Study of phase modulation techniques to concentrate laser radiation in turbid media for phototherapy
Abstract
Diagnostic and therapeutic techniques leveraging electromagnetic radiation as their pri- mary effector are abundant in the context of biomedical engineering. Its interaction mecha- nisms with matter though are often difficult to control, with this unpredictability stemming mainly from scattering phenomena for biological tissues. This study aims to address this through iterative feedback-based phase-only wavefront modulation. As such, an experimental testing procedure where two different feedback mech- anisms are evaluated is implemented. For both setups an 808 nm wavelength laser beam is used, with its already lower absorption and scattering characteristics for biological tissues mak- ing it relevant for potential applications. Also common to both experimental setups are the two different tissue simulating optical phantoms considered. Set to mimic the optical proper- ties of 1.1 mm thick human skin, they were composed of a mixture of agar, distilled water and milk, with the concentration of milk setting the scattering behavior of the turbid samples. The first feedback signal to be tested was gathered by a NIR camera placed behind the phantoms. The latter received the transmitted laser beam's profile after it had been modulated by a spatial light modulator (SLM). This feedback is then sent to the computer and processed in MATLAB by the iterative optimization algorithms implemented. These will finally send new phase masks to the SLM and continue this feedback loop until a…
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