Seed laser optical isolator, seed isolator module, EUV radiation source, lithographic apparatus and optical isolator operating method

A seed isolator module for an EUV source comprising:

• an optical isolator comprising:
• an acousto-optic modulator crystal configured to manipulate laser light incident thereto, and
• a first cooling system arranged at a first crystal surface of the acousto-optic modulator crystal;
• and
• a second cooling system arranged at a second crystal surface of the acousto-optic modulator crystal,
• wherein each of the first and second cooling systems comprise:
• a cooling element including one or more channels configure to allow a fluidic cooling medium, and
• a heat transfer assembly comprising an active heat transfer element, arranged between the crystal and the cooling element, and configured to transfer heat from the crystal to the cooling element.