Russian Physicists Determine Indices Enabling Prediction of Laser Behaviour
Russian scientists, including researchers at HSE University, examined the features of fibre laser generation and identified universal critical indices for calculating their characteristics and operating regimes. The study findings will help predict and optimise laser parameters for high-speed communication systems, spectroscopy, and other areas of optical technology. The paper has been published in Optics & Laser Technology.
Erbium fibre lasers are devices that generate light within a fibre doped with ions of the rare-earth element erbium. These lasers operate at a wavelength of approximately 1.5 micrometres, making them ideal for long-distance data transmission with minimal loss. Radiation at other wavelengths requires amplification every 20-30 kilometres when passing through optical fibre, whereas radiation from erbium lasers needs 2-3 times fewer amplifiers, significantly reducing equipment and operational costs. Moreover, erbium lasers can produce radiation with a narrow spectral linewidth (less than 1 kHz), which is used in high-precision optical sensors and transducers.
As demands for data transmission speed and capacity increase, there is a growing need to miniaturise lasers and shorten cavities without compromising their efficiency. A cavity is a component of a laser that consists of two mirrors and is responsible for amplifying light as it passes repeatedly through an active medium.
Depending on the cavity length and the concentration of erbium ions, the laser can operate in different regimes — either pulsed or continuous-wave (CW). The primary challenge is that reducing the size of the cavity requires an increase in the concentration of erbium ions. This causes the laser to operate in pulsed mode, which can result in data transmission instability, power limitations, and increased noise levels.
A group of Russian scientists, including physicists at HSE University, prepared two types of active fibres for seven lasers and compared the effects of erbium ion concentrations (ranging from 0.03% to 0.3%) on the laser parameters. As a result, they determined the parameters of the active medium and pump power that allow for a short cavity length and CW operation simultaneously, as well as the conditions under which the switching from CW to pulsed mode occurs.
'The transition from continuous-wave to pulsed operation regime is somewhat analogous to a classical phase transition, which follows mathematical laws and characterises processes in other systems, such as liquids and solids. Lasers with a high concentration of erbium ions exhibit two thresholds: the first is associated with the onset of pulsed mode operation, while the second marks the transition to continuous-wave mode. These laws resemble power-law dependencies and describe how the laser parameters change near the generation threshold,' explains Oleg Butov, co-author of the paper, Deputy Director and Head of the Laboratory of Fiber Optic Technologies at Kotelnikov Institute of Radioengineering and Electronics of RAS.
For the first time, researchers experimentally determined the critical indices for erbium lasers—specifically, the slopes of the logarithmic relationships between the frequency, duration, and amplitude of laser pulses and the laser radiation power.
'We have established that the calculated dependencies are universal for erbium lasers, regardless of significant variations in the core composition of the active fibre, cavity length, and Q-factor (a ratio of stored energy to energy consumed in one period). The results will enable predictions of the erbium fibre lasers radiation parameters and facilitate the optimisation of their operation for various applications,' according to Alexander Smirnov, co-author of the paper and Professor at the ‘Nanoelectronics and Photonics’ Joint Department with Kotelnikov Institute of Radioengineering and Electronics (RAS) of the HSE Faculty of Physics.
The study was supported by a grant from the Russian Science Foundation (No. 20-72-10057).
See also:
Esports Players Play Better Online
In competitions, esports players, like other athletes, face stress and show worse results due to pressure. A substantial decrease takes place in the performance of esports players during overtime. This effect, however, is significantly mitigated in online competitions compared to live events—the difference can reach 30%. A study by a team of authors from HSE University’s Moscow and Perm campuses and European University Viadrina (Germany) explores the phenomenon of choking under pressure within the context of esports. The study was published in the Journal of Economic Behavior & Organization.
Analysing Genetic Information Can Help Prevent Complications after Myocardial Infarction
Researchers at HSE University have developed a machine learning (ML) model capable of predicting the risk of complications—major adverse cardiac events—in patients following a myocardial infarction. For the first time, the model incorporates genetic data, enabling a more accurate assessment of the risk of long-term complications. The study has been published in Frontiers in Medicine.
A New Tool Designed to Assess AI Ethics in Medicine Developed at HSE University
A team of researchers at the HSE AI Research Centre has created an index to evaluate the ethical standards of artificial intelligence (AI) systems used in medicine. This tool is designed to minimise potential risks and promote safer development and implementation of AI technologies in medical practice.
Smoking Habit Affects Response to False Feedback
A team of scientists at HSE University, in collaboration with the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences, studied how people respond to deception when under stress and cognitive load. The study revealed that smoking habits interfere with performance on cognitive tasks involving memory and attention and impairs a person’s ability to detect deception. The study findings have been published in Frontiers in Neuroscience.
Children with Autism Process Auditory Information Differently
A team of scientists, including researchers from the HSE Centre for Language and Brain, examined specific aspects of auditory perception in children with autism. The scientists observed atypical alpha rhythm activity both during sound perception and at rest. This suggests that these children experience abnormalities in the early stages of sound processing in the brain's auditory cortex. Over time, these abnormalities can result in language difficulties. The study findings have been published in Brain Structure and Function.
Smartphones Not Used for Digital Learning among Russian School Students
Despite the widespread use of smartphones, teachers have not fully integrated them into the teaching and learning process, including for developing students' digital skills. Irina Dvoretskaya, Research Fellow at the HSE Institute of Education, has examined the patterns of mobile device use for learning among students in grades 9 to 11.
Working while Studying Can Increase Salary and Chances of Success
Research shows that working while studying increases the likelihood of employment after graduation by 19% and boosts salary by 14%. One in two students has worked for at least a month while studying full time. The greatest benefits come from being employed during the final years of study, when students have the opportunity to begin working in their chosen field. These findings come from a team of authors at the HSE Faculty of Economic Sciences.
Beauty in Details: HSE University and AIRI Scientists Develop a Method for High-Quality Image Editing
Researchers from theHSE AI Research Centre, AIRI, and the University of Bremen have developed a new image editing method based on deep learning—StyleFeatureEditor. This tool allows for precise reproduction of even the smallest details in an image while preserving them during the editing process. With its help, users can easily change hair colour or facial expressions without sacrificing image quality. The results of this three-party collaboration were published at the highly-cited computer vision conference CVPR 2024.
HSE Scientists Have Examined Potential Impact of Nuclear Power on Sustainable Development
Researchers at HSE University have developed a set of mathematical models to predict the impact of nuclear power on the Sustainable Development Index. If the share of nuclear power in the global energy mix increases to between 20% and 25%, the global Sustainable Development Index (SDI) is projected to grow by one-third by 2050. In scenarios where the share of nuclear power grows more slowly, the increase in the SDI is found to be lower. The study has been published in Nuclear Energy and Technology.
HSE Scientists Have Developed a New Model of Electric Double Layer
This new model accounts for a wide range of ion-electrode interactions and predicts a device's ability to store electric charge. The model's theoretical predictions align with the experimental results. Data on the behaviour of the electric double layer (EDL) can aid in the development of more efficient supercapacitors for portable electronics and electric vehicles. The study has been published in ChemPhysChem.