Dissipative phase transition in systems with two-photon drive and nonlinear dissipation near the critical point

We study dissipative phase transition near the critical point for a system with two-photon driving and nonlinear dissipation. The proposed mean-field theory, which explicitly takes into account quantum fluctuations, allowed us to describe properly the evolution dynamics of the system and to demonstrate the new effects in the steady-state. We show that the presence of quantum fluctuations leads to a power-law dependence of the anomalous average at the phase transition point, with which the critical exponent is associated. Also, we investigate the effect of the quantum fluctuations on the critical point renormalization and demonstrate the existence of a two-photon pump threshold. It is noteworthy that the obtained results are in a good agreement with the numerical simulations.Comment: 7 pages, 4 figure

Partially coherent conical refraction promises new counter-intuitive phenomena

In this paper, we extend the paraxial conical refraction model to the case of the partially coherent light using the unified optical coherence theory. We demonstrate the decomposition of conical refraction correlation functions into well-known conical refraction coherent modes for a Gaussian Schell-model source. Assuming randomness of the electrical field phase of the input beam, we reformulated and significantly simplified the rigorous conical refraction theory. This approach allows us to consider the propagation of light through a conical refraction crystal in exactly the same way as in the classical case of coherent radiation. Having this in hand, we derive analytically the conical refraction intensity both in the focal plane and in the far field, which allows us to explain and rigorously justify earlier experimental findings and predict new phenomena. The last include the counterintuitive effect of narrowing of the conical refraction ring width, disappearance of the dark Poggendorff’s ring in the Lloyd’s plane, and shift of Raman spots for the low-coherent conical refraction light. We also demonstrate a universal power-law dependence of conical refraction cones coherence degree on the input correlation length and diffraction-free propagation of the low-coherent conical refraction light in the far field

Modelling rotational failure in confined geometries using DLO

Discontinuity layout optimisation (DLO) is a generally applicable numerical limit analysis procedure that can be used to identify critical plastic collapse mechanisms in engineering problems. Considering the modelling of in-plane failure, the authors have previously presented a formulation capable of identifying rotational failure mechanisms in non-dilating media. However, the formulation presented did not explicitly address cases involving confined geometries, where curved slip lines could potentially intersect boundaries. In this paper, methods are outlined which permit efficient modelling of such cases. Details of the kinematic and equilibrium formulations are provided, which are then verified through application to various geotechnical and structural mechanics problems. It is shown that results of high accuracy can be obtained, both in terms of the predicted collapse load and the corresponding failure mechanism

QCL active region overheat in pulsed mode: effects of non-equilibrium heat dissipation on laser performance

Quantum cascade lasers are of high interest in the scientific community due to unique applications utilizing the emission in mid-IR range. The possible designs of QCL are quite limited and require careful engineering to overcome some crucial disadvantages. One of them is an active region (ARn) overheat, that significantly affects the laser characteristics in the pulsed operation mode. In this work we consider the effects related to the non-equilibrium temperature distribution, when thermal resistance formalism is irrelevant. We employ the heat equation and discuss the possible limitations and structural features stemming from the chemical composition of the AR. We show that the presence of alloys in the ARn structure fundamentally limits the heat dissipation in pulsed and CW regimes due to their low thermal conductivity. Also the QCL post-growths affects the thermal properties of a device only in (near)CW mode while it is absolutely invaluable in the pulsed mod

Laser beams with conical refraction patterns

Laser beams with cone-refracted output from the plane mirror is demonstrated for the first time in lasers based on intracavity conical refraction (CR) phenomenon. Transverse profile of such lasers comprises a crescent ring of CR-like distribution, where any opposite points are of orthogonal linear polarizations. We confirm the existence of such mode of CR lasers by two observations. First, cascaded CR in reflection geometry has been demonstrated for first time and it provides experimental prove that a light beam passed along optic axis of a biaxial crystal, reflected back from a plane mirror and passed again through the crystal is restored. Second, CR cavity mode with CR-like pattern through the plane mirror is experimentally and theoretically demonstrated for the first time

К 160-ЛЕТИЮ СО ДНЯ РОЖДЕНИЯ ПРОФЕССОРА СЕРГЕЯ ЯКОВЛЕВИЧА КУЛЬНЕВА

Professor Sergei Iakovlevich Kulnev, student and follower of the founder of the Russian syphilidology Veniamin Mikhailovich Tarnovsky, was the head of the Department of Skin and Venereal Diseases at St. Petersburg Medical Institute for Women in the difficult years of its formation – from 1903 to 1924. In fact, the merit of establishing the Department with clinic in the newly formed educational institution for women belongs to him. In 1913, with the active participation of S.Ia. Kulnev, the separate building for the Department of Skin and Venereal Diseases was built, and to this day, it is still located at this premise. Also, for almost a quarter of a century (from 1901 to 1924) S.Ia. Kulnev was the chief physician of the Kalinkinsky Hospital, the oldest specialized dermatological and venereal hospital in Russia and in Europe, where, in fact, Russian syphilidology was born.In Soviet times, the merits of S.Ia. Kulnev who was an actual state councillor and representative of the famous noble Russian family, as an organizer of the Department with Clinic of Skin and Venereal Diseases, was undeservedly ignored.His activity appeared to be in the shadow of achievements of his brightest students, graduates of Medical Institute for Women A. A. Sakhnovskaia and O.N. Podvysotskaia, who alternately headed the Department after the death of Sergei Iakovlevich.The objective of the article, dedicated to the 160th anniversary of the birth of Professor Kulnev, was the desire to pay tribute to the memory of a remarkable physician, teacher and man, whose whole life was devoted to the development of Dermatovenereology and the organization of women’s medical education in Russia. The property of S. Ia. Kulnev is not only a thing of the past. His works laid the foundation of today’s educational, scientific and medical activities of the Dermatovenereology Department of Pavlov First St. Petersburg State Medical University. Профессор Сергей Яковлевич Кульнев – ученик и последователь основоположника отечественной сифилидологии Вениамина Михайловича Тарновского – заведовал кафедрой кожных и венерических болезней Санкт-Петербургского Женского медицинского института в трудные годы ее становления – с 1903 по 1924. Фактически заслуга создания кафедры и клиники во вновь образованном учебном заведении для женщин принадлежит именно ему. При деятельном участии С.Я. Кульнева в 1913 г. было построено отдельное здание кафедры и клиники, в котором они размещаются по сей день. На протяжении почти четверти века (с 1901 по 1924 год) С.Я. Кульнев являлся также главным врачом Калинкинской больницы – старейшего специализированного кожно-венерологического учреждения в России и в Европе, где, по сути, зародилась отечественная сифилидология.В советское время заслуги С.Я. Кульнева – действительного статского советника, представителя прославленного в России дворянского рода – как организатора кафедры и клиники кожных и венерических болезней незаслуженно замалчивались. Его деятельность оказалась в тени достижений его ярких учениц, выпускниц Женского медицинского института А.А. Сахновской и О.Н. Подвысоцкой, поочередно возглавлявших кафедру после смерти Сергея Яковлевича.Целью статьи, приуроченной к 160-летию со дня рождения профессора Кульнева, явилось желание отдать дань памяти замечательному врачу, преподавателю и человеку, жизнь которого была целиком посвящена развитию российской дерматовенерологии и организации женского медицинского образования в России. Наследие С.Я. Кульнева – это не только достояние истории, его трудами была заложена основа сегодняшней учебной, научной и лечебной деятельности кафедры дерматовенерологии с клиникой Первого Санкт-Петербургского Государственного медицинского университета

Conical refraction with low-coherence light sources

We report on conical refraction (CR) with low-coherence light sources, such as light-emitting diodes and decoherentized HeNe laser radiation, and demonstrate different CR patterns. In our experiments, a variation of the pinhole sizes from 25 to 100 µm and the distances to pinhole from 50 to 5 cm reduced spatial coherence of radiation that resulted in the disappearance of the dark Poggendorff’s ring in the Lloyd’s plane. This is attributed to the interference nature of the Lloyd’s distribution and found to be in excellent agreement with the paraxial dual-cone model of conical refraction

Di-chromatic InGaN based color tuneable monolithic LED with high color rendering index

We demonstrate a phosphor free, dichromatic GaN-based monolithic white LED with vertically stacked green and blue emitting multiple quantum wells. The optimal thickness of GaN barrier layer between green and blue quantum wells used is 8 nm. This device can be tuned over a wide range of correlated color temperature (CCT) to achieve warm white (CCT = 3600 K) to cool white (CCT = 13,000 K) emission by current modulation from 2.3 A/cm2 to 12.9 A/cm2. It is also demonstrated for the first time that a color rendering index (CRI) as high as 67 can be achieved with such a dichromatic source. The observed CCT and CRI tunability is associated with the spectral power evolution due to the pumping-induced carrier redistribution

Conical refraction mode of an optical resonator

The fundamental mode of a conical refraction resonator, i.e., an optical cavity where light experiences conical refraction (CR) from a biaxial crystal, is experimentally demonstrated in the plano-concave cavity configuration. We have discovered that the fundamental CR mode is characterized by the polarization and intensity structures of CR beams between the plane mirror and CR crystal, and it resembles the fundamental Gaussian mode with homogeneous polarization between the crystal and concave mirror. We theoretically explained this fundamental CR mode using the dual cone model and symmetry of the CR phenomenon and confirmed this explanation by numerical simulations