Low Profile Apparatus and Method for Phototherapy

Disclosed herein are optical assemblies having thin, low profile shapes. These optical assemblies may be used with fiber coupled lasers and other light sources, including high power sources, to irradiate tissue at a wavelength suitable for inducing ablation or coagulation to a target depth, denaturation, thermal modification of a tissue, and/or preferential injury to a target tissue structure. Example optical assemblies can produce substantially uniform illumination patterns that are useful for treating superficial tissue, including the internal or luminal (e.g., esophageal) tissue. Some examples may have capability for cooling superficial tissue or skin, such as a detachable, reusable heat sink for active cooling without consumables, fluid pumps, or other cooling equipment.