Lasing and stimulated emission in ∏-conjugated polymers

Journal ArticleRecent studies of lasing and stimulated emission in luminescent -conjugated polymers performed by our group are presented. Optical properties of cylindrical high- polymer microcavities are discussed. The emission spectra of plastic microring and microdisk lasers are measured and analyzed. Light-emitting polymer microdiodes are demonstrated as possible candidates for electrically driven plastic lasers. In addition, two unusual regimes of stimulated emission characterized by narrow laser-like spectral lines are demonstrated in thin waveguiding polymer films. These regimes may be associated with random optical feedback introduced by light scattering inside the polymer films and amplified Raman scattering, respectively

Double-modulation electro-optic sampling for pump-and-probe ultrafast correlation measurements

Journal ArticleWe describe a novel electro-optic double-modulation (DM) sampling technique for ultrafast transient spectroscopy, which is characterized by a superior signal-to-noise ratio compared to that of a regular single-modulation technique. DM is achieved by a combined effect of a radio-frequency modulation, which eliminates most of the low-frequency noise, and an audio-frequency modulation, which makes use of a high-performance, low-frequency lock-in amplifier. The DM sensitivity is comparable to that of the more sophisticated schemes involving electrical mixing and the A - B noise reduction method. We show that the DM technique offers superior performance in two-beam transient pump-and-probe correlation measurements compared to the regular single frequency modulation technique and is an ideal scheme for three-beam picosecond correlation measurements

Plastic microring lasers on fibers and wires

Journal ArticlePhotopumped, pulsed, narrow line laser emission is demonstrated using cylindrical microcavities formed by p-conjugated polymer thin films wrapped around thin glass optical fibers and metal wires with various diameters D. A variety of cavity-dependent resonant laser mode structures were observed, which for D,10 mm contain a single resonant spectral line of less than 1 Å in width. The microring lasers are also characterized by a well-defined, very low threshold excitation intensity, at which beam directionality and polarization degree dramatically increase. These findings open up the fields of lasers and fiber optics to organic materials

Exciton dynamics in soluble poly(p-phenylene-vinylene): toward an ultrafast excitonic switch

Journal ArticleWe have applied a variety of ps transient and cw optical techniques to elucidate the dynamics, absorption, and emission properties of excitons in soluble derivatives of poly(p-phenylene vinylene) neat films and dilute solutions. We found that the photogenerated singlet excitons in both films and solutions are characterized by strong stimulated emission and two photoinduced absorption bands. We demonstrate that these bands can be used to form an ultrafast optical switch in the near IR spectral range with variable switching times

Ultrafast spectroscopy of even-parity states in ∏-conjugated polymers

Journal ArticleRelaxation dynamics of even parity (Ag) states in poly(p-phenylene vinylene) derivatives are studied using a novel fsec transient spectroscopy, in which two different excitation pulses successively generate odd parity (1 1Bµ) excitons at 2.2 eV and then reexcite them to higher Ag states. For reexcitation energies hω, 1.1 eV the decay occurs in a nonemissive state identified as a polaron pair, showing that the Ag states above 3.3 eV mediate charge transfer

Exciton dynamics in soluble poly(p-phenylene vinylene)

Journal ArticleWe report studies of poly(2,5-dioctyloxy paraphenylene vinylene) thin films and solutions by a variety of transient, steady state, and nonlinear optical techniques. The energy states and optical absorption of the dominant even and odd parity excitons have been determined. Photogenerated singlet excitons are characterized by strong stimulated emission and two photoinduced absorption bands. Triplet excitons are found to have a single absorption band; intersystem crossing time from the singlet to the triplet manifolds is estimated to be ~4 ns in films and ~20 ns in solutions