the excited to ground state dipole moment ratio (μ e /μ g ) was calculated through solvatochromic shift method for different nano-droplet concentrations. The results show that μ e /μ g of R6G in water nano-droplets is smaller than that of bulk water. At high enough dye concentration, μ e /μ g depends on the nano-droplets' dye content. The dye aggregation can affect the dipole moment R6G in microemulsion. Two photon absorption coefficient (β), nonlinear refractive index (n 2), the real third order susceptibility ([Formula: see text]) and the second order hyperpolarizability ([Formula: see text]) were measured using the Z-Scan technique at different nano-droplet concentration and two sizes of nano-droplet. The results show a good compatibility with the attained consequence by Quantum Perturbation theory. In this content, the interaction of nano-droplet was studied by dynamic light scattering, whose results indicate an ascending trend in mobility of nano-droplets by the increase of nano-droplets dye content. Hence increase of dye in nano-droplets influences the dye aggregation, fluorescence red shift and dipole moment ratio (μ e /μ g ) by the nano-droplet collision.