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The original goal of this project was to determine the role of non-linear interactions underlying the bioeffects induced by ultrashort pulse laser pulses. As initially conceived, this line of investigation was to be principally directed at understanding the contribution of multiphoton absorption. This indeed was a major focus of the research project, but for various reasons the scope of the work was expanded to include identification of the intracellular mechanisms that determine the cellular response to the absorption of optical radiation, and to develop and implement a non-invasive means for measuring the thermal gradients induced by the absorption of laser radiation in tissue. Both of these ancillary projects were successful in that (1) the transcription factor NF-B was found to be activated by visible laser exposure in a way that appeared to be dependent on the absorption of laser energy in the melanin granules of the retinal pigment epithelial cell, and (2) by exploiting the temperature-dependent nature of the proton resonance frequency (PRF), magnetic resonance thermography was successfully used to measure temperature gradients induced in tissue phantoms during laser exposure, and these gradients closely followed the spatial distributions predicted by classical heat diffusion theory.
This volume contains key papers that document the initial probing of the limits of subnanosecond pulses and the resulting discoveries of nonlinear effects. The papers tell the story of effects previously thought to be impossible to produce in tissue. If you read all the references carefully, you will see the studies evolve from speculation to experimentation to theory, and culminate in policy recommendations.
This second edition in paperback provides an up-to-date review of the state of the art in different generation processes for ultrashort laser pulses. Inaddition, extensive applications in a wide range of fields - in physics,engineering, chemistry, and biology - are discussed: Eight chapters dealwith the following topics: -the generation of picosecond and femtosecond laser pulses -nonlinear wave interactions - new investigations in solid-state physics - recent progress in optoelectronics - advances in coherent material excitations - ultrafast vibrational lifetimes and energy redistribution in liquids - new observations of chemical reactions in the liquid state - the primary processes of important biological systems The book is essential reading for scientists and engineers who want to know what is going on in this rapidly advancing field. It should also interest graduate students and others who seek an introduction to laserpulses.
Learn about the many biological and medical applications of ultrashort laser pulses. The authors highlight and explain how the briefness of these laser pulses permits the tracing of even the fastest processes in photo-active bio-systems. They also present a variety of applications that rely on the high peak intensity of ultrashort laser pulses. Easy-to-follow examples cover non-linear imaging techniques, optical tomography, and laser surgery.
Applications of ultrashort pulse laser systems have increased dramatically in the past several years. Retinal exposure to these laser pulses can produce visible lesions with pulse energies of less than 1 microjoule (microJ) per pulse. Our research has found a reduction in the energy required for retinal damage as pulse duration is decreased from the nanosecond (ns) to femtosecond (fs) regime. With this data, new laser safety standards are being proposed to reduce the dangers and uncertainties when working around these lasers.
The use of laser light for targeting devices and weapons has sharply increased the likelihood that aircrew and support personnel will be exposed to laser light during operations. The increased potential for exposure of humans highlights the fact that there is a need for scientifically based safety standards for laser exposure at the ultrashort pulse lengths. Current safety standards are largely extrapolations of exposure limits at longer pulse lengths using a minimal visible lesion endpoint in the Rhesus monkey retinal model. A non-animal model for assessing laser-light damage to tissue, particularly human, is quite desirous for obvious scientific, political, and fiduciary reasons. I assessed the sublethal insult to human cells using a tissue culture system for specific genes that have been shown to be important in several biological processes that could lead to cancer or cell death. Using the CAT-Tox (L) (xenometrix, Inc.) assay, it appears that 532 nm nanosecond pulse of laser light are sensed and induces several stress response genes including FOS in a roughly dose dependent fashion. This approach provides insight into a more global methodology for characterizing environmental stressors via genetic profiling.
Broadband spectral content is required to support ultrashort pulses. However this broadband content is subject to dispersion and hence the pulse duration of corresponding ultrashort pulses may be stretched accordingly. I used a commercially-available adaptive ultrashort pulse shaper featuring multiphoton intrapulse interference phase scan technology to characterise and compensate for the dispersion of the optical system in situ and conducted experimental and theoretical studies in various inter-linked topics relating to the light-matter interaction. Firstly, I examined the role of broadband ultrashort pulses in novel light-matter interacting systems involving optically co-trapped particle systems in which inter-particle light scattering occurs between optically-bound particles. Secondly, I delivered dispersion-compensated broadband ultrashort pulses in a dispersive microscope system to investigate the role of pulse duration in a biological light-matter interaction involving laser-induced cell membrane permeabilisation through linear and nonlinear optical absorption. Finally, I examined some of the propagation characteristics of broadband ultrashort pulse propagation using a computer-controlled spatial light modulator. The propagation characteristics of ultrashort pulses is of paramount importance for defining the light-matter interaction in systems. The ability to control ultrashort pulse propagation by using adaptive dispersion compensation enables chirp-free ultrashort pulses to be used in experiments requiring the shortest possible pulses for a specified spectral bandwidth. Ultrashort pulsed beams may be configured to provide high peak intensities over long propagation lengths, for example, using novel beam shapes such as Bessel-type beams, which has applications in biological light-matter interactions including phototransfection based on laser-induced cell membrane permeabilisation. The need for precise positioning of the beam focus on the cell membrane becomes less strenuous by virtue of the spatial properties of the Bessel beam. Dispersion compensation can be used to control the temporal properties of ultrashort pulses thus permitting, for example, a high peak intensity to be maintained along the length of a Bessel beam, thereby reducing the pulse energy required to permeabilise the cell membrane and potentially reduce damage therein.
This second edition in paperback provides an up-to-date review of the state of the art in different generation processes for ultrashort laser pulses. Inaddition, extensive applications in a wide range of fields - in physics,engineering, chemistry, and biology - are discussed: Eight chapters dealwith the following topics: -the generation of picosecond and femtosecond laser pulses -nonlinear wave interactions - new investigations in solid-state physics - recent progress in optoelectronics - advances in coherent material excitations - ultrafast vibrational lifetimes and energy redistribution in liquids - new observations of chemical reactions in the liquid state - the primary processes of important biological systems The book is essential reading for scientists and engineers who want to know what is going on in this rapidly advancing field. It should also interest graduate students and others who seek an introduction to laserpulses.