Current treatment modalities include drugs and surgery, and several other therapies are in clinical evaluation including RF, cryoablation and microwave ablation and implantable defibrillators; however, all are considered sub-optimal. Our proposed work focuses on the development of a photonic based ablation system designed for use in the three areas targeted in the ablation of atrial arryhthmias. Diffusing tip designs will be tested for their potential to ablate atrial flutter, and atrial fibrillation by studying the formation of continuous linear lesions with energy from a high power diode laser system. Catheter systems will be proposed and tested, with the goal of creating linear lesions in one single application of energy, therein significantly reducing procedure times. Experiments are designed to explore the dosimetry of photonic energy application to the three different tissue types relevant to the ablation; design and test a novel deflectable catheter to create ablation lines near the vena cava and atrial roof via percutaneous delivery of photonic energy; and design and test a newly conceived 'halo' shaped optical diffuser for ablation in pulmonary veins. PROPOSED COMMERCIAL APPLICATIONS: Atrial fibrillation is the most common sustained cardiac rhythm disorder and is estimated to afflict 2.5 MM people in the US and over 5 MM people worldwide. Non-surgical treatment of atrial fibrillation and atrial flutter offers a significant opportunity to address this huge market need. Lightstic diffusers are capable of producing continuous linear lesions necessary to ablate multi-reentrant arrhythmia. This new minimally invasive photonic based procedure offers several potential advantages over other energy sources such as, radio frequency, cryo-ablation or microwave.