Nanoparticles as compact laser sources
Ranging from 2 to 10 nm (10–50 atoms) in size, QDs exhibit quantum size effects such as discrete quantised energy levels. Manipulation of those effects has opened the door to applications in quantum computing, medical imaging, photovoltaics and detectors. Nanocrystals can produce different colours depending on the size of the particles. The colours, representing different energies, can be exploited in laser sources as an alternative to expensive, complex and cumbersome solid-state devices. Scientists set out to develop novel materials, devices and design systems relevant to QD-based compact laser devices with EU support of the project QDLASER. The focus was on epitaxial growth of QD-based laser structures and associated testing and measurements of materials and devices. Researchers targeted QD materials working in the spectral range of 1,0–1,6 microns for highly efficient, ultra-short pulse (down to 100 femtoseconds) laser sources. They utilised the indium arsenide/indium phosphide material system that has a wavelength range around 1,5 microns. QDs were synthesised primarily via self-assembly (using the Stranski–Krastanow growth method). Following characterisation, scientists evaluated the properties of the assembled QDs as a gain medium. The QD materials were implemented in laser devices (narrow-ridge single-mode lasers and photonic crystal cavity lasers) in which lasing in the continuous mode was successfully demonstrated. Scientists developed tailored growth regimes for self-assembly of QDs and also conducted a first experiment on a new approach to QD synthesis (selective area growth approach assisted by diblock copolymer lithography). The team is on its way to femtosecond laser operation and an emission wavelength of 1,5 microns, expected to be accomplished in the near future. Technology has the potential to enhance performance of a number of devices in applications including telecommunications, medical imaging and metrology.
Keywords
Quantum dots, laser devices, epitaxial growth, self-assembly, selective area growth