Los sistemas de microfluídica conocidos con el nombre de lab-on-a-chip han contribuido al avance en áreas como la química, la biología, la biomedicina, la biodefensa y la microelectrónica, entre otras. Sin embargo, a pesar de sus beneficios, su comercialización está principalmente limitada por los altos costes de producción derivados de las técnicas utilizadas para su fabricación. Es por ello que actualmente se están centrando esfuerzos en utilizar técnicas que disminuyan los costes pero que conserven o incrementen los beneficios de estos dispositivos. Este trabajo de investigación presenta una nueva modalidad de escritura directa con láser (LDW) como una prominente técnica de fabricación, que puede beneficiar el desarrollo de nuevos dispositivos de microfluídica en 3 dimensiones: la escritura directa con láser en 3 dimensiones (LDW-3D). En ella se combinan los beneficios de la técnica de la LDW y una clase de vidrios conocidos con el nombre de vidrios cerámicos fotoestructurables (PSGCs). Con esta técnica se pueden obtener motivos tridimensionales focalizando un haz láser en el interior de un material, el cual debe ser transparente a la radiación que emite dicho láser. La técnica se basa en el efecto de la modificación estructural de un vidrio PSGC conocido con el nombre comercial de Foturan® tras la irradiación con un láser. Luego éste se somete a un tratamiento térmico y finalmente a un ataque químico con HF. Se realizaron ensayos irradiando muestras de Foturan con un láser UV con una duración de pulso de 10 ns y una longitud de onda de 355 nm (nsUV) y un láser de femtosegundos IR con una duración de pulso de 450 fs y una longitud de onda de 1027 nm (fsIR). Los estudios realizados revelan que el láser de nsUV produce un efecto de fotoionización en el Foturan a partir de la absorción de 2 fotones que sensibilizan al agente fotoionizador (Ce+3) contenido en su matriz. En el caso de utilizar el láser de fsIR, la fotoionización de este tipo de vidrio se produce mediante la absorción multifotónica de 8 fotones, actuando sobre niveles de energías que están asociados a defectos e impurezas localizados en la banda prohibida del Foturan. También se han evaluado los diferentes parámetros tecnológicos que permiten la aplicación de la técnica LDW-3D para la fabricación de microestructuras en 3D tales como microcanales y microdepósitos con buen aspecto y correspondencia entre sus dimensiones. En base a estos estudios se fabricó un sistema tridimensional en Foturan utilizando el láser fsIR. Este sistema presenta características que hacen que pueda ser aprovechado en el campo de la microfluídica como micromezclador de soluciones o analizador de microorganismos. / Microfluidic systems known as lab-on-a-chip have contributed to progress in areas such as chemistry, biology, biomedical, biodefense and microelectronics, among others. However, despite their benefits, their marketing is mainly limited by the high production costs resulting from the techniques involved in their manufacture. This is why nowadays researchers are focusing efforts in new techniques to reduce costs but maintaining or increasing the benefits of these devices.This research presents a new type of laser direct writing (LDW) as a prominent fabrication technique, which can benefit the development of new microfluidic devices in three dimensions: laser direct write in 3 dimensions (LDW-3D). It combines the benefits of the technique LDW and a type of glasses known as photo-structural glass ceramics (PSGCs). 3D structures can be obtained through this technique by focusing a laser beam inside a material, which has to be transparent to the radiation emitted by the laser. The technique is based on the effect of structural modification of a PSGC glass called Foturan® after laser irradiation. Afterwards, the glass is submitted to a standard thermal treatment and finally, to an etching step with HF. Tests were performed by irradiating Foturan samples with an UV nanosecond laser with 10 ns pulse duration and 355 nm wavelength (nsUV), and an IR femtosecond laser with 450 fs pulse duration and 1027 nm wavelength (fsIR).The results show that nsUV laser produces the photoionization effect on the Foturan through a 2-photon absorption process which sensitizes the photoactive agent (Ce+3). In the case of using the fsIR laser, photoionization is produced by a 8-photon multiphoton absorption process, involving energy levels that are associated with localized defects and impurities in the Foturan gap. Different technological parameters have been evaluated in order to study the viability of the LDW-3D technique for producing 3D microstructures, such as microchannels and microreservoirs showing good aspect-ratio. Based on these studies, a 3D-system in Foturan was produced by using the fsIR laser. This system presents special features that make it suitable in the field of microfluidics as micromixer or microorganisms analyzer.

After an intense development of optical tweezers as a biophysical tool during the last decades, quantitative experiments in living cells have not found in this technique its best ally, due, in part, to the lack of a reliable method to measure forces in complex environments. The attempts to overcome this problem either require complicated in situ calibrations, which make their use impossible in the study of dynamic processes, or they are inaccurate. Using a different approach, Steven Smith at Carlos Bustamante’s lab at the University of Berkeley developed a method based on the direct measurement of the momentum change of the trapping beam. However, its diffusion has been modest mainly because it requires a counter-propagating optical trapping system, which is difficult to implement and combine with other techniques. Although it has not been used for this purpose yet, it seems a more suitable method for in vivo experiments since the measurement depends only on some properties of the sensor apparatus but not on the experiment itself. On the other hand, the use of holographic optical tweezers in molecular biology experiments involving force and position measurements is still far from established. The existence of different effects associated to the use of spatial light modulators to create the optical traps has restricted their use. In this thesis, I present the work that I carried out in the Optical Trapping Lab – Grup de Biofotònica at the University of Barcelona related to these two subjects. During these years, I have focused on the implementation of the force detection method based on the conservation of the light momentum in single-beam optical traps, and on the analysis of several aspects of holographic tweezers oriented to their use in quantitative experiments.

En aquest treball s'ha estudiat la dinàmica dels làsers de classe A i de classe B en termes del potencial de Lyapunov. En el cas que s'injecti un senyal al làser o es modulin alguns dels paràmetres, apareix un comportament moltmés complex i s'estudia el conjunt de bifurcacions.1) Als làsers de classe A, la dinàmica determinista s'ha interpretat com el moviment damunt el potencial de Lyapunov. En la dinàmica estocàstica s'obté un flux sostingut per renou per a la fase del camp elèctric.2) Per als làsers de classe A amb senyal injectat, s'ha descrit el conjunt de bifurcacions complet i s'ha determinat el conjunt d'amplituds i freqüències en el quals el làser responajustant la seva freqüència a la del camp extern. 3) S'ha obtingut un potencial de Lyapunov pels làsers de classe B, només vàlid en el cas determinista, que inclou els termes de saturació de guany i d'emissió espontània.4) S'ha realitzat un estudi del conjunt de bifurcacions parcial al voltant del règim tipus II de la singularitat Hopf--sella--node en un làser de classe B amb senyal injectat.5) S'han identificat les respostes òptimes pels làsers de semiconductor sotmesos a modulació periòdica externa. S'han obtingut les corbes que donen la resposta màxima per cada tipus de resonància en el pla definit per l'amplitud relativa de modulació i la freqüència de modulació. / In this work we have studied the dynamics of both class A and class B lasers in terms of Lyapunov potentials. In the case of an injected signal or when some laser parameters are modulated, and more complex behaviour is expected, the bifurcation set is studied. The main results are the following:1) For class A lasers, the deterministic dynamics has been interpreted as a movement on the potential landscape. In the stochastic dynamics we have found a noise sustained flow for the phase of the electric field. 2) For class A lasers with an injected signal, we have been able to describe the whole bifurcation set of this system and to determine the set of amplitudes frequencies for which the laser responds adjusting its frequency to that of the external field. 3) In the case of class B lasers, we have obtained a Lyapunov potential only valid in the deterministic case, including spontaneous emission and gain saturation terms. The fixed point corresponding to the laser in the on state has been interpreted as a minimum in this potential. Relaxation to this minimum is reached through damped oscillations. 4) We have performed a study of the partial bifurcation set around the type II regime of the Hopf-saddle-node singularity in a class B laser with injected signal. 5) We have identified the optimal responses of a semiconductor laser subjected to an external periodic modulation. The lines that give a maximum response for each type of resonance are obtained in the plane defined by the relative amplitude modulation and frequency modulation.