Richard G. S. Pong

Optical limiter using a lead phthalocyanine

The performance of an optical limiter based on Pb‐tetrakis(cumylphenoxy)phthalocyanine, a robust organic material with a large χ(3) and figure of merit, χ(3)/α0, is described. In an f/5 limiter with a sample transmission of 0.68, the threshold for limiting was 8±2 nJ and the dynamic range was greater than a factor of 103. The threshold for the PbPc(CP)4 limiter was ∼15 times smaller and the high intensity transmission ∼4–5 times lower than an equivalent limiter based on a thermal nonlinearity.

Indium phthalocyanines and naphthalocyanines for optical limiting

Abstract In this work, an overview of optical limiting processes in phthalocyanines is given. The synthesis and the linear and nonlinear optical properties of a series of highly soluble axially substituted indium(III) phthalocyanines and the analogous series of naphthalocyanines are described. Several techniques, such as transient absorption, Z-scan, and degenerate four-wave mixing (DFWM), were used for assessing the optical properties and optical limiting performance of the indium phthalo- and naphthalocyanines.

Off-resonant nonlinear optical properties of C60 studied by degenerate four-wave mixing

Abstract Pure C 60 was deposited on optical substrates in vacuo and spectroscopically characterized. A small linear absorption coefficient α =6 cm −1 was measured at 1.064 μm. Time-resolved degenerate four-wave mixing experiments were conducted on films of pure C 60 using a 35 ps Nd: YAG laser at 1.064 μm. The third-order optical susceptibility x xxxx (3) of C 60 , derived from its phase conjugate signal, is 7×10 −12 esu. The nonlinear optical temporal response was largely laser-pulse limited. Evidence for a fifth-order contribution to the nonlinear optical response was observed at high laser intensities.

Synthesis, aggregation behavior and nonlinear absorption properties of lead phthalocyanines substituted with siloxane chains

The synthesis and characterization of polysiloxane substituted metal-free and lead phthalocyanines are described. These materials form a class of isotropic liquid phthalocyanines that combine a large nonlinear absorption with an exceptionally large nonlinear thermal refractive effect. These materials effectively couple the nonlinear absorption characteristics of the phthalocyanine (Pc) moiety with the thermorefractive properties typical of siloxanes. The room temperature index of these phthalocyanines can be varied by the choice of the siloxane substituent. Furthermore, the siloxane substituents are effective at inhibiting aggregation of the phthalocyanine rings. The observed aggregation constants in toluene solutions are very small and only a small degree of aggregation is observed even in the pure liquid phthalocyanines. Nonlinear transmission, z-scan, transient absorption and degenerate four-wave mixing studies confirm that the Pb substituted materials possess a broad spectral region of induced absorption with nonlinear absorption coefficients similar to that observed from other lead substituted phthalocyanines. The observed ground state molar absorption coefficients of the siloxy phthalocyanines are somewhat smaller than comparable alkyl substituted phthalocyanines. Taken together, these properties make these materials very useful for practical nonlinear optical applications. The coupling of siloxane chains to the Pc rings represents a promising way to achieve some important properties that are difficult to achieve by other means.

Oligooxyethylene liquid phthalocyanines

A series of methyl-terminated oligooxyethylene (CH3(OCH2CH2)nO, n = 8.8)-substituted phthalocyanines with peripheral substitution at four β positions, at four α positions and at the eight α positions was synthesized and structurally characterized. These compounds are isotropic liquids above 10 °C. Non-linear optical properties of the tetra-α- and tetra-β-substituted compounds were examined. Both are reverse saturable absorbers in the visible region of the spectrum, but the tetra-α-substituted compound has the larger non-linear absorption coefficient and can be a useful optical limiter in cases where a non-volatile liquid is desirable.

Lead phthalocyanine reverse saturable absorption optical limiters

Systematic studies of the nonlinear optical properties of organic materials have led to the development of promising new materials for optical limiting. Several heavy metal substituted phthalocyanines are effective materials for optical limiters in the visible and near IR. Nonlinear absorption is the principal mechanism near the limiting threshold. In fast optical systems, refractive contributions also contribute at higher energies. These refractive contributions are predominantly thermal. The spectral window over which the limiter operates can be engineered by altering both the main ring and peripheral substitution of the molecules.

Persistent infrared laser induced spectral holes in hydrogen bonded polymers

Persistent spectral holes were burned into the profile of the hydrogen bonded OH stretching absorption, near 3500 cm−1, of three polymeric alcohols. The mechanism is an IR induced conformational change of a H‐bonded OH group to weaken the hydrogen bond. In one polymer, an empirical quantum efficiency of about 5×10−3 was measured and a hole depth of 20% of the absorption was achieved with a low power cw laser. The conformational changes occur near the bond which is excited and before extensive intramolecular vibrational randomization.

Optical limiting properties of nonlinear multimode waveguides

An experimental investigation of the transmission of multimode capillary waveguides with a nonlinear absorber in the core shows an enhanced nonlinear absorption relative to the same length of bulk material. The results are consistent with partial mode filling within the cores of the waveguides. This study confirms the promising optical limiting capabilities of multimode nonlinear waveguides and implies that the mode structure should be considered in the design and evaluation of capillary array optical limiters.

Limiting Mechanisms in a Photoconducting Liquid Phthalocyanine

Photoexcitation of a new pure liquid phthalocyanine gives both a strong nonlinear absorption and photoalectrical charge generation. The novel photoelectrical properties of the material lead to plasma formation, an additional limiting mechanism, at moderate fluences.

Syntheses, characterization and properties of soluble and liquid phenanthralocyanines

Phenanthralocyanine compounds with cumylphenoxy, nonylphenoxy and oligodimethylsiloxane phenoxy peripheral substitution were synthesized by nucleophilic aromatic substitution reaction between 3,6-difluoro-9,10-dicyanophenanthrene and the corresponding phenolic precursor. Structural characterization includes IR, NMR, UV-vis and mass spectroscopies. The nonylphenoxy and oligodimethylsiloxane phenoxy phenanthralocyanines were soluble in common organic solvents, and the siloxane product was an isotropic liquid. Compared with the phthalocyanine analog, the Q bands of the Pb, H2 and Cu phenanthralocyanine were slightly red shifted and variably broadened (small for the Pb compound but large for the H2 and Cu compounds). The nominal red shift is a consequence of an angular annelation of the benzene rings to the phthalocyanine system. Aggregation was not detected in toluene solution, and the Q band broadening was attributed to a distortion of the tetraazaporphyrin ring to a nonplanar conformation. The siloxane substituted lead phenanthralocyanine neat liquid was evaluated as an optical limiter material. As a neat film a substantial broadening and weakening of the Q band results in a broad visible transmission window and a relatively neutral light olive hue. Upon excitation, there is a rapid decay of the initially excited state so the initial optical limiting is predominately due to a thermorefractive effect rather than a nonlinear absorption.