Pierre Blandin

Visible supercontinuum generation controlled by intermodal four-wave mixing in microstructured fiber.

We present an experimental and numerical study of supercontinuum generation extended in the visible part of the spectrum by using a selective optical coupling of the pump wave in the largely anomalous dispersion regime. The broadband frequency generation is induced by an initial four-wave mixing process that converts the pump wave at 1064 nm into 831 nm anti-Stokes and 1478 nm Stokes wavelengths. Phase matching is ensured on such a large frequency shift thanks to a microstructured multimodal fiber with a specific design. Continuum generation is therefore enhanced around the two generated sidebands.

Diode-pumped passively mode-locked Nd:YVO4 laser at 914 nm

We demonstrate, for the first time, to our knowledge, a diode-pumped passively mode-locked Nd:YVO4 laser, operating on the 4F(3/2)-4I(9/2) transition of the neodymium ion at 914 nm. We obtained 8.8 ps pulses at approximately 914 nm at a repetition rate of 94 MHz, and an averaged output power of 87 mW by using a semiconductor saturable absorber mirror.

Time-gated total internal reflection fluorescence microscopy with a supercontinuum excitation source

We present the instrumental development of a versatile total internal reflection fluorescence lifetime imaging microscopy setup illuminated by a supercontinuum laser source. It enables performing wide-field fluorescence lifetime imaging with subwavelength axial resolution for a large range of fluorophores. The short overall acquisition time and the axial resolution are well suited for dynamic neurobiological applications.

Ultra-pure, water-dispersed Au nanoparticles produced by femtosecond laser ablation and fragmentation

Aqueous solutions of ultra-pure gold nanoparticles have been prepared by methods of femtosecond laser ablation from a solid target and fragmentation from already formed colloids. Despite the absence of protecting ligands, the solutions could be (1) fairly stable and poly size-dispersed; or (2) very stable and monodispersed, for the two fabrication modalities, respectively. Fluorescence quenching behavior and its intricacies were revealed by fluorescence lifetime imaging microscopy in rhodamine 6G water solution. We show that surface-enhanced Raman scattering of rhodamine 6G on gold nanoparticles can be detected with high fidelity down to micromolar concentrations using the nanoparticles. Application potential of pure gold nanoparticles with polydispersed and nearly monodispersed size distributions are discussed.

Efficient versatile-repetition-rate picosecond source for material processing applications

We report on the development of an efficient and simple picosecond diode-pumped solid-state laser source with a versatile repetition rate (typically 1 Hz-1 MHz) for material processing applications. The laser source is based on a 4 MHz repetition rate mode-locked oscillator and a passive 3D multipass amplifier both based on Nd:YVO(4) crystals. Micromachining experiments were performed to study the influence of pulse energy on the machining quality for Al, Cu, paper, and glass.

Picosecond polarized supercontinuum generation controlled by intermodal four-wave mixing for fluorescence lifetime imaging microscopy

We present the generation of a picosecond polarized supercontinuum in highly birefringent multimodal microstructured fiber. The initial steps of the spectral broadening are dominated by intermodal four-wave mixing controlled by the specific fiber design. Using a low repetition rate ultra-stable solid state laser, a pulse train well-suited for versatile time-domain fluorescence lifetime imaging applications is obtained.

Nanofabrication with pulsed lasers

The employment of pulsed lasers offers a novel unique tool for nanofabrication [1]. When focused on the surface of a solid target, pulsed laser radiation causes a variety of phenomena, including heating, melting, and finally ablation of the target, and such processes can lead to an efficient material nanostructuring. First, the laser-assisted removal of material from the irradiated spot can result in a spontaneous formation of variety of periodic nanoarchitectures within this spot. Second, laser ablation of material from a solid target leads to the production of nanoclusters, which can then be either deposited on a substrate to form a nanostructured film or released into a liquid environment to form a colloidal nanoparticle solution. Our on-going projects on laser nanofabrication include the following activities: 1. Laser-assisted self-structuring to form nanoscale features on the surface. In this case, we consider spontaneously formed architectures on the surface under laser-matter interactions. In the first method, fs laser ablation in residual gas leads to a formation of micro-scale spikes on Si surface, which condition a drastic increase of the absorption of the treated surface (“black silicon”) that is important for photovoltaic applications [2]. In the second method, we create hot, highly absorbing laser plasma by a phenomenon of laser-induced gas breakdown and use it to treat surfaces and thus form unique “photon crystal-like” structures, which are of importance for optoelectronics applications [3,4]. 2. Pulsed Laser ablation in liquids. In this method, fs laser radiation is used to ablate a solid target in liquid ambience (aqueous solutions of biopolymers etc) to form colloidal nanoparticles [5–7]. Nanomaterials synthesized by this method exhibit unique proper-ties, which can not be reproduced by conventional chemical routes, including small size (down to 1 nm) and size dispersion, unique surface chemistry, and the absence of toxic contaminants on nanoparticle surface. Such properties give a promise for successful “in vivo” applications of nanoparticles. In particular, we showed that Si nanoparticles pre-pared by laser ablation are fluorescent and capable of exhibiting singlet oxygen under photoexcitation, making them excellent candidates for PDT of cancer [8]. 3. Near-field nanoparticle-assisted nanostructuring of surfaces: fabrication of patterned nanoarrays. In these methods, laser ablation through glass nanoparticles dispersed on the surface is used in combination with photolithography to form nanoplasmonics arrays for biosensing applications [9].

Impact of cholesterol on APP dimers' formation, using FRET detection and fluorescence decay imaging

as the Ab42/Ab40 ratio, were increased in Purkinje neurons from sporadic AD cases as compared to controls. However, the levels of Ab42 as well as Ab40 were clearly lower in Purkinje neurons than in pyramidal neurons. Based on the volume of the captured neurons the intraneuronal molar concentrations of Ab were calculated. Conclusions: We suggest that the concentration of intracellular Ab42 correlates to the neuropathology of Alzheimer’s disease.

FRET detection for neurobiological applications using a Total Internal Reflection Fluorescence Lifetime Imaging Microscope

We present the development of a time resolved TIRF microscope illuminated by a supercontinuum laser source. It permits to perform wide-field fluorescence lifetime imaging of neurobiological processes at the plasma membrane with subwavelength axial resolution.

FRET detection in the plasma membrane using Total Internal Reflection Fluorescence Lifetime Imaging Microscopy

We developed a total internal reflection fluorescence lifetime imaging microscope to perform functional imaging of living cells membranes labeled with FRET couples. Forster resonance energy transfer efficiency can thus be followed with subwavelength axial resolution.