THz and mir source at room temperature in dfg-qcls

The THz frequency spectrum offers a wide range of applications, including medical, electronics, metrology, material testing and process monitoring. Yet, the supply of commercial THz sources is very limited and the few available options are not very convenient. An ideal source for THz applications is considered to be cheap, compact, robust and easy to operate, i.e. moderate input powers and room temperature operation.

The recently emerged THz DFG QCL is the only semiconductor laser providing these advantages, combining the advantage of a semiconductor laser while operating at room temperature. However, the performance of the state of the art configuration of this device type suffers from a large and unsymmetrical far field, complex processing technology and limited design choices. These disadvantages disqualify the device type for many potential applications.

The subject of this invention is an efficient method to extract THz radiation from a THz DFG-QCL and offers a new configuration to this particular device type. Contrary to the state of the art, this invention allows for a narrow far field, room temperature THz source in the form of a simple semiconductor laser. It further simplifies the process technology and potentially increases its efficiency and THz output power enabling production on an industrial scale.

The invention is based on two transversally superimposed gratings. The first grating selects two mid-infrared wavelengths and defines their respective spatial phase relation of the standing wave pattern. This allows for a precise placement of the second grating, which is realized as a second order metal top grating. This second grating enables THz emission normal to the device surface. Through this configuration, THz radiation is efficiently extracted from the device and emitted in a narrow far field.

Prototypes of this technology are realized as a conventional edge emitter with doped substrates. Further possibilities of this invention include different waveguide configurations, as the invention lifts design restrictions regarding choice of substrate and wave-guide form.

• THz sources at room temperature operation
• Wide choice of substrate and wave-guide form
• Compact, robust and easy to operate

The technology has already been prototyped as a ridge waveguide laser with THz surface emission