Surface characteristic determining apparatus

Surface characteristic determining apparatus for determining a characteristic of a sample surface, the apparatus comprising:

• a first light source to provide light of one of a plurality of first wavelengths;
• a second light source to provide light of a second wavelength;
• a combiner to combine light from the first and second light sources to produce combined light;
• a director to direct combined light along a reference path towards a reference surface and along a measurement path towards a sample surface such that light reflected by the sample surface and light reflected by the reference surface interfere to provide interference light,
• a first detector to detect interference light of the first wavelength;
• a second detector to detect interference light of the second wavelength;
• an electro-optic modulator to control the relative lengths of the reference and measurement paths on the basis of interference light detected by the second detector;
• a determiner to determine a characteristic of a sample surface on the basis of interference light detected by the first detector;
• and
• a light source controller to change the wavelength of the first light source to change the location of the sample surface on which light from the first light source is incident to enable the surface characteristic to be determined for different sample surface locations.

Surface characteristic determining apparatus for determining a characteristic of a sample surface, the apparatus comprising:

• a first light source to provide light of a first wavelength, wherein the first light source comprises a source of coherent light;
• a director to direct light along a reference path towards a reference surface and along a measurement path towards a sample surface such that light reflected by the sample surface and light reflected by the reference surface interfere to provide interference light,
• a first detector to detect interference light of the first wavelength;
• a determiner to determine a characteristic of a sample surface on the basis of interference light detected by the first detector;
• a second light source to provide light of a second wavelength, wherein the second light source comprises a source of coherent light;
• a combiner to combine light from the first and second light sources to produce combined light to cause the director to direct combined light along the reference and sample paths;
• a second detector to detect interference light of the second wavelength;
• and
• a path length controller to control the relative lengths of the reference and measurement paths on the basis of interference light detected by the second detector;
• and
• wherein the measurement path includes an acousto-optical element to control the location of the sample surface on which light from the first light source is incident to enable the surface characteristic to be determined for different sample surface locations.