State Absorption Cross Section Research Articles

Absorption cross-sections of Cr4+:YAG at 946 and 914 nm

Abstract The ground and excited state absorption cross-sections of the Cr4+:YAG saturable absorber at the 4F3/2–4I9/2 transition wavelengths of Nd3+ (946 nm for Nd3+:YAG, 914 nm for Nd3+:YVO4) are measured by a pump–probe method.

NONLINEAR OPTICAL RESPONSE AND REVERSE SATURABLE ABSORPTION OF RARE EARTH PHTHALOCYANINE IN DMF SOLUTION

Nonlinear optical response and reverse saturable absorption behavior of various rare earth phthalocyanines such as Nd , Eu , Sm and La in dimethyl formamide (DMF) solution were studied under high power Nd:YAG laser excitation. Excited state absorption cross-sections and two-photon absorption cross-sections of these systems are measured from the limiting characteristics. The SmHPc 2 system yields maximum value for excited state absorption cross-section and its potential application in DMF as a suitable optical limiter is also discussed.

Optical limiting properties of water-soluble phthalocyanine derivatives

The optical-limiting properties of several water-soluble phthalocyanine derivatives in aqueous solution were measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex of the derivatives were determined with the Z-scan technique. The results showed that the phthalocyanine derivatives are materials for reverse saturable absorption. It was noted that the optical limiting performance of the phthalocyanine derivatives in aqueous solutions can be controlled through the addition of alkalis. These phthalocyanine derivatives possess good solubility in water and optical limiting controllability, which give rise to their use for practical applications.

The primary investigation of optical-limiting effects of optical active phthalocyanine derivative TMBO-SiPc

Abstract The optical-limiting property of an optically active phthalocyanine derivative with different configuration in chloroform solution was measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σ ex of the derivative was determined with the Z-scan technique. The results showed that the phthalocyanine derivative possesses larger σ ex than the ground state absorption cross-section σ 0 , indicating that it is a material for reverse saturable absorption. And it is specially noticed that the change in the optically active configuration affects its optical-limiting property significantly.

Optical nonlinearity of organic dyes as studied by Z-scan and transient grating techniques

The excited state absorption cross-section of 5,5′-dichloro-11-diphenyl-amino-3,3′-diethyl-10, 12-ethylinethiatricarbocyanine perchlorate (IR140) have been measured by using a single beam transmission technique. Z-scan experiments have been used to find out a few nonlinear parameters. The excited state relaxation times have also been measured by using laser induced transient grating (LITG) technique.

Optical limiting and picosecond relaxation of carbocyanines upper electronic states

Nonlinear absorption, anomalous fluorescence and relaxation of high-lying electronic states in six carbocyanine dyes, including cryptocyanine (DCI), DDI, DTDCI, DTTCI, DOTCI and HDIDCI, in solution and in polymer, were studied by means of picosecond transient absorption spectroscopy and nonlinear transmission experiments. Absorption cross-sections of the S 1 →S n transition, and decay rates of the second singlet excited state, S 2 , were measured. All dyes showed strong reverse saturable absorption in the 450–600 nm region with large excited to ground state absorption cross-section ratios. For DTDCI this ratio, at 470 nm, was measured to be 350, which is the largest ever reported. All molecules have shown strong optical limiting effect. However, in all molecules except DCI a saturation of the optical limiting process was observed as expected, owing to relatively long, up to 17.5 ps, lifetime of the S 2 state. The S 2 state fluorescence quantum yields were also measured.

Investigation of optical nonlinearities of azo nickel chelate compound by the Z-scan technique

Abstract With picosecond pulses at a wavelength of 532 nm, we measured the nonlinear transmittance of Ni-azo metal chelate compound film by the Z -scan technique. The nonlinear optical response was determined fluence dependent. The excited singlet state absorption cross-section σ es and the nonlinear refraction cross-section σ r as well as the effective third-order nonlinear refractive index n 2 eff have been obtained.

Wavelength dependent studies of nonlinear absorption in zinc meso-tetra(p-methoxyphenyl)tetrabenzoporphyrin (Znmp TBP) using Z-scan technique

We report here, our experimental results and theoretical analysis of the dispersion data of nonlinear absorption in zinc meso-tetra-(p-methoxyphenyl)tetrabenzoporphyrin (ZnmpTBP). Using a ns optical parametric oscillator (OPO) we obtain the open aperture Z-scan data over the visible region starting from 480 nm to 600 nm. We use a more general five-level model for evaluating the excited state parameters like excited state absorption coefficients, two-photon absorption coefficient, etc. Due to its large excited state absorption cross-sections this material acts as a very good candidate for a broadband optical limiter in the visible region.

Optical limiting properties of optically active phthalocyanine derivatives

The optical limiting properties of four optically active phthalocyanine derivatives in chloroform solutions and epoxy resin thin plates were measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex and refractive-index cross-section σr were determined with the Z-scan technique. These chromophores possess larger σex than the ground state absorption cross-section σ0, indicating that they are the potential materials for reverse saturable absorption (RSA). The negative σr values of these chromophores add to the thermal contribution, producing a larger defocusing effect, which may be helpful in further enhancing their optical limiting performance. The optical limiting responses of the thin plate samples are stronger than those of the chloroform solutions.

Excited state absorption around 1060 nm of Nd 3+ ions in Ba 2NaNb 5O 15 crystal

Abstract The Judd–Ofelt intensity parameters of Nd3+ ions in the nonlinear Ba2NaNb5O15 crystal have been determined, presenting values of Ω 2 =1.91×10 −20 , Ω 4 =2.61×10 −20 and Ω 6 =2.36×10 −20 cm2. These values were used to calibrate the excited state excitation measured around the main laser radiation at 1060 nm ( 4 F 3/2 → 4 I 11/2 channel) in terms of absorption cross-section units (cm2). The experimental results, using a two-beam experiment, show a low value of the excited state absorption cross-section (

Nonlinear light absorption in meso-substituted tetrabenzoporphyrin and tetraarylporphyrin solutions

The characterization of fluence-dependent nonlinear absorption and the excited state absorption cross-sections of the zinc complexes of tetrabenzoporphyrin with meso-substituents of phenyl and thienyl (Ia and Ib), and the zinc and lead complexes of porphyrin with meso-substituent of 3,4,5-trimethoxyphenyl (IIa and IIb) are determined with the Z-scan method. The results from Ia and Ib are comparable with the literature report. The lead porphyrin of IIb gives the largest triplet excited state absorption cross-section (σexT=3.3×10−16cm2) among these compounds, and shows very strong optical limiting power as a result. Whereas we obtain the smallest σexT=2.5×10−17 cm2 for the zinc porphyrin bearing four electron withdrawing groups of benzoquinone (compound III), which exhibits unique linear absorption property at 532 nm. This result could be due to the rapid decay of its lowest triplet state to yield both long-lived triplet biradicals and S0 states.

Excited state absorption of pump and laser radiations in NYAB non-linear crystal operating at 1.3µm for visible laser light generation

Excited state absorption of laser (≅ 1.3 µ m, corresponding to the laser channel) and pump (790-860 nm) radiation have been investigated in Nd doped YAl 3 (BO 3 ) 4 non-linear laser crystal. Laser gain slope efficiency measurements as a function of pump wavelength have been used to estimate the excited state absorption of pump radiation. On the other hand, excited state absorption cross-section in the 1300−1400 nm wavelength range has been measured by using two beam spectroscopy. We have obtained that excited state absorption cross-section for pump radiation is negligible whereas around 1.3 µ m it is comparable to the stimulated emission cross-section from 4 F 3/2 state, so that the net gain cross-section becomes negative for certain wavelengths.

Excited state absorption at 1.06 μm as the origin of non-unity quantum yield in neodymium doped glasses

Abstract The presence of excited state absorption at the 1.06 μm lasing wavelength of Nd doped glasses is demonstrated. The excited state absorption cross-section for silicate (LG680) and phosphate (LG760) glasses was extracted from gains measurements associated to a theoretical model which is described in this paper. From both measurements and the Judd–Ofelt formalism calculation, we show that excited state absorption effect in Nd-doped glasses is at the origin of non-unity quantum yield. The values obtained imply that excited state absorption in Nd doped glasses may constitute a significant optical loss, especially for silicate glass.

Effective stimulated emission and excited state absorption measurements in the phenylene–vinylene oligomer (1,4-bis-(alpha-cyanostyryl)-2,5-dimethoxybenzene))

Abstract The pump probe technique was used to measure the effective stimulated emission and excited state absorption cross-sections of the phenylene–vinylene oligomer (1,4-bis-(alpha-cyanostyryl)-2,5-dimethoxybenzene) dissolved in toluene for different probe wavelengths. The effective stimulated emission cross-section was calculated from σ SE-eff = σ SE − σ ESA and found to be positive. The possible laser tuning ranges have been determined. The spectral and temporal behavior of the optical transitions were investigated. The dynamics of these optical transitions permitted direct measurements of the lifetime of the lowest triplet state, and was found to be of the order of 11 ms.

Two-photon absorption and two-photon-induced absorption of some organic liquids at 347.15 nm

The two-photon absorption cross-sections and effective excited- state absorption cross-sections at 347.15nm of the organic liquids ethylene glycol, methanol, ethanol, tetrahydrofuran, glycerol, cyclohexane, 1,4-dioxane, 1,2-dichloroethane, dichloromethane, chloroform, dimethylsulfoxide, N,N-dimethylformamide, o-xylene, m- xylene, p-xylene and xylene (isomer mixture) have been determined using second harmonic picosecond pulses of a mode-locked ruby laser system. Linear and circular polarized pump pulse transmission measurements were performed to determine the two linear independent two-photon absorption susceptibility components. Linear polarized probe pulse transmission measurements after pump-pulse passage were carried out to determine excited singlet state relaxation times.

Synthesis and Optical Limiting Characterization of a Porphyrin-Buckminsterfullerene Dyad

ABSTRACTThe optical limiting performances of donor-buckminsterfullerene (C60) dyads have hitherto been unreported. The predicted large excited state absorption cross-section of such dyads in their charge-separated states would enable them to exhibit enhanced optical limiting relative to their individual components. We report herein the synthesis and optical limiting characterization of a novel porphyrin-buckminsterfullerene dyad, in which the porphyrin and C60 moieties are held within close proximity of one another by an o-phenylene bridge. The porphyrin-C60 dyad was synthesized via 1,3-dipolar azomethine ylide cycloaddition, and was obtained in 37.0% yield. Optical limiting measurements at 532 nm using 3-ns pulses show that the limiting performance of the dyad is poorer compared to its model compounds. Possible reasons for the worsened performance of the dyad will be discussed.

Comparative study of the spectroscopic properties of Cr 4+-doped LiAlO 2 and LiGaO 2

Abstract A detailed spectroscopic study of the optical characteristics of the tetrahedrally coordinated Cr4+ ion in LiAlO2 and LiGaO2 is given. From absorption and excitation measurements the crystal field parameter Dq and the Racah parameter B were determined to be Dq=1065 cm−1, B=450 cm−1, and Dq/B=2.4 for LiAlO2 and Dq=1055 cm−1, B=428 cm−1, and Dq/B=2.5 for LiGaO2. For the Racah parameter C only a lower limit can be given, i.e. 2417 cm−1 for LiAlO2 and 2667 cm−1 for LiGaO2. Due to the strong crystal field splitting — caused by the low site symmetry — the 3 B ( 3 T 2 ) crystal field component is the metastable and thus the emitting level. In the low-temperature absorption and emission spectra the expected three spin–orbit components of the 3 B level are found at 8273, 8296, and 8300 cm−1 for Cr4+:LiAlO2 and 8610, 8623, and 8632 cm−1 for Cr4+:LiGaO2. The emission lifetime of Cr4+ in LiAlO2 is 95 μs at 10 K and single exponential. In Mg-codoped LiAlO2 and in LiGaO2 the Cr4+ decay is double exponential. In Cr,Mg:LiAlO2 two centers can be clearly distinguished, while in Cr:LiGaO2 a variety of centers are observed, probably due to different charge compensation processes between Li, Ga, and Cr. The quantum efficiencies at room temperature are 42% for Cr:LiAlO2 and 23% for Cr:LiGaO2. Already at low temperature nonradiative decay processes occur. The temperature dependence of the lifetimes were analyzed with the model of Struck and Fonger. Excited state absorption measurements indicate that in the spectral region of the emission the excited state absorption cross-section is larger than the stimulated emission cross-section. Therefore laser oscillation is unlikely in these systems.

The excited state absorption of Er3+:LiYF4 and Er3+:Na5Y9F32

The excited state absorption cross-sections in π and σ polarisations are obtained for the transition 4I13/2→4I11/2 and 4I13/2→4I9/2 in Er3+:LiYF4. The population ratio between the two excited states 4I11/2 and 4I13/2 in Er3+:LiYF4 and Er3+:Na5Y9F32 have been performed using the measured gain cross-sections in the range 2.6–3 μm. The experiments have been done for two pump wavelengths—488 nm and 1.534 μm.

Resonant Nonlinear Optical Studies on Porphyrin Derivatives

The nonlinear optical properties of three porphyrin derivatives (T3,4 BCEMPP, T4 CEMPP and TPP) doped in boric acid glass were probed using the Z-scan technique at different argon-ion laser wavelengths. The nonlinear transmission characteristics of T3,4 BCEMPP and T4 CEMPP exhibit saturable absorption at 457.9 nm and 476.5 nm while these are dominated by excited state absorption at 488.0 nm. However, in the case of TPP, the excited state absorption dominates the nonlinear characteristics except at 457.9 nm. The experimental observations are explained by using the four-level saturable absorber model. Saturation intensity, excited state absorption cross-section, light-induced changes in the absorption and the refractive index along with its sign were determined at these argon-ion laser wavelengths. Furthermore, optical limiting characteristics of these samples were studied. The observed limiting action is consistent with the Z-scan studies.

Z-scan studies in fluorescein-doped boric acid glass

The non-linear response of fluorescein-doped boric acid glass was probed using the Z-scan technique. A striking contrast was observed in its non-linear transmission characteristics at different argon-ion laser wavelengths. The non-linear transmission characteristics exhibit strong saturation behaviour at 457.9nm whilst at 476.5nm and 488.0nm the response is dominated by intense excited state absorption. The experimental observations are explained using the four-level saturable absorber model. The excited state absorption cross-section, saturation intensity, light induced absorption and refraction changes have been determined along with the sign of the non-linearity at various argon laser wavelengths. The optical limiting characteristics of fluorescein at 476.5 nm and 457.9 nm are also reported. The behaviour of the sample was in agreement with the Z-scan observations.