Harmonic Wavelength Research Articles

Simulation Study on Optically Designed Refractive Beam Expander for Nd: YAG Laser Harmonics for 7 Km Detection Range

The simulation study has been conducted for the harmonics of Nd: YAG laser, namely the second harmonic generation SHG, the third harmonic generation THG, and the fourth harmonic generation FHG. Determination of beam expander's expansion ratio for specific wavelength and given detection range is the key in beam expander design for determining minimum laser spot size at the target. Knowing optimum expansion ratio decreases receiving unit dimensions and increases its performance efficiency. Simulation of the above mentioned parameters is conducted for the two types of refractive beam expander, Keplerian and Galilean. Ideal refractive indices for the lenses are chosen adequately for Nd: YAG laser harmonics wavelengths, so that increasing transmission of laser beam, consequently the received power to the detector for practical convenience.

Simulation Study on Optically Designed Refractive Beam Expander for Nd: YAG Laser Harmonics for 7 Km Detection Range

The simulation study has been conducted for the harmonics of Nd: YAG laser, namely the second harmonic generation SHG, the third harmonic generation THG, and the fourth harmonic generation FHG. Determination of beam expander's expansion ratio for specific wavelength and given detection range is the key in beam expander design for determining minimum laser spot size at the target. Knowing optimum expansion ratio decreases receiving unit dimensions and increases its performance efficiency. Simulation of the above mentioned parameters is conducted for the two types of refractive beam expander, Keplerian and Galilean. Ideal refractive indices for the lenses are chosen adequately for Nd: YAG laser harmonics wavelengths, so that increasing transmission of laser beam, consequently the received power to the detector for practical convenience.

Computation and interpretation of vibrational spectra on the structure of Losartan using ab initio and Density Functional methods

The solid phase FTIR and FT-Raman spectra of Losartan have been recorded in the region 400–4000cm−1. The spectra were interpreted in terms of fundamental modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by Quantum chemical methods. The vibrational frequencies yield good agreement between observed and calculated values. The infrared and Raman spectra were also predicted from the calculated intensities. (1)H and (13)C NMR spectra were recorded and resonance chemical shifts of the molecule were calculated. UV–Visible spectrum of the compound was recorded in the region 200–600nm and the electronic properties HOMO and LUMO energies calculated by TD-HF approach. NBO atomic charges of the molecules and second order perturbation theory analysis of Fock matrix also calculated and interpreted. The geometrical parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, and absorption wavelengths were compared with experimental and theoretical data of the molecule.

Tunable coherent soft X-ray source based on the generation of high-order harmonic of femtosecond laser radiation in gas-filled capillaries

We have carried out experimental and theoretical investigations of a tunable coherent soft X-ray radiation source in the wavelength range based on the generation of high-order harmonics of femtosecond laser radiation propagating in a dielectric xenon-filled capillary. The long path of laser pulse propagation through the capillary permits tuning the generated harmonic wavelengths to almost completely span the range under consideration.

Evaluation of plasma produced by first and second harmonic nano-second laser for enhancing the capability of laser induced breakdown spectroscopy technique

Evaluation of plasmas produced and optimized for improving the capability of convenential laser induced breakdown spectroscopy (LIBS) for analytical purposes of solid samples is the main goal of the present work. The plasma produced in the present study was generated by focusing a single nano-second Nd:YAG laser at the fundamental wavelength of 1064 nm and at the second harmonic wavelength of 532 nm on an Al target in air at atmospheric pressure. The emission spectrum was recorded time resolved over the whole UV-NIR (200–1000 nm) spectral range. This work describes an extension of previously reported studies and focuses now on the determination of the plasma parameters at the optimum condition – highest signal-to-noise ratio (SNR) and minimum limit of detection (LOD) — of the LIBS technique, which is now widely applied to the elemental analysis of materials in atmospheric air. Parameters of the produced plasma in the time interval from 0 to 10 μs are determined for to further understanding the LIBS plasma dynamics. O I and Mn I spectral lines are used in the present work as thermometric lines for the determination of the plasma temperature based on Boltzmann plots. Stark broadening of lines yields the electron density. The widths of the H α -line at 656.27 nm, of the O I line at 844.65 nm, of Al II lines at 281.65 nm and 466.30 nm and of the Si I line at 288.15 nm has been utilized for that. The plasma temperature ranged from 0.73 eV to around 1 eV for the different laser energies with both laser wavelengths for the optimized plasma used for LIBS analysis. This temperature is very close to that well known for the other spectrochemical analytical techniques or in excitation sources such as inductively coupled plasma-optical emission spectrometry (ICP-OES).

High harmonic generation from atom clusters

High harmonics generation driven by 40 fs laser pulses is investigated in three different noble gases, both in gas and cluster regime depending on gas type and backing pressure. Pressure dependence of the harmonic intensity shows different scaling laws in case of cluster formation compared with monomer gas. Both the higher harmonic yield and the stronger spectral broadening of harmonics in xenon gas show the presence of clusters in the jet. The central wavelength of harmonics has a blue shift increasing with increasing laser intensity which is a consequence of free electron contribution to the phase matching.

Strong emission from nano-iron using laser-induced breakdown spectroscopy technique

In this paper, we report a strong enhanced emission from laser produced plasma in air from iron oxide nano-material in comparison with the corresponding bulk samples. The enhancement strength differs with different Nd:YAG laser harmonics wavelengths. The analysis showed that such enhancement increased exponentially with the plasma evolution time, while it declines as the laser fluence increased. Experimental data analysis clearly showed that the observed enhancement is mainly associated with the change in the plasma electron density. We claim that this strong enhanced optical emission from laser produced plasma is due to the surface plasmon resonant excitation preferably on nano-oxide materials. Such experimental findings could improve the laser-induced breakdown spectroscopy sensitivity down to extremely low concentrations.

Nonlinear Plasmonic Nanorulers

The evaluation of distances as small as few nanometers using optical waves is a very challenging task that can pave the way for the development of new applications in biotechnology and nanotechnology. In this article, we propose a new measurement method based on the control of the nonlinear optical response of plasmonic nanostructures by means of Fano resonances. It is shown that Fano resonances resulting from the coupling between a bright mode and a dark mode at the fundamental wavelength enable unprecedented and direct manipulation of the nonlinear electromagnetic sources at the nanoscale. In the case of second harmonic generation from gold nanodolmens, the different nonlinear sources distributions induced by the different coupling regimes are clearly revealed in the far-field distribution. Hence, the configuration of the nanostructure can be accurately determined in 3-dimensions by recording the wave scattered at the second harmonic wavelength. Indeed, the conformation of the different elements building the system is encoded in the nonlinear far-field distribution, making second harmonic generation a promising tool for reading 3-dimension plasmonic nanorulers. Furthemore, it is shown that 3-dimension plasmonic nanorulers can be implemented with simpler geometries than in the linear regime while providing complete information on the structure conformation, including the top nanobar position and orientation.

General Analytical Model of Magnet Average Eddy-Current Volume Losses for Comparison of Multiphase PM Machines With Concentrated Winding

This paper studies magnet eddy-current losses in permanent-magnet (PM) machines with concentrated winding. First, space harmonics of magnetomotive force (MMF) and their influence on magnet losses in electrical machines are investigated. Second, an analytical model of magnet volume losses is developed by studying the interaction between MMF harmonics wavelengths and magnet pole dimensions. Different cases of this interaction are exhibited according to the ratio between each harmonic wavelength and magnet pole width. Then, various losses submodels are deduced. Using this analytical model, magnet volume losses for many slots/poles combinations of three-, five-, and seven-phase machines with concentrated winding are compared. This comparison leads to classify combinations into different families, depending on their magnet losses level. Finally, in order to verify the theoretical study, finite-element models are built and simulation results are compared with analytical calculations.

Optical recording in copper–silica nanocomposite

The application of field enhancement effect, which takes place when light, interacts with surface plasmon, for optical recording has been suggested. Copper–silica nanocomposite demonstrates possibility of optical writing and erasing under irradiation by second harmonic (400nm) and fundamental wavelength (800nm) of femtosecond titanium–sapphire laser, respectively.

Quasi-phase-matched second harmonic generation in silicon nitride ring resonators controlled by static electric field

Actively-controlled second harmonic generation in a silicon nitride ring resonator is proposed and simulated. The ring was designed to resonate at both pump and second harmonic wavelengths and quasi-phase-matched frequency conversion is induced by a periodic static electric field generated by voltage applied to electrodes arranged along the ring. Nonlinear propagation simulations were undertaken and an efficiency of -21.67 dB was calculated for 60 mW of pump power at 1550 nm and for a 30V applied voltage, which compares favorably with demonstrated all-optical second harmonic generation in integrated microresonators. Transient effects were also evaluated. The proposed design can be exploited for the construction of electro-optical devices based on nonlinear effects in CMOS compatible circuits.

Iron Oxide Nanocrystals Synthesis by Laser Ablation in Water: Effect of Laser Wavelength

In this research the synthesis of nanocrystalline iron oxides by laser ablation in pure water has been performed by two different wavelengths (first and second harmonics) of high frequency Nd:YAG laser. The obtained results from the X-ray diffraction and transmission electron microscopy analysis of the synthesized samples show the formation of spherical nanocrystalline magnetite with narrow particle size distribution and average diameters of 7 and 17 nm for the samples obtained by first and second harmonics of laser, respectively. According to the hysteresis loops measured by vibrating sample magnetometer, formation of the superparamagnetic nanoparticles (NPs) is confirmed. Investigating the magnetic properties of the two samples indicates a rise in the amount of magnetization of the sample produced by first harmonic of the laser compared to the one produced by the second harmonic wavelength. So it is obtained that the main wavelength of Nd:YAG laser (1,064 nm) results to finer iron oxide NPs with better magnetic properties.

Study of HfO2/SiO2 dichroic laser mirrors with refractive index inhomogeneity

HfO2/SiO2 dichroic mirrors, having high reflectance at 1064 nm and high transmittance at 532 nm, play an important role in high-power laser systems. However, the half-wave hole effect, caused mainly by the refractive index inhomogeneity of hafnia, affects the spectra and application of these mirrors. Two approaches to eliminate the half-wave hole effect have been proposed. Both approaches attempt to shift the location of the half-wave hole in comparison with the original wavelength. One approach broadens the reflectance band of the first harmonic wavelength and simultaneously adjusts the central reflectance band to a longer wavelength, whereas the other approach combines the two stacks to adjust the location of the half-wave hole far away from the wavelength of interest. Two kinds of dichroic mirrors have been successfully fabricated; moreover, it was found that the method of a two-stack combination, 0.9(HL)8 and 1.1(HL)8, provides designs that can be fabricated more easily and with better quality spectral characteristics.

Comparative studies of resonance enhancement of harmonic radiation in indium plasma using multicycle and few-cycle pulses

Enhanced single harmonic generation is analyzed in indium laser ablation plasmas at excitation conditions of multicycle (30 fs) and few-cycle (3.5 fs) pulses. We demonstrate the strong influence of pulse duration, on the emission spectra from the indium plasma. For few-cycle pulses, the enhanced emissions do not coincide with the expected harmonic wavelengths, which is the case for multicycle pulses. We test the coherent properties of an enhanced emission around 20 eV using polarization and double-slit interference techniques. We also characterize the dynamics of the emissions from the indium plasma by tuning the laser pulse duration. A theoretical analysis is presented to describe the indium plasma emission upon excitation by few-cycle pulses.

Analysis of multiple wavelengths of Lamb waves generated by meander-line coil EMATs

The electromagnetic acoustic transducers (EMATs) with a meander-line coil possess the capability of generating Lamb waves carrying multiple wavelengths, and the characteristics of multiple wavelengths is analyzed by developing a spatial transversal filter model for the EMAT. It is shown that the characteristics is due to the wavelength spectrum of the EMATs, which is a wavelength-domain representation of information about the wavelength components, and the magnitude of each components is modulated by an envelope which depends on the geometric pattern of the meander-line coil. The characteristics of multiple wavelengths might cause the multi-modes phenomenon, therefore a method for removing the effect of multiple wavelengths is proposed. It is shown that the effect can be removed by designing an EMAT which can produce a special envelop to suppress the harmonic wavelengths. Experiments are set up to study the characteristics of multiple wavelengths and verify the validity of the proposed method.

Influence of laser wavelength on the laser induced breakdown spectroscopy measurement of thin CuIn 1− xGaxSe2 solar cell films

Laser induced breakdown spectroscopy (LIBS) measurement of thin CuInxGa1−xSe2 (CIGS) films (1.2–1.9μm) with varying Ga to In ratios was carried out using the fundamental (1064nm) and second harmonic (532nm) wavelength Nd:YAG lasers (τ=5ns, spot diameter=150μm, top-hat profile) in air. The concentration ratios of Ga to In, xGa≡Ga/(Ga+In), of the CIGS samples ranged from 0.027 to 0.74 for which the band gap varied nearly proportionally to xGa from 0.96 to 1.42. It was found that the LIBS signal of 1064nm (1.17eV) wavelength laser was significantly influenced by xGa, whereas that of the 532nm (2.34eV) laser was consistent for all values of xGa. The observed dependency of the LIBS signal intensity on the laser wavelength was attributed to the large difference of photon energy of the two wavelengths that changed the absorption of incident laser energy by the film. The 532nm wavelength was found to be advantageous for multi-shot analysis that enabled depth profile analysis of the thin CIGS films and for improving measurement precision by averaging the multi-shot LIBS spectra.

Optically Pumped Semiconductor Lasers for Precision Spectroscopic Applications

Optically pumped semiconductor lasers in conjunction with intra-cavity frequency conversion and tuning elements offer high continuous-wave power, narrow linewidth, and broad tunability. As a result, they are well suited to precision spectroscopic applications. We describe the development and testing of optically pumped semiconductor lasers operating at fundamental wavelengths of 1119 and 1178 nm. The fourth and second harmonic wavelengths are resonant with transitions in Mg II and Na I, respectively. We demonstrate continuously tunable, single-frequency lasers with watt-level average power at 1119, 1178, and 589 nm.

Enhanced short wave IR third order nonlinearity of gold nanoparticle embedded ZnO thin films

Gold nanoparticle embedded ZnO thin films have been studied at the fundamental and second harmonic wavelengths of a picosecond laser by Z-scan technique. The films exhibit the effect of saturable absorption and self-defocusing. Large value third order nonlinear susceptibility (∼10−8 esu) has been observed at 1064 nm. Fast relaxation time measurements have been performed with the diffraction of the probe beam with laser-induced transient grating technique. Figure of merit values for optical switching applications have been obtained. One of the samples has been tested for passive mode-locking applications in combination with the standard saturable absorber, IR26.

Laser radiation frequency conversion in carbon- and cluster-containing plasma plumes under conditions of single and two-color pumping by pulses with a 10-Hz repetition rate

This work reviews a series of investigations of different plasma plumes using single- and two-color laser systems that emit femtosecond pulses with a 10-Hz repetition rate. Results of investigation of the resonant enhancement of harmonics in tin plasma with the use of two types of pumps are analyzed, and it is shown that the tuning of the wavelengths of harmonics to ion-resonance levels plays an important role in increasing the conversion efficiency to high-order harmonics of the radiation to be converted. Investigations of different carbon-containing plasma media (carbon nanotubes, graphite, carbon aerogel, etc.) exhibit attractive properties of the nonlinear medium of this type for efficient generation of high-order harmonics. The results of the first experiments on the use of nanoparticles produced directly in the course of laser ablation of metals for increasing the efficiency of harmonics generated in this cluster-containing medium are analyzed. It is shown that new approaches realized in these investigations give hope that the nonlinear optical response of plasma media in the far-ultraviolet range can be further increased.

Augmenting Second Harmonic Generation Using Fano Resonances in Plasmonic Systems

Significant augmentation of second harmonic generation using Fano resonances in plasmonic heptamers made of silver is theoretically and experimentally demonstrated. The geometry is engineered to simultaneously produce a Fano resonance at the fundamental wavelength, resulting in a strong localization of the fundamental field close to the system, and a higher order scattering peak at the second harmonic wavelength. These results illustrate the versatility of Fano resonant structures to engineer specific optical responses both in the linear and nonlinear regimes thus paving the way for future investigations on the role of dark modes in nonlinear and quantum optics.