Jacek Swiatkiewicz

Organics and Polymers with High Two-Photon Activities and their Applications

This review describes some of the recent developments in materials which exhibit enhanced two-photon absorption that can initiate photopolymerization or up-converted emission. Various optical methods including femtosecond time-resolved pump-probe experiments to characterize the two-photon properties are discussed. Finally, the applications of two-photon processes to optical power limiting, up-converted lasing, 3-D data storage, 3-D micro-fabrication, two-photon fluorescence microscopy and bio-imaging, and two-photon photodynamic therapy are presented.

Two-photon fluorescence imaging and spectroscopy of nanostructured organic materials using a photon scanning tunneling microscope

Photon scanning tunneling microscopy and spectroscopy using femtosecond two-photon excitation are demonstrated. The measurement of both intensity dependence and spectral dependence is performed on a two-photon chromophore. A subdiffraction-limited resolution is obtained, and the domain-size dependence of spatial and spectral features is observed, which indicates the high degree of molecular order in the isolated nanoparticle. It is shown that the light confinement due to a quadratic dependence of the fluorescence intensity leads to an optical contrast enhancement with a coated probe.

Third‐order nonlinear optical interaction and conformational transition in poly‐4‐BCMU polydiacetylene studied by picosecond and subpicosecond degenerate four wave mixing

The electronic third‐order nonlinear optical interaction in a solution cast film of a polydiacetylene has been studied by degenerate four wave mixing. The results demonstrate a subpicosecond response and a very high χ(3) value. The χ(3) value changes considerably during the thermally induced conformational transition in the film in which the effective π‐electron conjugation is reduced.

Energy transfer coupling of two-photon absorption and reverse saturable absorption for enhanced optical power limiting.

We introduce a new approach to enhancing the optical power-limiting function at near-IR wavelength (~800 nm) by coupling effective two-photon absorption in one molecule with excited-state absorption in another molecule. We experimentally demonstrate this approach by using a strong two-photon absorbing dye, AF-380, and a strong reverse saturable absorber, C(60) . A nanosecond time-resolved experiment is used to show that energy transfer from AF-380 to C(60) generates triplet excitation in C(60) that further absorbs the pump beam to enhance the power-limiting function.

Dynamics of third‐order nonlinearity of canthaxanthin carotenoid by the optically heterodyned phase‐tuned femtosecond optical Kerr gate

It is shown that polarization sensitive (optically heterodyned) detection combined with π/2 optical phase biasing between the optical Kerr gate signal and the local oscillator signal provides an effective method for the investigation of dynamics of third‐order nonlinear optical processes. The method permits selective enhancement of either the real or the imaginary component of the nonlinear optical response of the medium under study. Both the magnitudes and the signs of the real and the imaginary components of the complex third‐order optical susceptibility, contributing to the Kerr gate phenomenon, can thus be determined independently. The method is used to investigate the third‐order nonlinear optical response of solutions of canthaxanthin (4,4’‐dioxo‐β‐carotene) in tetrahydrofuran. With the use of ultrafast 60 fs laser pulses at 620 nm, the instantaneous, coherent part of the response is separated from an incoherent, time‐delayed response. The real and the imaginary components of the instantaneous compl...

Third order non-linear optical properties of poly-p-phenylene benzobisthiazole and its novel composite with Zytel processed via methane sulphonic acid solution extrusion

Abstract It was found that improved optical quality films of poly-p-phenylene benzobisthiazole (PBZT) and of a novel composite of PBZT and nylon (Zytel 330) can be produced by extruding below critical concentration solutions in methane sulphonic acid. The linear refractive indices and their dispersion behaviour in these films have been determined by analyses of the interference fringes observed in the optical transmission spectra. A relatively large value of the linear refractive index is obtained for PBZT. The third-order non-linear optical susceptibility, χ(3), is determined for the films of PBZT and PBZT/Zytel composite using subpicosecond degenerate four-wave mixing. The χ(3) value observed for this PBZT film is almost an order of magnitude larger than that previously reported for PBZT films of a rather inferior quality processed through polyphosphoric acid solution. This result emphasizes the importance of polymer processing to produce better optical quality films for evaluation of intrinsic χ(3) values of polymers. The response time of the non-linearity is limited by the laser pulse width, indicating that the non-linear response is derived from the coherent electronic χ(3). The χ(3) value of the PBZT/Zytel composite is lower than that for pure PBZT because of the reduced number density. However, determination of the optical loss, α, in these films yields a much lower value of α for the PBZT/Zytel composite film, resulting in an improved value of the often used device figure of merit χ (3) α . This result suggests that composite structures may be useful for optimizing the χ (3) α ratio.

Second-harmonic and sum-frequency imaging of organic nanocrystals with photon scanning tunneling microscope

Second-harmonic generation and sum-frequency generation with photon scanning tunneling microscopy and shear-force detection are used to map the nonlinear optical response and the surface topograph of N-(4-nitrophenyl)-(L)-prolinol crystals with a subdiffraction-limited resolution. The domain-size dependence of the spatial feature is obtained, which shows the local orientational distribution of the optical near field radiated by nonlinear nanocrystals and reveals the difference between nanoscopic and macroscopic second-order optical nonlinearities of molecular crystals.

Anisotropy of the linear and third‐order nonlinear optical properties of a stretch‐oriented polymer film of poly‐[2, 5‐dimethoxy paraphenylenevinylene]

Large linear refractive index birefringence, strong dichroic behavior, and highly anisotropic χ(3) have been observed for a uniaxially oriented poly (2, 5‐dimethoxy paraphenylene vinylene) film. A subpicosecond time‐resolved degenerate four‐wave mixing study reveals an unusual behavior. Along the draw direction χ(3) is complex with a negative real part and has a response time that is longer than the optical pulse resolution. In contrast, χ(3) along the transverse direction is largely real and positive. Its response time is much faster, and is limited by the laser pulse width of ∼400 fs.

Enhancement of two-photon emission in photonic crystals

We report the influence of photonic stopgaps on two-photon excited emission from highly efficient nonlinear chromophores infiltrated into high-quality photonic crystals. We have observed a sharp decrease (filter effect) in emission within the frequency range and direction of the stopgap as well as sharp enhancement of the two-photon excited emission associated with the stopgaps edge. This effect may be important for the development of low-threshold upconversion lasers.

Anisotropy in the complex refractive index and the third‐order nonlinear optical susceptibility of a stretch‐oriented film of poly(p‐phenylene vinylene)

Birefringence, dichroism, and dispersion of the refractive indices of a free‐standing film of poly(p‐phenylene vinylene) (PPV) were measured by several techniques. The results are applied to an analysis of anisotropy of the third‐order nonlinear optical susceptibility of this material. The anisotropy of both the linear and nonlinear susceptibilities is accounted for by the one‐dimensional character of the lowest‐energy electronic transition in PPV.