Chi-Kyun Park

Efficient, two-photon pumped green upconverted cavity lasing in a new dye

Abstract Two-photon pumped green cavity lasing has been observed in a solution of a new dye in N,N-dimethyl formamide (DMF). The dye, 4-[N-(2-hydroxyethyl)-N-(methyl) amino phenyl]-4′-(6-hydroxyhexyl sulfonyl) stilbene, abbreviated as APSS, shows a strong two-photon absorption induced fluorescence when excited at 800 nm. The molecular two-photon absorption cross section was measured to be σ 2 = 1.5 × 10 −19 cm 4 /GW or σ ′ 2 = 3.8 × 10 −47 cm 4 /photon/s, and is 1 to 2 orders of magnitude higher than Rhodamine 6G. The peak of the lasing spectrum was around 555 nm, and is to the best of our knowledge, the shortest wavelength obtained from a two-photon pumped dye laser. The conversion efficiency from the absorbed pump energy to the lasing output energy was as high as 2.8%. The absorption and the fluorescence spectra of the new dye, along with the spectral and temporal behavior of the two-photon pumped lasing output is presented.

TWO-PHOTON-PUMPED CAVITY LASING IN A DYE-SOLUTION-FILLED HOLLOW-FIBER SYSTEM

Two-photon-pumped cavity lasing has been achieved in a dye-solution-filled hollow-fiber configuration that provides both a longer gain length and a higher local pump intensity. The gain medium is a solution of the new dye 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4′-(6-hydroxyhexyl sulfonyl)stilbene in dimethyl sulfoxide, which shows a strong two-photon-absorption-induced fluorescence when excited with near-infrared radiation. When the system is pumped with 800-nm 5-ns laser pulses, frequency-upconverted cavity lasing can be observed with a peak lasing wavelength near 565 nm and a 2–3.5-ns pulse duration. One of the major advantages of using a hollow-fiber geometry is the low two-photon pump threshold, which was measured to be as low as 20–30 μJ for a 15-cm-long hollow-fiber sample of 100-μm internal diameter. The conversion efficiency from the absorbed pump energy to the upconverted lasing output was 2.3%.

Dye film leaky waveguide laser

Abstract Based on a dye-doped polymer film with a refractive index less than that of the glass substrate, a leaky waveguide laser device has been investigated. The film is made from a polyurethane based commercial epoxy which is doped with a newly synthesized dye material: trans-4-[P-(N-ethyl-N-hydroxylethylamino) styryl]-N-methylpyridinium tetraphenylborate. The key element of the laser device is a flint-glass made equilateral prism on one surface of which the dye doped film forms a leaky waveguide structure. By combining this prism with a lateral linear pump source and two cavity mirrors, the quasiwaveguide lasing can be obtained. The absorption and fluorescence spectra of the new dye doped film, and the spatial, spectral and temporal behavior of the lasing output from the device are presented. Under pump conditions of 532 nm wavelength, 10 ns pulsewidth and 5 Hz repetition rate, this device provides the peak lasing wavelength at ∼ 590nm, a lasing efficiency of ∼ 12%, and a lasing lifetime ⩾ 3 X 10 4 pulses.

Second-harmonic generation studies of Langmuir-Blodgett monolayers of indodicarbocyanine and hemicyanine dyes and stilbazium salts

Second harmonic generation and UV-visible spectroscopic measurements have been performed on a series of Z-type Langmuir-Blodgett monolayer of indodicarbocyanine, hemicyanine and stilbazium salts. Optical spectra of these monolayer indicate the presence of hypsochromically shifted aggregates on the silica surface. The extent of aggregation is found to be largely dependent on the nature of the counter-ion as well as on the conditions of the monolayer preparation. The SHG intensity of dye aggregates are much smaller compared to that of monomeric dye molecules. In the case of amphiphillic counter-ion containing stilbazium salt compression speed of the monolayer has very little effect on the second harmonic signal and on the absorption spectrum, presumably due to the suppression of aggregation. It seems that the contribution from nonlinear optically active amphiphillic counter-ion to the SHG intensity is not that significant.

Two-photon pumped lasing dyes and their sol-gel glass/polymer composites

A newly synthesized laser dye, trans-4-[P-(N-ethyl-N-hydroxyethylamino)styryl]- N-methylpyridinium tetraphenylborate (dye I), has high thermal- and photo-stability as well as strong two-photon-induced upconversion emission. Utilizing dye I doped bulk polymer rods, two-photo pumped frequency unconverted cavity lacing has been accomplished using a Q- switched Nd:YAG laser as the pump source. The upconversion lacing efficiency was 3.5%, and the cavity lacing lifetime, in terms of pulse numbers, was more than 4 by 104 pulses at 2 Hz repetition rate. By impregnating these dyes into a silica-gel:polymethylmethacrylate (PMMA) and Vycor-PMMA composite glasses, two-photon cavity lacing properties have also been studied.

Photorefractive processes in polymers and organic-inorganic glass composites.

We report on the studies of three photorefractive (PR) polymeric systems: two different multifunctinal polymeric composites and one doped polymer. The doped polymer system consisted of charge transporting polymer, a plasticizer, a photocharge generation sensitizer, and a second-order nonlinear optical chromophore. The measurements of the electric field and light fluency dependencies of charge photogeneration efficiency, response speed, carrier mobility and diffraction efficiency provided information about the kinetics of the photorefractive effect. The two new multifunctional photorefractive polymers each contains a second-order nonlinear chromophore and a charge transporting molecule covalently attached to the polymer backbone (methacrylate chain or silica). The charge transporting and the second- order NLO segments of the polymer are the N-alkylated carbazole group and the stilbene derivative, respectively. Fullerene C60 or charge transfer complex of trinitrofluorenone:carbazole was utilized as charge generating sepcies. The specific advantages of sol-gel processing of organically modified silanes render optical quality materials having the properites of both oxide glass and organic compounds. Electro-optic and PR responses in these composites have also been measured.