Abstract: An assembly and method for separating first radiation and second radiation in the far field, wherein the first radiation and the second radiation have non-overlapping wavelengths, The assembly comprises a capillary structure, wherein the first radiation and the second radiation propagate coaxially along at least a portion of the capillary structure, and an optical structure configured to control the spatial distribution of the first radiation outside of the capillary structure, through interference, such that the intensity of the first radiation in the far field is reduced along an optical axis of the second radiation.

Abstract: Disclosed is an illumination source comprising a gas delivery system being configured to provide a gas target for generating an emitted radiation at an interaction region of the gas target, and an interferometer for illuminating at least part of the gas target with an interferometer radiation to measure a property of the gas target.

Abstract: A high harmonic generation assembly and method for generating high harmonic radiation. The assembly comprises a cavity configured to receive input radiation and increase the intensity of the input radiation inside the cavity for forming drive radiation suitable for use in high harmonic generation. The assembly further comprises an interaction region within the cavity at which, in use, a medium is present, the medium being configured to generate harmonic radiation by high harmonic generation when the drive radiation is incident thereupon, and an optical assembly configured to direct the drive radiation to pass through the interaction region, and comprising an output coupler comprising an aperture through which at least a part of the generated harmonic radiation is able to exit the cavity. The optical assembly is further configured to shape the drive radiation into a converging hollow beam before the drive radiation passes through the interaction region.

Abstract: An illumination source apparatus (500), suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the illumination source apparatus comprising: a high harmonic generation, HHG, medium (502); a pump radiation source (506) operable to emit a beam of pump radiation (508); and adjustable transformation optics (510) configured to adjustably transform the transverse spatial profile of the beam of pump radiation to produce a transformed beam (518) such that relative to the centre axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the centre axis of the transformed beam has a non-zero intensity, wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation (540), wherein the location of said outer region is dependent on an adjustment setting of the adjustable transformation optics.

Abstract: Methods and corresponding apparatus operable to cause an interaction between a drive radiation beam and a medium for generation of emitted radiation by high harmonic generation, the arrangement comprising: an interaction region positioned at an interaction plane and configured to receive the medium; a beam block positioned upstream of the interaction plane at a beam block plane and configured to partially block the drive radiation beam; a beam shaper positioned upstream of the beam block plane at an object plane and configured to control a spatial distribution of the drive radiation beam; and at least one lens positioned upstream of the interaction plane and downstream of the beam block plane, wherein the lens being positioned such that an image of the spatial distribution of the drive radiation beam is formed at the interaction plane.

Abstract: An illumination source apparatus (500), suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the illumination source apparatus comprising: a high harmonic generation, HHG, medium (502); a pump radiation source (506) operable to emit a beam of pump radiation (508); and adjustable transformation optics (510) configured to adjustably transform the transverse spatial profile of the beam of pump radiation to produce a transformed beam (518) such that relative to the centre axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the centre axis of the transformed beam has a non-zero intensity, wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation (540), wherein the location of said outer region is dependent on an adjustment N setting of the adjustable transformation optics.

Abstract: An illumination source apparatus (500), suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the illumination source apparatus comprising: a high harmonic generation, HHG, medium (502); a pump radiation source (506) operable to emit a beam of pump radiation (508); and adjustable transformation optics (510) configured to adjustably transform the transverse spatial profile of the beam of pump radiation to produce a transformed beam (518) such that relative to the centre axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the centre axis of the transformed beam has a non-zero intensity, wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation (540), wherein the location of said outer region is dependent on an adjustment setting of the adjustable transformation optics.

Abstract: Methods and corresponding apparatus operable to cause an interaction between a drive radiation beam and a medium for generation of emitted radiation by high harmonic generation, the arrangement comprising: an interaction region positioned at an interaction plane and configured to receive the medium; a beam block positioned upstream of the interaction plane at a beam block plane and configured to partially block the drive radiation beam; a beam shaper positioned upstream of the beam block plane at an object plane and configured to control a spatial distribution of the drive radiation beam; and at least one lens positioned upstream of the interaction plane and downstream of the beam block plane, wherein the lens being positioned such that an image of the spatial distribution of the drive radiation beam is formed at the interaction plane.

Abstract: An illumination source apparatus (500), suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the illumination source apparatus comprising: a high harmonic generation, HHG, medium (502); a pump radiation source (506) operable to emit a beam of pump radiation (508); and adjustable transformation optics (510) configured to adjustably transform the transverse spatial profile of the beam of pump radiation to produce a transformed beam (518) such that relative to the centre axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the centre axis of the transformed beam has a non-zero intensity, wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation (540), wherein the location of said outer region is dependent on an adjustment setting of the adjustable transformation optics.