Harmonic Of Nd Research Articles

Photocatalytic conversion of CO2 into value-added hydrocarbon (methanol) with high selectivity over ZnS nanoparticles driven by 355-nm pulsed laser

In the present investigation, monochromatic 355-nm pulsed laser radiations generated by third harmonic of Nd:YAG laser (1,060 nm) were applied as an excitation light source for conversion of CO2 into value-added hydrocarbon (methanol) with high selectivity over ZnS particles through photo-catalytic process. The microstructure and optical band absorption of as-prepared ZnS nanoparticles were characterized by means of XRD, UV–Vis absorption spectrum, TEM, SAED, and EDX spectrum. The effect of irradiation time as well as the pulsed laser energy on methanol yield and photoefficiency were investigated and discussed in detail. Furthermore, a possible mechanism for such conversion process is also discussed based on the band edge of ZnS semiconductor and the unique monochromatic characteristic of the adopted 355-nm pulsed laser.

Diagnostic Study of an Fe-Ni Alloy Plasma Generated by the Fundamental (1064 nm) and Second (532 nm) Harmonics of an Nd: YAG Laser

We studied the spatial evolution of the Fe-Ni plasma generated by the fundamental (1064 nm) and second (532 nm) harmonics of a Q-switched Nd: YAG laser. The experimentally observed line profiles of the neutral iron (Fe I) have been used to extract the plasma temperature (Te) using the Boltzmann plot method, whereas the electron number density (Ne) has been determined from the Stark broadening. In addition, we studied the spatial behavior of Te and Ne with the variation of laser energy for iron plasma by placing the target material (iron-nickel alloy) in air at atmospheric pressure for both modes of the Nd: YAG laser.

Experimental and Theoretical Investigations of High Power Sub-Millimeter Wave Emission at Two-Stream Instability of High-Current REB

Sub-mm radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation at strong Langmuir turbulence (LT) via the two-stream instability induced by a high current relativistic electron beam (REB). A plasmon scattering on plasma density fluctuations produces EM emission at the plasma frequency ωp (“ωp process”). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2nd harmonic of the plasma frequency 2ωp (2ωp process”). For plasma densities 1020-1021 m-3, these frequencies are in the range of sub-mm waves: 180-566 GHz. The power density of sub-mm-wave emission from plasmas in the multi-mirror trap GOL-3 (BINP) during injection of a 10-μs-REB at plasma densities ne ≈ (1-5)·1020 m-3, electron temperatures Te ≈ 1-3 keV and magnetic field B ≈ 4 T was measured to be up to 1 kW/cm3 in the frequency band above 100 GHz.To calculate the second harmonic emission power from turbulent magnetized plasma we use the model of coalescence of two upper-hybrid waves. Results of these calculations and measured power are in good coincidence in the investigated area of plasma density.

Auto bias control technique for optical OFDM transmitter with bias dithering

In coherent optical communication systems, the transmitter usually employs an optical in-phase and quadrature (IQ) modulator to perform electrical-to-optical up-conversion. However, some environmental factors, such as temperature and mechanical stress, strongly influence the stability. To stabilize the quality of the transmitted signal, auto bias control (ABC) is essential to keep modulator in optimum bias. In this paper, we present a novel method of ABC for the optical orthogonal frequency division multiplexing (O-OFDM) signal. In the proposed scheme, a small cosine/sine wave dither signal is added on to the I/Q baseband signal, respectively. Based on the power monitoring of the 1st and 2nd harmonics of the dither signal, the biases of the optical IQ modulator for O-OFDM system can be adjusted very precisely. The simulation and experimental results show good performance on locating the optimum bias voltages for the IQ modulator with high precision.

Generation of High-Power Sub-THz Waves in Magnetized Turbulent Electron Beam Plasmas

Sub-THz radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation in a plasma with strong Langmuir (LT) turbulence produced via a two-stream instability of a high current relativistic electron beam (REB). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2nd harmonic of the plasma frequency 2ωp (“2ωp-process”). For plasma densities of 1014 − 1015 cm−3, these frequencies are in the range of sub-THz waves at 370–570 GHz. The specific power density of sub-THz-wave emission from plasmas in the multi-mirror magnetic trap GOL-3 (at BINP) during injection of a 10-μs-REB with a current density of about 1 kA/cm2 at plasma densities ne ≈ 5∙1014 cm−3, electron temperatures Te ≈ 1.5 keV and magnetic induction B ≈ 4 T was measured to be approx. 1 kW/cm3 in the frequency band around 300 GHz. In the case of a weakly relativistic 100-μs-electron beam (90 keV) with 250 A/cm2 the corresponding results are 700 W/cm3 around 90 GHz with an efficiency of 1–2 % at ne ≈ 3∙1013 cm−3 (total power ≈ 30 kW). Theoretical investigations show that at a density of ne ≈ 3∙1015 cm−3 and a turbulence level of 5 % the generated sub-THz power can reach ≈ 1 MW/cm3.

Crystal Structure and Optical Properties of a New Nonlinear Optical Chalcone Crystal

New nonlinear chalcone derivative: 3-(2,3-dichlorophenyl)-1-(pyridin-2-yl)prop-2-en-1-one (DCPP), has been synthesized and crystallized using dimethylformamide as solvent. The lattice parameters for the grown crystals were determined by using single crystal x-ray diffraction analysis; the DCPP crystallizes in the monoclinic system with P21 space group. The unit cell parameters of the crystal are: a = 7.4229(2) Å, b = 3.9889(1) Å, c = 21.2685(6) Å, β = 98.212(2), and V = 623.29(3)Å3. DCPP crystals were characterized by thermal and FTIR and UV-Vis spectral techniques. DCPP crystals are thermally stable up to 146.9°C. The UV absorption cut off wavelength is observed at 350 nm. DCPP crystals generate second harmonics of Nd:YAG laser operating at 1064 nm wavelength. The second harmonic generation (SHG) efficiency of the powdered DCPP sample was measured using Kurtz and Perry technique. The SHG efficiency is found to be equal to that of urea.

High-order harmonic generation of picosecond laser radiation in carbon-containing plasmas

A study of the high-order harmonic generation of picosecond laser radiation in the carbon-containing plasmas is reported. The materials studied for plasma formation were the graphite, glassy carbon, pyrographite, boron carbide, silicon carbide, and pencil lead. We show that picosecond pulses (t=38  ps) can be efficiently converted in the short wavelength range using the laser-produced plasmas. We also demonstrate the resonance-induced enhancement of the seventh harmonic of Nd:YAG laser (152 nm), which few times exceeded the intensity of the fifth harmonic.

YAl3(BO3)4:TM (TM = Mn, Co, Cr) nanocrystals synthesis for laser operated nonlinear optics

An attempt to synthesize YAB matrices doped with cobalt, manganese, and chromium ions by means of the Pechini method for photo-induced nonlinear optics was performed. The best results were obtained for the Cr doped samples. It may be related with the fact that YAB:Cr main absorption peak is situated near the photo-inducing green second harmonics of Nd:YAG laser at 532 nm. It was established that after 600 s of samples illumination there was observed some maximum of the SHG. With the further treatment of the materials the SHG starts to decrease. The maximal enhancement was achieved at 150 K. After the switching off of the photo-inducing treatment the output SHG was relaxed to initial state during 2–3 min. Local increase of temperature due to heating did not exceed 6 K. For the Mn doped YAB NC the behavior is quite non-monotonic. The SHG changes are within the accuracy of the YAB NC NLO measurements. One can see two slight maxima at 200 and 800 s. At the same time Co suppress the output SHG, which may be caused by specific features of Co ions.

Enhancement in Sensitivity Using Multiple Harmonics for Miniature Fluxgates

The miniature fluxgates, or microfluxgates, are magnetic field sensors promising in applications of modern portable electronic devices, e.g., motion trackers and digital compasses. In comparison with the bulky traditional fluxgates, the major drawback arising from miniaturization is the reduced sensitivity and the enhanced noise level. In this work, we proposed the method to enhance the sensitivity of a miniature fluxgate by adding up the responses of four even harmonics. Numerical simulation shows that the harmonic spectrum of the induced voltage waveform consists of high-order even harmonics when the excitation current is strong enough to saturate the magnetic cores. Since the magnitude of high-order even harmonics are comparable to that of the second harmonic, it is possible to enhance the sensitivity by detecting several important harmonics. To implement the multiple-harmonic detection technique, the sensitivity and noise of a parallel-gating miniature fluxgate is investigated using the proposed method. With the reference waveform consisting of square waves at 2nd, 4th, 6th, and 8th harmonics of excitation, the sensitivity of the sensor is found to be enhanced by a factor of 2.6 in comparison with the case for a 2nd-harmonic reference alone. The field noise level is found to be reduced from 0.5 nT/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\surd$</tex></formula> Hz to 0.2 nT/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\surd$</tex></formula> Hz. The proposed method is promising in improving the sensitivity and reducing the field noise of a chip-scale fluxgate.

Pulsed Focused Nonlinear Acoustic Fields from Clinically Relevant Therapeutic Sources in Layered Media: Experimental Data and Numerical Prediction Results

Abstract In many therapeutic applications of a pulsed focused ultrasound with various intensities the finite- amplitude acoustic waves propagate in water before penetrating into tissues and their local heating. Water is used as the matching, cooling and harmonics generating medium. In order to design ultrasonic probes for various therapeutic applications based on the local tissue heating induced in selected organs as well as to plan ultrasonic regimes of treatment a knowledge of pressure variations in pulsed focused nonlinear acoustic beams produced in layered media is necessary. The main objective of this work was to verify experimentally the applicability of the recently developed numerical model based on the Time- Averaged Wave Envelope (TAWE) approach (Wójcik et al., 2006) as an effective research tool for predicting the pulsed focused nonlinear fields produced in two-layer media comprising of water and tested materials (with attenuation arbitrarily dependent on frequency) by clinically relevant axially-symmetric therapeutic sources. First, the model was verified in water as a reference medium with known linear and nonlinear acoustic properties. The measurements in water were carried out at a 25◦C temperature using a 2.25 MHz circular focused (f/3.0) transducer with an effective diameter of 29 mm. The measurement results obtained for 8-cycle tone bursts with three different initial pressure amplitudes varied between 37 kPa and 113 kPa were compared with the numerical predictions obtained for the source boundary condition parameters determined experimentally. The comparison of the experimental results with those simulated numerically has shown that the model based on the TAWE approach predicts well both the spatial-peak and spatial-spectral pressure variations in the pulsed focused nonlinear beams produced by the transducer used in water for all excitation levels complying with the condition corresponding to weak or moderate source-pressure levels. Quantitative analysis of the simulated nonlinear beams from circular transducers with ka ≫ 1 allowed to show that the axial distance at which sudden accretion of the 2nd or higher harmonics amplitude appears is specific for this transducer regardless of the excitation level providing weak to moderate nonlinear fields. For the transducer used, the axial distance at which the 2nd harmonics amplitude suddenly begins to grow was found to be equal to 60 mm. Then, the model was verified experimentally for two-layer parallel media comprising of a 60-mm water layer and a 60-mm layer of 1.3-butanediol (99%, Sigma-Aldrich Chemie GmbH, Steinheim, Germany). This medium was selected because of its tissue-mimicking acoustic properties and known nonlinearity parameter B/A. The measurements of both, the peak- and harmonic-pressure variations in the pulsed nonlinear acoustic beams produced in two-layer media (water/1.3-butanediol) were performed for the same source boundary conditions as in water. The measurement results were compared with those simulated numerically. The good agreement between the measured data and numerical calculations has shown that the model based on the TAWE approach is well suited to predict both the peak and harmonic pressure variations in the pulsed focused nonlinear sound beams produced in layered media by clinically relevant therapeutic sources. Finally, the pulsed focused nonlinear fields from the transducer used in two-layer media: water/castor oil, water/silicone oil (Dow Corning Ltd., Coventry, UK), water/human brain and water/pig liver were predicted for various values of the nonlinearity parameter of tested media.

The Studies of Ac Magnetic Susceptibility and Higher Harmonics in Cd&lt;sub&gt;0.88&lt;/sub&gt;Cr&lt;sub&gt;1.96&lt;/sub&gt;V&lt;sub&gt;0.31&lt;/sub&gt;Se&lt;sub&gt;4&lt;/sub&gt; Semiconductor

The complex ac dynamic magnetic susceptibility was used to study the magnetic state in the polycrystalline Cd0.88Cr1.96V0.31Se4 spinel. The temperature dependences of the zero field in-phase (real part) and out-of-phase (imaginary part) components of fundamental susceptibility showed the mictomagnetic behavior at low temperature and a weak Hopkinson-like effect close to the ordering temperature. These effects are also evidenced by the non-vanishing both the real and imaginary components of the 2nd and 3rd harmonics in the region of magnetic order.

Pulsed laser-induced photocatalytic reduction of greenhouse gas CO2 into methanol: A value-added hydrocarbon product over SiC

CO2 was converted into value-added hydrocarbons (methanol) by laser-induced photocatalytic reduction of CO2 over commercially available silicon-carbide (SiC) granules as catalyst. The conversion of CO2 was carried out in a glass reactor having quartz window and equipped with stirring system and was provided with continuous CO2 flow at ambient conditions. Laser radiations of 355 nm, which were generated by third harmonics of Nd:YAG laser (1060 nm) were applied as an excitation source. The methanol yield as a function of irradiation time and catalysts dosage were monitored by the gas chromatographic analysis (GD-FID) of water samples collected at prescribed intervals. A specific GC column was used which separated hydrocarbons efficiently without any interference from water present in the sample. The study indicated that the commercially available SiC granular material is an excellent catalyst in laser-induced photocatalytic conversion of CO2 into high value hydrocarbons.

Processing of amorphous Si by pulsed laser irradiation at different wavelengths

Amorphous Si thin films deposited on thermally oxidized Si wafers have been processed by the 2nd and 3rd harmonics of Nd:YAG laser. Surface modification of amorphous silicon layers have been investigated by scanning electron microscopy before and after chemical etching of processed silicon films. The super-lateral crystal growth regime was achieved with laser fluence of 280 mJ/cm2 for the 2nd harmonics and 155 mJ/cm2 for the 3rd harmonics. The grain size in polycrystalline Si samples prepared by successive crystallization in the lateral growth regime is about 0.5 - 1 μm.

IMAGING OBSERVATIONS OF QUASI-PERIODIC PULSATIONS IN SOLAR FLARE LOOPS WITHSDO/AIA

Quasi-periodic pulsations (QPPs) of flaring emission with periods from a few seconds to tens of minutes have been widely detected from radio bands to gamma-ray emissions. However, in the past the spatial information of pulsations could not be utilized well due to the instrument limits. We report here imaging observations of the QPPs in three loop sections during a C1.7 flare with periods of P = 24 s-3 minutes by means of the extreme-ultraviolet 171 angstrom channel of the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory. We confirm that the QPPs with the shortest period of 24 s were not of an artifact produced by the Nyquist frequency of the AIA 12 s cadence. The QPPs in the three loop sections were interconnected and closely associated with the flare. The detected perturbations propagated along the loops at speeds of 65-200 km s(-1), close to those of acoustic waves in them. The loops were made up of many bright blobs arranged in alternating bright and dark changes in intensity (spatial periodical distribution) with the wavelengths 2.4-5 Mm (as if they were magnetohydrodynamic waves). Furthermore, in the time-distance diagrams, the detected perturbation wavelengths of the QPPs are estimated to be similar to 10 Mm, which evidently do not fit the above ones of the spatial periodic distributions and produce a difference of a factor of 2-4 with them. It is suggested that the short QPPs with periods P 60 s were the higher (e. g., > 2nd) harmonics of slow magnetoacoustic waves.

Imaging method for vibrating scanning force microscopy cantilevers for the analysis of mode shapes and nonlinear harmonic motion

► SFM and SEM are used as hybrid instrument. ► Modes and harmonics of cantilever motion are measured with high precision. ► Nonlinearities of motion are not directly coupled to deflection amplitudes. A specially designed scanning force microscope (SFM, atomic force microscope – AFM) was incorporated into the chamber of a commercial scanning electron microscope (SEM) to investigate vibrating SFM cantilevers at their resonance. Inherently, the spatial resolution of electron microscopy is higher than that of optical methods. In this paper we present vibration modes (eigenmodes) of two different SFM cantilevers. Their nonlinear behavior is also explored in order to depict their 2nd harmonics (twice the fundamental frequency). Imaging of the local vibration is performed by measuring the frequency- and phase-selective responses of the SE signal at different X and Y positions of the scanned electron beam.

Investigation on Micro-Machining Characteristics and Phenomenon of Semiconductor Materials by Harmonics of Nd:YAG Laser

Precision micro-machining without crack and heat affected zones is required in order to use high-performance materials such as silicon and silicon carbide, and it is expected that the higher harmonics of the Nd:YAG laser can perform precision micro-machining due to its high photon energy. However, even by using the harmonics of the Nd:YAG laser, a heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma on the processing results, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma in micro-drilling of silicon carbide was observed by a high-speed shutter camera, and the influence of laser wavelength and surrounding conditions on the machining characteristics were experimentally investigated. The removal depth increased with decreasing wavelength and the surrounding gas pressure. The surface integrity was improved by the combination of shorter wavelength and reduced pressure conditions. The behavior of laser induced plasma was different from the wavelength of the laser beam and the surrounding gas pressure. Under atmospheric pressure conditions, the plasma grew greatly and affected the wider surface around the drilled hole with increasing wavelength. Under reduced pressure conditions, there was little difference in plasma size by wavelength, and the affected zone around the drilled hole became relatively smaller. It became clear that a low surrounding gas pressure and shorter wavelength were important to obtain better surface integrity and highly efficient processing.

Rotating-Sample Magnetometer for Measuring Crystal Field Parameters

A method of measuring crystal field parameters by means of a rotating-sample magnetometer is presented. The measurement is performed by registering 2nd, 4th and 6th harmonics of the signal that is proportional to magnetization change due to rotation of the sample in a magnetic field. Experimentally measured temperature dependence of the amplitudes of these harmonics is used to determine the crystal field parameters within the framework of the theoretical model proposed in [. The signal is detected by a digital lock-in amplifier, while temperature is controlled by a PID controller. The sample and pickup coils are located in the bore of a Halbach permanent magnet. The measurements are fully automated. Magnitude of the expected signal was estimated. Test measurements of magnetization of the Tb single crystal along a axis (in the easy crystallographic plane a-b) in the permanent magnetic field 2.7 T at room temperature were performed. The results show that sensitivity of the instruments and the proposed design of the equipment allows us to determine crystal field parameters of heavy rare-earth metals. Testing of the control software showed that computer-device communications and execution of the software blocks are correct.

Research on Satellite Autonomous Orbit Determination Method Based on the Unscented Particle Filter with Embedded Earth Sensor Correction

The direct earth horizon and starlight observation with earth sensor and star sensor is often used in the satellite autonomous orbit determination, which is a stable autonomous navigation method but with some defects that need to be improved. On the one hand, both the orbit state equation and measure equation are nonlinear, in which only the 2nd zonal harmonic of the non-spherical earth gravity is introduced while the other perturbation terms are regarded as white noise, which in fact all these terms have certain models themselves that are usually non-Gaussian distribution. In this case, Unscented Particle Filter (UPF) is present to be used for the satellite autonomous orbit determination; On the other hand, the error of earth sensor is a vital problem for the precision of satellite-earth center distance determination, which will damage the observation of orbit information. In this paper, the UPF uses the Unscented Kalman Filter (UKF) to generate sophisticated proposal distributions. It can not only avoid the limitation of the UKF which only apply to Gaussian distributions but also avoid the limitation of the standard PF which can not include the new measurements. The other improvement to the autonomous orbit determination method is embedding a earth correction based on star sensor measurement into the UPF observation step, which enhances the final orbit determination precision a lot. The simulation results show that the presented method has higher accuracy and more stable characteristic than the standard PF and UKF, especially when the earth correction is absent.

Time-integral type strongly correlated electronic thin-film laser energy meter

Strongly correlated electronic (SCE) systems, such as high-temperature superconducting (HTSC) cuprate and colossal magnetoresistance (CMR) manganite thin films, exhibit giant laser-induced thermoelectric voltage (LITV) effect due to anisotropic Seebeck effect and have a great potential for laser detector applications. In this work, we develop a novel time-integral type LaSrMnO thin-film laser energy meter based on anisotropic Seebeck effect. An epitaxial LaSrMnO thin film prepared by means of the pulsed laser deposition method onto a vicinal cut LaAlO3 substrate is irradiated by a 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics at room temperature. The time integral of the LITV signal shows a good linear relationship with the laser energy per pulse in the measured wavelength range, which not only confirms the theoretical analysis, but also provides the basis for designing time-integral type laser energy meter. The advantages over other conventional laser detectors, such as fast (nanosecond order) response, spectrally broadband (from infrared to ultraviolet) and flat response, exceptional chemical and thermal stability, real-time measurement, and energy savings, make the device a promising candidate for next-generation laser detectors and laser energy/power meters.

Separation of free and bound harmonics in waves

Free and bound (phase-locked) waves with the same frequency cannot be distinguished simply in a frequency domain. A 1-Hz wave propagating over a submerged rectangular step was physically investigated and used to generate higher free and bound harmonic components in waves. The time history of a 3.28m surface profile above the submerged step was measured and analyzed using two-dimensional Fourier Transform and Morlet wavelet transform sequentially. Incident and reflected waves as well as the associated free and bound components of each harmonic (through the 3th harmonic) were separated successfully. The spatial phase information of the 2nd free-mode and bound-mode harmonics were obtained which gave a good physical explanation of amplitude recurrence. It was observed that wave lengths of harmonics vary in space and phase shift occurs as the 1st harmonic catches up the 2nd free-mode harmonic. It was also found that the 2nd free-mode harmonic gained more energy from the 1st harmonic before entering deep water.