According to a first aspect of the invention, there is provided a radiation device fur generating broadband output radiation upon receiving pulsed input radiation, the radiation device comprising: an oscillating cavity comprising a first reflecting surface and a second reflecting surface; and anonlinear medium located between the first reflecting surface and the second reflecting surface; wherein the oscillating cavity is configured to receive and to oscillate therewithin said pulsed input radiation such that the pulsed input radiation undergoes a iilamentalion process resulting in formation of one ot more filaments in the nonlinear medium and such that the pulsed input radiation undergoes a plurality of passes through the nonlinear medium such that it is spectrally broadened by the nonlinear medium to form the broadband output radiation. According to a second aspect of the invention, there is provided a radiation source, comprising a radiation device according to the first aspect, and a pump radiation source configured to output the pulsed input radiation. According to a third aspect of the invention, there is provided a method for configuring a radiation device according to the first aspect, comprising: providing the pulsed input radiation having an input spectrum; defining a target output spectrum; determining an amount of nonlinear spectral broadening required for broadening the input spectrum to the target output spectrum via the nonlinear spectral broadening process; determining a total number of passes through the nonlinear medium for achieving the determined amount of nonlinear spectral broadening; determining an input direction for the pulsed input radiation to enter into the oscillating cavity so as to achieve the determined total number of passes through the nonlinear medium; and directing the pulsed input radiation to follow the determined input direction. According to a fourth aspect of the invention, there is provided a method for configuring a radiation source according to the second aspect, comprising: determining a critical power for self-focusing in the nonlinear medium; configuring the pump radiation source such that the pulsed inpul radiation has a peak power equal to or greater than the determined critical power for self-focusing; determining a focused beam size of the pulsed input radiation in the oscillating cavity having a sufficient intensity for enabling the filamentation process: determining a radius of curvature of the first reflecting surface and/or a radius of curvature of the second reflecting surface such that upon heing reflected by any of the first reflecting surface and the second reflecting surface, the pulsed input radiation is focused to have a beam size substantially the same as the determined focused beam size at the locus plane of the oscillating cavity; and separating the first reflecting surface and the second reflecting surface along a common longitudinal axis by a distance equal to one half of a sum of the radius of curvature of the first reflecting surface ami the radius of curvature of the second reflecting surface. According to a fifth aspect of the invention, there is provided a method for generating a broadband output radiation, comprising: generating a pulsed input radiation; repeatedly reflecting the pulsed input radiation buck and forth in a plurality of passes through a nonlinear medium such thai the pulsed input radiation undergoes a filamentaiion process resulting in formation of one or more filaments in the nonlinear medium and such thai the pulsed input radiation is spectrally broadened by the nonlinear medium to fotm the broadband output radiation after the plurality passes through the nonlinear medium; and outputting the broadband output radiation. Other aspects of the invention comprise metrology device comprising a radiation source according the second aspect.
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