A bifurcating cyclical-ignition pulse (also called Waterproof Casing) was a pulse that enabled a lightsaber to activate underwater with the help of two crystals. Without special modifications, a lightsaber submerged underwater would short out and would require minor repairs before working again.

Are lightsabers scientifically possible?

“Yes, you can create a sword-shaped shaft of glowing, high-energy plasma that is floating in the air without a tangible container, using strong magnetic fields.

Is there anything that can withstand a lightsaber?

Amphistaff's are some of the most durable known objects and were impenetrable to lightsabers. As a hardened staff, it would be unfazed and absorb a lightsaber blow and possessed the ability to wind around a lightsaber blade unharmed and attack the Jedi or Sith's face with venomous jaws.