Nonlinear Absorption Effect Research Articles

Sulfur-bridged iron and manganese carbonyl clusters: synthesis, structure and nonlinear optical properties of [(μ-SPh) 2Fe 2(CO) 6] 2(μ 4-S) and [PPN][(μ 3-S) 2Mn 3(CO) 9

Two sulfur-bridged carbonyl clusters [(μ-SPh) 2Fe 2(CO) 6] 2(μ 4-S) 1 and [PPN][(μ 3-S) 2Mn 3(CO) 9] 2 were synthesized for study of the third-order nonlinear properties. Cluster 1 consists of two doubly bridged Fe 2(CO) 6 fragments bonded for a center μ 4-sulfur atom of the distorted tetrahedron. Each fragments is also bridged with the sulfur from a thiophenol group. Cluster 2 exhibits a D 3 h equilateral triangular frame with three Mn(CO) 3 units apically bicapped by the two μ 3-sulfur atoms. The moderate third-order optical nonlinear absorption and refraction effects of clusters 1 and 2 in CH 2Cl 2 solution were observed at 532 nm by using of the z-scan measurements of an 8-ns pulsed laser. The third-order nonlinear optical susceptibilities, χ (3), were detected with 5.4×10 −13 and 1.2×10 −13 esu for 1 and 2, respectively, in solution. The structure–property relationship in clusters is also discussed in the paper.

Optical 3D-storage in sol–gel materials with a reading by optical coherence tomography-technique

We report on the recording of 3D optical memories in sol–gel materials by using a non-linear absorption effect. This effect induces a local change in optical properties of the material which is read and quantified with a high-resolution full-field optical coherence tomography setup. It is the first time that this technique is used for this purpose. Data recording was performed by focused picosecond (ps) single-pulse irradiation at 1064 nm with energy densities of 10 and 33 J/cm 2 per pulse.

Effect of nonlinear refraction and two-photon absorption on the optical limiting in amorphous chalcogenide films

This paper reports on the results of investigations into the nonlinear optical characteristics of chalcogenide films (As2S3, As20S80, 2As2S3/As2Se3, 3As2S3/As2Se3). The nonlinear refractive indices and two-photon absorption coefficients for these films are measured using the Z-scan technique at wavelengths of a picosecond Nd: YAG laser (λ=1064 and 532 nm). The optical limiting due to Kerr-type nonlinearities is analyzed.

Mid-infrared laser ablation of a hard biocomposite material: mechanistic studies of pulse duration and interface effects

Cortical bone is a hard biocomposite material comprising protein, mineral crystal and water. We have studied mid-infrared laser ablation of bovine cortical bone using a free-electron laser (FEL) and an Er:YAG laser at a wavelength of 2.94 μm, comparing pulse duration and interface effects. Bovine bone samples were irradiated both in air and while irrigating with biologically inert perfluorocarbon. The perfluorocarbon dissipates heat and acoustical stress, and at the lowest scanning speeds, appears to inhibit carbonization. The ablation efficiency and etch rates are critically dependent on scanning speed, laser fluence, and the molecular weight and depth of the perfluorocarbon. The observed phenomenology is consistent with an explosive vaporization as the principal mechanism of ablation; in addition, there may be nonlinear absorption effects.

Experimental evaluation of indicators of nonlinearity for use in ultrasound transducer characterizations

Because the number of applications for medical ultrasonic devices continue to increase and, hence, the number of diagnostic ultrasound (US) systems increase, there is a need to reliably characterize the sources in terms of their output pressures. Currently, the transducers are characterized by making pressure measurements in water for every voltage range applied to the source and, then, linearly derate the measured pressure values to estimate the derated acoustic pressure levels. The process is time-consuming and inaccuracies are introduced in the derating process due to nonlinear effects. Therefore, there is a need to find an indicator of nonlinearity that could classify the measured pressure waveform as either linear, where the derating procedure would yield an accurate derated acoustic pressure estimate, or nonlinear, where the derating process would fail. Eight different indicators of nonlinearity were evaluated experimentally using spherically focused US transducers. The transducers were selected to test the indicator sensitivity to frequency (3 to 8 MHz), f-number (1 and 2), and transducer diameter (1.905 and 5.08 cm). Sensitivity to drive voltage conditions was also tested by exciting one of the transducers with pulses of different duration and phase. None of the eight nonlinearity indicators yielded consistent results. The lack of consistency resulted from the competing effects of nonlinear absorption and asymmetrical distortion, which have yet to be combined into a unified theory. (E-mail: wdo@uiuc.edu)

Properties of polarized laser-induced birefringent gratings in azobenzene-doped poly(methyl methecrylate) optical fibers

Birefringent gratings induced by 532 nm polarized laser in an azobenzene-doped polymethyl methacrylate (PMMA) fibers and blocks were investigated. Significant photo-induced birefringence with about 3.0×10 −5 has been observed from the fiber. It was found that there is an intensity threshold, which is 0.29 mW/cm 2 at 532 nm. The birefringence decayed gradually when the writing laser turned off. So the dynamic process of the birefringence was studied. Both the rise and the decay processes of the birefringence include an initial “fast” response mode and a subsequent “slow” response mode. Both the fast response and the slow response become faster with increasing irradiating laser intensity. The birefringence was induced by the combination of the nonlinear absorption, linear absorption and thermal effect.

Third order nonlinear optical studies in europium naphthalocyanine using degenerate four wave mixing and Z-scan

Third order nonlinear susceptibility χ (3) and second hyperpolarizability 〈 γ〉 of a bis–naphthalocyanine viz. europium naphthalocyanines, Eu(Nc) 2, were measured in dimethyl formamide solution using degenerate four wave mixing at 532 nm under nanosecond pulse excitation. Effective nonlinear absorption coefficient, β eff and imaginary part of nonlinear susceptibility, Im( χ (3)) were obtained using open aperture Z-scan technique at the same wavelength. Optical limiting property of the sample was also investigated. The role of excited state absorption in deciding the nonlinear properties of this material is discussed.

Study on a series of pentanuclear planar ‘open’ clusters: synthesis, characterization, strong third-order optical nonlinearities and superior optical limiting properties

A series of new candidates as nonlinear optical materials, heterothiometallic clusters [MS4Cu4X2(py)6] (X = I, M = W, 1, Mo, 2; X = Br, M = W, 3, Mo, 4) have been synthesized via two comparative synthetic routes for third-order NLO studies. Single-crystal X-ray diffraction shows that the neutral clusters assume pentanuclear planar ‘open’ structures. Their optical responses to incident pulsed laser exhibit very large optical limiting effects, which are simulated by using excited-state absorption theory, with limiting thresholds of 0.07–0.10 J cm−2 for clusters 1–4, and these effects should make this series of clusters among the most promising optical limiters. The strong third-order optical nonlinear absorption and optical self-focusing effects of clusters 1–4 in DMF solution were observed in the Z-scan measurements of an 8-ns pulsed laser at 532 nm. The corresponding effective third-order nonlinear optical susceptibilities of this series of clusters were found to be the largest among all kinds of heterothiometallic clusters, and their third-order nonlinear hyperpolarizabilities are also reported. The nonlinear effects for these four clusters in DMF solution have also been investigated by time-resolved pump–probe experiments to provide direct evidence on the physical origin of the observed OL effects. The nonlinear optical properties of this series of clusters 1–4 were compared with other NLO cluster compounds studied previously and revealed a qualitative structure/NLO property correlation.

Optical bistability derived from the negative nonlinear absorption effect in erbium doped materials

Optical bistability derived from the negative nonlinear absorption effect was investigated in erbium-doped garnet crystals, glasses and semiconductors using a 1.53 μm laser diode. The optical bistability was observed in a laser intensity range of the order of mW cm −2. The transmitted laser intensity, propagating through the sample, decreased exponentially by the familiar exponential law. However, the amplitude of the optical bistability increased logarithmically as the sample length was increased. The amplitude decreased exponentially when the incident laser intensity was decreased. The optical bistability can be explained by considering an enhanced absorption for a multi-level system of the erbium ion.

All-optical signal inverter derived from negative nonlinear absorption effect

A model of the negative nonlinear absorption effect (NNA effect) with the laser wavelength of about 1.5 μm is proposed. When the intensity of the incident laser irradiated on Er doped materials varied in Er:yttrium aluminum garnet (YAG), the NNA effect was observed, i.e. the transmitted laser intensity shows opposite phase of the incident laser at the wavelength of about 780 nm. The wavelength of the laser is related to the both of the 4I 15/2– 4I 9/2 and the 4I 13/2– 2H 11/2 transitions of Er 3+ ion. In addition, the NNA effect is found in erbium-doped materials of another wavelength (about 1.5 μm) of the laser, which is related to the both of the 4I 15/2– 4I 13/2 and the 4I 9/2– 2H 11/2 transitions of Er 3+ ion. In the model we have pursued the energy-level system of the Er 3+ ion for the former wavelength. In this study, we analyzed the mechanism of the NNA effect at the wavelength of about 1.5 μm.

Linear and Nonlinear Optical Properties of an Erbium Two-Photon Dye Salt

The optical properties of erbium tri-4-{[4-(2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl)-phenyl]-phenyl-amino}-benzoate, viz., an erbium two-photon dye salt, were investigated in THF solutions. Using the corresponding two-photon dye monomer acid as a reference material, we observed that the photoluminescence of the erbium two-photon dye salt was quenched significantly while nonlinear absorption for infrared nanosecond excitation was enhanced compared to the monomeric form. On the other hand, femtosecond Z-scan measurements suggest the same two-photon absorption coefficient for the dye in both forms. A possible explanation is that the presence of erbium enhances the intersystem crossing rate and that the nonlinear absorption effect must be due to two-photon absorption and subsequent triplet−triplet excited-state absorption for nanosecond pulsed excitation. Our analysis of the nonlinear absorption (power limiting) data suggests that the intersystem crossing rate is 3 orders of magnitu...

NONLINEAR ABSORPTION AND OPTICAL LIMITING IN SOLUTIONS OF SOME RARE EARTH SUBSTITUTED PHTHALOCYANINES

Effective nonlinear absorption coefficient, β eff , of solutions of some rare earth substituted phthalocyanines (viz: Sm(Pc)2, Eu(Pc)2 and LaPc) was measured using open aperture Z-scan technique under nanosecond pulse excitation at 532 nm. The effect of nonlinear absorption on optical limiting in these samples was also investigated. Both nonlinear absorption and optical limiting phenomena in these samples are attributed to sequential two-photon absorption (STPA) process.

All-optical inverted operational amplifier derivedfrom negative nonlinear feedback systems

An all-optical inverted operational amplifier that has the characteristic of being both an optical inverter and an amplifier designed based on the negative nonlinear absorption effect has been realised by using an erbium-doped fibre amplifier with a feedback ring resonator. A NOR-type logic gate operation has been demonstrated using two optical signals of 1.53 µm.

All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals

All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals were demonstrated using a feedback ring resonator and an erbium-doped fiber amplifier. The output modulation degree depends on the dosage of erbium and the amplifier gain. The maximum value was 83% when the input modulation degree was 55%. The inverted output signal was amplified by approximately ten times as large as the input signal. The output modulation degree increased abruptly at an amplifier gain of more than 25 dB when it has feedback. The device was characterized by the property that optical signals for 1.53 μm light can be inverted and amplified.

Optical Bistability of the Negative Nonlinear Absorption Effect in Erbium-Doped Fibers Using a 1.5 µm Laser Diode

Optical bistability derived from the negative nonlinear absorption effect was investigated in 470 ppm erbium-doped fibers using a 1.5 µm laser diode. Optical bistability was observed in a laser intensity range of 0.3 W/cm2 to 2.5 kW/cm2 at a fiber length of 6 m. The transmitted laser intensity (Iout), propagating through the fiber, decreased exponentially in accordance with the well-known exponential law. However, the amplitude of the optical bistability (ΔIout) increased logarithmically as the fiber length was increased. It was clarified that ΔIout was proportional to the product of exp (-L) and log (L) as a function of the fiber length (L). The optical bistability can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.

Nonlinear optical properties of mixed Mo/Fe, mixed chalcogen clusters Cp 2Mo 2Fe 2STe(CO) 7 and Cp 2Mo 2Fe 2(μ3-S)(μ3-Te)(μ2-SPh)(μ3-H)(CO) 5

Studies of the third order optical nonlinearity of the mixed-metal, mixed chalcogen clusters Cp 2Mo 2Fe 2STe(CO) 7 and Cp 2Mo 2Fe 2(μ3-S)(μ3-Te)(μ2-SPh)(μ3-H)(CO) 5 using 532 nm, 6 ns laser pulses are reported. The second compound is the first example in literature of a mixed Fe/Mo mixed chalcogen complex containing a bridging thiolate group. The effective nonlinear absorption coefficient and nonlinear index intensity coefficient of these compounds are measured by the Z-scan technique, from which the corresponding cubic hyperpolarizabilities are evaluated. The obtained values indicate a high nonlinearity comparable to some of the best values reported previously for cluster compounds. Both compounds show strong optical limiting. In addition, their photostability is found to be much superior to many of the previously reported highly nonlinear clusters.

Thermo-optical effect and saturation of nonlinear absorption induced by gray tracking in a 532-nm-pumped KTP optical parametric oscillator

We present experiments that show that gray tracking modifies the parametric gain and the generated wavelengths of a KTP optical parametric oscillator pumped at 532 nm near degeneracy. These perturbations occur over a limited range of pump intensity. We propose a satisfactory model that takes into account photochromic damage, the thermo-optical effect, and the combined processes of creation and saturation of a two-photon absorber at 532 nm. The temperature dependence of Sellmeier equations of KTP is also established at 20-200 degrees C.

Nonlinear optical absorption in undoped and cerium-doped BaTiO3 thin films using Z-scan technique

BaTiO 3 and BaTiO3:Ce thin films with good surface morphology and tetragonal perovskite structure were fabricated on quartz substrates by pulsed-laser deposition technique at a deposition temperature of 750 °C. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties of the films were investigated using Z-scan method. The films display large nonlinear absorption effects. The two-photon absorption coefficients of the BaTiO3 and BaTiO3:Ce films were determined to be 51.7 and 59.3 cm/GW, respectively. All the results show that undoped and cerium-doped BaTiO3 ferroelectric thin films have potential applications in absorbing-type optical devices.

PHOTON ABSORPTION OF CONDUCTION BAND ELECTRONS AND ITS EFFECTS ON THE DAMAGE PRO CESSES

By second-order and third-order perturbation theory, the one-photon and two-phot on absorption rates of conduction band electrons are calculated. The effects of nonlinear absorption and the absorption with electron-hole scattering on the dam age processes are discussed.

Optical Bistability and Negative Nonlinear Absorption Effect at 1.5 .MU.m in Highly Er3+-Doped Glasses.

The dependence of the negative nonlinear absorption effect at 1.5μm on the sample temperature, the modulation frequency and the sample length were investigated in glasses containing amounts higher than 20mol% Er3+. Reversed-phase waveforms were observed in the temperature range -260-600°C and at modulation frequencies from 1kHz to 10GHz in an erbium-doped phosphate glass. With increasing temperature, the amplitude of the reversed-phase waveforms decreases exponentially according to two separate steps. Optical bistability in the transmitted laser was observed in the range of incident laser intensity of 30μW/cm2-2.4mW/cm2. The transmitted laser intensity propagating through the glass decreased exponentially according to the well-known exponential law. However, the amplitude of the optical bistability increased logarithmically as the sample length was increased. The negative nonlinear absorption effect can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.