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.

The main purpose of this research was to investigate new medical applications of femtosecond laser ablation. A near-infrared femtosecond laser was tested and proved to be able to overcome the existing limitations and outperform the conventional long-pulse lasers in the areas of human urinary calculus (kidney stone) lithotripsy and skin treatment. The two primary objectives of my research are: 1) to investigate the feasibility of using femtosecond pulsed laser radiation to ablate urinary calculus of various compositions. The laser-calculus interaction mechanism was characterized using pump probe imaging and fast flash imaging. A novel fiber delivery system was developed to transmit and focus high energy femtosecond pulses for urinary calculus lithotripsy. The successful demonstration of the femtosecond laser lithotripsy provided a promising treatment method better than the existing long-pulse laser lithotripsy in a few different aspects, including less collateral damage to surrounding tissue, small-size debris and more controlled experimental condition. 2) to investigate the depth limitation of femtosecond subsurface ablation in scattering skin sample and develop a prototype tissue optical clearing device to enhance femtosecond beam penetration for deeper subsurface cavitation production in the skin. The successful demonstration of the device has potential benefits to new femtosecond-based therapies for reshaping or removing subcutaneous tissues. / text

Surgery of axons in C. elegans using ultrafast laser pulses, and observing their subsequent regrowth opens a new frontier in neuroscience, since such research holds a great potential for the development of novel therapies and cures to neurodegenerative diseases. In order to make the required large-scale genetic screenings in C. elegans possible and thus obtain statistically significant biological data, an automated laser axotomy system needs to be developed. Microfluidic devices hold the promise of improved throughput by integrating different functional modules into a single chip. The first step to developing a microfluidic device for laser axotomy is to devise an on-chip worm trapping method, which maintains a high degree of immobilization to sever axons without using anesthetics. In this thesis, we present a novel method that uses a thin, deflectable PDMS membrane that individually traps worms in a microfluidic device. Axons can successfully be severed with the same accuracy as those using conventional paralyzing techniques. This device also incorporates recovery chambers for housing worms after surgery and for time-lapse imaging of axonal regrowth without the repeated use of anesthetics. Towards accomplishing an automated, high-throughput laser axotomy system, we developed an improved microfluidic design based on the same mechanical immobilization technique. This second generation device allows for serially processing of a large quantity of worms rapidly using a semi-automated system. Integrated to the opto-mechanical platform, a software program utilizing image processing techniques is developed. This semi-automated program can automatically identify the location of worms, their neuronal cell bodies, focus on the axons of interest, and align the laser beam with the axon via a PID based viso-servo feedback algorithm. Statistic data demonstrate that there is no significant difference in axonal reconnection rates between surgeries performed on-chip and using anesthetics. To improve flow control, a three-dimensional novel microfluidic valve structure is designed and fabricated. This novel valve structure allows for a complete sealing of the flow channel, without degrading optical conditions for imaging and laser ablation in the trapping area. Finally, we developed a prototypical microfluidic assembly that will eventually be able to interface a well-plate to automatically deliver population of worms from individual wells to the automated chip for axotomy. This interface consists of a microfluidic multiplexer to significantly reduce the number of solenoid valves needed to individually address each well. / text

This dissertation describes methodology that significantly improves the state of femtosecond laser writing of metals. The developments address two major shortcomings: poor material quality, and limited 3D patterning capabilities. In two dimensions, we grow monocrystalline silver prisms through femtosecond laser irradiation. We thus demonstrate the ability to create high quality material (with limited number of domains), unlike published reports of 2D structures composed of nanoparticle aggregates. This development has broader implications beyond metal writing, as it demonstrates a one-step fabrication process to localize bottom-up growth of high quality monocrystalline material on a substrate. In three dimensions, we direct laser write fully disconnected 3D silver structures in a polymer matrix. Since the silver structures are embedded in a stable matrix, they are not required to be self-supported, enabling the one-step fabrication of 3D patterns of 3D metal structures that need-not be connected. We demonstrate sub-100-nm silver structures. This latter development addresses a broader limitation in fabrication technologies, where 3D patterning of metal structures is difficult. We demonstrate several 3D silver patterns that cannot be obtained through any other fabrication technique known to us. We expect these advances to contribute to the development of new devices in optics, plasmonics, and metamaterials. With further improvements in the fabrication methods, the list of potential applications broadens to include electronics (e.g. 3D microelectronic circuits), chemistry (e.g. catalysis), and biology (e.g. plasmonic biosensing). / Engineering and Applied Sciences

Darbo tikslas – ištirti puslaidininkiniais lazeriais kaupinamos Yb:KGW femtosekundinės sistemos, susidedančios iš osciliatoriaus ir regeneratyvinio stiprintuvo, veikos dinamiką ir panaudojant gautus rezultatus optimizuoti spinduliuotės parametrus. Darbe nagrinėta termo-lęšio bei netiesinio Kerro elemento poveikis rezonatoriaus stabilumui. Panaudojus gautus rezultatus sukurtas trumpiausius impulsus (31 fs) generuojantis iterbio jonais legiruotą strypinį aktyvųjį elementą turintis lazeris. Taip pat pasiūlytas ir eksperimentiškai realizuotas pakreiptų impulsų stiprinimo metodas, kurį taikant optinio plėstuvo plėtimo mastas priklauso tik nuo pluošto matmenų ir gardelės rėžių skaičiaus ir nepriklauso nuo impulso spektro pločio. Impulsų spūdai optimizuoti pasiūlytas ir eksperimentiškai pademonstruotas naujos konstrukcijos vienašūvis autokoreliatorius, kuriame tiriamojo impulso spektrą paskleidžiant kampine dispersija pasižyminčiu optiniu elementu, gaunama informacija apie įvairių spektrinių komponenčių išsidėstymą laike su skiriamąja geba, kuri priklauso tik nuo panaudoto elemento kampinės dispersijos. Šis metodas yra tinkamas vienareikšmiškai charakterizuoti femtosekundinių impulsų spūdą ir tuo yra paprastesnis už plačiai naudojamus FROG, GRENOUILLI ir SPIDER metodus. Tiriant puslaidininkiniais lazeriais kaupinamo Yb:KGW regeneratyvinio stiprintuvo dinamika nustatyti reiškiniai ribojantys maksimalią impulso energiją ir maksimalią išvadinę galią. Panaudojus tyrimo rezultatus... [toliau žr. visą tekstą] / The objective of the present work is to examine the dynamics diode pumped femtosecond Yb:KGW laser consisting of an oscillator and a regenerative amplifier and to optimize its radiation parameters using the results obtained. The thermal-lens and nonlinear Kerr medium effect on the stability of the resonator has been studied. On the basis of the results obtained an oscillator which generates 31 fs pulses has been developed. To our knowledge they are the shortest pulses reported from the laser with a bulk ytterbium doped gain medium. We have also proposed and experimentally demonstrated the tilted pulse amplification method. Applying this method the scale of pulse stretching in the optical stretcher depends only on the beam size and the diffraction grating grooves density and does not depend on the bandwidth of the pulse. In order to optimized the compression of amplified pulses we have also proposed and experimentally tested a new design of single shot autocorrelator which disperses the given pulse spectrum by help of optical component with the angular dispersion. It this way the information is obtained about the distribution of various time-dependent spectral components with the resolution which depends only on the angular dispersion of the optical component used. The present method gives unambiguous characterization of the pulse compression which makes it less complex than widely used FROG, GRENOUILLI and SPIDER methods. The maximum pulse energy and the maximum output power... [to full text]

The objective of the present work is to examine the dynamics diode pumped femtosecond Yb:KGW laser consisting of an oscillator and a regenerative amplifier and to optimize its radiation parameters using the results obtained. The thermal-lens and nonlinear Kerr medium effect on the stability of the resonator has been studied. On the basis of the results obtained an oscillator which generates 31 fs pulses has been developed. To our knowledge they are the shortest pulses reported from the laser with a bulk ytterbium doped gain medium. We have also proposed and experimentally demonstrated the tilted pulse amplification method. Applying this method the scale of pulse stretching in the optical stretcher depends only on the beam size and the diffraction grating grooves density and does not depend on the bandwidth of the pulse. In order to optimized the compression of amplified pulses we have also proposed and experimentally tested a new design of single shot autocorrelator which disperses the given pulse spectrum by help of optical component with the angular dispersion. It this way the information is obtained about the distribution of various time-dependent spectral components with the resolution which depends only on the angular dispersion of the optical component used. The present method gives unambiguous characterization of the pulse compression which makes it less complex than widely used FROG, GRENOUILLI and SPIDER methods. The maximum pulse energy and the maximum output power... [to full text] / Darbo tikslas – ištirti puslaidininkiniais lazeriais kaupinamos Yb:KGW femtosekundinės sistemos, susidedančios iš osciliatoriaus ir regeneratyvinio stiprintuvo, veikos dinamiką ir panaudojant gautus rezultatus optimizuoti spinduliuotės parametrus. Darbe nagrinėta termo-lęšio bei netiesinio Kerro elemento poveikis rezonatoriaus stabilumui. Panaudojus gautus rezultatus sukurtas trumpiausius impulsus (31 fs) generuojantis iterbio jonais legiruotą strypinį aktyvųjį elementą turintis lazeris. Taip pat pasiūlytas ir eksperimentiškai realizuotas pakreiptų impulsų stiprinimo metodas, kurį taikant optinio plėstuvo plėtimo mastas priklauso tik nuo pluošto matmenų ir gardelės rėžių skaičiaus ir nepriklauso nuo impulso spektro pločio. Impulsų spūdai optimizuoti pasiūlytas ir eksperimentiškai pademonstruotas naujos konstrukcijos vienašūvis autokoreliatorius, kuriame tiriamojo impulso spektrą paskleidžiant kampine dispersija pasižyminčiu optiniu elementu, gaunama informacija apie įvairių spektrinių komponenčių išsidėstymą laike su skiriamąja geba, kuri priklauso tik nuo panaudoto elemento kampinės dispersijos. Šis metodas yra tinkamas vienareikšmiškai charakterizuoti femtosekundinių impulsų spūdą ir tuo yra paprastesnis už plačiai naudojamus FROG, GRENOUILLI ir SPIDER metodus. Tiriant puslaidininkiniais lazeriais kaupinamo Yb:KGW regeneratyvinio stiprintuvo dinamika nustatyti reiškiniai ribojantys maksimalią impulso energiją ir maksimalią išvadinę galią. Panaudojus tyrimo rezultatus... [toliau žr. visą tekstą]

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

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.