Chalmers’ blue laser project, led by Åsa Haglund – Assistant Professor in the Optoelectronics Group – is currently in a collaborative project with EPFL (École Polytechnique Féderale de Lausanne) to create a new semiconductor-based laser structure for blue emission. This laser will have a vertical cavity instead of a horizontal one that is used in today’s blu-ray DVD players. It enables very low power consumption due to its very small size (≈10x10x10 µm3). The vertical-cavity also provides emission from the semiconductor wafer surface instead of emission from the edges. This allows for early screening of non-functioning devices in the production, which dramatically reduces cost. The surface emission makes it also simple to create two dimensional arrays of these lasers, of high interest in high-resolution laser printers and lab-on-a-chip applications.
 

In the vertical-cavity laser configuration, see Figure, light bounces back and forth between an upper and a lower mirror and is amplified in the very thin (~10 nm thick) amplification region. The amplification is achieved by pumping this region with an electrical current. Since the amplification region is very thin, high reflectivity mirrors (>99%) are necessary to achieve lasing. These mirrors consist of alternating quarter-wavelength-thick layers with high and low refractive index material. These two materials must have a large refractive index difference, and at the same time be lattice matched to the materials used in the light amplification region. This is one of the two main challenges in realizing blue vertical-cavity lasers. The second main challenge is to achieve an efficient current pumping since the materials (III-nitrides) have poor electrical conductivity.
 

Illustration: schematic view of an electrically pumped blue vertical-cavity laser (not to scale).

This novel blue laser could provide enormous benefits to several industries due to its low power consumption and low cost. For example, the biomedicine industry can use blue laser light to distinguish between normal and cancer cells through fluorescence studies, without sampling human body tissue. This would drastically lower costs and rationalize the cancer diagnostics process. Another example is the oral health care industry where blue laser has been demonstrated to be able to spot tooth decay. New applications are continuously arising. Besides improved health care and higher resolution laser printers, these blue lasers will have ultra-low power consumption and thereby play an important role in today’s battle for a sustainable future.