Поглощение мощного света свободными электронами в кристаллах: внутризонные электрон-фононные осцилляции Раби

Absorption of high-intensity visible or near-IR pulsed laser radiation at free electrons in crystals is calculated in the modified resonance approximation. The probabilities $W_{exc}$ of intraband transitions with a change in the electron energy by $\hbar(\omega\pm\omega_l)$, where $\omega$ is the radiation frequency and $/omega_l$ the frequency of longitudinal optical phonons involved in the process, are derived. It is shown that specific electron–phonon Rabi oscillations with the frequency $\Omega_R$ can occur and radiation is absorbed only until the point in time $\tau_1$, at which the first maximum in the dependence $W_{exc} (t)$, where t is the time elapsed from the beginning of the laser pulse, is reached. It is shown that, in the case of prebreakdown radiation intensities, the processes of high orders in field of the radiation wave substantially influence $W_{exc}$, $\tau_1$, and $\Omega_R$.

Dynamic Response of a Gangway Between Two Floating Bodies in a Side-by-Side Configuration

A number of tender assisted drilling platforms (TAD) are built to offer comfortable accommodation for crew, onsite construction and maintenance for production platforms. The two platforms are usually connected by a telescopic gangway. The safety and feasibility of gangway are essential during personnel transfer operation. In this paper, a TLP-TAD coupled system was investigated numerically and experimentally to study the gangway motion responses. The numerical model was established in frequency domain using 3D multi-body diffraction/radiation wave theory. Then time domain simulation was performed to consider the second-order drift loads and nonlinearity of mooring lines and hawsers. A systematic model test was also conducted for the coupled system. The connection point between gangway and platform was regarded as a joint, so gangway motion could be derived by global motions of TLP and TAD. Both single-body and multi-body cases were studied for comparison. The differences of global responses between two cases were relatively small, indicating that multi-body hydrodynamic interaction was not quite significant. The interaction aroused sway-surge and sway-heave coupling, and shielding effect also existed. Based on the above, gangway extension was investigated to analyze which degree of freedom (DOF) of global motion governed it.

Research of the Spectral Characteristics of Apodized Fiber Bragg Gratings

Fiber Bragg Gratings (FBG) are widely used in different areas of the state-of–the -art fiber optics. Every task imposes specified requirements to the FBG spectral characteristics, which are scheduled at the gratings manufacturing stage. Manufacturing and using the Bragg fiber-optic gratings is impossible without measuring their characteristics at every stage of manufacturing the gratings themselves and devices on their basis. To select FBG’s optimal parameter we will compare the parameter SGW with several different the most widely used apodization functions. Upon manufacturing the FBG there applied strict requirements to their parameters. Recording or manufacturing the fiber Bragg gratings might be classified according to the type of the laser being used, radiation wave length, recording techniques, irradiation material and grating type. The article is dedicated to the techniques of computing and measuring the FBG’s principal parameters; it is necessary to define optimal parameters of the characteristics for the grating quality operation.

Pre-service Physics Teachers’ Opinions about the Difficulties in Understanding Introductory Quantum Physics Topics

The aim of this study is to identify the opinions of pre-service physics teachers about the difficulties in introductory quantum physics topics. In this study conducted with twenty-five pre-service physics teachers, the case study method was used. The participants were interviewed about introductory quantum physics topics. The interviews were coded using content analysis and were divided into different categories. In this way, we tried to reveal the opinions of pre-service physics teachers about the difficulties of these topics. In conclusion, it can be said that the participants had the most difficulty in transition from classical physics to quantum physics. This is especially evident in quantum physics topics that require a different understanding such as black body radiation, wave-particle structure of light and the uncertainty principle. It was also found that the participants had no difficulties in terms of mathematical calculations, and that approaches based on visualizing the topic were received positively.