So-called 'terahertz' waves, which lie in the far infrared red range between mid-infrared and microwaves, have the property of penetrating skin, clothing, paper, wood, cardboard or even plastic. These advantages offer numerous applications in medical imaging, spectroscopy, security, and the environment. This is why terahertz cascade laser - a new family of semiconductor lasers that emit in the frequency range of the terahertz - rates such interest. However, although they are now the only compact sources smaller than the millimeter operating within this frequency range, they have a major drawback: the strong divergence of their output beam which prevents their widespread use.
To solve the problem, French researchers at the Institut d'Electronique Fondamentale (CNRS-Paris-Sud 11 University) and at the Laboratory for Materials and Quantum Phenomena (CNRS-Paris Diderot-Paris 7 University), headed by Raffaele Colombelli, working with teams from the Cambridge and Leeds Universities, used very small structures called photonic crystals, to influence the optical properties of the material and thus control the light trajectory. By combining these components with the terahertz laser, the researchers managed to design an ingenious system emitting terahertz waves but also, and above all, that enables precise control of the laser beam, which now diverges very little.
The researchers now have to maximize the output power of the lasers. Also, better control of photonic crystal technology may enable the design of new terahertz lasers of an even smaller size. The technique they have developed is advantageous because it could be applied to other lasers operating in different wavelength ranges. The research was made possible by the EURYI award given to Raffaele Colombelli in 2004. Launched in 2002 in Athens, the EURYI awards scheme is coordinated by the European Science Foundation. It purpose is to promote the excellence of European research in every field. Thanks to the award, Raffaele Colombelli was able to create her own team at IEF where he supervises the doctoral thesis of Yannick Chassagneux, the lead author of the research paper published in the January 8, 2009 issue of Nature.
