Aug 16 2018
Leading engineers handling terahertz frequency technology have been investigating the way individual frequencies are selected upon turning on a laser, and speed at which the selection is done.
The creation of particular terahertz equipment has enabled them to analyze this process for the first time. The outcomes of the study have been reported in Nature Communications and will be the basis for the development of semiconductor lasers in future, including those employed in public and private sector-owned telecommunications systems.
For several years, researchers have predicted that operating frequencies of semiconductor lasers stabilize on a timeframe of a few nanoseconds, or few billionths of a second, and can be modified within a few hundreds of picoseconds, or one-thousandth of a nanosecond.
However, to date, there has been no detector with the ability to measure and prove this in a precise manner, and the optimal results have been realized only on nanosecond timescales, which are very slow to enable ideally efficient analysis or to be used to create the most effective new systems.
At present, scientists from the University of Leeds have collaborated with international colleagues from École Normale Supérieure in Paris, France and the University of Queensland in Brisbane, Australia to use terahertz frequency quantum cascade lasers and a method known as terahertz time-domain spectroscopy to gain insights into this laser stabilization process.
The terahertz-powered technology has the ability to measure the wavelength of light in femtosecond timescales, one-millionth of a nanosecond, offering unmatched levels of detail. Highly efficient systems and devices can be developed by having knowledge of the speed at which wavelengths vary within lasers, and the events occurring at the time of that process within minuscule time frames.
The Leeds elements of the research were performed in the University’s Terahertz Photonics Laboratory, part of the University’s Bragg Centre for Materials Research.
According to Dr Iman Kundu, principal author of the research paper reporting the findings of the team, “We’ve exploited the ultrafast detection capabilities of terahertz technology to watch laser emissions evolve from multiple colours to a single wavelength over less than a billionth of a second.”
“Now that we can see the detailed emission of the lasers over such incredibly small time frames, we can see how the wavelength of light changes as one moves from one steady state to a new steady state.”
“The benefits for commercial systems designers are potentially significant. Terahertz technology isn’t available to many sectors, but we believe its value lies in being able to highlight trends and explain the detailed operation of integrated photonic devices, which are used in complex imaging systems which might be found in the pharmaceutical or electronics sectors.”
“Designers can then apply these findings to lasers operating at different parts of the electromagnetic spectrum, as the underlying physics will be very similar.”
In the words of Professor Edmund Linfield, Chair of Terahertz Electronics at the University of Leeds, who was also involved in the study, “We’re using the highly advanced capabilities of terahertz technology to shine a light on the operation of lasers.”
“Our research is aimed at showing engineers and developers where to look to drive increased performance in their own systems. By doing this, we will increase the global competitiveness of the UK’s science and engineering base.”
The study was supported by the Engineering and Physical Sciences Research Council (HyperTerahertz programme grant), which is part of UKRI; the Royal Society, the Wolfson Foundation; the European Union’s ULTRAQCL grant and the Centre National de la Recherche Scientifique, France.