Balloon, light irradiation device, and treatment method

A balloon insertable into a living body,

• the balloon comprising an expansion portion that defines a central axis extending along an insertion direction from a proximal side to a distal side,
• the expansion portion comprising:
• a transmissive layer capable of transmitting light emitted inside to an outside;
• and
• a light shielding layer covering the transmissive layer and having a transmittance of the light lower than a transmittance of the transmissive layer,
• the expansion portion comprising:
• a window region in which the transmissive layer is not covered with the light shielding layer;
• and
• a light shielding region in which the transmissive layer is covered with the light shielding layer, and
• the window region of the expansion portion in an expanded state comprising:
• a first window portion;
• and
• a second window portion arranged spaced apart on the proximal side with respect to the first window portion and more inclined with respect to the central axis than the first window portion.