New record operation temperature for quantum-cascade lasers

For astronomers, terahertz radiation provides new insights in the investigation of so-called cold matter. This kind of matter does not emit visible light such as the stars, but electromagnetic radiation in the infrared to microwave range. The German Aerospace Center (DLR) measures such emission lines with high precision within the US-German Stratospheric Observatory for Infrared Astronomy (SOFIA) project. One key element of the detector system is a quantum-cascade laser developed at the PDI.

Fig1. Chip with nine terahertz quantum-cascade lasers with different grating periods. The lasers are contacted by gold wires, which are visible on the top and right side of the image.

Fig2. (a) Laser output power vs. current for the device operating up to 129 K. The inset depicts the emission spectrum at 129 K. (b) Far-Field of a laser with a third-order grating.

One problem of these lasers are the rather low operating temperatures, which are typically even below the temperature of liquid nitrogen of 77 Kelvin or -196 °C for continuous-wave operation. We have now developed a terahertz quantum-cascade laser, which operates at significantly higher temperatures than previously achieved: the new lasers operate up to 129 Kelvin (-144 °C) improving the previous record by more than 10 degrees. In combination with a significantly reduced power dissipation of the new lasers, it allows for the use of much smaller mechanical coolers. Thereby, it will be possible to reduce the size of systems based on terahertz quantum-cascade lasers in the future — an important point for flight missions such as SOFIA.

 

The high operating temperatures have been achieved by developing a semiconductor heterostructure, which requires only a very low driving power. The laser ridge is only about 10-15 microns high and 15 microns wide, while the emission wavelength is about 100 microns. The active region is confined by two metal layers, which are almost perfect mirrors in the terahertz range. This combination results in very low power dissipation and operation at low current densities and voltages.

 

The strong spatial confinement of the light in the laser cavity due to the two metal layers results in an extremely divergent beam profile for common Fabry-Pérot devices. By applying a grating on top of the laser ridge, a so-called third-order grating, the laser emission is collimated, since the grating acts as a directive antenna.

Publication

1 Autor M. Wienold , B. Röben , L. Schrottke , R. Sharma , A. Tahraoui , K. Biermann , H. T. Grahn
Titel

High-temperature, continuous-wave operation of terahertz quantum-cascade lasers with metal-metal waveguides and third-order distributed feedback

Source Opt. Express , 22 , 3334 ( 2014 )
DOI : 10.1364/OE.22.003334 | Download: PDF | 2503 Cite : Bibtex RIS
M. Wienold, B. Röben, L. Schrottke, R. Sharma, A. Tahraoui, K. Biermann, and H. T. Grahn