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Graphic element Research > Growth > Research projects > Measurements & testing projects > UNISEL: Europe takes the lead in laser sensing devices
Graphic element UNISEL: Europe takes the lead in laser sensing devices

Unipolar semiconductor lasers or quantum cascade (QC) lasers were developed at Bell Laboratories in the USA in the eighties, with the help of some key European researchers. The Europeans eventually opted to come back across the Atlantic and continue their work on home ground. Under Brite/Euram project UNISEL, they have demonstrated successful use of a new class of devices for gas sensing applications in the areas of environmental monitoring and process control.

QC lasers exploit the quantum behaviour whereby electrons assume a series of discrete energy levels. When electrical or light energy is applied to these minuscule devices, they produce powerful emissions at certain specific wavelengths. By adjusting the thickness and composition of the semiconductor layers in a microchip it is possible to tune the emission wavelength to a desired value.

Promising field

Of particular interest for industrial purposes are wavelengths in the mid-infrared range (3-15 µm). Using light sources in this spectral range, molecular spectroscopy techniques enable various gases to be detected and identified at concentrations as low as a few parts per billion. These methods have great potential for monitoring trace discharges of waste gases, as well as for checking combustion efficiency and controlling processes in industries such as foods, beverages and pharmaceuticals.

To date, however, the only commercially available sources for such applications have been semiconductor lead salt lasers, which function only at cryogenic temperatures. The original unipolar semiconductor lasers, manufactured from indium phosphide, suffered from similar temperature limitations.

The aim of UNISEL was therefore to support the first European research in this area, demonstrating that other semiconductor materials could be employed for laser production and seeking to achieve operation at ambient temperatures. The consortium, led by the Thompson CSF Central Research Laboratory (now Thales), brought together a number of the former Bell workers and other researchers. It included academic participants from the Universities of Paris, Neuchâtel, and Vienna, and Italy's INFM (Institute of Material Physics), together with industrial partners Mütek and Orbisphere Laboratoires.

Success on several fronts

During the initial year of the 36-month project, the group was able to reproduce the QC effect using various materials. In particular, they focused on gallium arsenide (GaAs), which is a readily available compound semiconductor already widely used in the electronics industry. While the optical and electrical characterisation of materials and devices continued in the second year, the effort shifted progressively towards the development of unipolar lasers into devices for spectroscopic applications.

Two major requirements for an infrared technology suitable for gas detection and trace gas analysis were wavelength stabilisation control and the elimination of cryogenic cooling. By creating novel designs and processing architectures, the group succeeded in both respects. It has produced devices that emit at well-defined wavelengths, and demonstrated unsurpassed electrical tunability at a fixed temperature of -10 Cº. Cooling to temperatures in this range can easily be achieved with thermo-electric (Peltier) coolers. Improvements in the performance of optically pumped lasers have also led to devices with a record peak power of more than 15W.

A further practical achievement of UNISEL was the establishment of design rules for device packaging and power supplies, facilitating exchanges among the partners and producing standard components for supply to end users.

During the second year, industrial partners worked actively, studying and preparing detection systems that incorporate the unipolar semiconductor lasers. Two different approaches have been tried: the first of these is based on conventional absorption spectroscopy, while the second, more suitable for implementation in low cost systems, uses photoacoustic techniques. Both are now at the prototype stage, and could reach commercialisation within one or two years.

  Multiple benefits

As well as giving Europe a clear global lead in QC laser, and especially the GaAs-based QC laser market, UNISEL has produced a number of other spin-off benefits. Following involvement in the project, EC scholarship student Hideaki Page has found permanent employment as an engineer with Thales, while an earlier PhD student has joined Orbisphere. A new start-up company, Alpes Laser, formed as an offshoot of the University of Neuchâtel will become the first volume producer of such devices. Moreover, their application in environmental monitoring and process quality improvement will have positive implications for businesses and citizens throughout the EU.

UNISEL is a good example of how the 'vertical integration' of basic research on the materials system, devices and components, and end-user applications can lead to novel product prototypes.

Promising field
Success on several fronts
Multiple benefits

Key data

Research and development in the area of gas sensing devices is covered within the Measurements and testing generic activity. Under the Fourth Framework Programme, similar work included:

Mid infrared laser diodes from iii-v semiconductors for pollution monitoring - this project developed lasers for a large variety of gas sensing applications (FMBI971960).

BRPR-CT97-0557, UNISEL Unipolar Semiconductor Lasers Start 1/12/97, duration 36 months Fourth Framework Programme, Brite-Euram, Materials

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