External Laser Radiation Research Articles

Thermal analysis of laser-controlled 5-aminotetrazole propellant

Resorting to the continuous assistance of external laser radiation, laser augmented chemical propulsion (LACP) reveals superior combustion performance. However, the corresponding combustion theories have still to be ascertained for this innovative propulsion technique. Thermal characteristics of 5-aminotetrazole (5-ATZ) propellant are studied for LACP. In nitrogen environment, unique structures of burning surface are formed under laser ablation in bare samples of 5-ATZ propellant pressed powders. Resorting to an outer tube, a thermocouple is inserted in 5-ATZ propellant samples to obtain the temperature trace during combustion. In analogy with the burning surface structure reconstructed by micro computed tomography (MicroCT), the temperatures values of three significant regions were obtained. The experimental dependences of the measured temperatures on environment pressure and laser power are discussed.

Laser field control of subradiant states of a system of several atoms in a configuration close to a regular polygon

Some collective excitations of an ensemble of closely spaced (two-level) atoms can be characterised by extremely low rates of radiation decay, which is of considerable interest for storing quantum information. Such (dark) states are realised, for example, in planar geometry when atoms are located at the nodes of a regular polygon. However, the decay rate of such excitations increases markedly when the geometry deviates from ideal. Using the example of small deformation of a square in a rhombus, we show that an increase in the decay rate of the dark state due to symmetry breaking can be compensated for by adjusting the transition frequency of some atoms exposed to external laser radiation.

Analysis of Methods of Investigation of the Vibration–Rotation Spectrum of Monomers and Dimers of Sulphur Hexafluoride Isotopes

The stability of the system of sulphur hexafluoride dimer SF6 under the action of external laser radiation has been estimated using ab initio quantum-chemical calculations of the vibration–rotation spectrum of SF6 monomers as well as homo- and heterodimers. It is noted that for simple CO molecule as an example, the most widely used method of calculations based on the Hessian matrix approach cannot serve as a reliable instrument in quantitative calculations of some molecular systems. As a potential analog, we have tested the algorithm for obtaining the vibration–rotation spectrum based on molecular dynamics data.

Goniometric complex for investigation the optical characteristics of radiation of luminescent structures

In this paper we describe an automated goniometric complex for investigation the optical characteristics and them spatial distribution of luminescent structures.On the market most instruments for measuring of the spatial distribution of radiation are designed for commercial light sources, such as LEDs, incandescent lamps, fluorescent lamps. Often scientific research requires measurements of the spatial distribution of emitted or scattered radiation upon excitation by external laser radiation. Therefore, the device for these measurements was designed and manufactured. In the article the design and principle of operation of the complex are described and its main technical characteristics are presented. During metrological certification specially developed five reference LEDs with different spectral characteristics were used to ensure traceability to the national measurement standards of the Republic of Belarus. The automated goniometric complex allows one to measure the spatial distribution of luminescence and scattering radiation with external laser excitation in the units of the spectral irradiance, luminous flux, chromaticity coordinates and correlated color temperature.The main metrological characteristics of the complex: spectral range — from 396 nm to 753 nm with a spectral resolution of 0.5 nm; power spectral density measurement range — from 3.5∙102 W/m3 to 1∙106 W/m3 in the spectral range from 400 nm to 750 nm with relative combined standard uncertainty of 7.8 %; chromaticity coordinate measurement range for coordinate x from 0.088 to 0.676, for coordinate y — from 0.160 to 0.715, with relative combined standard uncertainty of 5.5 % for coordinate x and 8.4 % for coordinate y; measurement range of correlated color temperature — from 2000 K to 7000 К with relative combined standard uncertainty of 9.3 %; luminous flux measurement range — from 0.6 lm to 35.0 lm with relative combined standard uncertainty of 9.3 %; rotation angle — from minus 90° to plus 90° in tangential direction and from minus 180° to plus 180° in radial direction with angular resolution of 0.5°.Measurement results are processed by specially developed software. Results can be presented in the form of three-dimensional diagrams for selected units of measurement or in form of a text file.

Inversionless amplification of light by molecules selectively oriented over states in the field of laser radiation

A possibility of inversionless amplification of light by non-dipole molecules oriented state-selectively by means of superimposing of external laser radiation is considered. Various variants of mutual direction of electrical vectors of the probe and orienting fields are numerically analysed for specific ratios of the orientation parameters of the ground and excited states both in pulsed and stationary regimes. It is shown that the variant in which the signs of the orientation parameters of the ground and excited states are opposite is the most promising. The latter can be implemented in selection of the orienting field frequency.

Negative absorption coefficient of a weak electromagnetic wave caused by electrons confined in rectangular quantum wires in the presence of laser radiation

Analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) caused by electrons confined in rectangular quantum wires (RQWs) in the presence of laser radiation are calculated using the quantum kinetic equation for electrons in the case of electron-optical phonon scattering. The dependence of the ACF of a weak EMW on the intensity E01 and the frequency Ω1 of the external laser radiation, the intensity E02 and the frequency Ω2 of the weak EMW, the temperature T of the system and the size L (Lx and Ly) of the RQWs is obtained. The results are numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results show that the ACF of a weak EMW in RQWs can have negative values. Thus, in the presence of laser radiation, under proper conditions, a weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case without laser radiation

CALCULATION ABSORPTION COEFFICIENT OF A WEAK ELECTROMAGNETIC WAVE BY CONFINED ELECTRONS IN CYLINDRICAL QUANTUM WIRES IN THE PRESENCE OF LASER RADIATION BY USING THE QUANTUM KINETIC EQUATION

We calculated analytic expressions for the absorption coe-cient (ACF) of a weak electromagnetic wave (EMW) by conflned electrons in cylindrical quantum wires (CQW) in the presence of laser radiation by using the quantum kinetic equation for electrons in the case of electron-optical phonon scattering. The ACF of a weak EMW depends on the intensity E01 and frequency ›1 of the external laser radiation (~ E1 = ~ E01 sin(›1t+'1)); the intensity E02 and frequency ›2 of the weak EMW ( ~ E2 = ~ E02 sin(›2t)), the temperature T of the system and the radius R of CQW. Then, the analytic results are numerically calculated and discussed for GaAs=GaAsAl CQW. The numerical results show that the ACF of a weak EMW in a CQW can have negative values. So, in the presence of laser radiation, under proper conditions, the weak EMW is increased. This is difierent from the similar problem in bulk semiconductors and from the case of the absence of laser radiation.

Dissipative plasmon‐solitons in multilayer graphene

AbstractNonlinear properties of a multi‐layer stack of graphene sheets are studied. It is predicted that such a structure may support dissipative plasmon‐solitons generated and supported by an external laser radiation. Novel nonlinear equations describing spatial dynamics of the nonlinear plasmons driven by a plane wave in the Otto configuration are derived and the existence of single and multi‐hump dissipative solitons in the graphene structure is predicted.

Modeling and Improvement of Breast Cancer Site Temperature Profile by Implantation of Onion-Like Quantum-Dot Quantum-Well Heteronanocrystal in Tumor Site

In this paper, we investigate one of the important parameters (increase of infrared imaging sensitivity) in bioimaging applications that play a vital role (easy detection by nonsensitive detector) in the thermal imaging of breast cancer. It is known that differences in energy consumption exist for normal and abnormal tissue and that these differences lead to small but detectable local temperature changes if a tumor in the breast cancer is full grown. Infrared imaging has been used in tumor detection, but if the tumor is in the early stage of development, the common instrumentation is not sensitive enough to detect the subtle changes in temperature required for accurate diagnosis. Therefore, the disease can enter a dangerous stage of rapid growth. For detection of its early-stage progression, the onion-like quantum-dot quantum-well (QDQW) heteronanocrystal (CdSe/ZnS/CdSe/ZnS), for the first time, is proposed and used to increase the sensitivity of thermal detection. Indeed, the injected quantum-dots in the breast are excited by an external laser radiation source. In this study, the bioheat transfer equation is solved by the 2-D finite element approach for a simplified model of a female breast and a cancerous tumor. The results of simulations will reveal that the local temperature change detections considerably increased by using a new modified structure of quantum dot localized in tumor site.

Switching of lasing wavelength in a sol—gel laserwith dynamic distributed feedback

A scheme of switching the lasing wavelength of active centres in a sol—gel matrix excited by external laser radiation is proposed. A distributed feedback is formed during pumping by using a right-angle prism due to the interference of the direct and reflected pump beams. The lasing wavelength is determined by the period of the interference pattern, which depends on the convergence angle of interfering beams. Control is performed by a liquid-crystal cell, which changes the pump radiation polarisation, and a birefringent prism. As a result, the convergence angle of interfering beams changes, leading to a change in the interference pattern period and the excited radiation wavelength.

Loop laser cavities with self-pumped phase-conjugate mirrors in low-gain active media for phase-locked multichannel laser systems

It is proved that lasers with different loop cavities with self-pumped phase-conjugate mirrors in low-gain active media can operate under injection of external laser radiation and can be used for the development of diode-pumped phase-locked multichannel neodymium laser systems operating both on the fundamental laser transition with the wavelength λ = 1.06 μm and on the transition with λ = 1.34 μm. The phase-conjugate oscillation thresholds in the case of injection of an external signal are determined for a multiloop cavity configuration and an increased number of active elements in the cavity. It is shown that phase-conjugate oscillation can occur even if the single-pass gain of the active element is as low as only ∼2. Under high-power side diode pumping of a multiloop Nd:YAG laser, single-mode output radiation was achieved at λ = 1.064 μm with a pulse energy up to 0.75 J, a pulse repetition rate up to 25 Hz, an average power up to 18.3 W, and an efficiency up to 20%. In a multiloop Nd:YAG laser with three active elements in the cavity, single-mode radiation at λ = 1.34 μm was obtained with a pulse energy up to 0.96 J, a pulse repetition rate up to 10 Hz, and an average power up to 8.5 W.

Commentary on: Treatment of Cellulite Using a 1440-nm Pulsed Laser With One-Year Follow-Up: Preliminary Report

In my opinion, there are four holy grails of cosmetic surgery that the baby boomer generation has been actively pursuing over the last 20 years: noninvasive skin tightening, localized noninvasive fat reduction, stretch mark improvement, and treatment of cellulite. In his study, Dr. DiBernardo introduces an interesting, novel, and promising new approach to the last of these goals. As the author points out, his study is limited by a small number of patients (10). However, this study is well designed as a prospective controlled model. The clear strengths of the study include the full year of follow-up, the clearly-demonstrated photographic improvement, and the objective measurements of skin elasticity and thickness. One of the most confusing areas of laser surgery is the area of optimal wavelength utilization. Anderson et al outlined the optimal wavelengths for fat absorption.1 However, that study actually outlined fat absorption from external laser radiation and did not examine the effectiveness of absorption when the laser was fired into the hypodermis in direct contact with the fat itself. Many wavelengths are utilized in the melting of fat (eg, 920 nm, 975 nm, 1064 nm, 1320 nm, and 1440 nm), and the characteristics of each are beyond the scope of this commentary. However, the 1440-nm wavelength—the one administered in Dr. …

Semiclassical description of high harmonic generation during the above-threshold ionization of atoms

A simple analytical formula for evaluating the intensity of high-frequency emission from an atom is obtained proceeding from the classical notions about the motion of an electron in the field of the atomic core and an external laser radiation field. Calculations using this formula are performed for a hydrogen atom that occurs initially in the ground state and is exposed to the action of ultrashort radiation pulses involving various numbers of field oscillations.

Dynamics of interaction between two-level atoms in a laser field and linear stationary optical dimensional resonances

Formulas for radiative forces acting on the atoms of a diatomic object in a field of external laser radiation are obtained with allowance made for the interatomic dipole-dipole interaction. It is shown that one can control the motion of the atoms by gradually varying the frequency of external laser radiation due to the presence of optical dimensional resonances in the spectrum of the diatomic object.

Numerical study of compression and heating of conical targets

This paper presents some results of two-dimensional calculations (using Euler variables) of conical targets, performed on the basis of the coservative variant of the grid characteristic method. The mathematical model of the physical processes occurring in the high temperature plasma includes absorption of external laser radiation, the hydrodynamic motion, electron thermal conductivity, and electronion collision relaxation. The basic system of two-dimensional non-steady-state equations for the two-temperature plasma is presented and supplemented by an equation for the mass concentration of one of the components of the two-component mixture of ideal gases.