Guibao Xu

Synthesis, structure and properties of a new two-photon photopolymerization initiator

A new two-photon free-radical photopolymerization initiator, (E,E)-4-{2-[p′-(N,N-di-n-butylamino)stilben-p-yl]vinyl}pyridine (abbreviated to DBASVP), has been synthesized. Quantum chemistry calculations showed that the new initiator possesses a large delocalized π electron system, a large change in dipole moment on transition to the excited state and a large transition moment. The calculated two-photon absorption cross-section is as high as 881.34 × 10−50 cm4 s photon−1. The single-photon and two-photon absorption and fluorescence properties in various solvents have been investigated carefully. The new initiator exhibits outstanding solvent-sensitivity, which experimentally interprets the excellent electron delocalized properties of the molecule. A microstructure has been fabricated under irradiation at 800 nm using a 200 fs, 76 MHz Ti:sapphire femtosecond laser.

Synthesis and nonlinear optical properties of novel multi-branched two-photon polymerization initiators

Efficient Witting and Pd-catalyzed Heck coupling methodology are employed to synthesize three multi-branched two-photon photopolymerization initiators diphenyl-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to DPVPA), phenyl-bis-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to BPVPA) and tris-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to TPVPA). The experimental results confirm that all these compounds are good two-photon absorbing chromophores and operative two-photon photopolymerization initiators. The calculated two-photon absorption cross sections of DPVPA, BPVPA and TPVPA for the lowest excited state are 59.3, 30.2 and 42.4 × 10−50 cm4 s photon−1, respectively. A microstructure using BPVPA as initiator has been fabricated under irradiation of 200 fs, from a 76 MHz Ti∶sapphire femtosecond laser at 820 nm. The possible photopolymerization mechanism is discussed.

High-power Nd:GdVO4 laser at 1.34 μm end-pumped by laser-diode-array

Abstract A diode-end-pumped high-power Nd:GdVO 4 laser operating at 1.34 μm has been demonstrated. The maximum continuous-wave output power of 4.62 W was obtained at the incident pump power of 14.75 W, with the corresponding optical conversion efficiency of 31.3% and the average slope efficiency of 33.1%. By using the experimentally measured threshold pump power and slope efficiency, the stimulated emission cross-section of Nd:GdVO 4 crystal at 1.34 μm was determined to be 1.78×10 −19 cm 2 .

Actively Q-switched intracavity second-harmonic generation of 1.06 μm in BiB3O6 crystal

Abstract We have investigated the acousto-optically Q-switched intracavity second-harmonic generation of 1.06 μm in a 1.9-mm-long BiB3O6 crystal, cut for type-I phase-matching direction of (θ,ϕ)=(168.9°,90°), performed in a diode-end-pumped Nd:YVO4 laser. When the incident pump power was 4.3 W at 30 kHz of pulse repetition frequency, a maximum average green output power of 480 mW , the shortest pulse with FWHM width of 72 ns , the highest single pulse energy of 16 μJ and the maximum peak power of 222 W were obtained, giving the corresponding optical conversion efficiency of 11.2%. The effect of varying temperature in BIBO crystal on the average green output power was also investigated.

Frequency up-conversion of s-triazine derivatives via two photon absorption and second-harmonic generation

A three-branched octupolar compound, 2,4,6-tris[2-(4-N,N-diethylamino)phenylethenyl]-1,3,5-s-triazine (compound III), as well as its one- and two-branched analogues (compounds I and II respectively) have been synthesized. The structures of I and II have been determined by X-ray diffraction. The linear and nonlinear spectra of these compounds regularly vary: (1) the spectral positions (λmax values) of the linear absorption, the single-photon excited fluorescence (SPEF) and the two-photon excited fluorescence (TPEF) show regular red-shifts when the branch number increases from 1 to 3; (2) the spectral intensities, including the linear absorbance emax and the two-photon absorption cross-section σ, the SPEF and the TPEF intensities are all increased significantly when going from I to III. The values of emax/MW and σ/MW (of compounds I, II and III) vary with the ratios of 1.0 : 1.3 : 1.7 and 1.0 : 1.4 : 1.3, respectively. All the photophysical data indicate that by incorporating more branches into the triazine ring, the linear and nonlinear optical responses have been significantly enhanced, and that the spectral behaviour of II is closer to that of III, while more different from that of I. The single-branched compound I crystallizes in the noncentrosymmetric polar space group Cc. Its crystalline powder sample shows remarkable macro second-order nonlinear response with a SHG intensity of 46.8 times that of urea under a fundamental picosecond Nd : YAG laser beam (1064 nm). An important factor of such a large SHG intensity is that all the molecular dipoles take the same-oriented packing style that makes the crystal maximally polarized, fulfilling the optimization in the sense of crystal engineering.

Diode-laser-array end-pumped 1W CW Nd:YVO4/BIBO green laser

Abstract This paper discusses a diode-laser-array end-pumped Nd:YVO4/BIBO green laser. Using a three-mirror folded cavity (V-shaped), a 1.06 W CW green output was obtained at an incident pump power of 8.5 W; the corresponding optical conversion efficiency was 12.5%. The relationship between the green output and the temperature of the BIBO crystal was investigated. The laser damage threshold of BIBO crystal was measured to be 600 MW cm−2 and 400 MW cm−2 at 1064 nm and 532 nm, respectively.

Diode-end-pumped solid-state ultraviolet laser based on intracavity third-harmonic generation of 1.06 μm in YCa4O(BO3)3 crystal

Abstract Intracavity type-I sum-frequency mixing of 1.06 μm and 532 nm with a (θ,ϕ)=(106°,77.2°)-cut YCOB crystal was performed in a compact laser-diode-pumped solid-state laser. Three type-II phase-matching KTP crystals with different length were used to generate 532 nm light by frequency-doubling of 1.06 μm . The 355 nm output power was measured with the three KTP crystals for Q-switched and continuous-wave (CW) operation, respectively. The maximum ultraviolet output power of 1305 μW was obtained with a 15 mm KTP crystal for CW operation, while the maximum ultraviolet average output power of 124 mW was obtained with a 10 mm KTP crystal for Q-switched operation.

Structures and nonlinear optical properties of new symmetrical two-photon photopolymerization initiators

Four new symmetrical, two-photon photopolymerization initiators, 9-(4-{(1E,11E)-4-[(E)-4-(9H-carbazol-9-yl)styryl]-2,5-dimethoxystyryl}phenyl)-9H-carbazole (1), N-(4-{(1E,8E)-4-[(E)-4-(diphenylamino)styryl]-2,5-dimethoxystyryl}phenyl)-N-phenylbenzeneamine (2), 1,4-bis{2-[4-(2-pyridin-4-ylvinyl)phenyl]vinyl}-2,5-bisdimethoxybenzene (3) and 1,4-bis{2-[4-(2-pyridin-4-ylvinyl)phenyl]vinyl}-2,5-bisdodecyloxybenzene (4), have been synthesized and characterized. One-photon fluorescence, one-photon fluorescence quantum yields, one-photon fluorescence lifetimes, and two-photon fluorescence have been investigated. The results show that they are all good two-photon absorbing chromophores and effective two-photon photopolymerization initiators. The two-photon absorption cross-sections of these molecules have been evaluated by theoretical calculations. Microfabrication via two-photon-initiated polymerization has been studied and the possible photopolymerization mechanism is discussed.

Noncollinear second-harmonic generation in BiB 3 O 6

Noncollinear second-harmonic generation (SHG) in a BiB3O6 crystal was investigated. Using a picosecond Nd:YAG laser as the fundamental light source, we achieved two efficient types of noncritical noncollinear SHG. A total reflection technique was employed to make the experimental setup quite simple. The noncollinear SHG efficiency could be as high as 49.2%.

Laser-diode-array end-pumped 8.2-W CW Nd : GdVO/sub 4/ laser at 1.34 /spl mu/m

A laser-diode-array end-pumped 0.3-at.% Nd-doped GdVO/sub 4/ high-power continuous-wave (CW) laser operating at 1.34 /spl mu/m has been demonstrated. The maximum CW output power of 8.23 W was obtained at the incident pump power of 27.9 W, giving the corresponding optical conversion efficiency of 29.5% and the average slope efficiency of 30.2%. Two Nd : GdVO/sub 4/ crystals with Nd/sup 3+/ concentration of 0.5 and 1.14 at.% were also investigated for the comparison to show the advantage of lowly Nd-doped crystals applied to high-power lasers.