Quantum cascade laser
The quantum cascade laser (QKL) Quantum Cascade Laser (QCL), is a semiconductor laser for wavelengths in the middle and far infrared ( terahertz radiation ). In contrast to normal semiconductor lasers, the laser light is not generated by the radiating recombination of an electron of the conduction band with a hole in the valence band of the semiconductor (interband transition), but rather by intersubband transitions of electrons within the conduction band.
In 2010, devices for exhaust gas analysis were commercially available
history
The theoretical concept for quantum cascade lasers was developed in 1971 by RF Kazarinov and RA Suris . However, the experimental implementation succeeded Jérôme Faist , Federico Capasso , Deborah Sivco, Carlo Sirtori, Albert Hutchinson and Alfred Y. Cho only in 1994 at Bell Laboratories with the help of molecular beam epitaxy .
The wavelengths that can be achieved with this type of laser are currently (i.e. at the beginning of 2004) in the range between 3.5 µm and 141 µm. This wavelength range is as good as not developed by other types of lasers, so QCLs are almost unrivaled here. In addition, like other semiconductor lasers, quantum cascade lasers can be manufactured with very small dimensions.
construction
The structure of the quantum cascade laser is based on a semiconductor laser material consisting of a large number of layers with a thickness in the range of a few nanometers. Here, very thin layers (a few nm) of materials with different band gaps (e.g. GaAs and AlGaAs ) are used alternately . This creates so-called quantum films , and thus an electrical potential that changes spatially depending on the material. The resulting quantum states of the electrons can couple with neighboring states, as a result of which they split and form so-called mini - bands (see band model ). The functioning of the laser depends critically on the correct sequence of different layer thicknesses of the quantum films and the doping .
For this purpose, a number of semiconductor layers are produced as two-dimensional quantum wells , which have several quantized energy levels relative to the material energy level. By applying a voltage, the absolute quantized energy levels of adjacent quantum wells are aligned with one another in such a way that electrons can get through quantum mechanical tunneling from a low energy level of one quantum well to a high energy level of another. Then the energy difference between high and low energy level can be emitted in the form of photons , and the next similar semiconductor layer sequence ( cascade ) can be run through.
A voltage is applied perpendicular to the quantum films. Electrons can now pass through the quantum films, always assuming quantum states. The area relevant for the emission consists of two different zone types which are repeated several times (e.g. 25 times), namely emission zone and injector area . In the injector area there are mini-bands that are used to temporarily store electrons. The emission zone can consist of three different energy levels, for example. Electrons pass from the higher levels to the lower ones with the emission of a photon (see laser under the keyword three-level). In addition to the Fabry-Perot resonator , which is formed by the end faces of the material, the DFB concept (distributed feedback) is used to generate monochromatic radiation .
Areas of application for these types of laser are, for example, trace gas analysis , free beam transmission technology and medical technology .
Individual evidence
- ↑ 1HORIBA presents new emission measurement technology based on a quantum cascade laser. HORIBA Automotive Test Systems, June 22, 2010, accessed on January 28, 2020 .
- ↑ J. Faist, F. Capasso, DL Sivco, C. Sirtori, AL Hutchinson, AY Cho: Quantum Cascade Laser. In: Science. 264, 1994, pp. 553-556, doi : 10.1126 / science.264.5158.553 .
Web links
- J. Faist, F. Capasso, DL Sivco, C. Sirtori, AL Hutchinson, AY Cho: Quantum Cascade Laser. In: Science. 264, 1994, pp. 553-556, doi : 10.1126 / science.264.5158.553 .