Photon Absorption Coefficient Research Articles

Assessment on third order non linearity and other optical analyses of l-Asparagine Monohydrate single crystal: An efficient candidate for harmonic conversions

Single crystal of l-Asparagine Monohydrate, an organic material has been successfully grown by slow evaporation solution growth technique at ambient condition. The lattice parameters and its strain of the grown crystal have been evaluated from powder X-ray diffraction and found that it belongs to orthorhombic crystal system. The polarizability has been measured by using the Clausius–Mossotti relation. The crystalline perfection of grown single crystal has been examined by high resolution X-ray diffraction and its imperfection in the diffraction plane was clearly visible by recording topographical image of the plane. From the high resolution XRD, it confirms that the crystal contained high crystalline perfection. The optical behavior was analyzed by photoluminescence and birefringence methods. In the photoluminescence, a broad peak has been observed at 475nm which suggest that it emits blue light. The decay tendency of the material has also been observed by calculating decay constant. The optical homogeneity has been determined by the dispersion pattern of the material. The two photon absorption coefficient was further calculated by Z-scan, which gives the information about the third order non linear optical behavior of the material. The value of two-photon absorption coefficient is 4.25×10−12m/W. The thermal parameters like thermal effusivity, thermal diffusivity, specific heat and thermal conductivity was obtained by using photopyroelectric technique. The ferroelectric behavior of the grown specimen was analyzed from PE (polarization VS electric field) loop. The loop suggests that the material was a nearly equivalent to ideal capacitor.

Z-scan measurement of the nonlinear refractive index of monolayer WS(2).

Transition metal dichalcogenides (TMDCs), such as tungsten disulfide (WS(2)), are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Recent advances in nanoscale materials characterization and few layer TMDCs' unique optical properties make them a research hot-spot in nonlinear optics. In this work, the nonlinear refractive index of monolayer WS(2) has been characterized with Z-scan measurement under 800nm femtosecond pulsed laser excitation, and a value of n2 ≃ (8.1 ± 0.41) × 10(-13)m(2)/W is obtained. A shift from saturable absorption to reverse saturable absorption was observed at higher input pump intensities in the experiments. The transition process was analyzed using a phenomenological model based on two photon absorption, and the two photon absorption coefficient was estimated about (3.7±0.28)×10(-6)m/W.

Study of vibrational spectroscopy, linear and non-linear optical properties of Sm3+ ions doped BaO–ZnO–B2O3 glasses

Samarium oxide doped Barium–Zinc–Borate glasses with compositions xSm2O3−(100−x)[0.1BaO–0.4ZnO−0.5B2O3]; x = 0.0, 0.5, 1.0, 1.5 and 2.0 have been prepared by melt quench technique. The amorphous nature of as-prepared glasses has been ascertained by X-ray diffraction patterns. The observed values of density and molar volume of the glass samples are found to increase with the increase in concentration of Sm2O3. Fourier Transform Infrared spectra of the prepared glasses indicate that Sm2O3 acts as glass modifier. With the increase in Sm2O3 content, BO4 structural units start converting into BO3 structural units. The values of optical energy band gap (Eg), estimated from Tauc's plots, are observed to decrease with the increase in Sm2O3 content. The nonlinear optical properties of glass samples have been investigated by Z-scan method with nanosecond pulsed laser at ∼532 nm in both open and close aperture geometries. The values of two photon absorption coefficient (β) and nonlinear refractive index (n2) have been estimated by fitting of experimentally observed data with theoretical models and both are found to increase with the increase in Sm3+ ions concentration in the glass matrix. The total third order nonlinear susceptibility (χ(3)) have been calculated and observed to increase with the increase in Sm3+ ions concentration.

Growth and characterization of a new organic nonlinear optical crystal: 1-(3-Nitrophenyl)-5-phenylpenta-2,4-dien-1-one

Abstract Organic nonlinear optical single crystal of 1-(3-Nitrophenyl)-5-phenylpenta-2,4-dien-1-one (Ci3NC) with dimensions 25×15×10 mm3 was successfully grown for the first time by the slow evaporation solution growth technique (SEST). The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements, and it was found that the crystalline perfection is reasonably good having very low angle (tilt angle ≤1′) internal structural grain boundary. Thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder test with Nd:YAG laser radiation shows second harmonic generation which is about 7 times that of urea. The optical transmittance window and the lower cutoff wavelength of the Ci3NC have been identified by UV–vis–NIR studies. Third-order nonlinear optical (NLO) response of Ci3NC has been examined using Z-scan technique with femtosecond (fs), MHz pulses at wavelengths of 870 nm and 900 nm. Various NLO coefficients such as two-photon absorption (2PA) coefficient (β), three photon absorption (3PA) coefficient (γ), and nonlinear refractive index (η2) were evaluated.

Nanosecond and ultrafast optical power limiting in luminescent Fe2O3 hexagonal nanomorphotype

Nonlinear optical absorption and optical power limiting properties of Fe2O3 hexagonal nanomorphotype are investigated using open aperture Z-scan technique with the 5 ns and 100 fs laser pulses, at 532 nm and 800 nm excitation domains. At relatively low pulse energies (below 5 μJ), sample shows saturable absorption (SA), but on going to the higher energies an interesting switchover from saturable absorption to effective two photon absorption is observed in both excitation domains. The magnitude of effective two photon absorption coefficients is calculated to be in the range of 10−10 m/W for nanosecond and 10−15 m/W for femtosecond laser pulse energies, respectively. XRD and TEM study reveals the polycrystalline nature, hexagonal morphology, and size of the nanostructure. The luminescence emission property is examined by photoluminescence spectroscopy (PL). It is found that some strange features exist in the luminescence spectra that are consistent with the nanoparticles size distribution. The PL emission lines are explained as originated from various optical band edges due to the size induced quantum confinement and band gap resonant PL absorption/emission behavior of semiconductor nanostructures.

Cross two photon absorption in a silicon photonic crystal waveguide fiber taper coupler with a physical junction

Cross two photon absorption in silicon is characterized using a tapered fiber photonic crystal silicon waveguide coupler. There is a physical junction between the tapered fiber and the waveguide constituting a stand-alone device. This device is used to obtain the spectrum for cross two photon absorption coefficient per unit volume of interaction between photons of nondegenerate energy. The corresponding Kerr coefficient per unit volume of interaction is also experimentally extracted. The thermal resistance of the device is also experimentally determined and the response time of the device is estimated for on-chip all-optical signal processing and data transfer between optical signals of different photon energies.

GaSe晶体的双光子吸收对太赫兹输出的影响

The broadband THz generation from 0. 2 to 2. 5 THz was measured as a function of pump intensity in a single pure gallium selenide crystal based on the optical rectification of ultrafast laser pulses. Two-photon absorption at 800 nm can generate free charge carriers which can absorb the generated THz radiation,and finally attenuate THz output. The result indicates that the pump intensity dependence of ouput THz radiation changes from square to sub-linear relationship and the saturation of output THz radiation appears at high pump intensity. To study the impact of two photon absorption on THz generation,the two photon absorption coefficient of Ga Se at 800 nm is measured to be 0. 165 cm / GW,which is determined by the measured nonlinear transmission. The THz output fitting result taking account of the free charge carrier absorption cross section of 1 × 10-15cm2 is consistent with the experiment data very well. This estimation result can be used to optimize the conversion efficient of THz generation in Ga Se crystal under intense laser pump.

Si, GaAs, and InP as cathode materials for photon-enhanced thermionic emission solar cells

Photon-enhanced thermionic emission (PETE) solar cells are photovoltaic devices designed for high temperature operation. The use of Si, GaAs, and InP as the cathode (i.e. the absorber and the electron-emitter electrode) materials in PETE solar cells is investigated with numerical device models. The models describe the cathode one dimensionally and are valid also at high injection levels. The temperature dependence of the photon absorption coefficients and temperature and doping dependencies of electron mobilities are modelled. Simulated device characteristics are presented and the factors determining the efficiency of the PETE devices are discussed. Our results show that Si, GaAs, and InP are all promising materials for PETE solar cells, if the surface recombination, effective electron affinities, and thermal stability of these materials can be optimized. Owing to their strong absorption, GaAs and InP show higher efficiencies (20–25%) than Si (10–15%) in spite of their intense radiative recombination. Especially, InP is a promising candidate for PETE cathodes as it shows higher efficiency than GaAs due to its stronger photon absorption properties.

Investigation on third order nonlinear optical, electrical and surface properties of organic stilbazolium crystal of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate

The third order nonlinear optical, electric and dielectric properties of an organic stilbazolium derivative of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate (DSMOS) crystal are reported. The nonlinear refractive index (n2), two photon absorption coefficient (β) and third order optical susceptibility χ(3) have been measured by Z-scan technique using Gaussian beam from the Nd:YAG laser at 1064nm. The results show a large negative nonlinear refractive index (n2=−1.122×10−9cm2/W) with a molecular two photon absorption coefficient β value of 3.625×10−6cm/W. The low dielectric constant observed in the high frequency region indicates the suitability of the sample for electro-optic applications. The surface features are also investigated by atomic force microscopy (AFM).

3D Wire‐Shaped Dye‐Sensitized Solar Cells in Solid State Using Carbon Nanotube Yarns with Hybrid Photovoltaic Structure

A novel 3D solid-state wire-shaped dye-sensitized solar cell (DSSC) with a hybrid photovoltaic (PV) structure is demonstrated. Carbon nanotube yarn provides excellent interfacial and electrocatalytic properties. The quantum dots (QDs) have been applied due to their high photon absorption coefficient. Finally, the cell shows an outstanding operational flexibility with an efficient photovoltaic efficiency (7.39%).

Impurity mediated large three photon absorption in ZnS:Cu nanophosphors

Copper doped ZnS nanophosphors with the cubic zinc blende (Sphalerite) structure have been prepared through the wet chemical route in aqueous media. The ZnS:Cu nanoparticles display a widening in the band gap with increase in Cu dopant concentration. The observed green photoluminescence (PL) in ZnS:Cu originates from the transition between the conduction band and the copper acceptor levels. The open aperture Z-scan traces of the ZnS:Cu nanoparticles embedded in PVA matrix, excited at 800nm using 100fs laser pulses, show an optical limiting type nonlinearity which is attributed to three photon absorption. An increase in the value of the three photon absorption coefficient is observed with increase in the Cu doping concentration. The increase in the density of intermediate defect levels plays a significant role in the enhancement of three photon absorption in Cu doped ZnS. These studies reveal that Cu doped ZnS nanoparticles in polymer matrices are potential candidates for ultra fast optical limiting applications.

Observations on nonlinear optical properties of ZnS nanosheet, ZnS–ZnO composite nanosheet and porous ZnO nanostructures dispersed in aqueous medium

The nonlinear optical (NLO) absorption and refraction properties of different nanostructures, such as ZnS nanosheets, ZnS–ZnO composite and porous ZnO nanostructures, dispersed in de-ionized water, are reported by performing the z-scan technique with 532nm ns pulsed laser radiation. The values of NLO coefficients of the materials are extracted from the experimental z-scan data. The two-photon induced free carrier absorption has been observed in the samples. The experimentally obtained two photon absorption coefficient of ZnS–ZnO nanocomposite is an order-of-magnitude larger that of ZnS nanoparticles. The presented results may open up new possibilities of using these materials in different NLO devices.

Axion-induced birefringence effects in laser driven nonlinear vacuum interaction

The propagation of a probe electromagnetic field through a counterpropagating strong plane wave is investigated. The effects of the electromagnetic field-(pseudo)scalar axion field interaction and of the self-interaction of the electromagnetic field mediated by virtual electron-positron pairs in the effective Lagrangian approach are included. First, we show that if the strong field is circularly polarized, contrary to the leading-order nonlinear QED effects, the axion-photon interaction induces a chiral-like birefringence and a dichroism in the vacuum. The latter effect is explained by evoking the conservation of the total angular momentum along the common propagation direction of probe and the strong wave, which allows for real axion production only for probe and strong fields with the same helicity. Moreover, in the case of ultra-short strong pulses, it is shown that the absorption coefficients of probe photons depend on the form of the pulse and, in particular, on the carrier-envelope phase of the strong beam. The present results can be exploited experimentally to isolate nonlinear vacuum effects stemming from light-axion interaction, especially at upcoming ultra-strong laser facilities, where stringent constraints on the axion-photon coupling constant are in principle provided.

INFLUENCE OF ANNEALING TEMPERATURE ON CHARACTERISTICS OF BISMUTH DOPED ZINC OXIDE FILMS

In this study, Bismuth (Bi) doped ZnO thin films were deposited on quartz substrates by a sol-gel spin coating method and annealed at different annealing temperatures of 200, 300, 400, 500, 600 and 700°C, respectively. Structural and optical properties of nanocrystalline Bi-doped ZnO film on quartz were investigated by using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and UV-VIS spectrophotometer. The high annealing temperature of 700°C as a critical temperature causes the crystallographic reorientation plane in ZnO:Bi nanostructure mostly due to the initial formation of the polycrystalline phase with the inter-grain segregation of Bi dopant atoms. Bi-incorporating ZnO films with an increase in annealing temperature resulted in a blue wavelength shift of the photon absorption edge. The optical band gap of the films was increased from 3.27 eV to 3.34 eV. By decreasing the annealing temperatures from 700 to 200°C, the grain size of Bi-doped ZnO decreased from 18 nm to 8 nm. The effect of the annealing temperature on the electrical conductivity had been considered. The low electrical conductivity of 0.9 (Ω.cm)-1 was obtained for ZnO:0.2 film annealed at 600°C with good nano-crystallization. However, the Bi-doped ZnO films prepared by cost-effective spin coating technique provided to have a very high photon absorption coefficient (104-105 cm-1) and did not appreciably affect the optical transparency. ZnO films doped with 0.2% at. Bi can be used as a high resistive buffer layer for solar cell application.

Searching for minicharged particles via birefringence, dichroism and Raman spectroscopy of the vacuum polarized by a high-intensity laser wave

Absorption and dispersion of probe photons in the field of a high-intensity circularly polarized laser wave are investigated. The optical theorem is applied for determining the absorption coefficients in terms of the imaginary part of the vacuum polarization tensor. Compact expressions for the vacuum refraction indices and the photon absorption coefficients are obtained in various asymptotic regimes of interest. The outcomes of this analysis reveal that, far from the region relatively close to the threshold of the two-photon reaction, the birefringence and dichroism of the vacuum are small and, in some cases, strongly suppressed. On the contrary, in a vicinity of the region in which the photo-production of a pair occurs, these optical properties are manifest with lasers of moderate intensities. We take advantage of such a property in the search of minicharged particles by considering high-precision polarimetric experiments. In addition, Raman-like electromagnetic waves resulting from the inelastic part of the vacuum polarization tensor are suggested as an alternative form for finding exclusion limits on these hypothetical charge carriers. The envisaged parameters of upcoming high-intensity laser facilities are used for establishing upper bounds on the minicharged particles.

Linear and Nonlinear Optical Properties of Expanded Porphyrins: A DMRG Study

We study absorption spectra and two photon absorption coefficient of expanded porphyrins (EPs) by the density matrix renormalization group (DMRG) technique. We employ the Pariser-Parr-Pople (PPP) Hamiltonian which includes long-range electron-electron interactions. We find that, in the 4n+2 EPs, there are two prominent low-lying one-photon excitations, while in 4n EPs, there is only one such excitation. We also find that 4n+2 EPs have large two-photon absorption cross sections compared to 4n EPs. The charge density rearrangement in the one-photon excited state is mostly at the pyrrole nitrogen site and at the meso carbon sites. In the two-photon states, the charge density rearrangement occurs mostly at the aza-ring sites. In the one-photon state, the C-C bond length in aza rings shows a tendency to become uniform. In the two-photon state, the bond distortions are on C-N bonds of the pyrrole ring and the adjoining C-C bonds which connect the pyrrole ring to the aza or meso carbon sites.

Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film

We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is ~3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites.

Photon absorption coefficient (α) for a low-dimensional CdS/CdTe absorber by a partial k-selection approach

The dependence of photon absorption by a low-dimensional cadmium-sulfide/cadmium-telluride (CdS/CdTe) heterostructured absorber on the thickness and number of CdTe active layers is investigated. The equation for the photon absorption coefficient (α) used is based on the partial momentum k -selection approach. Theoretical results show that absorption greater than 4×10 4 cm −1 is obtained when the thickness of the active layer reaches 50 A. Similarly, with each additional CdTe active layer in the heterostructured absorber, a relative increase of 0.5×10 4 cm −1 in photon absorption is achieved. The relation between photoelectric quantum efficiency and photon absorption is determined by the number and thickness of the CdTe active layers in the heterostructured absorber. A quantum efficiency greater than 0.9 is obtained using 15 active layers with a thickness of 50 A.

On the effect of superfluid flows on the interaction of microwaves with He II

The paper proposes a possible mechanism of interaction of microwaves with superfluid helium that results in an experimentally observed narrow peak of microwave absorption on the frequencies by the order of the roton frequency. The obtained microwave photon absorption coefficient depends on the local equilibrium distribution function which is established due to fast roton-roton and roton-phonon interactions. With the availability of superfluid flows, the local equilibrium distribution function depends on their velocity. The critical velocity of the flows, at which the absorption of microwaves is replaced by their radiation, is found.

Enhanced nonlinear optical response of metal nanocomposite based photonic crystals

We demonstrate enhanced nonlinear optical response from a one-dimensional metal nanocomposite based photonic crystal. A three-fold increase in the two photon absorption coefficient was observed for the photonic crystal structure when compared to a single layer of the metal nanocomposite having comparable metal content. The photonic crystal structure also shows a reduction in the optical limiting threshold by a factor of seven. The combination of metal nanoparticles with appropriately designed plasmon resonance in combination with photonic crystal structure provides an attractive approach for developing practical nonlinear optical devices with low thresholds and wide spectral bandwidth.