Lithographic apparatus

A source for generating electromagnetic radiation, the source comprising:

• a laser amplifier configured to amplify a laser beam and comprising a main conduit, a gas recirculation system, and first and second heat exchangers, wherein:
• the main conduit is provided with electrodes configured to transfer energy to a gas in the main conduit for amplification of a laser beam;
• the gas recirculation system includes a gas conduit configured to deliver the gas to the main conduit or remove the gas from the main conduit;
• the first and second heat exchangers are configured to be in thermal contact with the gas conduit;
• the first heat exchanger is configured cool the gas, using a cooling fluid that is passively cooled, to a gas temperature between a high temperature at an input of the gas conduit and a low temperature at an output of the gas conduit;
• and
• the second heat exchanger is configured to use a further cooling fluid for cooling the gas to the low temperature at the output of the gas conduit.

A method comprising:

• amplifying a laser beam using a gas as an amplifying medium, wherein
• the gas flows through a main conduit and
• the amplifying comprises transferring energy to the gas in the main conduit using electrodes;
• delivering the gas to the main conduit or removing the gas from the main conduit using a gas recirculation system;
• cooling the gas to a gas temperature between a high temperature at an input of a gas conduit of the gas recirculation system and a low temperature at an output of the gas conduit using a cooling fluid and a first heat exchanger;
• passively cooling the cooling fluid;
• and
• cooling the gas to the low temperature at the output of the gas conduit using a further cooling fluid and the second heat exchanger.