Super-Resolution Thermographic Imaging

The saying A picture says more than a thousand words illustrates the great amount of information contained in pictures. Imaging methods are therefore extremely important for scientific examinations, in medicine, and also in testing the reliability of e.g. aircraft components. In earlier times, pictures showed what the human eye could see. "Looking below the surface", which is also essential in a figurative sense, was only possible for optically transparent samples. This changed suddenly with the discovery of X-rays. Nowadays, not only visible light, but the entire spectrum from microwaves to heat radiation to X-rays, but also e.g. very high frequency sound waves (ultrasound) are used to "look below the surface". The following applies to all of these methods: the deeper we want to look, the more we see smaller objects blurry, i.e. the worse is the resolution. In microscopy, the resolution is limited by the wavelength of the light used or, in the case of ultrasound, by the sound wavelength. This resolution limit, discovered by Ernst Karl Abbe in 1873, was valid for more than 120 years. Then scientists, who were awarded the Nobel Prize for this, discovered that this so-called diffraction limit can be overcome. One possibility for this is structured illumination, in which not the entire object is illuminated uniformly, but individual areas are illuminated differently. This process is repeated several times. This means that all areas of the object are illuminated evenly on average. A super-resolution image with a correspondingly high resolution can be calculated from all these images using a reconstruction algorithm. In this project, the heat is used to look under the surface. A strong light source such as a laser is deflected in various directions e.g. in human tissue, i.e. the light is scattered and therefore you cannot look directly into the body. The scattered light can penetrate several centimeters under the skin and heats light absorbing structures such as blood vessels there. This heat spreads through the body and can be measured on the surface of the skin. By accurately measuring the temperature at many points on the surface as a function of time e.g. with an infrared camera after a short pulse of light, it is possible to image the structures inside. Here again, the deeper these structures are below the surface, the more blurred is their image. Structured illumination inside can be used again to calculate a super-resolution image. This is the goal of the project. The structured illumination inside should be generated automatically by "speckles", which arise when differently scattered light beams from the laser overlap in the tissue.