Do Quang Hoa

Fluorescence lifetime measurement of dibenzofuran and monochlorodibenzofuran

Abstract The fluorescence lifetime of dibenzofuran and monochlorodibenzofuran was measured directly using a picosecond distributed-feedback dye laser and a fast-response microchannel-plate photomultiplier. The fluorescence lifetimes for dibenzofuran and monochlorodibenzofuran were determined to be 10.8±0.5 ns and ca. 1 ns, respectively, suggesting that the fluorescence quantum yield is reduced 10-fold by intersystem crossing induced by a chlorine atom in a dibenzofuran molecule. These findings highlight the advantages of a picosecond laser for the efficient multiphoton ionization of polychlorinated dibenzofurans.

Direct generation of a tunable nearly transform-limited picosecond pulse in the ultraviolet region using a distributed-feedback dye laser

A new design and the characteristics of operating a distributed-feedback dye laser (DFDL) pumped by the fourth-harmonic emission of a Q-switched Nd:YAG laser are described. An ultraviolet nearly transform-limited picosecond pulse was generated by means of two right-angle prisms in the pumping geometry, and the laser wavelength was continuously tunable from 318 to 369 nm using two dye solutions (BM-terphenyl and BMQ). The application of this DFDL to the lifetime measurement of a fluorescent dye is also presented.

A hybrid laser system consisting of a frequency-doubled, narrow-line-width, distributed-feedback dye laser oscillator and a high saturation-fluence Ce:LiCaAlF6 crystal amplifier

A tunable narrow-band picosecond dye laser emitting in the ultraviolet region was amplified using a Ce:LiCaAlF6 crystal pumped by the fourth-harmonic emission of a Nd:Y3Al5O12 laser. The single-pass gain obtained exceeded 2 in the spectral range of 288 to 297 nm.A tunable narrow-band picosecond dye laser emitting in the ultraviolet region was amplified using a Ce:LiCaAlF6 crystal pumped by the fourth-harmonic emission of a Nd:Y3Al5O12 laser. The single-pass gain obtained exceeded 2 in the spectral range of 288 to 297 nm.

Detection of polychlorinated biphenyls in transformer oils in Vietnam by multiphoton ionization mass spectrometry using a far-ultraviolet femtosecond laser as an ionization source

Polychlorinated biphenyls (PCBs) in transformer and food oils were measured using gas chromatography combined with multiphoton ionization mass spectroscopy. An ultrashort laser pulse emitting in the far-ultraviolet region was utilized for efficient ionization of the analytes. Numerous signal peaks were clearly observed for a standard sample mixture of PCBs when the third and fourth harmonic emissions (267 and 200nm) of a femtosecond Ti:sapphire laser (800nm) were employed. The signal intensities were found to be greater when measured at 200nm compared with those measured at 267nm, providing lower detection limits especially for highly chlorinated PCBs at shorter wavelengths. After simple pretreatment using disposable columns, PCB congeners were measured and found to be present in the transformer oils used in Vietnam.

Near‐Infrared Photothermal Response of Plasmonic Gold‐Coated Nanoparticles in Tissues

We propose a new approach to understand the time-dependent temperature increasing process of gold-silica core-shell nanoparticles injected into chicken tissues under near-infrared laser irradiation. Gold nanoshells strongly absorb near-infrared radiations and efficiently transform absorbed energy into heat. Temperature rise given by experiments and numerical calculations based on bioheat transfer are in good agreement. Our work improves the analysis of a recent study [Richardson et al., Nano Lett. 9, 1139 (2009)] by including effects of the medium perfusion on temperature increase. The theoretical analysis can also be used to estimate the distribution of nanoparticles in experimental samples and provide a relative accuracy prediction for the temperature profile of new systems. This methodology would provide a novel and reliable tool for speeding up photothermal investigations and designing state-of-the-art photothermal devices.

Spectral evolution of distributed feedback laser of gold nanoparticles doped solid-state dye laser medium

Characteristics of suppressed relaxation oscillation of a distributed feedback dye laser (DFDL) based on the energy transfer process in a mixture of spherical gold nanoparticles-doped solid-state polymethylmetacrylate dissolved 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye was theoretically and experimentally studied. Single pulse generation regime of the DFDL can be obtained with a suitable gold nanoparticle concentration and ratio of pump power over lasing threshold. Numerical analysis and experimental approach showed that in this regime, the first-pulse laser pulsewidth is rather unchanged while varying the gold nanoparticles concentration in the range of 2.0 × 109–2.0 × 1010 par cm−3. The enhancement of first pulse and the suppression of the secondary pulses by bi-direction energy transfer of spherical gold nanoparticles were experimentally observed.

Theranostic Gold Nanoshells: from Synthesis to Imaging and Photothermal Therapy Applications

Gold nanoshells (GNSs) were grown on monodispersed aminoprotpyltriethoxysilane (APTES) functionalized of silica nanoparticles (NPs) cores with varying sizes ranging from 40-180 nm synthesized by Stober route. Gold shells were deposited onto the surface of silica NPs by tetrakis(hydroxymethyl) phosphonium chloride (THPC) and electroless gold plating method. The coverage of the gold nanoshells on the surfaces of the silica NPs was evaluated using UV-VIS/NIR spectrospcopy and transmission electron microscopy (TEM). The plasmon resonance wavelengths of these gold nanoshells were tunable from visible to near infrared region. The GNSs were also bioconjugated with anti-HER2 monoclonal antibody for diagnostic breast cancer cells using dark field microscope technique. These GNS NPs play a role as nanoheaters transforming light to heat. With the present of these GNS NPs at volume density of 3.6×1010 NPs.cm3 in chicken tissue samples, illuminated by 808 nm laser at the power density of 62 W.cm2 the temperature of tissue sample reachs 110 ̊ C after 20 minutes illumination.

Synthesis and Optical Characterization of Dye Doped in Ormosil Nanospheres for Bioapplications

Dye-doped ORMOSIL (organically modified silicate) nanoparticles (NPs) have significant advantages over single-dye labeling in signal amplification, photostability and surface modification for various biological applications. The dyes: Rhodamine 6G (R6G) and Rhodamine B (RB) were successfully incorporated into ORMOSIL nanoparticles fabricated by micellar nanochemistry from Trimethoxysilane CH3Si(OCH3)3 precursor. The optical characterization of dye-doped ORMOSIL NPs was studied in comparison with its of free dye in solution. The results shown that the photostability of ORMOSIL dye doped nanospheres is much improved in comparison with its of dye in solution. Other studies of the photophysical properties such as anisotropy, fluorescence lifetime and energy transfer were also done.

Picosecond solid-state dye lasers based on a spectro-temporal selection

A very fast spectral evolution in the broadband pulsed solid-state dye laser emissions generated from low-Q and short cavities is proved both experimentally and theoretically with a rate equation model extended to a multiwavelength analysis. This leads to a fast oscillation damping on the short-wavelength wing of the broadband solid-state dye laser spectrum. As a result, the direct generation of picosecond (~ 90 ps) laser pulses adjustable in the 545 - 650 nm spectral range is achieved with a spectral selection in a very simple, compact solid-state dye laser pumped by a standard nanosecond laser.

Generation of spectrally adjustable picosecond pulses using STS dye laser

The spectral evolution of broadband dye laser emissions generated from low-Q, short laser resonators have been investigated experimentally and theoretically with a rate equation model extended to a multiwavelength analysis. The influences of cavity quality and pumping parameters on the spectral dynamics of the broadband dye laser emissions are studied. From these results, the development of a picosecond pulse compressor and direct generation of tunable picosecond (< 90 ps) dye laser pulses are demonstrated using a single nanosecond pumping laser and a spectro-temporal selection of dye broadband laser emission.