Surface shape measurement device and surface shape measurement method

A surface shape measuring device using holography, comprising:

• a data acquisition unit for acquiring data of an object light (O) that is a reflected light of a spherical wave illumination light (Q) illuminating a surface to be measured and data of an inline spherical wave reference light (L) that is inline with respect to the object light (O), respectively, as an object light off-axis hologram (IOR) and an reference light off-axis hologram (ILR), using an image sensor;
• and
• an image reconstruction unit for deriving data of surface shape by reconstructing an image of the surface to be measured from the data acquired by the data acquisition unit, wherein
• the data acquisition unit comprises:
• an optical system which is configured to make both an illumination light condensing point (PQ) being a condensing point of the spherical wave illumination light (Q) and a reference light condensing point (PL) being a condensing point of the inline spherical wave reference light (L) be arranged in a mirror image of each other with respect to a virtual plane (VP) being virtually set so as to contact the surface to be measured, and configured to make the inline spherical wave reference light (L) obliquely pass through the virtual plane (VP) and enter the image sensor, and
• the image reconstruction unit comprises:
• an object light hologram generation unit for generating an object light hologram (g) representing the light wave of the object light (O) by a calculation process using the data of the two kinds of off-axis holograms (IOR, ILR), position information of the reference light condensing point (PL), and the fact that the light emitted from the reference light condensing point (PL) is a spherical wave;
• a reconstructed object light hologram generation unit for generating a reconstructed object light hologram (hV) on the virtual plane (VP) by performing a light wave propagation calculation and a rotational transformation on the object light hologram (g);
• a reference point detection unit for detecting, by performing a light wave propagation calculation on the object light hologram (g), a position at which the object light (O) is condensing, and for setting the position as a reference point (S1), to be used for shape measurement, having more precise information than the position information of the reference light condensing point (PL);
• an analytical light hologram generation unit for analytically generating a spherical wave light hologram (sV) that is a hologram, on the virtual plane (VP), of a spherical wave light emitted from the reference point (S1);
• and
• a shape measuring unit for generating a measurement hologram (JVos=hV/sV) by dividing the reconstructed object light hologram (hV) by the spherical wave light hologram (sV), and for obtaining a height distribution of the surface to be measured of the object using a phase distribution of the measurement hologram (JVos).