| dc.description.abstract | The introduction of the laser in the 1960s brough forth the discovery of many nonlinear phenomena and marked the beginning of the field of nonlinear optics. Nonlinear spectroscopy offers many additional features over conventional linear spectroscopy which can be useful towards biomedical applications. In this work, we employ nonlinear spectroscopy and phenomena towards solving problems in biomedical fields.
In the first study, the visible light generation following filamentation is studied to address knowledge gaps within the American National Standard for the Safe Use of Lasers (ANSI Z136.1-2014). The ANSI standards provide maximum permissible exposure (MPE) values for skin and retinal tissue; however, nonlinear optical effects that cause visible light generation are currently not addressed. In this study, we measure the visible light following filamentation of ultrafast near- to mid- infrared (IR) light. Near-IR light, which normally attenuates before reaching the retina in the eye, was found to generate sufficient visible light following filamentation to exceed the MPE values set by ANSI.
In the next two studies, ultrafast transient absorption spectroscopy is used to study the mechanisms underlying the photobiomodulation (PBM) effect. PBM is the use of low irradiance light in the red to near-IR range to stimulate beneficial effects in tissues and cells. However, the electronic or molecular mechanisms which initiate that effect are not well understood. In our first study, we introduce a novel methodology which couples a continuous wave (CW) laser with ultrafast transient absorption spectroscopy (TAS), coined as CW-TAS, and test the proof-of-principle with the mitochondrial protein, cytochrome c (Cyt c). The TAS data for Cyt c remained intact and unperturbed with the addition of the CW light compared to standard TAS. This indicated that CW-TAS can be used on the more complex mitochondrial proteins suspected to be involved in PBM, and it provided further evidence that Cyt c was not an initiator of the PBM effect. In our second study, we apply the CW-TAS technique to the more complex mitochondrial protein, Complex III (C-III), from a mammalian source. This study provided the first TAS characterization for C-III from specifically a mammalian source. In addition, the photodissociation and recombination of the axial ligand that was tested with TAS was found to not exhibit changes when measured with CW-TAS. Therefore, we conclude that this electronic process of C-III is eliminated from being a potential initiator of the PBM effect.
In the final study, beam shaping techniques were applied to improve the spectral resolution of impulsive stimulated Brillouin scattering (ISBS) spectroscopy towards cellular studies. Brillouin spectroscopy, which studies the elastic properties of materials, has been demonstrated to be useful for biomedical imaging and sensing. In particular, ISBS microscopy has recently been introduced towards biomedical applications; however, improvements to the spectral resolution have not been currently addressed. In this study, we expand the initial pump beam diameter with a 4f configuration and employ the use of a cylindrical lens to focus it into the system. The ISBS linewidth in the Fourier domain was found to be dependent on the pump beam’s spatial geometry. By increasing the spectral resolution, close elastic signals can be resolved which is important in biological and cellular studies where samples contain a high water content. | |
