Apparatus and method for determining a material property of a test specimen in a test specimen region near the surface

A method for photothermal determination of a material property of a test specimen in a test specimen region near a surface of the test specimen, the method comprising:

• providing an apparatus that comprises:
• at least one electromagnetic radiation source for heating at least one surface region of the test specimen;
• an AC voltage source providing intensity-modulated and frequency-modulated control of the at least one electromagnetic radiation source, wherein the at least one electromagnetic radiation source can be controlled so as to provide a frequency change that occurs in discrete steps;
• a detection device for detecting thermal radiation emitted by the at least one surface region and/or for detecting radiation reflected from the at least one surface region of the test specimen;
• and
• an evaluation device for ascertaining the material property to be determined on the basis of the emitted thermal radiation and/or the reflected radiation
• positioning the test specimen such that the at least one surface region of the test specimen is operably coupled to the electromagnetic radiation source and the detection device;
• heating the at least one surface region of the test specimen with the electromagnetic radiation source;
• detecting the thermal radiation emitted by the at least one surface region and/or the radiation reflected from the at least one surface region of the test specimen with the detection device;
• and
• ascertaining the material property of the test specimen on the basis of the emitted thermal radiation and/or the reflected radiation with the evaluation device.