ABSTRACT
We propose using cross-correlation frequency-resolved optical gating for dispersion characterization of optical elements with high dispersion, such as ultrashort pulse stretchers and compressors. The technique is based on spectrally resolved second-order cross correlation (sum frequency generation) of a stretched pulse with a reference short pulse. Dispersion of optical elements with a high pulse stretching ratio can be completely characterized using this method, even with moderate resolution of spectral measurements of the cross-correlation signal. The proposed technique is used to measure dispersion of a chirped Bragg grating recorded in photo-thermo-refractive glass. It was found that dispersion of these gratings is almost linear with wavelength and has approximately the same slope with opposite signs for two orientations of the grating with opposite faces of the grating used as the input face. Analysis of higher-order dispersion of the grating shows some variations of dispersion across the aperture of the grating, mostly in the amount of third-order dispersion contribution.
ABSTRACT
Herein, we report the study of the three-photon absorption cross-section dependence on solvents parameters for a highly conjugated organic dye, 2,2'-(4,4'-(1E,1'E)-2,2'-(9,9-didecyl-9H-fluorene-2,7-diyl) bis(ethene-2,1-diyl)bis(4,1-phenylene))dibenzo[d]thiazole (A-pi-pi-pi-A). The three-photon absorption cross-section was measured for this organic dye in solution in four different solvents with polarity function, Deltaf between 0.162 and 0.247. The experiments show how the solvent's reorientation of the electrons and polarity contribute to the 3PA cross-section. Multiphoton-absorption experiments of A-pi-pi-pi-A in all four different solvents were performed with a tunable OPG pumped by a 25 picosecond Nd-YAG laser.
ABSTRACT
The three-photon absorption cross sections of three different fluorene derivatives, with extended pi-electron conjugation lengths was experimentally measured and compared with shorter pi-electron conjugation length analogs. The effect of the conjugation length on the three-photon absorption cross section sigma(3) (') of this family of molecules has been elucidated. It is demonstrated that sigma(3) (') of the asymmetric compound D-pi-pi-pi-A is 6.6 times larger than its shorter configuration D-pi-A, while for the symmetric compounds D-pi-pi-pi-D and A-pi-pi-pi-A a two-fold enhancement was found relative to their shorter conjugation length analogs. Measurements of the three-photon excitation of these compounds in THF solution (10(-3)M) were accomplished with a tunable optical pulse generation pumped by a 25 ps Nd-YAG laser.
ABSTRACT
Herein we present experimental evidence of the strong surface plasmon enhancement of two- and three-photon absorption of Hoechst 33 258 (2'-(4-hydrophenyl)-5-(4-methyl-1-piperazinyl)-2,5'-bis(1H-benzimidazole)) pentahydrate in an aqueous solution containing activated gold colloid. The 480-fold enhancement in two-photon absorption and 30-fold in three-photon absorption are predominantly attributed to the electric-field enhancement via surface plasmon resonance. The greater enhancement observed in two-photon absorption is due to the characteristic two- and three-photon absorption cross-sections of the dye.
ABSTRACT
Herein we report an extraordinary three-photon absorption cross-section (sigma'3) enhancement in J-aggregates supramolecular systems. The much higher value of sigma'3 in PIC J-aggregate (2.5 x 10(-71) cm6 s2 ph(-2)) compared to typical values obtained in organic molecules (10(-80) cm6 s2 ph(-2)) is attributed to the strong molecular transition dipole moment coupling in the supramolecular assembly. Three-photon absorption of PIC J-aggregates and monomer aqueous solutions were measured using the well known open aperture Z-scan technique pumping with a 25 ps pulse laser-OPG system at 1720 nm. This novel result opens new expectations for applications of supramolecular systems in bioimaging and medicine.
Subject(s)
Chemistry, Physical/methods , Photochemistry/methods , Quinolines/chemistry , Absorption , Models, Chemical , Models, Theoretical , Molecular Conformation , Molecular Structure , Photons , Spectrophotometry, Ultraviolet , Spectroscopy, Near-InfraredABSTRACT
High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.
Subject(s)
Fluorenes/radiation effects , Fluorescence Resonance Energy Transfer/methods , Fluorescent Dyes/chemical synthesis , Fluorescent Dyes/radiation effects , Microscopy, Fluorescence, Multiphoton/methods , Thiazoles/radiation effects , Benzothiazoles , Dose-Response Relationship, Radiation , LasersABSTRACT
We measure the optical limiting behavior of carbon black suspensions in various viscosity solvents by using a 10-Hz repetition rate, 532-nm, 5-ns pulsed laser. We found that, for common solvents used in the past such as water and ethanol, the limiting behavior ceases after a few laser firings and a turnover in the limiting curve appears. This can be explained by depletion of the carbon black within the focal volume. This turnover shifts to lower energies as the viscosity of the solvent becomes greater. However, for low viscosity liquids, such as carbon disulfide or pentane, the limiting is unaffected by the repetition rate, at least for frequencies up to 10 Hz, because of diffusion of the carbon black particles. This diffusion allows fresh material to replace the irradiated volume within the time between pulses.
