Quantum Dot-Based Lasers Emitting Colors Throughout the Visible Spectrum


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Laser light can have different colors. Photo by Photopedia

A new quantum dot-based laser device that can shoot multicolored laser beams throughout the visible spectrum (red, blue or green colors) with a lower energy requirement – new technology from Brown University’s School of Engineering, published recently in Nature Nanotechnology.

What are Lasers?

Lasers (Light Amplification by Stimulated Emission of Radiation) are devices which, after an appropriate stimulation (pumping), can emit light in the form of an electromagnetic radiation. The emitted radiation has particular properties – it has, for instance, a high level of coherence; this means that all the photons emitted will have the same wavelength λ. Furthermore, the light is also polarized; this means that all the radiation propagates only along one plane.

Due to these characteristics, the light emitted by the lasers usually has very high power.

Different Laser Devices

The different laser devices commercially available today are based on different kinds of materials; gas lasers and solid-state lasers are, for instance, two very common types of lasers. In the first case, an appropriate gaseous substance is employed; helium-silver vapor laser is an example. In the second case, a solid material is used, for instance, glass modified with neodymium (Nd).

Depending on its characteristics, each device will emit light with just one specific wavelength; we can have, for instance, red or green lasers.

In some particular cases, lasers can emit several different wavelengths, but they will all be relatively close in the electromagnetic spectrum, generally belonging to the same color group (i.e. a laser emitting at two wavelengths, but they are both red).

Red, Green and Blue Lasers

In recent years, many attempts have been made to develop a laser which could cover the full visible spectrum, that is the three colors red, green and blue.

Important results in this field were achieved at the School of Engineering of Brown University (Rhode island, US). The work was performed by Dr. Cuong Dang and his coworkers; their results were published in April 2012 in Nature Nanotechnology.

Quantum dots can emit different colors, depending on their size. Photo by Argonne National Laboratory

Use of Quantum Dots

Dr. Dang and his coworkers used Quantum Dots (QDs) for the fabrication of their laser devices; more specifically, they considered the particular properties that some QDs have regarding the emission of light.

QDs are nanorods or nanoparticles made of a semiconductor material. Semiconductors have a band gap, which may fall in the visible spectrum; in this case, semiconductor materials will emit visible (colored) light.

In the case of QDs, however, the value of the bandgap does not depend only on the nature of the material, but also on the dimensions of the nanoparticles. It is possible, therefore, to have QDs of the same material that emit light of different colors.

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