Confocal THz Laser Microscope

Metrological Instrumentation

The terahertz (THz) range refers to frequencies between 0.1 and 10 THz and represents the spectral gap between the microwave and infrared region. Over the past few years, there has been a significant interest in employing THz technology in spectroscopy, imaging, and recently in short-range communication systems.

THz radiation can be generated by different schemes. Among them are the FIR lasers which are preferred for their high continuous-wave output power. Their generation process relies on transitions between different rotational and vibrational levels of a molecular species and can emit several mW of power at discrete THz frequencies ranging from less than 300 GHz to more than 10 THz. In this thesis we present a FIR laser and describe its working mechanism in detail.

Since THz waves are able to penetrate most non-metallic objects, early detection of possible terrorist attacks, mail inspection, quality control and molecular spectroscopy are among the foreseen potential applications for terahertz technology. THz radiation poses no health risk for human beings as they do not have any ionizing properties unlike for example X-rays.

An effective technique for imaging of infinitesimal thin planes in thick samples is the so-called confocal microscopy. This technique which was invented in 1957 is widely used in biology for imaging of in-vivo and in-vitro specimen. In this work we transfer the principle of optical confocal microscopy to the THz range using a FIR laser source.

For a reliable THz system, not only a robust setup is required but also an efficient detector. Detection of THz radiation represents one of the major hurdles which impede the existence of a practical and cost-effective THz system. Recent theoretical research has shown that the strong many-body interactions in the electron-hole plasma in semiconductor lasers efficiently interact with THz radiation. This means that room temperature THz detection with a simple diode laser might be possible. Here we show practical measurements that were obtained in cooperation with different research institutes supporting these studies.

TU Braunschweig
Ph.D. student: