Yiping Cui

Studies of two-photon pumped frequency-upconverted lasing properties of a new dye material

The two-photon absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) lasing properties of a new dye, trans-4[p-(N-hydroxyethylN-methylamino)stryryl]-N-methylpyridinium iodide (abbreviated as ASPI) were experimentally investigated. This new dye has a moderate TPA cross section (σ2≈3.9×20−20 cm4/GW in benzyl alcohol), but exhibits a low lasing threshold and high lasing efficiency when pumped with a 1064 nm pulsed laser beam. Furthermore, the TPA-induced fluorescence yield is strongly dependent on the polarity of the solvent, making it a promising dye for sensing applications. The spectral, temporal, and spatial structures as well as the output/input characteristics of the TPP cavity lasing and the superradiant (cavityless) lasing are systematically measured using a 1 cm path quartz cuvette filled with the ASPI solution or a doped polymer rod. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the ∼615 nm upconverted cavity lasing energy was foun...

Photorefractive effect in a new organic system of doped nonlinear polymer

We report an experimental observation of the photorefractive effect in a new polymeric system in which a nonlinear organic polymer was doped with a photosensitizer, borondiketonate (BDK), and a hole transport agent, tri‐p‐tolylamine (TTA). The photoconductivity and the electro‐optic effect have been studied. The process of grating formation with the applied field is presented. A strong electric field dependence of the diffraction coefficient has been observed.

Zero‐order and first‐order theory of the formation of space‐charge gratings in photoconductive polymers

When a photoconducting polymer is illuminated by light with an intensity that varies sinusoidally with position, the space‐charge electric field, hole density, ionized photosensitizer density, hole trap density, and other properties, will also vary with position. We derive an expression for the zero‐order Fourier component of the hole density and a linear system of equations for the first‐order Fourier component of a number of variables. The system of equations is solved for the steady‐state first‐order Fourier component of the electric field for the case in which hole untrapping is negligible or no hole traps are present. Next, the equations are simplified for the case in which the initial trap density is far greater than the density of holes, and for the case of no hole traps. Finally, we compare the zero‐order hole density and first‐order electric field calculated from our equations to values obtained by Fourier transforming the results of numerical calculations.

Temperature-dependence studies of photorefractive effect in a low glass-transition-temperature polymer composite

The temperature dependence of the photorefractive effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N- diethylamino)-β-nitrostyrene is presented. The photoconductive, electro-optic and photorefractive properties of the material have been studied in the temperature range of 22–61u2009°C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between the p- and s-polarized readouts is consistent with what would be expected on the basis of directly measured effective electro-optic coefficients. By correlating the electro-optic value with the diffraction efficiency, the temperature dependence of the space-charge field is obtained and explained by temperature dependencies of the dark conductivity and the photoconductivity of the material.

Dynamics of photorefractive grating erasure in polymeric composites

Theoretical and experimental studies are presented of the dynamics of photorefractive grating erasure in polymeric photorefractive materials with hole traps. A bi-exponential decay for the rate of optical erasing of the space-charge field has been obtained by theoretical solution. The optically induced erasure rate for polymeric photorefractive materials is theoretically predicted to depend on optical intensity as a sublinear relation of Iα, in which α is dependent on the electric field. The characteristics of the traps in a photorefractive material play a key role in the dynamics of grating erasure. Experimentally studied was the dynamic process of erasing the photorefractive grating in a polymeric composite, poly-N-vinylcarbazole:fullerene:diethyl aminonitrostyrene:tricresyl phosphate. The theoretical analysis and experimental results reveal that shallow traps are dominant in this photorefractive material.

Two-, three-, and four-photon-pumped stimulated cavityless lasing properties of ten stilbazolium-dyes solutions

Two-, three-, and four-photon-pumped stimulated emission (cavityless lasing) properties of ten novel stilbazolium dyes in solution phase have been comprehensively studied. These newly synthesized multiphoton active dye compounds have the same molecular backbone but differ either in their electron donors or in their electron acceptors and can be utilized to generate highly directional stimulated emissions over a broad visible spectral range (from 490 to 618 nm) under multiphoton-pump conditions. The pump source was a powerful Ti:sapphire oscillator-amplifier system associated with an optical-parametric generator, which could specifically provide ∼160 fs duration and ∼775, 1320, and 1890 nm laser pulses for two-, three-, and four-photon excitation, respectively. The spectral, spatial, and temporal properties as well as the efficiency of multiphoton-pumped lasing output from different dye-solution samples have been studied. Based on the measured results, two salient features have been found: (i) the threshold pump-energy values for two-, three-, and four-photon-pumped lasing were quite close (within a factor of 3-4); and (ii) there was an obvious wavelength difference (10-30 nm) between the forward and backward lasing output under three- and four-photon-pump conditions.

Intracavity upconversion lasing within a Q-switched Nd: YAG laser

Abstract Two-photon pumped upconversion intracavity lasing is achieved by placing a 1 cm-long dye-solution filled liquid cell inside a Q -switched Nd: YAG pulsed laser cavity. The upconversion gain medium is the solution of a new dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide, abbreviated as ASPI, which has strong two-photon absorption and subsequent upconversion fluorescence emission when excited with 1.06 μm laser radiation. The spectral, temporal, and spatial properties of the upconverted cavity lasing output are investigated. The key parameters for upconversion lasing are emission wavelength of ∼623 nm, pulse duration of ∼ (2–10) ns, and beam divergence of ∼(2.5–4) mrad. The corresponding parameters for the pump lasing from the same cavity are ∼ 1.06 μm, ∼ 20 ns, and ∼ (5–7) mrad, respectively. The net conversion efficiency from the absorbed IR pump laser pulse energy to the visible lasing pulse energy is measured to be ∼ 8.5%.

Difference of spectral superbroadening behavior in Kerr-type and non-Kerr-type liquids pumped with ultrashort laser pulses

The spectral superbroadening behavior of forward coherent radiation from a 10-cm-long liquid-filled cell is investigated by using an ultrashort (∼0.5 ps) and intense (∼10 GW/cm(2)) laser pulse as the pump source. Five different transparent liquids (heavy water, water, carbon tetrachloride, benzene, and carbon disulfide) have been studied with a special experimental design that can distinguish the predominant contributions from the various possible mechanisms. Under the same pump condition, a very wide and symmetrical superbroadening (continuum) is observed on both the Stokes and the anti-Stokes side of the pump line for non-Kerr-type liquids such as heavy water and water, whereas only a red-shifted spectral broadening can be observed on the Stokes side for Kerr-type liquids such as carbon disulfide and benzene. For an explanation of the latter behavior, the dominant contributions from stimulated Rayleigh-Kerr and Raman-Kerr scattering are proposed.

Two-photon excited intramolecular energy transfer and light-harvesting effect in novel dendritic systems

Two-photon absorption excited intramolecular energy transfer and light-harvesting effects are demonstrated in three novel dendritic systems. These systems contain both an antenna structure that can effectively absorb two-photon energy at approximately 800 nm and emit fluorescence at approximately 515 nm and a core moiety that can absorb one-photon energy at approximately 520 nm and emit at approximately 590 nm. Covalently combining the core and antenna functionalities intrinsically changes the optical behavior of the component pieces. The two-photon energy absorbed by the antenna structure is resonantly transferred to the core, where the cores emission intensity is enhanced by 8, 20, and 34 times for the three dendritic systems.

PHASE-CONJUGATE BACKWARD STIMULATED EMISSION FROM A TWO-PHOTON-PUMPED LASING MEDIUM

Optical phase conjugation of the two-photon-pumped frequency upconversion backward stimulated emission of a new dye solution has been demonstrated. When the 1064-nm pump intensity reaches a certain threshold value, a highly directional and phase-conjugate backward stimulated emission at ~616-nm wavelength can be observed. After backward passage through an aberration plate placed in the input pump beam path, the introduced aberration influence (1.6-1.8 mrad) can be entirely compensated by backward stimulated emission with a final beam divergence of only 0.23 mrad. The net conversion efficiency from the absorbed IR pump energy to the backward visible stimulated emission energy can reach 10%.