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:
Russian Scientists Develop New Compound for Treating Aggressive Tumours
A team of Russian researchers has synthesised a novel compound for boron neutron capture therapy (BNCT), a treatment for advanced cancer that uses the boron-10 isotope. The compound exhibits low toxicity, excellent water solubility, and eliminates the need for administering large volumes. Most importantly, the active substance reaches the tumour with minimal impact on healthy tissues. The study was published in the International Journal of Molecular Sciences shortly before World Cancer Day, observed annually on February 4.
Scientists Discover Link Between Brain's Structural Features and Autistic Traits in Children
Scientists have discovered significant structural differences in the brain's pathways, tracts, and thalamus between children with autism and their neurotypical peers, despite finding no functional differences. The most significant alterations were found in the pathways connecting the thalamus—the brain's sensory information processing centre—to the temporal lobe. Moreover, the severity of these alterations positively correlated with the intensity of the child's autistic traits. The study findings have been published in Behavioural Brain Research.
Earnings Inequality Declining in Russia
Earnings inequality in Russia has nearly halved over the past 25 years. The primary factors driving this trend are rising minimum wages, regional economic convergence, and shifts in the returns on education. Since 2019, a new phase of this process has been observed, with inequality continuing to decline but driven by entirely different mechanisms. These are the findings made by Anna Lukyanova, Assistant Professor at the HSE Faculty of Economic Sciences, in her new study. The results have been published in the Journal of the New Economic Association.
Russian Physicists Discover Method to Increase Number of Atoms in Quantum Sensors
Physicists from the Institute of Spectroscopy of the Russian Academy of Sciences and HSE University have successfully trapped rubidium-87 atoms for over four seconds. Their method can help improve the accuracy of quantum sensors, where both the number of trapped atoms and the trapping time are crucial. Such quantum systems are used to study dark matter, refine navigation systems, and aid in mineral exploration. The study findings have been published in the Journal of Experimental and Theoretical Physics Letters.
HSE Scientists Develop Application for Diagnosing Aphasia
Specialists at the HSE Centre for Language and Brain have developed an application for diagnosing language disorders (aphasia), which can result from head injuries, strokes, or other neurological conditions. AutoRAT is the first standardised digital tool in Russia for assessing the presence and severity of language disorders. The application is available on RuStore and can be used on mobile and tablet devices running the Android operating system.
HSE Researchers Discover Simple and Reliable Way to Understand How People Perceive Taste
A team of scientists from the HSE Centre for Cognition & Decision Making has studied how food flavours affect brain activity, facial muscles, and emotions. Using near-infrared spectroscopy (fNIRS), they demonstrated that pleasant food activates brain areas associated with positive emotions, while neutral food stimulates regions linked to negative emotions and avoidance. This approach offers a simpler way to predict the market success of products and study eating disorders. The study was published in the journal Food Quality and Preference.
Russian Scientists Demonstrate How Disorder Contributes to Emergence of Unusual Superconductivity
Researchers at HSE University and MIPT have investigated how the composition of electrons in a superconductor influences the emergence of intertype superconductivity—a unique state in which superconductors display unusual properties. It was previously believed that intertype superconductivity occurs only in materials with minimal impurities. However, the scientists discovered that the region of intertype superconductivity not only persists but can also expand in materials with a high concentration of impurities and defects. In the future, these superconductors could contribute to the development of highly sensitive sensors and detectors. The study has been published in Frontiers of Physics.
HSE Scientists Take Important Step Forward in Development of 6G Communication Technologies
Researchers at HSE MIEM have successfully demonstrated the effective operation of a 6G wireless communication channel at sub-THz frequencies. The device transmits data at 12 Gbps and maintains signal stability by automatically switching when blocked. These metrics comply with international 6G standards. An article published on arXiv, an open-access electronic repository, provides a description of certain elements of the system.
AI vs AI: Scientists Develop Neural Networks to Detect Generated Text Insertions
A research team, including Alexander Shirnin from HSE University, has developed two models designed to detect AI-generated insertions in scientific texts. The AIpom system integrates two types of models: a decoder and an encoder. The Papilusion system is designed to detect modifications through synonyms and summarisation by neural networks, using one type of models: encoders. In the future, these models will assist in verifying the originality and credibility of scientific publications. Articles describing the Papilusion and AIpom systems have been published in the ACL Anthology Digital Archive.
Acoustic Battles for the Harem: How the Calls of Siberian Wapiti Reveal Their Status and Individuality
Researchers at HSE University, Lomonosov Moscow State University, and the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences have studied the distinctive vocalisations of Siberian wapiti (Cervus canadensis sibiricus) stags during the peak of the mating season, when males produce rutting calls (bugles) to attract females (hinds) and deter rivals. The scientists have discovered how the acoustic parameters of these rutting calls reflect the stag's status—whether he currently holds a harem or is still attempting to acquire one—as well as his individual characteristics. The study has been published in Journal of Zoology.