Photothermal test process, apparatus for performing the process and heat microscope

Process for testing the properties of materials by the photothermal effect, which comprises:

• a) generating a pure-mode laser beam with a laser light source,
• a1) modulating the laser beam for attaining a desired pulse-width modulation,
• a2) emitting the laser beam toward a region of a surface of a material sample to be tested,
• a3) focussing the laser beam to a desired measurement point diameter at most equal to 10 .mu.m at a target light spot of the material sample with an optical means so that a proportion of the amount of light energy with irradiated volume elements of the material sample is absorbed and infrared light signals in the form of thermal waves are emitted from the surface of the volume elements and volume elements adjacent thereto;
• b) conducting the emitted IR light signals back through the optical means to a decoupling element disposed downstream of the optical means as seen along the course of the emitted IR light signals for decoupling the IR light signals;
• c) further conducting and focusing the decoupled IR light signals onto receiving surfaces of at least one IR light detector for converting received IR light signals into corresponding electrical signals for further signal processing;
• and
• d) conducting the laser beam from the laser light source to the optical means, transmitting and reflecting the laser beam at the respective optical means with a first resulting degree of transmission and reflection of at least 60% and conducting the IR light signals emitted by the material sample to the at least one IR light detector with a second resulting degree of transmission and reflection of at least 60%,
• wherein the first resulting degree of transmission and reflection is defined as the product of the ratios of transmission and reflection of the respective optical elements disposed in a laser light path from the laser light source to the surface of the material sample, and the second resulting degree of transmission and reflection is defined as the product of the ratios of transmission and reflection of the respective optical elements disposed in a light path of the reflected infrared radiation from the surface of the material sample to the IR light detector.