Schematic representation of the proposed structure using two materials. n1 and 2 are the refractive indexes. The incident light is transversely magnetic polarized. Credit: Koivurova et al.
In the last few years, engineers and physicists have created a growing array of optical technologies and photonic devices that can emit, detect, and manipulate light. These systems would be able to control the coherence properties of light beams emitted, opening up new opportunities for their use in other applications.
Theoretically, researchers from Tampere University (Finland) have developed a strategy to control the coherence of laser light beams. The strategy was presented in a paper published by Physical Review Letters. It is based upon the use of an enhanced-epsilon–near-zero mirror (ENZ), a metamaterial, which is a synthetic composite with properties not found in natural materials.
Matias Koivurova told Phys.org that the study was a result of a collaboration effort in Finland under the Academy of Finland's flagship project Photonics Research and Innovation. "I did my PhD at the University of Eastern Finland on the coherence of light. After that, I went to Tampere University and started working under the flagship project. The collaboration had one goal: to examine how exotic matter (epsilon-near zero (ENZ), affects the coherence properties light.
After becoming familiar with the basic properties and characteristics of metamaterials Koivurova began to explore the possibility of alternating films of ENZ materials with dielectric materials. This is insulating materials that transmit electricity but not conduct it. His research led to the creation of eENZ, an enhanced ENZ material.
Koivurova, along with his colleagues, builds upon the previous work by theorizing the potential of their eENZ material. It provides an example of how this new material can be used to improve photonic technology.
Schematic representation of the near-plane parallel laser cavity. From front to back, the device consists of an eENZ mirror, a polarization rotator and gain media. Credit: Koivurova et al.
Koivurova stated that the theoretical basis for our study is very simple. We start by making an initial guess about the electric field in a laser cavity. Next, we numerically propagate the field between cavity mirrors taking into account the polarization. We were able construct the correlation functions for our output light by investigating both polarizations.
Koivurova and colleagues demonstrated that the insertion in a cavity of a laser could allow significant control over the coherence. The control over the coherence properties is truly remarkable. This theoretically allows the switching of light between incoherent (e.g. light from an incandescent lamp) and coherent (e.g. laser beam) within one device.
Koivurova stated that these properties were previously considered mutually exclusive, with the exception of a few cases. "Moreover, our study demonstrates how eENZ can also be used to build very high-quality lasers using almost arbitrary cavity parameters.
The team of researchers' recent research could simplify the design and development process of lasers in the future. It also reduces the manufacturing cost. It could also open the door to new imaging and illumination devices that emit light beams of controlled coherence.
The results that Koivurova has gathered so far are only theoretical. They plan to create eENZ mirrors, characterize them and test their hypothesis in real world experiments.
Koivurova said, "After we have found the best recipe for fabrication," and that they will then demonstrate their properties and build a prototype laser around them. We have many samples that are ready for characterisation and we are excited to continue exploring this area."
Further reading: Tiny lasers working together as one: Topological vertical cavities laser arrays
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