Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Lasing applications have spread over various aspects of human life. To meet the developing trends of the laser industry towards being miniature, portable, and highly integrated, new laser technologies are in urgent demand. Organic semiconductors are promising gain medium candidates for novel laser devices, due to their convenient processing techniques, ease of spectral and chemical tuning, low refractive indexes, mechanical flexibilities, and low thresholds, etc. organic solid-state lasers (OSSLs) open up a new horizon of simple, low-cost, time-saving, versatile and environmental-friendly manufacturing technologies for new and desirable laser structures (micro-, asymmetric, flexible, etc.) to unleash the full potential of semiconductor lasers for future electronics. Besides the development of optical feedback structures, the design and synthesis of robust organic gain media is critical as a vigorous aspect of OSSLs. Herein, we provide a comprehensive review of recent advances in organic gain materials, mainly focused on organic semiconductors for OSSLs. The significant breakthroughs toward electrical pumping of OSSLs are emphasized. Opportunities, challenges and future research directions for the design of organic gain media are also discussed.

Organic solid-state lasers: a materials view and future development.

One of the most widely used and important groups of functional dyes are the styryl dyes and a review of this functional dye class has not been published for more than 15 years. In this review article, we describe the new trends in the synthesis of a range of novel intermediates and styryl dyes and include the most interesting examples of their high-tech applications. However, this review is not intended to be comprehensive because of the large number of styryl dye studies that have been carried out in this time. Styryl cyanine dyes are widely used in optical recording media in laser discs, as flexible dyes, laser dyes, as optical sensitisers and in various other fields, for example dye-sensitised solar cells and dyes with non-linear optical properties. Additionally, the most important applications for these dyes are in bio-labelling and in medicinal analysis.

Styryl dyes – synthesis and applications during the last 15 years

By using the femtosecond laser spectroscopic techniques, we have studied the ultrafast response and the nonlinear optical properties of three molecules with donor−acceptor structure (denoted as T01, T02, and T03). Two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique were determined to be 77, 90, and 410 GM for T01, T02, and T03, respectively. The relaxation dynamics of the excited states were measured by two-color femtosecond pump−probe and time-resolved photoluminescence (PL) experiments. By changing the solvent from chloroform (CHCl3) to dimethyl sulfoxide (DMSO), the transient dynamics was found changed significantly and the decay time of PL emission decreased dramatically because DMSO with large dipole moment accelerates the cross-transfer process and the nonradiative process in the molecules.

The Ultrafast Dynamics and Nonlinear Optical Properties of Tribranched Styryl Derivatives Based on 1,3,5-Triazine

We report a series of stiff dendrimers (referred to as T1, T2, T3, and T4) that have both gigantic two-photon absorption (TPA) cross sections up to 25 000 GM and strong two-photon excited fluorescence (TPEF) with fluorescence quantum yield of ∼0.5. The large TPA cross sections and high quantum yields of these dendrimers are directly related to their geometrical structures, where the polycyclic aromatic pyrene is chosen as the chromophoric core because of its planar and highly π-conjugated structure, fluorene moieties as dendrons extend the conjugation length through the planar structure, and carbazole moieties are modified at three-, six-, and nine-positions as electron donor. All of these groups are linked with acetylene linkage for effective π-electron delocalization, leading to large TPA cross section and high fluorescence quantum yield. The spectral properties of all dendrimers are investigated by one- and two-photon excitations. Furthermore, steady-state fluorescence excitation anisotropy and quantum...

Gigantic two-photon absorption cross sections and strong two-photon excited fluorescence in pyrene core dendrimers with fluorene/carbazole as dendrons and acetylene as linkages.

The fluorescence properties of a new two-photon absorption chromophore in dimethyl formamide, methanol, acetone, benzyl alcohol, methylene chloride and chloroform are reported. The lifetime, intensity and central wavelength of the fluorescence signal vary significantly in different solvents. The fluorescence properties are explained by using the twisted intra-molecular charge-transfer model, the viscosity of the solvents and the formation of the hydrogen bond. For the dye in all solvents, the longer the fluorescence lifetime, the higher the fluorescence intensity. Generally, the higher the dipole moments, the longer the central wavelengths of the dye.

Two-photon fluorescence properties of a styrylpyridinium derivative organic chromophore in different solvents

Two-photon-absorption (TPA)-induced upconverted amplified spontaneous emission (ASE) and cavity lasing of a styrylpyridinium dye: trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) in poly(2-hydroxyethyl methacrylate) (abbreviated as PHEMA) polymer were observed under a picosecond pump condition. The spectral and temporal behaviors of TPA-induced fluorescence, ASE and cavity lasing were studied. The cavity lasing with a total oscillation time of more than 200 ps was achieved when pumped with 1064-nm, 50-ps laser irradiation. The population inversion could persist for three times longer than the duration of the pump pulse. The gain coefficients of the dye-doped polymer at various wavelengths were calculated based on cavity lasing spectra and one-photon fluorescence spectra.

Two-photon-pumped amplified spontaneous emission and cavity lasing of an organic dye HEASPS in PHEMA polymer

Two-photon absorption and excited state absorption properties of an organic dye PSPI

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Two-photon fluorescence properties of a styrylpyridinium derivative organic chromophore in different solvents

Two-photon-pumped amplified spontaneous emission and cavity lasing of an organic dye HEASPS in PHEMA polymer

Two-photon absorption and excited state absorption properties of an organic dye PSPI