An optical detection technique is developed to detect and measure the resonant vibration of the cellular membrane. Biological membranes are active components of living cells and play a complex and dynamic role in life processes. They are believed to have oscillation modes of frequencies in the range of 1 to 1000 GHz. To measure such a high-frequency vibration, a linear laser cavity is designed to produce a train of femtosecond pulses of adjustable repetition rate. The method is then directly applied to liposomes, "artificial membrane", stained with a liphophilic potential sensitive dye. The spectral behavior of a selection of potential sensitive dyes in the membrane is also studied.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Pour des applications technologiques d’enregistrement magnétique de l’information à haute densité et vitesse d’écriture et de lecture ultra-rapide, les chercheurs se sont penchés vers des méthodes de manipulation de l’aimantation sans application de champ magnétique externe. Il a été découvert qu’il était possible de renverser de manière déterministe l’aimantation de plusieurs matériaux ferri- et ferro-magnétiques à l’aide uniquement d’impulsions laser ultracourtes polarisées circulairement. Ce retournement tout-optique s’est avéré être un processus cumulatif nécessitant plusieurs impulsions ultracourtes dans les matériaux ferromagnétiques. Notamment dans les multicouches (Co/Pt), le retournement tout-optique se fait en deux étapes : une désaimantation indépendamment de l’hélicité suivie d’une ré-aimantation dans une direction ou l’autre selon l’hélicité. Pour autant, le mécanisme à l’origine du rétablissement de l’ordre magnétique n’a pas été étudié jusqu’à présent. Dans cette thèse, nous avons étudié le mécanisme de renversement de l’aimantation dans les couches ferromagnétiques résultant de l’excitation par impulsions laser ultracourtes polarisées circulairement. Pour cela, nous étions intéressé par la réponse d’une paroi de domaine dans les couches minces de Pt/Co/Pt à la suite d’une excitation laser et en fonction de la polarisation de la lumière. Nous avons démontré la possibilité d’induire un déplacement tout-optique et déterministe d’une paroi de domaine. Nous montrons que la propagation de la paroi résulte de la compétition entre trois contributions : le gradient de température dû aux effets de chauffage par le laser, l’effet de l’hélicité de la lumière et les effets de piégeages de la paroi. Par ailleurs, par mesures expérimentales du dichroïsme circulaire, nous excluons un mécanisme purement thermique du déplacement de paroi. Ainsi nous confirmons que le retournement tout-optique des couches ferromagnétiques se fait par une nucléation suivie d’une ré-aimantation par propagation déterministe des parois de domaines selon l’hélicité. De plus, nous avons exploré la possibilité d’utiliser le retournement tout-optique dans des dispositifs spintroniques pour l’enregistrement de l’information à haute densité. Pour se faire, il est nécessaire d’étudier les effets de tailles du retournement lorsque le matériau est structuré en îlots à l’échelle du micro- ou nanomètre. Nous avons montré qu’un plus grand nombre d’impulsions laser est nécessaire afin de renverser l’aimantation de micro-disques comparés à la couche continue ferromagnétique. Il en résulte que le champ dipolaire aide le renversement de l’aimantation dans les couches continues rendant ainsi le retournement tout-optique énergétiquement plus favorable / Over the past decade, the demand for an even higher capacity to store data has been gradually increasing. To achieve ultrafast and ultrahigh density magnetic data storage, low-power methods to manipulate the magnetization without applying an external magnetic field has attracted growing attention. The possibility to deterministically reverse the magnetization with only circularly polarized light was evidenced in multiple ferri- and ferro-magnetic materials. This phenomenon was called helicity-dependent all-optical switching (HD-AOS). In ferromagnets, it was demonstrated that HD-AOS was a cumulative and multishot process with a helicity-independent demagnetization followed by a helicity-dependent magnetization recovery. Yet, the microscopic mechanism of this helicity-dependent remagnetization remained highly debated. In this thesis, we investigated the magnetization reversal mechanism of all-optical switching in ferromagnetic materials. To explore a potential switching process through domain nucleation and domain wall (DW) propagation, we studied the response of a DW upon femto- or pico-second laser irradiation in Co/Pt thin films that exhibit HD-AOS. We reported helicity-dependent all-optical domain wall motion. We demonstrated that it results from the balance of three contributions: the temperature gradient due to the laser heating, the helicity effect and the pinning effects. By measuring the magnetic circular dichroism, a purely thermal mechanism of the laser-induced DW motion appears to be excluded. Furthermore, we examined the size effects in AOS in Co/Pt films patterned into microdots with a diameter between 10 and 3 μm. This allowed us to explore the role of the dipolar field in the switching mechanism. We discovered that a larger number of laser pulses was required to reverse the magnetization of a microdot compared to the continuous film. This indicated that the dipolar field actually eases the magnetization reversal in the full film. Thus, AOS is less energy-efficient in patterned films, hence making Pt/Co/Pt multilayers not an ideal candidate for integrating AOS in spintronic devices

Se describe la aplicación de pulsos láser ultracortos (≤10fs) en espectroscopía y microscopía de dos fotones llevada a cabo en nuestro grupo de investigación, subrayando las ventajas y requerimientos de este enfoque. Además se presenta una breve descripción de la manipulación de pulsos, de las distorsiones de fase experimentadas por los pulsos láser de femtosegundo y de cómo corregir tales distorsiones utilizando manipuladores de pulsos. / Femtosecond laser pulses in two-photon spectroscopy and microscopy: The application of shaped ultrashort laser pulses (≤10fs) in two-photon spectroscopy and microscopy carried out in our group is  described, highlighting the advantages and requirements of this approach. In addition, a brief description of pulse shaping, phase distortions experienced by femtosecond laser  pulses and how to correct these distortions using a pulse shaper is also presented.

Recently, laser light sources of different regimes have emerged as an essential tool in the biophotonics research area. Classic applications include, for example: manipulating single cells and their subcellular organelles, sorting cells in microfluidic channels and the cytoplasmic delivery of both genetic and non-genetic matter of varying sizes into mammalian cells. In this thesis several new findings specifically in the optical cell sorting as well as in the photo-transfection study fields are presented. In my optical cell sorting and guiding investigations, a new technique for enhancing the dielectric contrast of mammalian cells, which is a result of cells naturally engulfing polymer microspheres from their environment, is introduced. I explore how these intracellular dielectric tags influence the scattering and gradient forces upon these cells from an externally applied optical field. I show that intracellular polymer microspheres can serve as highly directional optical scatterers and that the scattering force can enable sorting through axial guiding onto laminin coated glass coverslips upon which the selected cells adhere. Following this, I report on transient photo-transfection of mammalian cells including neuroblastomas (rat/mouse and human), embryonic kidney, Chinese hamster ovary as well as pluripotent stem cells using a tightly focused titanium sapphire femtosecond pulsed laser beam spot. These investigations permitted advanced biological studies in femtosecond laser transfection: firstly, the influence of cell passage number on the transfection efficiency; secondly, the possibility to enhance the transfection efficiency via whole culture treatments of cells thereby, synchronizing them at the mitotic (M phase) as well as the synthesis phases (S phase) of the cell cycle; thirdly, this methodology can activate the up-regulation of the protective heat shock protein 70 (hsp70). Finally, I show that this novel technology can also be used to transfect mouse embryonic stem (mES) cell colonies and the ability of differentiating these cells into the extraembryonic endoderm.

Cette thèse porte sur l’assemblage de verres par impulsions laser femtosecondes. Une source laser femtoseconde à haute fréquence de répétition a été utilisée pour souder des lames de borosilicate de haute qualité de surface. La technique d’assemblage mise en œuvre diffère de la littérature par le système de focalisation utilisé. Un plan d’expériences a été réalisé afin de déterminer l’influence des différents paramètres laser sur les performances des soudures obtenues, démontrant que l’augmentation de la quantité d’énergie déposée améliore les performances mécaniques et thermiques. Les assemblages soudés peuvent atteindre une haute résistance mécanique supérieure à 25 MPa et supporter des chocs thermiques supérieurs à 300 ° C. L’adaptation des paramètres laser en fonction de la distance entre les lames de verre permet de souder des verres hors contact optique. Cette méthode a également été implémentée avec succès à l’assemblage de verre sur du silicium. / This PhD thesis is about glass bonding by femtosecond laser pulses. A femtosecond laser source generating high repetition rate laser pulses has been used to weld borosilicate glass plates with high surface quality. The method presented in this work differs from the literature by the focusing system implemented. The influence of the laser parameters on the bonded samples performances has been studied implementing a design of experiments, demonstrating that the mechanical and thermal resistance of the samples can be improved by increasing the amount of deposited. Thebonded samples provide high mechanical resistance, higher than 25 MPa, can held high thermal shock above 300 °C and present high transparency above 90 %. Glass bonding with a distance between the glass plates has been performed by adapting the laser parameters. Bonding of glass on silicon has also been performed successfully.

O poli (p-fenilenevinileno), ou PPV, é um polímero de grande relevância tecnológica devido a suas propriedades eletroluminescentes, que têm sido exploradas em diodos emissores de luz orgânicos, displays flexíveis e outros dispositivos optoeletrônicos. Embora o PPV seja um material de importância para muitas aplicações, a sua síntese na nano/microescala não pode ser obtida através do método padrão, o qual utiliza o aquecimento de um polímero precursor poli (cloreto de xileno tetrahidrotiofenio) (PTHT). Este trabalho mostra como a microestruturação com pulsos de femtosegundo pode ser empregada para a síntese de PPV em regiões pré-determinadas, empregando três diferentes abordagens, permitindo uma nova metodologia para a fabricação precisa de microcircuitos poliméricos complexos, (i) na primeira abordagem, o processo de conversão é obtido pela irradiação de filmes de PTHT com pulsos laser ultracurtos em regiões previamente determinadas, o que leva ao controle espacial da formação de PPV em microescala, (ii) na segunda abordagem, microestruturas tridimensionais dopadas com PTHT foram fotopolimerizadas por absorção de dois fótons. A conversão de PTHT para PPV nestas microestruturas dopadas foi obtida após um tratamento térmico, (iii) na terceira abordagem, a transferência direta induzida por laser (LIFT) com pulsos de femtossegundos permite a deposição controlada de PPV com alta resolução espacial, fornecendo micropadrões 2D, preservando sua estrutura e propriedades ópticas. As estruturas foram caracterizadas por microscopia eletrônica de varredura, microscopia óptica de transmissão, microscopia de fluorescência e microscopia confocal de fluorescência. Suas propriedades ópticas foram analisadas através de sistemas de micro-fotoluminescência e micro-absorção implementadas em um microscópio invertido. Medidas de espectroscopia Raman, microscopia de força atômica e medidas elétricas também foram realizadas. Este trabalho mostra como a microestruturação com laser de fs pode ser explorada para a síntese de PPV em regiões pré-determinadas para fabricar uma variedade de microdispositivos, abrindo novos caminhos na optoeletrônica baseada em polímeros. / Poly(p-phenylenevinylene), or PPV, is a polymer of great technological relevance due to its electroluminescent properties, which have been exploited in organic light emitting diodes, flexible displays and other optoelectronic devices. Although PPV is a material of foremost importance for many applications, its synthesis at the nano/micro scale cannot be achieved through the standard method that uses heating of a precursor polymer poly(xylene tetrahydrothiophenium chloride)(PTHT). This work demonstrates the use of direct laser writing with femtosecond pulses to obtain the synthesis of PPV in pre-determined regions, by applying three different approaches, allowing the precise fabrication of complex polymeric microcircuits, (i) in the first approach the conversion process is achieved by irradiating PTHT films with ultra-short laser pulses in previously determined regions, which leads to the spatial control of PPV formation at microscale, (ii) in the second approach, three-dimensional microstructures doped with PTHT were photopolymerized by two photons absorption. The conversion of PTHT to PPV in these doped microstructures was obtained by a subsequent thermal treatment, (iii) in the third approach, laser-induced forward transfer (LIFT) with femtosecond pulses enables the controlled deposition of PPV with high spatial resolution, providing 2D micropatterns, while preserving its structure and optical properties. The structures were characterized by scanning electron, fluorescence, transmission and confocal fluorescence microscopies. Their optical properties were analyzed by micro-photoluminescence and micro-absorption setups assembled on an inverted microscope. Raman spectroscopy, electrical measurements and atomic force microscopy were also performed. This thesis shows the use of fs-laser writing methods for the synthesis of PPV in pre-determined regions, to fabricate a variety of microdevices, thus opening new avenues in polymer-based optoelectronics.