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The fast development of the 5th generation (5G) mobile networks and human-centered communications is leading to the increasing proliferation of wireless devices resulting in ubiquitous exposure of people of all ages. This study investigates the effect of ageing on the power deposition at 26 GHz and 60 GHz, frequencies upcoming for 5/6G. The exposure under near-field conditions induced by multibeam radiating structures is compared to the one induced by a plane wave. The highest variation of the averaged absorbed power density with respect to the typical value for adults is observed at 70 years and corresponds to 8.8% at 26 GHz and 6.9% at 60 GHz. The maximum decrease is obtained for children at 5 years and is of -4.5% at 26 GHz and -3.7% at 60 GHz. At 26 GHz, the plane-wave model results in an underestimation of the averaged power density variations obtained with a multi-beam antenna, while at 60 GHz the variations with the two sources of exposures are almost identical.

When an antenna is located close to a lossy medium, nearfield interactions appear and may modify the incident electromagnetic field. In this stydy, we analyse for the first time analyticaly and numericaly the impact of antenna/human body interactions on the absorbed power density (APD) at 60 GHz using a skin-equivalent model. To this end, equivalent sources and patch antenna arrays are used. The results demonstrate that the antenna/body interactions result in an increase of the average APD (increase up to 84.1%, 98.3%, and 103.3% for adult dry, adult wet, and children skin, respectively) and modification of its spatial distribution. These results suggest that APD is underestimated in free-space measurements and that accurate experimental dosimetry requires taking into account the presence of the human body.

A Tm:YAP laser with an output wavelength of 1989 nm was selected for the first time as the pump source of a Q-switched Ho:YAP laser. When the absorbed power was 30 W, an average power of 18.02 W with the pulse width of 104.2 ns acousto-optic (AO) Q-switched Ho:YAP laser was obtained at a repetition frequency of 10 kHz. The slope efficiency was 70.11%, and the optical-optical conversion efficiency was 43.03%. The output center wavelength was 2129.22 nm with the line width of 0.74 nm.

This paper introduces the concept of automatic differentiation in the evaluation of the absorbed power density in the mmWave frequency spectrum for the new generation of mobile telecommunication technology. Automatic differentiation has been shown to be far superior over numerical differentiation by means of speed and accuracy. To demonstrate the full capacity of the proposed method, a comprehensive analysis of computing the absorbed power density on the surface of irradiated human skin in various configurations is presented.

In this work, we present some general considerations for the design of ultra-narrow-band metasurface absorbers that are independent of the incident angle. Specifically, we show that, for the broad class of absorbers considered here, there is a tradeoff between the maximum absorbed power and the angular dependence. Finally, we theoretically demonstrate an ultra-narrow-band omnidirectional metasurface absorber based on the concept of embedded eigenstates and optimize it taking into considerations these tradeoffs.

An in vivo validation study was performed to confirm the accuracy of extraoral photobiomodulation therapy (PBMT) dosimetry determined by modelling. The Monte Carlo technique was utilized to calculate the fluence rate and absorbed power of light delivered through multi-layered tissue. Optical properties used during Monte Carlo simulations were taken from the literature. Morphological data of four study volunteers were acquired using magnetic resonance imaging (MRI) scans. Light emitting diode (LED) coupled to a power meter were utilized to measure transmitted power through each volunteer’s cheek, in vivo. The transmitted power determined by Monte Carlo modelling was compared to the in vivo measurements to determine the accuracy of the simulations. Experimental and simulation results were in good agreement for all four subjects. The difference between the mean values of the measured transmission was within 12% from the respective transmission obtained using Monte Carlo simulations. The results of the study indicate that Monte Carlo modelling is a robust and reliable method for light dosimetry.

Here is presented our numerical investigations based on the rigorous solution of the Maxwell’s equations for analyses of absorbed and scattered powers of a semiconductor-metamaterial array with a window defect. The array structure consists of a finite set of infinite parallel, circular cylinders that can be made of the different lossy and/or lossless isotropic materials. We used our developed computer code, which allowed us to consider an array consisting of an arbitrary number of cylinders. According to our code, cylinders can be located at different distances and have differing diameters. There is a limitation: Cylinders should not cross each other. We numerically examined two cylindrical arrays with electromagnetic (EM) band-gap (EBG) defects. The absorbed and scattered powers were analyzed there for parallel and perpendicular polarizations of the incident microwave. We investigated dependencies on the operating frequency and the radius (R) of an arc of the arranged thirteen n-Si cylinders with the low semiconductor specific resistivity of 0.5, 2, and 10 Ω∙m. We have discovered that the arrays may have features of a waveguide or a microwave reflector., This article belongs to the Special Issue Photonic and Plasmonic Crystals

This paper presents an in-depth analysis of various aspects of small-scale Linear Fresnel Concentrators (LFCs). As we shall see, the influence of the lateral study of the actual absorbed power is very important in this type of LFC. In order to consider the end-effect of the absorber tube, two types of losses need to be taken into account: the end loss and the reflected light loss. Focussing on the optimization of the length and position of the absorber tube, a new mathematical method is presented. The method based on a geometric algorithm allows the straightforward deduction of the optimal design of a small-scale LFC. Numerous numerical simulations are presented for different configurations. This study constitutes the basis of the prototype that is being constructed at a vocational training centre (CIFP-Mantenimiento y Servicios a la Produccion) in La Felguera, Asturias, Spain. Asturias, Spain.

A continuous-wave (cw) self-mode-locked Tm:YAG laser at 2015 nm is successfully demonstrated by suppressing the self-pulsing behavior. By using rate equations to simulate the laser temporal dynamic, the theoretical analysis indicates that the reabsorption-induced self-pulsing for the Tm:YAG laser can be suppressed with sufficient pump power. It is experimentally confirmed that at absorbed powers higher than 6 W, the self-pulsing can be eliminated and a cw self-mode-locked pulse is generated instead of the Q-switched mode locking. At an absorbed power of 6.8 W, the output power of the self-mode-locked Tm:YAG laser reaches 1.22 W with corresponding pulse duration of 3 ps and a repetition rate of 3.376 GHz.

Photothermal technology provides sensitive detection of the optical absorption in bulk materials and coatings. To obtain the absolute absorption numbers it requires a proper calibration. In this work a new, “proxy pump” calibration approach is described. The proxy pump has a wavelength at which the material exhibits high enough optical absorption to be evaluated via direct loss measurements. The pump beam is shaped to have the same spot size as the main pump at which the optical absorption of the material is to be determined. Once the thermal field in the material has the same profile both with the proxy and main pump, the sample is self-referenced. Consecutive tests with proxy and main pumps provide absolute absorption numbers. LBO crystals are notorious objects for which the photothermal response is not easy to calibrate since the material has very low absorption in the UV, visible and near IR. In order to calibrate these materials using the above approach we used 2.3 nm laser as a proxy pump. At this wavelength LBO absorbs more than 15 % per cm length. For crystals oriented in XY and YZ planes the photothermal response was found to be 3 times weaker than for Schott glass NG12 with the same amount of absorbed power. With this correction, NG12 glass that has absorption more than 45 %/cm in the wide range of wavelengths can be used as a reference calibration material for LBO crystals.

A visible Q-switched pulse train at 639 nm was successfully generated in a Pr-doped double-clad structured waterproof fluoride glass fibre with a semiconductor saturable absorber mirror. The slope efficiency was calculated as 36.3%. The pulse duration and the radio frequency were measured as 270 ns and 107 kHz at 596 mW of absorbed power, respectively. The pulse energy and the pulse peak power were calculated as 1.32 μJ and 4.87 W, respectively.

In this contribution, we review our latest results about the unprecedented possibilities enabled by electromagnetic cloaking in antenna theory and applications. In particular, we show that, in the receiving regime, cloaking allows designing antennas exhibiting a minimum level of scattering for a given level of absorbed power, whereas, in the transmitting one, cloaking enables the co-sitting of different antennas in a confined region. Both full-wave and experimental results are presented to support the theoretical considerations.

We present a single-mode, 2.09 μm holmium-doped silica fibre laser resonantly pumped by a 1.95 μm thulium-doped fibre laser. The slope efficiency of 87% versus absorbed power is to our knowledge the highest reported to date.

A high efficient diode-pumped passively mode-locked Nd:Lu3Al5O12 (Nd:LuAG) laser is demonstrated with a semiconductor saturable-absorber mirror for the first time to our best knowledge. With an absorbed power of 10.5 W, a maximum output power of 1.05 W at 1064.4 nm was obtained, corresponding to an optical-optical conversion efficiency of 10% and a high slope efficiency of 60.2%. The mode-locked pulses have a pulse width of 5.4 ps. Our experimental results show that Nd:LuAG crystal could be an excellent alternative for high efficient diode-pumped passively mode-locked pulses generation.

A diode-pumped 937 nm Nd:GGG laser operating on the quasi-three-level under direct pumping at wavelength of around 882 nm is demonstrated, and its performances are investigated. A maximum output power of 358 mW at 937 nm was achieved at absorbed pump power of 4.8 W. The optical-to-optical conversion efficiency and the slope efficiency relative to absorbed power were 7.5 and 11.2%, respectively.

A highly efficient Nd:Gd0.6Y0.4VO4 laser by direct in-band pumping at 914 nm is demonstrated for the first time. With an absorbed power of 3.7 W, a maximum output power of 2.65 W at 1064 nm was obtained, corresponding to an optical conversion efficiency of 72%. We also experimentally observed that the laser system could be efficiently operated in the self-mode-locked state in the range of 0.9–3.3 GHz. The pulse width was measured to be 16 ps at a repetition rate of 1.75 GHz.

We report on the crystal growth, spectroscopic properties and visible laser performances of Pr3+-doped Sr0.7La0.3Mg0.3Al11.7O19 (ASL). ASL crystals doped with 2 at.% and 4 at.% Pr3+ were grown by Czochralski method. The laser experiments were carried out in a plane-concave resonator under excitation at 486 nm, provided from a 2ω-OPSL. Efficient laser emission was obtained with an 8 mm long sample of Pr(2at.%):ASL. The maximum output power amounted to 267 mW, 52 mW, and 318 mW at an absorbed power of 1.2W for red, orange, and deep red emission, respectively.

Heat release in Yb:GGG crystals with various Yb3+ ion concentrations was studied depending on the absorbed power of laser diode pumping. Initially, the heat release in Yb:GGG samples under study significantly (by a factor of 2–4) exceeded theoretically expected values. Additional annealing of samples in an oxygen atmosphere made it possible to significantly decrease the heat release in crystals to the theoretically expected value. Thus, it was shown that one of the major causes of the increased heat release in Yb:GGG crystals can be the presence of color centers in them.

Activities on diode pumped alkali laser (DPAL) in Japan is reviewed. We have started alkali laser works in 2011, and currently, we are the only players in Japan. Our interests are application oriented, and it is not only defense but also industrial. DPAL is a good candidate as a source of remote laser machining, thanks to its scalability and extremely good beam quality. We are studying on scientific and engineering problems of Cs DPAL with a small-scale apparatus. A commercial diode laser with volume Bragg grating outcoupler is used to pump the gain cell longitudinally. A 6.5 W continuous-wave output with optical to optical efficiency of 56% (based on the absorbed power) has been achieved. Numerical simulation codes are developed to understand the physics of DPAL and to help future developments.

Infrared camera images are used to calculate the power deposited on a target by a millimeter wave source. Thin carbon-impregnated sheets of Kapton are illuminated with RF energy, and then infrared images in the 3-5 /spl mu/m band provide temperature data that is used to numerically solve the heat equation and obtain absorbed power values. Techniques to determine the electrical properties of Kapton up to 94 GHz were developed.

We report an all-solid-state laser giving 67 mW of 309 nm output when pumped with a frequency-quadrupled, all-solid-state Raman-shifted Nd:YAG laser. This efficient laser source has an optical-to-optical conversion efficiency of 41%, with respect to 289 nm conversion to 309 nm, and slope efficiencies of up to 62% (based on absorbed power).

We present a new technique to analyze the absorption efficiency of the active medium for a LD side-pumped Nd:YAG laser. A detailed ray trace has been carried out to evaluate the route of the pump LD-rays propagating inside the diffusing chamber. The method, named the infinite convergence approach, is used to determine the total absorbed power of a Nd:YAG rod when random reflection takes place at the inner surface of the reflector wall. By reason of losses caused by slits milled the reflector wall, there is an optimum slit width corresponding to the maximum absorption efficiency. It has been theoretically determined that the absorption efficiency can be summarized by a convergent result for the infinite energy transfer process inside the diffusing chamber. The method is applicable to the cavity design for any LD side-pumped solid-state lasers.

This paper discusses the wave absorber which is best suited to use on cylinders with a resistive film. Mode expansion is applied in the analysis. Various design charts are provided. The effectiveness of the method is verified by designing a wave absorber using the design charts and calculating the absorbed power. This wave absorber is analyzed by calculating the power scattered by the wave absorber and the actually absorbed power. In addition, the degradation of absorbance due to deformation of the spacer in fabricating an absorber of this kind is examined by the point matching method. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 53–60, 2002

Ceramic Yb:YAG samples have been investigated spectroscopically and utilized in laser experiments. Pumping with a fiber-coupled diode at 940 nm and 15.5 W absorbed power, output power up to 5.1 W with slope efficiency up to 44.3% has been achieved in continuous wave operation. The performance is comparable with single-crystal Yb:YAG in the same setup. Employing passive Q-switching with Cr:YAG saturable absorber, we obtained 4.4 W at 48 kHz, with 7-ns pulses.

As a method for evaluating the electromagnetic exposure of biological bodies, a visualization technique of the absorbed power inside the phantom using high-molecular-weight gel is proposed. Such gel containing a small amount of nonionic surfactants has the property of quickly becoming clouded at a temperature above a certain value. Therefore, it is possible to observe the portion with a temperature increase due to absorption of electromagnetic energy as a clouded region. The surface of the clouded region represents an equitemperature surface indicating the temperature at which the phantom is clouded. Hence, this is basically the equal power absorption surface. However, depending on the influence of the thermal conduction, the shape of the clouded region and the absorption power distribution may not coincide. In this paper, the equality of the clouded region shape and the equal power absorption surface is verified. The measured shape of the clouded region formed inside the phantom and the absorbed power distribution within the phantom derived by the three-dimensional FD-TD (Finite-Difference Time-Domain) method are compared. In addition, the influence of thermal conduction on the temperature distribution in the phantom is discussed. It is confirmed that the clouded shape caused by electromagnetic wave exposure and the computed equal power absorption surface agree well if the electromagnetic wave illumination time is less than about 1 minute. The validity of this method measuring the amount of electromagnetic wave exposure from the clouded shape is confirmed. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(3): 51–60, 2002

Cryogenic temperature operation of a 〈010〉-cut microchip Tm,Ho:Lu2SiO5 laser end-pumping by a fiber-coupled laser-diode is presented. A 2.73 W absorbed pump power is used to generate a maximum laser output of 470 mW, representing a 17.2% optical-to-optical conversion efficiency and a 61.7% slope efficiency corresponding to absorbed power. In the experiment, the oscillating wavelength shifting from 2.03 to 2.08 µm has been observed and a single 2.03 µm wavelength oscillation has obtained. To our knowledge, this work is the first time to investigate the Cryogenic temperature operation of microchip Tm,Ho:Lu2SiO5.

In this letter, a diode-pumped passively mode-locked Nd:Lu1.5Y1.5Al5O12 (Nd:LuYAG) laser is demonstrated for the first time, to the best of our knowledge. With a semiconductor saturable-absorber mirror, a maximum output power of 0.85 W at 1064 nm was obtained under an absorbed power of 8.51 W, corresponding to a high slope efficiency of 44%. The mode-locked pulses were estimated to be 6.6 ps. The results of our experiment show that Nd:LuYAG crystal could be a promising material for diode-pumped ultra-short laser generation.

A diode-pumped thin-disk laser based on Tm:KLu(WO4)2/KLu(WO4)2 epitaxies is realized. The emission is in the 1850-1945 nm spectral range for Tm-doping between 5 and 15 at. %. The maximum slope efficiency of 47% with respect to the absorbed power obtained with 5 at. % Tm:KLu(WO4)2/KLu(WO4)2 corresponds to a maximum output power of ~6 W in cw operation.

We present the first 1.9 µm diode pumped Ho:Lu2O3 laser at room temperature with an output power of 15 W. The optical-to-optical efficiency with respect to the absorbed power is estimated to exceed 50 %.

We demonstrate efficient continuous-wave (CW) and passively Q-switched Tm:LiLuF(4) laser operation near 1.9 μm. The CW slope efficiency reached 54.8% with respect to absorbed power. Stable passive Q-switching with Cr(2+):ZnS saturable absorbers resulted in minimum pulse duration of 7.6 ns and maximum pulse energy and peak power of 1.26 mJ and 166 kW, respectively.

We have demonstrated the first resonantly pumped double-clad holmium-doped fibre laser. An output power of 99W with 65% slope efficiency versus absorbed power was achieved at 2.12μm.

Thermal behavior in an edge-pumped $Yb:YAG$ thin disk laser is presented. Ray tracing method is used to calculate absorbed power through the disk. Temperature distribution, stress, displacement in crystal and optical path differences are calculated.

Using a combined ray tracing and Fokker-Planck code, an investigation is made on the propagation and absorption of the launched power spectrum during lower hybrid (LH) current drive in tokamaks, in a situation where toroidally induced ray stochasticity is important. Stochastic effects are correctly taken into account by tracing a large number of rays. The influence of the balance between the wave damping and the stochastic divergence of nearby ray trajectories in governing the power spectrum dynamics and in establishing the characteristics of the LH power deposition patterns is illustrated. It is shown that, when strong wave damping prevails, the launched power spectrum behaves regularly: the LH power deposition is localized and the absorbed power spectrum is very similar in shape to the launched one, although some broadening and shifting in the parallel wave index generally occur. If the wave damping is weak and stochastic effects are important, the rays end by covering the entire plasma cross-section and the power spectrum dynamics follows a diffusive pattern: the LH power deposition turns out to be extended and the absorbed power spectrum is much broader than the launched one, as a result of strong spreading towards the high absolute values of the parallel wave index

Continuous-wave laser action has been observed from an ytterbium-doped monomode fibre laser on the three-level transition at 974 nm and on the four-level transition at 1036 nm with slope efficiencies of 67% and 77% respectively, with respect to absorbed power. Tuning behaviour is described, in which polarisation control by means of fibre loops has allowed smooth continuous tuning from 1·010 μm to 1·162 μm.

We report room-temperature operation of an all-solid-state broadly tunable continuous-wave Cr(2+):ZnSe laser. Output power of 250 mW, an absorbed power slope efficiency of 63%, and continuous tunability from 2138 to 2760 nm are demonstrated.

We report on continuous-wave lasing of Yb(3+) at room temperature in the noncentrosymmetric RbTiOPO(4) crystal, codoped with Nb(5+), for all three possible polarizations. A maximum output power of 154 mW at 1050 nm was obtained for an absorbed power of 386 mW. The highest slope efficiency reached approximately 60% and the lowest threshold (with respect to the absorbed power) was 18 mW. The laser was tunable from 1009 to 1081 nm.

Thin absorbers with improved performance based on the concept of Artificial Magnetic Conductors are proposed. Improvement is achieved by introducing perturbations in the unit cell of the AMC. Those result in excitation of the odd mode in the vicinity of the modal interaction null, with currents in successive elements flowing in opposite directions. As a result, significantly stronger currents are excited. Introducing loss in the conducting elements, the increased currents result in significantly higher levels of ohmic absorption. Full wave techniques are employed to demonstrate the concept. Improvement in the absorbed power of a thin absorber by a factor of 20 is demonstrated.

Efficient resonantly diode-pumped Er:YAG cryo-laser is demonstrated for the first time. Slope efficiency of 71.5% per absorbed power was achieved at 78°K in these initial experiments. Maximum quasi-CW power of over 63W is reported.

Continuous-wave mode locking (CW-ML) of a diode-pumped Nd3+:BaY2F8 laser is reported for the first time to our knowledge. Pulses as short as 4.8 ps were measured with a total output power of approximately 1 W at 1049 nm, corresponding to 3.4 W of absorbed power from the pump diode at 806 nm. A novel technique for passive stabilization of CW-ML has been demonstrated.

We demonstrate low‐threshold lasing at 4 K in optically pumped hemispherical In0.2Ga0.8As single‐quantum‐well microcavities. The incident threshold pump power density is 11 kW/cm2 corresponding to an absorbed power density of about 320 W/cm2, and the measured spontaneous emission factor β is about 0.01.

This paper describes a 2-mm pumped, kilohertz repetition rate, Cr2+:CdSe laser producing 500 mW of broadband output centered at 2.6 mm with 48% absorbed power conversion efficiency. With a larger pump beam to prevent coating damage, 815 mW was demonstrated.

We report what is to our knowledge the first laser operation of Nd3+-doped LiNbO3 near 900 nm. An absorbed power threshold of 26 mW was obtained when the device was pumped at 814 nm. The design of the waveguide geometry to favor laser operation at this wavelength is demonstrated.

Microwave discharges are widely used for generation of quasi-equilibrium and nonequilibrium plasma for different applications. Microwave plasma can be generated at pressures from 10 -5 Torr up to atmospheric pressure in the pulse and continuum wave regimes at incident powers ranged between several Watts and hundreds of kW. The plasma absorbed power can be high enough and runs up to 90% of the incident power. This paper reviews the methods of microwave plasma generation, general features of microwave plasma, and selected aspects of microwave plasma diagnostics.

We demonstrate continuous wave (CW) room temperature laser operation of the monoclinic Ho(3+)-doped KLu(WO(4))(2) crystal using a diode-pumped Tm(3+):KLu(WO(4))(2) laser for in-band pumping. The slope efficiency achieved amounts to ~55% with respect to the absorbed power and the maximum output power of 648 mW is generated at 2078 nm.

We demonstrate cooling of a 2 micron thick GaAs/InGaP double-heterostructure to 165 K from ambient using an all-solid-state optical refrigerator. Cooler is comprised of Yb3+-doped YLF crystal, utilizing 3.5 Watts of absorbed power near the E4-E5 Stark manifold transition.

A novel heating element powered by laser radiation via an optical fiber has been demonstrated. Temperatures approaching 2000 °C can be obtained with only a few watts of absorbed power. A prototype device has been used to join gold wires.

The effect of metallic implantations on the absorbed power distribution within a human head is studied numerically using a lossy dielectric sphere containing conducting elements excited by the near field of a dipole antenna.

Velocity-selective absorption by a long lifetime transition in a calcium atomic beam has been measured for two spatially separated counterpropagating laser beams. The observed variation of the absorbed power as well as of the Lamb dip depth with laser power and with velocity of the atoms is in agreement with calculations of Rabi cycles.

The first channel waveguide laser in Nd:YAG showing a threshold reduction of 20 times compared to a planar waveguide is described. With diode pumping this ion-implanted waveguide laser has been operated with absorbed power thresholds as low as ~500µW in good agreement with theoretical expectation. Output slope efficiencies of ~29% have also been demonstrated.