Incident Powers Research Articles

Vacuum Microwave Treatment of Potato Starch and the Resultant Modification of Properties

AbstractThe study focuses on the vacuum microwave treatment of low‐moisture potato starch. Typical temperature and drying profiles are presented and explained with the help of other process parameters such as sample weight, pressure, incident and absorbed microwave power. Subsequently water absorption capacity of vacuum microwave treated and conduction heated samples was investigated at 55 °C. During vacuum microwave treatment, 50 g samples were treated with incident powers of 460, 500 and 750 W at 3800 Pa for durations between 30 and 300 s. Water absorption capacity increased exponentially with the net absorbed energy but could not be functionally correlated to end temperature and incident power. During conduction heating, starch samples were treated at temperature values of 120, 130, 140, 150 and 160 °C, till constant weight. The water absorption capacity was observed to increase with increase in treatment temperature.

Microwave discharges: generation and diagnostics

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.

Effects of laser radiation on immobile and fast-moving targets

We have studied the effects of laser pulses up to 50 J in energy and up to 1100 μs in duration, with a rise time of ∼300 μs, on immobile and moving (linear velocity of up to 104 cm s-1) stainless steel targets. The results indicate that, in the vapour above an immobile target, optical breakdown develops at a spot-averaged power density of 5.5×106 W cm-2, against 7.3×106 W cm-2 in air. This undesirable effect can be eliminated even at an order of magnitude higher incident power density by rapidly rotating the target (linear velocity of ∼50 cm s-1 relative to the laser beam). At incident power densities in the range (0.6–1.2)×107 W cm-2 (incident powers from 12 to 24 kW), evaporation from a rotating target is intermittent. To interpret this effect, a numerical model is developed which takes into account the influence of target burning. Its predictions agree with the evaporation behaviour observed in our experiments. The thicknesses of the evaporated and molten layers are evaluated as functions of laser beam parameters and target velocity, with reference to the optimisation of laser surface processing conditions.

Visualization of focusing–refocusing cycles during filamentation in BaF2

Filamentation occurs within a 1.5 cm-long crystal of BaF2 during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing–refocusing cycles along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By measuring the radius (Lmin ) of single filament inside BaF2, we obtain estimates of peak intensities (Imax ) and electron densities (ρmax ) to be 3.26×1013 W cm−2 and 2.81×1019 cm−3, respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF2 is 0.33×10−70 cm12 W−6 s−1.

Conical Emission Patterns by Femtosecond Pulses with Different Spectral Bandwidths

Different conical emission (CE) patterns are obtained experimentally at various incident powers and beam sizes of pump laser pulses with pulse durations of 7 fs, 44 fs and 100 fs. The results show that it is the incident power but not the incident power density that determines a certain CE pattern. In addition, the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth. Furthermore, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is. This will hopefully provide new insights for the generation of CE pattern in optical medium.

Nonlinear properties of split-ring resonators

In this letter, the properties of split-ring resonators (SRRs) loaded with high-Q capacitors and nonlinear varactors are theoretically analyzed and experimentally measured. We demonstrate that the resonance frequency f(m) of the nonlinear SRRs can be tuned by increasing the incident power. f(m) moves to lower and higher frequencies for the SRR loaded with one varactor and two back-to-back varactors, respectively. For high incident powers, we observe bistable tunable metamaterials and hysteresis effects. Moreover, the coupling between two nonlinear SRRs is also discussed.

Depolarization of white light generated by ultrashort laser pulses in optical media

We report measurements of the extinction ratio (ER) of white light generated upon irradiation of BK7 glass by ultrashort (36 fs) laser pulses with incident power approximately 10(3) times larger than the critical power for self-focusing. At low incident powers, the continuum is symmetric about the incident laser wavelength; at high powers it becomes broader and distinctly asymmetric towards the blue side. We observe that ER degrades by 100-fold after the onset of multiphoton-induced free-electron generation (at incident intensity approximately 2 TW cm-2), which also corresponds to the onset of asymmetry in white-light spectra.

Intensity-dependent reflectance and transmittance of semiconductor periodic structures

The intensity-dependent response of nonlinear Bragg-periodic epitaxially-grown InGaAs-InAlGaAs-based optical elements is reported over a broad spectral range 1.3-1.6 μm. Large changes in the transmittance and reflectance are observed as a function of incident power. Over most of this spectral region, the nonlinear response is dominated by the saturation of absorption. In the vicinity of 1.5 μm, the optical elements exhibit fluence-dependent Bragg diffraction. For low incident powers, the indices of refraction of structures are uniform and no coherent scattering takes place. With increased incident power a Bragg grating appears, resulting in the emergence of a fluence-dependent stopband in the transmittance and reflectance spectra.

유기단결정 Polydiacetylene Para-toluene Sulfonate에서 2차원 공간고립파의 진행과 상호 작용 전산모의

2차원 공간 고립파는 비선형 굴절률이 빛의 세기에 따라 일정한 값에 수렴하는 포화 매질에서 안정적으로 전파될 수 있다. 그러나 빛의 세기가 크지 않은 경우, 5차 비선형 굴절률이 음수인 매질은 포화 매질의 특성을 가지므로 2차원 공간 고립파가 전파될 수 있다. 2차원 비선형 슈뢰딩거 방정식의 전산 시늉을 통하여 빛의 세기가 크지 않은 경우 가우시안 빛살이 5차 비선형 매질을 전파하는 과정을 조사하였다. 그 결과 자체 포획 일률로 입사시킬 때 가장 안정적으로 2차원 공간 고립파가 전파한다는 것을 알 수 있었다. 또한 위상차가 180<TEX>$^{\circ}$</TEX>인 두 공간 고립파를 0.05<TEX>$^{\circ}$</TEX>의 충돌각으로 충돌시키면서 한 쪽 고립파의 입사 일률을 조절한다면 출력단에서 두 공간 고립파의 완전 광 스위칭이 가능함을 확인하였다. Two dimensional solitary waves are stably propagated in a saturable medium which has a saturable nonlinear index as input intensity. However, in the case of low intensity. a negative fifth-order nonlinear medium has properties of a saturable medium. So a Gaussian beam travels stably. The propagation process into the fifth order nonlinear medium of the Gaussian beam with a weak intensity is investigated by using the computer simulation of the two-dimensional nonlinear Schrodinger equation. As a result, it is confirmed that the two-dimensional spatial solitary waves are stably propagated in this medium when the incident powers are self-trapping powers. In the condition of the phase difference and collisional angle between two input beams of 180 degree and 0.05 degree, respectively, we can confirm that all optical switching is as simple as controlling the incident power of one input beam.

High heat flux tests on beryllium and beryllium-copper joints

A large test program has been set up to evaluate the performance of beryllium as a plasma facing material for the divertor in thermonuclear fusion devices. Simulation of steady state heat loads of 5 MW m −2 and above on actively cooled divertor modules, and off-normal plasma conditions with energy densities in the range 1–7 MJ m −2, have been investigated. Thermal shock tests were carried out with the ITER reference grade S65-C and several Russian grades of beryllium. At incident energies up to 7 MJ m −2 the best erosion behaviour is observed for S65-C and for TGP-56. Steady state heating tests with actively cooled Be/Cu mock-ups were performed at incident powers of up to 5.8 MW m −2. All samples investigated in these tests did not show any indications of failure. A Be/Cu mock-ups with Incusil braze was loaded in thermal fatigue up to 500 cycles at an incident power of 4.8 MW m −2. Up to the end of the experiment no temperature increase of the surface and no indication of failure was observed.

Wavelength-dependent power-law Josephson photoresponse of a Tl2Ba2CaCu2O8 thin film.

The Josephson photoresponse of a current biased granular ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ thin film has been measured at 4.2 K for radiation frequencies \ensuremath{\omega} in the range 20--111 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The resulting photosignal s depends nonlinearly on the incident power P satisfying the relationship s=K(\ensuremath{\omega})${\mathit{P}}^{\mathrm{\ensuremath{\alpha}}(\mathrm{\ensuremath{\omega}})}$, where K is a frequency-dependent constant. The value of \ensuremath{\alpha} increases monotonically from 0.5 at 20.2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to 0.9 at 111 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. At 20.2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ this power law is valid for incident powers between 5 mW and 1 kW, a range of more than ${10}^{5}$. These limits are imposed by experimental constraints and not by deviations from the power-law behavior. As the frequency increases, the responsivity of the film drops strongly, K(\ensuremath{\omega}) decreasing approximately as ${\mathrm{\ensuremath{\omega}}}^{\mathrm{\ensuremath{-}}3}$, so that the power-law validity is established over three orders of magnitude at 111 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Such a behavior of the Josephson photoresponse has been previously observed, albeit over reduced dynamic ranges, in granular superconducting films of other materials. Thus we believe it to be an inherent characteristic of the random arrays of Josephson junctions contained in such films.

Application of surface laser-light scattering spectroscopy to photoabsorbing systems: The measurement of interfacial tension and viscosity in crude oil

We have successfully used surface laser-light scattering spectroscopy to measure the interfacial tension and viscosity in a strongly photoabsorbing crude oil system. Photothermal distortion of the sample interface was avoided by judicious choice of laser power, scattering angle, and optical configuration. Measurements were performed on a stock tank crude oil/air interface at ambient conditions for a series of incident laser powers. The measured interfacial tension was in good agreement with that obtained using the Wilhelmy plate technique. The measured viscosity was in good agreement with that obtained using low-shear viscometry. Both the interfacial tension and the liquid viscosity were independent of laser power for low incident powers. Surface laser-light scattering is now fully qualified for measurements of interfacial tension and viscosity of reservoir fluids at the elevated pressures and temperatures of an oil-field reservoir.

Transient light scattering in aqueous surfactant systems

A new phenomenon in aqueous surfactant systems is presented. Laser-induced timedependent changes in the H ν , V ν , and D ν light scattering at 90° have been measured in aqueous solutions of ionic surfactants both above and below the CMC. Parameters of the effect were determined in detail for cetyltrimethylammonium bromide, but the effect was seen in cetyltrimethylammonium chloride, sodium oleate, sodium dodecyl sulfate, and N,N,N-trimethylaminododecanimide as well. Other surfactant systems (oleyl- , tridecyl- , and nonylphenolethylene oxide adducts) did not exhibit the phenomena. The H ν and V ν intensities decayed in an exponential fashion from the time of first illumination with a time constant of the order of ∼2 sec for incident power densities of ≥50 W/cm 2 from an argon ion laser. Lesser incident powers produced longer decays. Evaluations of the dependence on temperature, concentration, and sampling were also made. The effect seems most consistent with a low concentration of a highly anisotropic structure in solution even below the CMC.

Anomalous absorption of intense electromagnetic radiation in a non-uniform overdense plasma

In this work, we present numerical computation of anomalous absorption of a powerful electromagnetic wave incident normally, on an isothermal plasma with a linear density gradient. We consider first, the “intensity” dependence of anomalous absorption treating two important cases: one that of a typical high temperature, high density fusion plasma occurring in a laser-pellet application and the other that of an ionospheric (F-layer) plasma. It is found that for low incident powers, reflection is almost constant, corresponding essentially, to classical electronion collisions. As we increase the incident power, however, we find that the reflection starts dropping and the absorption takes over. This result is interpreted in terms of the instability generated anomalous absorption of the incident wave. Next, we consider the “wavelength” dependence of anomalous absorption, wherein we observe that the effect of anomalous absorption is increasing for longer wavelengths of the incident laser radiation.