Plasma generating method including generating first plasma without supplying first gas in liquid and generating second plasma in first gas, and plasma generating apparatus

A plasma generating apparatus comprising:

• a container for holding a liquid;
• a first electrode;
• a second electrode disposed at a position in contact with the liquid when the liquid is held in the container;
• a power source that, in operation, applies a voltage between the first electrode and the second electrode;
• a gas supply device that, in operation, supplies a first gas in the liquid;
• and
• a control circuit that, in operation, controls operations of the power source and the gas supply device,
• wherein the control circuit causes:
• (I) in a first period, the gas supply device not to supply the first gas in the liquid and the power source to apply a first voltage between the first electrode and the second electrode so as to generate first plasma in a bubble containing a second gas generated by evaporation of the liquid, and
• (II) in a second period after the first period, the gas supply device to supply the first gas in the liquid and the power source to apply a second voltage between the first electrode and the second electrode so as to generate second plasma in the first gas.