Saturable Dye Research Articles

Laguerre–Gaussian vortex beam for reduced thermal effects in nonlinear optical studies

Interaction of an intense laser beam with a material induces many thermal effects. In this work, thermo-optic effects induced by fundamental Gaussian and Laguerre–Gaussian vortex (LGV) laser beams in a sample in nonlinear optical (NLO) experiments are compared and their impact on the accuracy of determining the nonlinear susceptibility is examined. A solution of saturable absorber dye IR 26 in dichloroethane with the technique of z-scan to determine its third order nonlinear susceptibility was used as a model system. The LGV beams were generated by passing the Hermite–Gaussian beams from an Ar-ion laser through a cylindrical lens mode converter. Pump–probe setup was used to study the thermo-optic effects. Experiments and simulations suggest that the LGV beam is advantageous to reduce the thermal effects.

Stimulated low-frequency Raman scattering of light: An effective way of laser Q-switching

Passive Q-switching of a ruby laser using stimulated low-frequency Raman scattering of light has been implemented. Suspensions of submicron dielectric and metal particles were used inside a laser cavity as a Q-switching device. The Q-factor of the resonator changed due to stimulated inelastic scattering by the coherent acoustic vibrations of particles. It has been shown that the pulse duration can vary from tens of nanoseconds to microseconds by changing the characteristics of the submicron system. The advantage of this method of passive Q-switching in comparison with a saturable dye is shown.

Polarization characteristics of nonlinear transmission in rigidly held saturable-dye molecules with random orientations

Polarization-dependent nonlinear transmissions are investigated by a pump-probe method in saturable-dye-doped films in which optically anisotropic saturable dyes are rigidly held with random orientations. The nonlinear transmissions measured by using uranine-doped poly(vinyl alcohol) films are compared with the theoretical predictions that are obtained by considering the effects of pump propagation and molecular orientation on the basis of a rate equation analysis for a four-energy-level model including an excited-state absorption. The measurements were conducted for the two cases of polarization states for which the polarization direction of the probe wave is either parallel or perpendicular to that of the pump wave; the experimental results considerably deviated from the theoretical ones for the probe wave perpendicularly polarized to the pump wave. It is shown that this is explained by modifying the energy level model to include the existence of a nearly-orthogonal component of the transition dipole moment associated with the ground-state absorption in uranine dyes.

Symmetric Versus Unsymmetric Platinum(II) Bis(aryleneethynylene)s with Distinct Electronic Structures for Optical Power Limiting/Optical Transparency Trade‐off Optimization

AbstractA new series of symmetric and unsymmetric Pt(II) bis(acetylide) complexes of the type DC≡CPt(PBu3)2C≡CD (DPtD), AC≡CPt(PBu3)2C≡CA (APtA) and DC≡CPt(PBu3)2C≡CA (DPtA) (D, donor groups; A, acceptor groups) are synthesized, and show superior optical power limiting (OPL)/optical transparency trade‐offs. By tailoring the electronic properties of the aryleneethynylene group, distinct electronic structures for these metalated complexes can be obtained, which significantly affect their photophysical behavior and OPL properties for a nanosecond laser pulse at 532 nm. Electronic influence of the ligand type and the molecular symmetry of metal group on the optical transparency/nonlinearity optimization is thoroughly elucidated. Generally, aryleneethynylene ligands with π electron‐accepting nature will effectively enhance the harvesting efficiency of the triplet excited states. The ligand variation to the OPL strength of these Pt(II) compounds follows the order: DPtD > DPtA > APtA. These results could be attributed to the distinctive excited state character induced by their different electronic structures, on the basis of the data from both photophysical studies and theoretical calculations. All of the complexes show very good optical transparencies in the visible‐light region and exhibit excellent OPL responses with very impressive figure of merit σex/σo values (up to 17), which remarkably outweigh those of state‐of‐the‐art reverse saturable absorption dyes such as C60 and metallophthalocyanines with very poor transparencies. Their lower optical‐limiting thresholds (0.05 J cm−2 at 92% linear transmittance) compared with that of the best materials (ca. 0.07 J cm−2 for InPc and PbPc dyes) currently in use will render these highly transparent materials promising candidates for practical OPL devices for the protection of human eyes and other delicate electro‐optic sensors.

Enhanced Absorption in a Reverse Saturable Absorbing Dye Blended with Carbon Nanotubes

Using nonlinear absorption at 532 nm in the nanosecond temporal regime, we have measured the low fluence nonlinear transmittance properties of the reverse saturable absorbing carbocyanine dye, 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HITCI), blended with well dispersed carbon nanotubes. The nonlinear optical properties of the blends are strongly dependent on the ratio of dye to nanotubes in solution. In the case where the nanotubes per dye molecule ratio is large, we see a distinctive enhancement in optical fluence limiting properties of the system, suggesting enhanced absorption of the excited states. However, when the nanotube to dye ratio decreases, the system's response is dominated by the behavior of the dye. We suggest that this can be understood as a two component system in which sensitized dye molecules associated with the nanotubes have an effectively different optical cross-section from the dye molecules far from the nanotubes. From classical antennae considerations, this is expected.

Polymeric saturable-absorber mirror for passive Q-switching of a laser-diode-pumped Nd^3+:YVO_4 microchip laser

A polymeric multilayered mirror doped with a saturable dye worked as a passive Q-switch of a laser-diode-pumped Nd(3+):YVO4 microchip laser. The multilayered mirror consisted of alternately spin-coated layers of polyvinylcarbazole (PVK) and cellulose acetate on a glass substrate. A dye of bis-(dimethylaminodithiobenzil)-nickel was doped in one of the layers of PVK, providing the repetitively Q-switched pulses. The pulse width and repetition rate were 4 ns and 68 kHz, respectively, for a laser-cavity length of 5 mm, and the average and the peak power were 40 mW and 156 W, respectively, for the highest pump power of 435 mW. The dependence of the Q-switched characteristics on the pump power and on the concentration of the doped dye is described.

Synthesis, Structures and Optical Power Limiting of Some Transition Metal and Lanthanide Monoporphyrinate Complexes Containing Electron‐Rich Diphenylamino Substituents

AbstractTransition metal and lanthanide monoporphyrinate complexes based on 5,10,15,20‐tetrakis[p‐(diphenylamino)phenyl]‐21H,23H‐porphine (H2tdpapp) have been synthesized and characterized and the X‐ray crystal structures of the palladium and platinum analogues [M(tdpapp)] (M = Pd, Pt) determined. Experimental investigations of the nonlinear optical transmittance characteristics at 532 nm show that most of these new metalated porphyrinate complexes are excellent optical limiters with performances comparable or superior to those of the benchmark reverse saturable absorption dyes such as fullerene C60 and (phthalocyanine)metal complexes. The nonlinear optical measurements reveal that the optical‐limiting effects of porphyrins can be enhanced greatly by incorporation of lanthanide ions and covalent attachment of the electron‐donating diphenylamino moieties to the parent porphyrinate ring. The optical‐limiting thresholds for these lanthanide monoporphyrinate complexes range from 0.09 to 0.30 J cm–2 at 82 % linear transmittance, which makes them attractive candidates as optical‐limiting materials for the protection of various optical devices. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Optical Power Limiters Based on Colorless Di‐, Oligo‐, and Polymetallaynes: Highly Transparent Materials for Eye Protection Devices

AbstractThe synthesis, characterization, and photophysics of a series of solution‐processable and tractable di‐, oligo‐, and polymetallaynes of some group 10–12 transition metals are presented. Most of these materials are colorless with very good optical transparencies in the visible spectral region and exhibit excellent optical power limiting (OPL) for nanosecond laser pulse. Their OPL responses outweigh those of the state‐of‐the‐art reverse saturable absorption dyes such as C60, metalloporphyrins, and metallophthalocyanines that are all associated with very poor optical transparencies. On the basis of the results from photophysical studies and theoretical calculations, both the absorption of triplet and intramolecular charge‐transfer states can contribute to the enhancement of the OPL properties for these materials. Electronic influence of the type, spatial arrangement, and geometry of metal groups on the optical transparency/nonlinearity optimization is evaluated and discussed in detail. The positive contribution of transition metal ions to the OPL of these compounds generally follows the order: Pt > Au > Hg > Pd. The optical‐limiting thresholds for these polymetallaynes can be as low as 0.07 J cm–2 at 92 % linear transmittance and these highly transparent materials manifest very impressive figure of merit σex/σo values (up to 22.48), which are remarkably higher than those of the benchmark C60 and metal phthalocyanine complexes. The present work demonstrates an attractive approach to developing materials offering superior OPL/optical transparency trade‐offs and these metallopolyynes are thus very promising candidates for use in practical OPL devices for the protection of human eyes and other delicate optical sensors.

White Metallopolyynes for Optical Limiting/Transparency Trade‐off Optimization

High-transparency optical limiters: A series of solution-processable white metallopolyynes are shown to be excellent optical power limiters (see picture) with optimized optical transparency/nonlinearity trade-off. They exhibit an optical-limiting performance superior to those of the common reverse saturable absorption dyes, such as C60 and metal phthalocyanine complexes. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z601651_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis of New Monoporphyrinato Lanthanide Complexes for Potential Use in Optical Limiting

Abstract Three monoporphyrinato lanthanide complexes based on 5,10,15,20-tetrakis(p-diphenylaminophenyl)-21H,23H-porphine (H2TDPAPP) were synthesized, and experimental investigations of the nonlinear optical transmittance characteristics at 532 nm show that they are excellent optical limiters with performance comparable or superior to those of the reverse saturable absorption dyes such as fullerene C60 and metal phthalocyanine complexes.

Large Optical-Limiting Response in Some Solution-Processable Polyplatinaynes

Experimental investigations of the nonlinear optical transmittance characteristics of a series of solution-processable platinum polyyne polymers at 532 nm show that they are excellent optical limiters with performance comparable or superior to those of the state-of-the-art reverse saturable absorption dyes such as fullerene C60 and metal phthalocyanine complexes. On the basis of results from photophysical studies, both the inclusion of a platinum chromophore for increasing the intersystem crossing rate and the formation of an intramolecular charge-transfer state between the electron-withdrawing and electron-donating moieties along the polymer chain are very effective approaches for the enhancement of the optical-limiting properties of these metal polyynes. The structural influence of the aryl linker units on the optical-limiting action has been evaluated in detail. The optical-limiting thresholds for these polymetallaynes range from 0.06 to 0.15 J/cm2 at 82% linear transmittance, and these polymeric materials are very promising candidates for use in practical optical-limiting devices.

Phase Conjugation in Saturable Absorbing Dye Films by Degenerate Four-Wave Mixing and Holographic Processes Using Nanosecond Pulse and CW Lasers

We report on the simultaneous generation of phase-conjugate signals by degenerate four-wave mixing (DFWM) and holographic processes using a nanosecond pulse and a CW lasers in polyvinyl alcohol (PVA) films doped with four kinds of saturable absorbing dyes. For the pulse laser, of the four kinds of dye-doped PVA films, the erythrosine B-doped PVA and uranine doped-PVA films generate PC signals only by the DFWM process, while the other dye-doped PVA films generate PC signals simultaneously by not only the DFWM process but also the holographic process. Especially, the safranin T-doped PVA film generates strong PC signals by the holographic process. In contrast, all of the dye-doped PVA films generate the two types of PC signals for the CW laser. The fading of dye molecules is found to result in the generation of the holographic component of PC signals which governs the temporal behavior of the total PC signals.

Self-diffraction of pico-second pulses in a saturable amplifier polymer dye

We present efficient self-diffraction of pico-second pulses in a solid-dye saturable amplifier. Experimental second-order (2nd-order) diffraction efficiency of as much as 5% at the wavelength of 560 nm was obtained.

Polarization-Dependent Phase-Conjugate Reflectivity in Randomly Oriented Saturable Absorbers: Effects of Direction of Transition Dipole Moment Associated with Excited-State Absorption

The effects of the direction of transition dipole moment on polarization-dependent phase-conjugate (PC) reflectivity by degenerate four-wave mixing in a saturable-dye-doped film are theoretically investigated. On the basis of a four-energy-level model for the saturable dyes, the pump-intensity dependence of the PC reflectivity is calculated for the two cases of a probe wave being polarized either parallel or perpendicular to pump waves, when the transition dipole moment associated with excited-state absorption tilts from that associated with ground-state one. For the parallel polarization, in the case of two transition dipole moments having different directions, a dip appears in the PC reflectivity curve near a resonant frequency on account of the characteristics of nonlinear absorption, whereas it disappears when the frequency of light is off resonance due to the influence of nonlinear refractive index.

Polarization dependence of phase-conjugate reflectivities in solid films containing randomly oriented saturable dyes

The properties of polarization-dependent phase-conjugate (PC) reflectivities by degenerate four-wave mixing in saturable-dye-doped films are investigated on the basis of a four-level model including an excited-state absorption. Numerical calculations are carried out by taking account of the effect of molecular orientation as well as of pump propagation under the assumption that optically anisotropic dye molecules are rigidly fixed in a solid matrix without any positional and orientational order, in which a PC wave can be generated even in the case of a probe wave perpendicularly polarized to pump waves. Two cases of the polarization state are employed, where the polarization direction of the probe wave is either parallel or perpendicular to that of the parallel linearly polarized pump waves. Numerically calculating the PC reflectivities as a function of the pump intensity, we show how the polarization properties of the PC-reflectivity curves depend on saturation parameters, and clarify the influences of the molecular orientational and the pump propagation effect. The numerical results are compared with the experimental results obtained by using eosin-Y-doped polyvinyl alcohol films as saturable absorbers.

Q switching by saturable absorption in microdroplets: elastic scattering and laser emission

Laser-induced modification of cavity Q's has been achieved in a microdroplet containing a saturable absorber. The elastic-scattering spectra from such droplets for higher incident intensities show that cavity Q's are increased when the absorption is bleached. The lasing spectra from a droplet containing a saturable absorber and laser dye are modified when an intense bleaching field is injected into the droplet cavity after the pump field has initiated the lasing.

Characterization of dye-doped media for real-time holography

Studies of saturable dyes used as holographic media where saturation gives rise to both amplitude and phase holograms are presented. Using a simple absorption model together with the Kramers-Kronig relation, a theory for the prediction of holographic diffraction efficiencies over a range of read-wavelengths was developed. Results of experimental tests are presented as support for the model.

Ultrashort pulse generation from an integrated single-chip dye laser

In distributed-feedback (DFB) dye lasers pumped by a nanosecond-pulse laser, a train of picosecond spikes is generated by the relaxation oscillation. A single spike with a pulse duration of 50 ps is extracted in a plastic-waveguide DFB dye laser using a quenching technique. To compress this to femtosecond pulse, a new type of integrated pulse compressor is proposed, and its performances are analyzed. The compressor is composed of a plastic waveguide in which amplifier dye and saturable dye are alternatively doped. Computer simulation shows that the 50-ps pulse is compressed to 120 fs by passing through four stages of amplifier and saturable absorber pair. Using this scheme, we expect to construct a very compact and simple ultrashort pulse generator in which the whole system is integrated on a chip of a plastic waveguide.

Theoretical Analysis of Photon-Mode Super-Resolution Optical Memory Using Saturable Absorption Dye

The possibility of a super-resolution optical memory using a saturable absorption dye mask layer is theoretically discussed. An equation which estimates the transmittance change of the mask layer has been derived. The numerical simulation shows that an efficient super-resolution is performed when the initial optical density of the mask layer is high.

On the possibility of mode-locking a dye laser by a fast saturable absorber

The problem of mode-locking a fully relaxing saturable (dye) laser medium by an instantaneously saturating (fast) absorber is theoretically considered when group velocity dispersion and Kerr-type nonlinearity are present. Off-resonant chirped solutions are found whose minimum duration is determined by the relative losses (saturable and nonsaturable) and by the saturation depth of the absorber. The addition of nonlinear elements can only broaden the stability range of the solution with respect to the group velocity dispersion.