Illumination apparatus and method for controlling energy of a laser source
View Patent ↗The disclosure relates to an illuminating apparatus for illuminating a sample on a work stage, optionally with a relatively narrow illuminating line of relatively controlled energy, as well as methods for controlling energy of a laser source when illuminating a sample on a work stage with a relatively narrow illuminating line.
1. An illuminating apparatus configured to illuminate a sample when the sample is in a work stage, the illuminating apparatus comprising:
a beam shaping optical system configured to shape a laser beam into a line-shaped laser beam having a dimension in a first direction that exceeds a dimension in a second direction perpendicular to the first direction, the laser beam being emitted during use by a laser source and propagating through the illuminating apparatus along a beam path, the beam shaping unit comprising a homogenizer configured to homogenize the laser beam at least along the first direction;
an energy measuring device configured to measure an energy of the line-shaped laser beam; and
an energy control system configured to generate a control signal based on the measured energy of the laser beam, the energy control system being configured to control energy output of the laser source and/or transmission of one or more components of the beam shaping optical system based on the control signal,
wherein the energy measuring device is in the beam path between the homogenizer of the beam shaping optical system and the work stage.
2. The illuminating apparatus according to claim 1 , wherein the control signal is indicative of an average beam energy of the line-shaped laser beam along the first direction.
3. The illuminating apparatus according to claim 1 , wherein the energy measuring device comprises:
a beam splitter configured to couple out a fraction of the line-shaped laser beam to provide a coupled out fraction; and
a detector configured to detect the coupled out fraction.
4. The illuminating apparatus according to claim 3 , wherein the detector comprises a plurality of photodiodes arranged side by side in the first direction, the plurality of photodiodes being configured to collect the coupled out fraction.
5. The illuminating apparatus according to claim 4 , wherein the detector further comprises a plurality of lenses configured to focus the coupled out fraction onto the plurality of photodiodes.
6. The illuminating apparatus according to claim 1 , further comprising reducing optics configured to reduce a size of the line-shaped laser beam in the second direction.
7. The illuminating apparatus according to claim 1 , further comprising imaging optics configured to image the line-shaped laser beam onto the sample.
8. The illuminating apparatus according to claim 1 , wherein the beam shaping optical system comprises a field defining optical device configured to define the dimension of the laser beam in at least in the second direction.
9. The illuminating apparatus according to claim 1 wherein the laser beam represents a XeCl laser beam.
10. The illuminating apparatus according to claim 1 wherein a ratio of said dimension in said first direction to said dimension in said second direction is at least 2.5×10 4 .
11. The illuminating apparatus according to claim 1 wherein the laser beam is a pulsed laser beam with a repetition rate between 100 Hz to 10 kHz.
12. The illuminating apparatus according to claim 5 wherein at least one of said plurality of lenses represents a spherical lens.
13. A method of illuminating a sample when the sample is in a work stage, the method comprising:
shaping a laser beam into a line-shaped laser beam with a beam shaping optical system which comprises a homogenizer configured to homogenize the laser beam at least along the first direction;
measuring an energy of the line-shaped laser beam;
generating a control signal based on the measured energy of the line-shaped laser beam; and
controlling an energy output of the laser source and/or transmission of one or more components of the beam shaping optical system based on the control signal,
wherein the energy of the line-shaped laser beam is measured at a location of a path of the line-shaped laser beam that is between the homogenizer of the beam shaping optical system and the work stage.
14. The method according to claim 13 , wherein the control signal is indicative of an averaged beam energy of the line-shaped laser beam along the first direction.
15. The method according to claim 13 , further comprising:
splitting the line-shaped laser beam to provide a coupled out fraction; and
detecting the coupled out fraction.
16. The method according to claim 15 , further comprising averaging an energy of the coupled out fraction along the first direction.
17. The method according to claim 16 , further comprising:
dividing the coupled out fraction into a plurality of beamlets; and
focusing the plurality of beamlets onto a plurality of photodiodes.
18. The method according to claim 13 , further comprising reducing the line-shaped laser beam in the second direction.
19. The method according to claim 13 , further comprising imaging the line-shaped laser beam onto the sample.
20. The method according to claim 13 , beam shaping comprises defining a dimension of the line-shaped laser beam at least in the second direction.