This protocol aims at assessing the efficacy of performing catheter ablation for atrial fibrillation (AF) with laser catheters versus performing it with radiofrequency (RF) catheters. In order to study laser catheter ablation efficacy, MRI analysis of the lesions 3 months after the procedure will be performed in both groups. MRI analysis will detect ablation gaps in the lesions encircling pulmonary veins. The primary endpoint will compare the number of gaps in the laser catheter and the RF group. The secondary endpoint of the study is recurrence of AF after 12 months. The target population of the study is patients with paroxysmal or persistent AF undergoing AF ablation.