Reverse Saturable Absorption Mechanism Research Articles

Generation of dark solitons in a self-mode-locked Tm-Ho doped fiber laser

We present the first experimental demonstration of self-mode-locked dark solitons in a Tm-Ho doped fiber laser at 1.93 μm with an average power of 149.6 mW and repetition rate of 15.9 MHz. In our system, the dark solitons are generated by self-mode-locking via exploiting the reverse saturable excited-state absorption of a gain fiber, which achieves a higher damage threshold and accordingly laser power over conventional methods based on extra saturable absorber or nonlinear polarization rotation. In the experiments, we study the evolution from high-order to low-order dark solitons by adjusting the pump power, which is attributed to the excited-state absorption in Tm3+ between 3F4 and 3H4 energy level. Simulations have been performed to show dark soliton generation by the reverse-saturable absorption mechanism in Tm-Ho doped fiber laser based on the extended nonlinear Schrödinger equation. The results confirm our new approach can generate stable dark solitons of high average power, which may find important applications in laser sensing and laser communications.

Optical nonlinearities of centrosymmetric pure and cerium doped calcium tungstate dumbbell shaped nanoparticles

An investigation was performed on the nonlinear optical behavior of pure and cerium (Ce3+) doped calcium tungstate (CaWO4) nanoparticles synthesized by hydrothermal method. The scheelite tetragonal structure was confirmed using X-ray diffraction. The morphological transformation from spherical to dumbbell-shaped particles was evidenced by FESEM micrographs augmented from the TEM images. Different vibrational modes obtained from Raman spectra confirms the presence of Ca–O–Ca and W–O–W functional groups. The Photoluminescence response was observed in the blue green region at an excitation wavelength of 325 nm. With the utilization of UV–Visible DRS spectroscopy the variations in the optical band gap was calculated. The valence state and chemical composition of the elements along with their binding energies has been calculated using XPS. The magnetic behavior of CaWO4 in its doped and undoped state is examined through VSM analysis. A measure of the nonlinearities with emphasis to the mechanism of Reverse Saturable Absorption (RSA) supported by open and closed aperture data is recorded. Kerr nonlinearity, Two photon absorption β and third order nonlinear susceptibility χ(3) were also calculated. The present work provides an insight on the dependence of linear and non-linear optical properties of CaWO4 with dopant concentration.

Tunneling-induced optical limiting in quantum dot molecules

We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecule system, induced by an interdot tunneling. Also, the effect of system parameters on the limiting performance is investigated; interestingly, the tunneling rate can affect the limiting performance of the system so that the threshold of the limiting behavior can be a function of the input voltage, allowing the optimization of the limiting action. Furthermore, by investigating the absorption of the probe field, it is demonstrated that the optical limiting is due to a reverse saturable absorption mechanism; indeed, analytical results show that this mechanism is based on a cross-Kerr optical nonlinearity induced by the tunneling. Additionally, the limiting properties of the system are studied by using a Z-scan technique.

The effects of intersystem and reverse intersystem crossing on the optical limiting properties of C60

By presenting a theoretical steady-state rate equation analysis, we demonstrate an efficient optical power limiting in a fullerene system, which can be attributed to a reverse saturable absorption mechanism. The limiting behavior, characterized by means of the sample’s transmittance, is explained via the population redistribution among singlet and triplet levels. In addition, the effects of intersystem crossing and reverse intersystem crossing rates on the limiting behavior are investigated. Our numerical results show how these rates alter the optical limiting performance; indeed, the intersystem crossing has a constructive role in decreasing the optical limiting threshold. In addition, a theoretical investigation of the z-scan technique is employed to further characterize the power limiting properties.

Photophysical and nonlinear optical characteristics of pyridyl substituted phthalocyanine - Detonation nanodiamond conjugated systems in solution

In this study photophysical, nonlinear absorption and optical limiting properties of detonation nanodiamonds (DNDs)-phthalocyanine nanoconjugate systems containing: 2,9(10),16(17),23(24)-tetrakis-(4-pyridyloxy) phthalocyaninato (H2TPPc), 2,9(10),16(17),23(24)-tetrakis-(4-pyridyloxy) phthalocyanato zinc(II) (ZnTPPc) and 2,9(10),16(17),23(24)-tetrakis-(4-pyridyloxy) phthalocyanato silicon(IV) hydroxide (Si(OH)2TPPc), were investigated in dimethylsulfoxide solution. Pcs were non-covalently linked to nanondiamonds (also covalently linked for Si(OH)2TPPc) and investigated using 532 nm laser excitation at 10 ns pulses for their optical limiting properties. Complexes that have higher triplet state absorption also possessed enhanced nonlinear optical behaviour following reverse saturable absorption mechanism. Superior optical performance is observed when the Pcs had a central metal with axial ligands conjugated to DNDs in solution. Nanoconjugate of DNDs-Si(OH)2TPPc and respective Pc in solution gave the highest imaginary third-order susceptibility (Im[X(3)]) and hyperpolarizability (γ) at 2.91 × 10−8 and 3.17 × 10−8 esu and 3.88 × 10−28 and 4.22 × 10−28 esu, respectively, with Ilim value of 0.47 and 0.39 J·cm−2.

Nonlinear optical study of 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts by Z-scan technique

Z-scan technique was used to investigate the nonlinear optical properties of 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts. The new 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts were synthesized and characterized using UV–visible, FTIR and NMR measurements and the characterization spectra confirm the expected molecular structure of the prepared salts. Measurements were performed with a CW Diode laser at 635nm wavelength and 26mW power. The nonlinear optical absorption coefficient (β) and nonlinear refractive index (n2) of the 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride was affected by OH group. The excited-state absorption cross sections (σex) and the ground -state absorption cross sections (σg) were calculated for the two studied compounds. It was found that the σex is larger than the σg, indicating that the reverse saturable absorption mechanism (RSA) is the dominating mechanism for the observed absorption nonlinearities.Our results suggest that this material should be considered as a promising candidate for future optical devices applications.

Z-scan measurements of single walled carbon nanotube doped acetylenedicarboxylic acid polymer under CW laser

Z-scan measurements of single walled carbon nanotube (SWCNT) doped with acetylenedicarboxylic acid (ADC) polymer are performed using a CW diode laser at 635nm wavelength with 17mW power. The nonlinear absorption coefficient (β), nonlinear refractive index (n2), the real and imaginary parts of the third-order nonlinear optical susceptibility (Re χ3), (Im χ3) of the investigated samples are calculated. It was found that the β values decrease with increase in on-axis input intensity I0. Also, these values are found to be proportional with sample concentrations. The excited-state absorption cross sections were calculated to be at σex=5.08×10−14cm2 for the (SWCNT) and at 15.1×10−14cm2 for the ADC polymer. It was found that the σex is larger than ground-state absorption cross sections, indicating that the reverse saturable absorption mechanism (RSA) is the dominating mechanism for the observed absorption nonlinearities.

Nonlinear dynamics and optical power limiting of nanoseconds pulses in naphthalocyanines and phthalocyanines with central metals gallium and indium

Abstract The optical dynamics of octa-(4-tert-butylphenoxy) substituted naphthalocyanines and phthalocyanines with different central metals (Ga, In) were investigated for 532 nm–7 ns laser pulses. In this work, we used numerical theoretical method with two-dimensional paraxial field equation and rate equations solving by Crank–Nicholson method. A five-level model was proposed to simulate the dynamical processes and the prominent optical limiting mechanism with long pulses is the sequential (singlet–singlet) × (triplet–triplet) two-photon absorption. The theoretical results indicate that both naphthalocyanines and phthalocyanines exhibit good optical limiting performances, which is attributed mainly to the reverse saturable absorption mechanism. The naphthalocyanines with larger difference of absorption cross sections and faster rate of the intersystem crossing transition between triplet and singlet states exhibit better optical limiting behaviour.

Wavelength dependent resonant nonlinearities in a standard saturable absorber IR26 on picosecond time scale

Nonlinear optical properties of a standard dye IR26 have been studied by using the Z-scan technique to decipher the difference in the mechanism of nonlinear absorption on picosecond time scale at two wavelengths i.e. at 1064 nm and 532 nm. A prominent contribution of nonlinear absorption is observed in the Z-scan profiles at 1064 nm. The dye exhibits the mechanism of self-defocusing at 1064 nm in contrast to that of self-focusing at 532 nm. While the two photon absorption has been found to be the dominant mechanism of reverse saturable absorption at 1064 nm, the mechanism of excited state absorption is operating at 532 nm. Additionally, the optical phase conjugate geometry of degenerate four wave mixing (DFWM) technique has been used to measure the third order nonlinear susceptibility values at 532 nm to compare with those obtained from the Z-scan profiles.

Photophysical properties and optical limiting property of a soluble chloroaluminum-phthalocyanine

A chloroaluminum-phthalocyanine (AlCl-Pc) with tetra-alpha-butoxy chains (AlCl-Pc-OC4) has been synthesized and the photophysical parameters have been determined using steady-state and time-resolved absorption as well as emission spectroscopy. A luminescence from S2 excited state with long lifetime (5.71ns) is observed. A multi level model has been proposed to explain the photophysical processes after Soret-band excitation (lambdaex=355nm). The optical limiting performance for 532nm-7ns laser pulses of AlCl-Pc-OC4 has been investigated in THF solution. The sigmaex and ratio of sigmaex/sigma0 has been calculated. The good optical limiting performance is attributed to a reverse saturable absorption mechanism. It indicates that AlCl-Pc-OC4 could be promising candidates for optical limiting material.

Synthesis, Characterization, and Optical-Limiting Properties of Axially Substituted Gallium(III) Naphthalocyanines

The soluble axially substituted naphthalocyanine monomers, tBu4NcGaCl (1) and tBu4NcGa(p-TMP) (p-TMP = p-trifluoromethylphenyl) (2) and the μ-oxo-bridged naphthalo-cyanine dimer [tBu4NcGa]2O (3) are synthesized under mild conditions. In comparison to the corresponding gallium phthalocyanine compounds, tBu4PcGaCl, tBu4PcGa(p-TMP), and [tBu4PcGa]2O, all gallium naphthalocyanines 1−3 are almost transparent in the yellow and red region of the UV/vis spectrum, suggesting that they are suitable for eye protection in a practical optical-limiting device. These compounds optically limit at sufficiently high intensity via a reverse saturable absorption mechanism into the excited T−T absorption band at 532-nm excitation. The substitution of the axially p-TMP ligand onto the central gallium atom results in a defocusing of the beam relative to the other gallium naphthalocyanine compounds. This added defocusing of the beam is important and desirable in practical optical limiters as it helps to spatially disperse the pu...

Mechanism of reverse saturable absorption in chloro-aluminum phthalocyanine solution studied with Z-scan

Using the Z-scan technique with 532 nm laser pulses of dual widths in the picosecond regime, we distinguish between two-photon absorption (TPA) and excited state absorption (ESA). To account for reverse saturable absorption in chloro-aluminum phthalocyanine dissolved in methanol both TPA and ESA, rather than either one, need be invoked.

Optical Limiting Properties of [60]Fullerene and Methano[60]fullerene Derivative in Solution versus in Polymer Matrix: The Role of Bimolecular Processes and a Consistent Nonlinear Absorption Mechanism

Optical limiting properties of tert-butyl methano[60]fullerene carboxylate were investigated systematically in room-temperature solution at a series of concentrations while the linear transmittance of the solution at 532 nm was kept constant. The results are compared with those of [60]fullerene (C60) obtained under the same experimental conditions. For both C60 and the methano-C60 derivative, optical limiting responses toward the second harmonic of a Q-switched Nd:YAG nanosecond pulsed laser at 532 nm are strongly dependent on the fullerene solution concentrations. The concentration dependence is not related to any special optical effects because the results of chloroaluminum phthalocyanine as a reference in the optical limiting experiments show no such dependence. Instead, the strong concentration dependence in the optical limiting performance of fullerenes in solution is likely due to concentration effects on optical limiting contributions that are associated with bimolecular excited-state processes in the fullerenes. For an examination of the medium viscosity dependence of the bimolecular excited-state processes, optical limiting responses of the methano-C60 derivative in highly viscous nonreactive solvent−polymer blends were determined and compared with those in solution at the same linear transmittances. The optical limiting responses are significantly weaker in the highly viscous media, consistent with medium viscosity effects on diffusional or pseudodiffusional bimolecular excited-state processes. Also consistent with such effects are the results that optical limiting responses of the methano-C60 derivative in poly(methyl methacrylate) polymer films are much weaker than those in room-temperature solution. A reverse saturable absorption mechanism that includes both unimolecular and bimolecular (self-quenching and triplet−triplet annihilation) excited-state processes of fullerenes is proposed. A consistent understanding of the optical limiting properties of fullerenes in room-temperature solution (including the strong concentration dependence), in a highly viscous solvent−polymer blend, and in polymer film is discussed within a single mechanistic framework.

High-pressure synthesis and optical limiting property of cyclic diphenylacetylene oligomer

New conjugated oligomers were synthesized by reacting diphenylacetylene under high pressure of 0.13–0.76 GPa at 250 and 300°C for 1–10 h. The number-average molecular weight Mn, and the weight-average molecular weight Mw increased with pressure, but those values were independent of temperature and time (Mn, 320–490; Mw, 350–580). Elementary analysis, field desorption mass spectrometry, Fourier transform infrared, and 13C nuclear magnetic resonance experiments revealed that the oligomer above and including pentamer was a new compound having cyclic structure. Toluene solutions of the oligomer (400 Mn) contained within a quartz cell were irradiated with the pulse from a frequency-doubled Nd : Yag laser at 532 nm. The transmittance of the solution decreased with input fluence, and we observed an optical limiting property with saturated output fluence. As the concentration of the oligomer increased, the saturated output fluence decreased. The optical limiting property was analyzed according to the reverse saturable absorption mechanism. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:129–135, 1998

Sol-gel materials embedding fullerene derivatives for optical limiting

Fullerene derivatives with high solubilities in polar solvents and able to covalently link to a silica matrix, have been prepared. Optical limiting (OL) properties of these molecules in solution have been measured and the comparison with the behavior of C 60 shows that their performance is better in the near-infrared region. This behavior can be understood on the basis of the reverse saturable absorption mechanism which determines the OL properties of these molecules. The sol-gel method is used to include the fullerene derivatives in a silica matrix and allows one to obtain films and bulk materials. The OL properties of the latter are also reported.

Optical-limiting property of cyclic phenylacetylene oligomer synthesized under high pressure

The optical-limiting property of a new cyclic phenylacetylene oligomer was investigated. Toluene solutions of the oligomer contained within a quartz cell were irradiated with the pulse from frequency doubled Nd: Yag laser at 532 nm. At low input fluence, the transmittance of the toluene solution was constant and agreed well with that obtained by spectrophotometer. At high input fluence, the transmittance of the solution above a concentration of 5 wt % decreased with input fluence. The oligomer had an optical limiting property. As the concentration of the oligomer increased from 5 to 20 wt %, the threshold for optical limiting decreased. The threshold was independent of the molecular weight. The optical limiting property was analyzed by the following equation obtained according to the reverse saturable absorption mechanism; log(I0/I) = K(I0 - I) + Ag, where I0 is the input fluence, I is the output fluence, K is a parameter depending on the absorption cross section and the relaxation time, and Ag is the absorbance of the ground state. © 1996 John Wiley & Sons, Inc.

Enhanced optical limiting in derivatized fullerenes

We have observed enhanced optical limiting behavior in solutions of a derivatized fullerene (phenyl-C(61)-butyric acid cholesteryl ester) from 532 to 700 nm. Transient absorption measurements determined the spectral and temporal regions of interest for optical limiting in C(60) and in C(60) derivatives that are due to a reverse saturable absorption mechanism and predicted enhanced limiting at longer wavelengths. Intensity-dependent transmission measurements made at several wavelengths confirmed these results. The increased solubility and the broadened ground-state absorption of the functionalized C(60) make it suitable for use as an optical limiter in the red and the near infrared.

Picosecond Kinetics and Reverse Saturable Absorption of Meso-Substituted Tetrabenzoporphyrins

The mechanism of reverse saturable absorption of meso-substituted tetrabenzoporphyrins was studied by means of picosecond transient spectroscopy. Characteristic 1(π,π*), 3(π,π*), and (d,d) transitions have been observed. The kinetics of the excited states vary with metal substitution. The nonlinear transmission of benzoporphyrins was measured, and the excited-state absorption was determined to be the dominant optical limiting mechanism. The results agreed very well with a five-level model.

Optical Limiting Property of a Polyacene-Based Oligomer Synthesized under High Pressure

The optical limiting property of a new polyacene-based diphenyldiacetylene oligomer was investigated. The oligomer was synthesized by reaction of diphenyldiacetylene under high pressure. Toluene solutions of the oligomer contained within a quartz cell were irradiated with the pulse from a frequency-doubled Nd:YAG laser at 532 nm. At low input fluence, the transmittance of the toluene solution obeyed the Beer-Lambert law. The transmittance was constant and agreed well with that obtained by a spectrophotometer. At high input fluence, the transmittance decreased with input fluence. The oligomer had an optical limiting property. As the concentration of the oligomer increased, the threshold for optical limiting and the saturated output fluence decreased. The inverse of saturated output fluence of the oligomer was about 1/5 of that of C 60 . According to the reverse saturable absorption mechanism, the following equation was obtained between the absorbance log(I 0 /I) and I 0 -I; log(I 0 /I)=K(I 0 -I)+A g , where I 0 is the input fluence, I is the output fluence, K is a parameter depending on the absorption cross section and the relaxation time, and A g is the absorbance of the ground state