Source: Laser Focus World.

A 3.4-THz-emitting quantum-cascade laser (QCL) created by a group at the School of Electronic and Electrical Engineering, University of Leeds, reaches a pulsed peak power of up to 1.01 W from a single facet when cooled to 10 K.1 The laser output is achieved using a broad-area configuration.

An aluminum gallium arsenide- based (Al0.16Ga0.84As/GaAs) heterostructure was grown on a semi-insulating GaAs substrate; ridges of widths from 145 to 425 ?m were pholithographically created. In the experiment, the lasers were pulsed at 10 kHz and a 2% duty cycle and cooled by liquid helium.

A version with a 3-mm-long cavity and a 425-?m-wide ridge emitted a peak power of 780 mW; when one facet was coated with a high-reflectivity coating, the peak power was boosted to 1.01 W.

This output more than doubles the output levels in terahertz QCLs developed ar the Massachusetts Institute of Technology (MIT; Cambridge, MA) and subsequently by a team from the Vienna University of Technology (Vienna, Austria) last year.

Widely publicized potential applications of terahertz radiation include monitoring pharmaceutical products, remote sensing of chemical signatures of explosives in unopened envelopes, and noninvasive detection of cancers in the human body. ¡°Although it is possible to build large instruments that generate powerful beams of terahertz radiation, these instruments are only useful for a limited set of applications,¡± says Edmund Linfield, one of the University of Leeds researchers. ¡°We need terahertz lasers that not only offer high power but are also portable and low cost.¡±

The quantum cascade terahertz lasers being developed by Leeds are only a few square millimeters in size.

Professor Edmund Linfield said: ¡°The process of making these lasers is extraordinarily delicate. Layers of different semiconductors such as gallium arsenide are built up one atomic monolayer at a time. We control the thickness and composition of each individual layer very accurately and build up a semiconductor material of between typically 1,000 and 2,000 layers. The record power of our new laser is due to the expertise that we have developed at Leeds in fabricating these layered semiconductors, together with our ability to engineer these materials subsequently into suitable and powerful laser devices.¡±

The work was mainly funded by the Engineering and Physical Sciences Research Council (EPSRC; Swindon, England).

REFERENCE:
1. Lianhe Li et al., Electronics Letters (2014); doi: 10.1049/el.2013.4035