Harmonic Wavelength Research Articles

Ultrafast intermodal third harmonic generation in a liquid core step-index fiber filled with C2Cl4.

Third harmonic generation in a circular liquid core step-index fiber filled with a highly transparent inorganic solvent is demonstrated experimentally using ultrafast pump pulses of different durations in the telecom domain for the first time. Specifically we achieve intermodal phase matching to the HE13 higher order mode at the harmonic wavelength and found clear indications of a non-instantaneous molecular contribution to the total nonlinearity in the spectral broadening of the pump. Spectral power evolution and efficiency of the conversion process is studied for all pulse parameters, while we found the greatest photon yield for the longest pulses as well as an unexpected blue-shift of the third harmonic wavelength with increasing pump power. Our results provide the basis for future studies aiming at using this tunable fiber platform with a sophisticated nonlinear response in the context of harmonic generation.

Generation of Coherent X-ray Harmonic Radiation in a Single-Pass Free-Electron Laser with Phase Shift of Electrons Relative to Photons

Evolution of bunching and harmonic power is theoretically studied for a single-pass free-electron laser (FEL) in which electrons are periodically phase-shifted relative to photons in intervals between undulators with harmonics of magnetic field. Analytical calculations are used to reveal the configuration of magnetic field of an asymmetric elliptical and planar undulators that make it possible to suppress the fundamental and amplify several higher harmonics. The evolution of power and bunching is analyzed using a phenomenological model of FEL that describes violation of bunching between the undulator stages and a relatively high sensitivity of electron–photon interaction at wavelengths of higher harmonics to energy spread, size, deflection of the beam from the axis, etc. Expressions for the Bessel coefficients of the planar and elliptical undulators with field harmonics are analytically studied. Such undulators can be used in phase-shifted FELs for an increase in the power of higher (X-ray) harmonics by a factor of up to 100 in comparison with conventional FELs.

Qualification of Operational Amplifier used in Satellite Subsystem using Picosecond Pulsed Laser System

Picosecond Pulsed Laser System (PPLS) was used to simulate the single event effects (SEE) on satellite electronic components. Single event transients effect induced in an operational amplifier (LM324) to determine how transient amplitude and charge collection varied with pulsed laser energies. The wavelength and the focused spot size are the primary factors generating the resultant charge density profile. The degradation performance of LM324 induced by pulsed laser irradiation with two wavelength (1064nm, 532nm) is determined as a function of laser cross section. The transient voltage changed due to pulsed laser hitting specific transistors. This research shows the sensitivity mapping of LM324 under the effect of fundamental and second harmonic wavelengths. Determine the threshold energy of the SET in both wavelength, and compare the laser cross section of 1064 nm beam and 532 nm beam.

Two-color symmetry breaking in laser-based secondary neutral mass spectrometry.

An alternative method of analysis for laser-based secondary neutral mass spectrometry is introduced. By mixing a fundamental 1240 nm wavelength of the near-infrared laser field with an intensity of 1 × 1015 W/cm2 with its second harmonic generation wavelength of 620 nm, control is attained over the ion yield in secondary neutral mass spectrometry for a native silver surface and a surface covered with silver nanoparticles. The ion yields of selected species in the mass spectra, such as a C2 H4 O2 surfactant fragment ion and the Ag ion, are enhanced or suppressed by a factor of 8 or 23, respectively, in comparison with single color post-ionization. In addition, a significant suppression of ion fragmentation is demonstrated for both the silver sample and silver nanoparticles. Periodic variation of the ion yield with a modulation depth of 4% is observed depending upon the relative phase between the fundamental and second harmonic generated fields. These variations are explained in terms of tunneling ionization with symmetry-broken fields. An additional degree of freedom in a form of additional second color is introduced in laser-based secondary neutral mass spectrometry. Ion yield control is extended in a form of symmetry-broken fields.

Few-Layer Bismuthene for Coexistence of Harmonic and Dual Wavelength in a Mode-Locked Fiber Laser.

Bismuthene, as a novel two-dimensional (2D) material, has attracted extensive attention because of its outstanding properties including narrow band gap, stability at room temperature, nonlinear optical transmission, and so on. In this paper, the physical characteristic, nonlinear optical response, and ultrafast photonics application of few-layer bismuthene are studied experimentally. By the balanced twin-detector measurement method, the saturable absorption property of few-layer bismuthene with a modulation depth of 2.5% and saturable intensity of 110 MW/cm2 at the optical communication band (C-band) is illustrated. Dependent on a few-layer bismuthene saturable absorber, an all-fiber ultrashort pulse laser is fabricated and the proposed fiber laser can operate with coexistence of harmonic mode-locking and dual-wavelength mode-locking. The different laser generations of harmonic and dual wavelength depend on the saturable absorption of few-layer bismuthene, the suitable birefringence and nonlinearity strength in the laser cavity. The results suggest that the ultrashort pulse laser obtained based on few-layer bismuthene could be applied to the field of pump-probe experiments and tunable terahertz radiation generation potentially.

First clinical evaluation of a quartz enhanced photo-acoustic CO sensor for human breath analysis

We present a carbon monoxide (CO) sensor dedicated to human breath analysis, based on quartz enhanced photo-acoustic spectroscopy (QEPAS). An off-beam configuration was chosen for the sensor, using a quantum cascade laser emitting at 4.7 μm. The detection was based on a second harmonic wavelength modulation scheme. A minimum detection limit of 20 parts per billions in volume (ppbv) in 1 s was obtained. First tests were performed on smokers/non smokers to validate the stability and the ability of the sensor to be used in vivo. Then a detailed validation of the sensor was performed in Montpellier Hospital by testing the CO-QEPAS performance versus reference methods: blood carboxy-hemoglobin (COHb %) and clinical status. Additionally, the performance was compared with commercial exhaled CO analyzer measurements. A full clinical evaluation of the sensor showed good reliability and agreement with the reference method (COHb %) of the CO-QEPAS in healthy subjects, confirming the ability of our CO sensor for measuring low level endogenous exhaled CO concentrations.

Surface wave effects on energy transfer in overlying turbulent flow

Phase-resolved wave simulation and direct numerical simulation of turbulence are performed to investigate the surface wave effects on the energy transfer in overlying turbulent flow. The JONSWAP spectrum is used to initialize a broadband wave field. The nonlinear wave field is simulated using a high-order spectral method, and the resultant wave surface provides the bottom boundary conditions for direct numerical simulation of the overlying turbulent flow. Two wave ages of and 25 are considered, corresponding to slow and fast wave fields, respectively, where denotes the celerity of the peak wave and denotes the friction velocity. The energy transfer of turbulent motions in the presence of surface waves is investigated through the spectral analysis of the two-point correlation transport equation. It is found that the production term has an extra peak at the dominant wavelength scale in the vicinity of the surface, and the energy transported to the surface via viscous and spatial turbulent transport is enhanced in the region of . The presence of surface waves results in an inverse turbulent energy cascade in the near-surface region, where small-scale wave-related motions transfer energy back to the dominant wavelength scale. Pressure-related terms reflecting the spatial and inter-component energy transfer are strongly dependent on the wave age. Furthermore, triadic interaction analysis reveals that the energy influx at the dominant wavelength scale is due to the contribution of the neighbouring streamwise turbulent motions, and those at the harmonic wavelength scales contribute the most.

Effect of laser energy and wavelength on average size of gold nanoparticles synthesized by pulsed laser ablation in deionized water

In this paper, the effect of Nd:YAG laser wavelength and energy on the synthesis of gold nanoparticles is reported. Gold nanoparticles colloidal solutions were prepared by pulsed laser ablation of gold target in deionized water. The Nd:YAG laser with repetition rate of 1 Hz was assigned to supply energy at fundamental and second harmonic wavelengths i.e., 1064 nm and 532 nm, respectively. Synthesized nanoparticles were characterized using particle size analyzer (PSA). Four different laser energies were used to ablate the samples and synthesize gold nanoparticles. The average size of gold nanoparticles was found to decrease with increasing laser energy. The gold nanoparticles of smaller size were obtained when the target was ablated with 532nm wavelength of Nd:YAG laser. Higher laser energies and efficient absorption of 532 nm wavelength resulted in size reduction by fragmentation of colloidal nanoparticles.

Enhanced nonlinear optical functionality in birefringence and refractive index dispersion of the deep-ultraviolet fluorooxoborates

As a promising candidate, the fluorooxoborate has enkindled new explorations of nonlinear optical materials to meet the deep-ultraviolet criteria. However, big challenges and open questions still remain facing this exciting new field, especially the birefringence and dispersion of refractive index which are fundamental parameters for determining the phase-matching second harmonic generation wavelength. Here we designed possible anionic groups in fluorooxoborates, and analyzed the optical anisotropy to check its influence on birefringence, which was proved further by the response electronic distribution anisotropy approximation. The functional modules modulating birefringence in fluorooxoborates were explored systematically. We developed an approach for evaluating the behavior of the refractive index dispersions and found that the fluorooxoborates had small refractive index dispersions owing to the introduction of fluorooxoborate modules. Our results demonstrate that fluorooxoborates can be utilized to realize short phase-matching wavelength markedly and offer a path toward novel performance-driven materials design.

Generation of an ultra-long sub-diffracted second-harmonic optical needle from a periodically poled LiNbO3 crystal

We experimentally demonstrate the use of a periodically poled LiNbO3 (PPLN) crystal to produce an ultra-long sub-diffraction optical needle via second-harmonic generation. When we input a radially polarized fundamental wave from a femtosecond laser, a sub-diffraction beam size of 0.45λSH and an ultra-long depth of focus (DOF) of 55λSH are experimentally realized, where λSH is the second harmonic wavelength. The lateral size of the second harmonic optical needle is reduced by a factor of 2 compared to the case using the fundamental wave. The compact experimental configuration can realize wavelength conversion and wave-front shaping simultaneously in a single PPLN crystal. In addition, the ultra-long DOF is potentially useful in observing thick samples. The unique characteristics of our second harmonic optical needle open the door for practical applications in super-resolution imaging and optical manipulation.

Synthesis and Characterization of Aluminum Nanoparticles Prepared in Vinegar Using a Pulsed Laser Ablation Technique

The second harmonic wavelength of a neodymium-doped yttrium-aluminum-garnet (Nd-YAG) laser (λ=532 nm) was used in a pulsed laser ablation technique (PLAL) to synthesize aluminum nanoparticles suspended in white vinegar from an aluminum target. The nanoparticles were characterized by HRTEM and UV-Vis spectrophotometry. They were found to range in size between 2 and 50 nm in diameter, with an average diameter of 12±9 nm. The nanoparticles had a maximum absorption peak at 237 nm and were found to exhibit a core-shell structure with an Al core coated by a thin layer of an amorphous material which could be attributed to amorphous carbon. HRTEM results revealed that the small nanoparticles (<20 nm) had an fcc phase of aluminum crystalline structure, where the larger particles represented alumina (γ-Al2O3) nanoparticles. Such observation suggests that the use of white vinegar as an ablation medium could facilitate the synthesis of aluminum nanoparticles with minimal evidence of the existence of aluminum oxide nanoparticles in the resultant suspension.

Генерация когерентного рентгеновского излучения гармоник в однопроходном лазере на свободных электронах со сдвигом фаз электронов относительно фотонов

Theoretical study of the radiated FEL power and bunching is conducted in single-pass free electron laser (FEL) with repetitive shift of the photon pulse with respect to the electron bunch in between the sections of the undulator with field harmonics. Using the analytical calculations, the asymmetric elliptic and planar undulator fields are identified for the undulators to be able to reduce the fundamental tone and enhance the harmonic radiation. This effect is amplified by the phase shift kπ/n, k=2,4,6… of the electrons and photons between the undulator sections. This allows n-th FEL harmonic reach its peak power beyond the fundamental saturation FEL length. It is not possible to achieve in a common FEL due to fast increase of the energy spread, induced by the fundamental tone along FEL and its early saturation. The phenomenological model of the FEL is used for the analysis of the bunching coefficients and harmonic powers evolution in the FEL. The model describes the debunching between the undulator sections, where the phase shift is imposed, and accounts for the higher sensitivity to losses of the electron-photon interaction at high harmonic wavelengths. The losses are due to the beam energy spread and emittance, deviation off the axis, diffraction etc. Explicit expressions for the Bessel coefficients of the planar and elliptic undulators with field harmonics are obtained and analyzed. The combination of the undulator field harmonics is identified, which reduces the fundamental tone and enhances the 3rd and 5th UR harmonics as compared with the radiation from a planar undulator. We propose the use of these undulators in a FEL with the electron-photon phase shift, which increases high harmonic powers in X-ray band by ~100 times with respect to common FELs.

Luminescence properties of laser-induced silver clusters in borosilicate glass

This paper describes the luminescence properties of small silver clusters formed by laser treatment of silver-doped borosilicate glass. Using irradiation by a Nd:YAG nanosecond laser system operating at the fourth harmonic wavelength (266 nm), areas are formed in the glass samples that emit bright luminescence peaking at about 600 nm when excited by UV light in the spectral range 300–390 nm. The influence is presented and discussed of the glass composition and the laser processing parameters on the emission characteristics. It is further shown that the luminescent properties are affected by the fluence of the excitation source, namely, a complete quenching of the emission is achieved above a certain value. The luminescence of the irradiated areas is explained by the formation of Ag clusters due to irradiation-induced reduction of Ag ions and increased atom mobility resulting from the local heating. The limited stability of the luminescent areas upon UV radiation can be related to heat-induced cluster decomposition and re-oxidation. The results obtained provide a new insight in the optical properties of noble-metal nanostructures and could form the basis of fabrication of complex optical systems and luminescent component used in the study of, e.g., biological systems.

A LIDAR Thomson Scattering System for the Divertor Tokamak Test (DTT) facility

In spite of its very high reliability, LIDAR Thomson Scattering (LIDAR-TS) has so far only been installed on JET. The new Divertor Tokamak Test (DTT) facility at Frascati will be similar in size to JET and thus is clearly suited for a LIDAR-TS system. The proposal here follows the concept of a no vignetting region, which circumvents the need for relative density calibrations and provides much better signals than those on the JET system, particularly at the outer boundary. The scattered spectrum reaches the spectrometer through a train of relay lenses. The spectrometer uses fast MCP-PMTs for detection of the scattered signal. The fast detectors are generally limited to a spectral range below 900 nm. Hence, a laser at a single wavelength slightly below 900 nm would be ideal. Here we investigate using an Nd:YAG laser, emitting simultaneously both the fundamental and the second harmonic wavelength. The expected performance is analyzed in a simulation program, confirming the ability of this choice to cover the full temperature range. The spatial resolution of the system on JET was about 7 cm. For DTT it is possible to improve this value both by using more modern hardware and by deconvoluting the measured signals. Using a commercially available Nd:YAG two wavelength system with 100 ps pulses in combination with 180 ps MCP-PMTs a resolution of less than 4 cm is achieved. Deconvolution works well at the outer boundary of an H-mode plasma. With deconvolution of the spectral channel signals, the effective spatial resolution in this region can be reduced to ∼2 cm.

Third harmonic generation and microscopy, enhanced by a bias harmonic field

We present strong enhancements of the signal yield in third harmonic generation microscopy by seeding the optically nonlinear sample with some intensity at the third harmonic wavelength, in addition to the driving fundamental beam. By applying a third harmonic bias pulse with a power of less then 0.1% of the fundamental beam, we boost the signal yield by more than a factor of 3000, compared to the conventional third harmonic signal from the microscopy sample. The signal enhancement is most pronounced at low laser intensity and/or weak nonlinear susceptibilities. This makes the concept particularly suitable to improve the signal-to-noise ratio from samples with weak signals, e.g., as typical for applications of nonlinear microscopy. Moreover, we demonstrate improved spatial resolution in beam propagation direction by more than an order of magnitude. This exploits the dependence of our approach for enhanced third harmonic generation from inevitable dispersion in the sample. The improvement is most evident in cases, where the sample geometry allows only weak focusing.

Analytical Description of Nonlinear Harmonic Generation Close to the Saturation Region in Free Electron Lasers

The phenomenological modeling of nonlinear harmonic generation in single-pass free electron laser (FEL) experiments was performed. The gradual saturation of the harmonic power and its evolution around the saturated regime was modeled. The model includes all major losses for each harmonic with account for the fact that the undulator radiation (UR) and the electron-wave interaction at higher harmonic wavelengths are more sensitive to the beam energy spread, divergence, and other factors. The results of the phenomenological modeling are compared with the experimental data of the corresponding FELs and with the numerical simulation. The proposed description of nonlinear harmonic generation appears to be in good agreement with the FEL experiments SALCA, LEUTL, LCLS, and others under various conditions. The results also match their numerical simulations; in contrast to the latter, our phenomenological model allows rapid, still, and accurate modeling of the FEL harmonic power and bunching evolution with a PC or even an engineering calculator. The model permits studying FEL radiation from undulators with arbitrary magnetic field configuration. Using the analytical FEL model, we demonstrate that, in contrast to the helical undulator, in whose spectrum the fundamental and the second harmonics prevail, the FEL radiation from the elliptical undulator with the third field harmonic has a distinct fifth UR harmonic as well as the fundamental one, whereas other harmonics can be ignored even close to the saturation length.

In Situ Decoration of Gold Nanoparticles on Graphene Oxide via Nanosecond Laser Ablation for Remarkable Chemical Sensing and Catalysis.

Gold decorated graphene-based nano-hybrids find extensive research interest due to their enhanced chemical catalytic performance and biochemical sensing. The unique physicochemical properties and the very large surface area makes them propitious platform for the rapid buildouts of science and technology. Graphene serves as an outstanding matrix for anchoring numerous nanomaterials because of its atomically thin 2D morphological features. Herein, we have designed a metal-graphene nano-hybrid through pulsed laser ablation. Commercially available graphite powder was employed for the preparation of graphene oxide (GO) using modified Hummers’ method. A solid, thin gold (Au) foil was ablated in an aqueous suspension of GO using second harmonic wavelength (532 nm) of the Nd:YAG laser for immediate generation of the Au-GO nano-hybrid. The synthesis strategy employed here does not entail any detrimental chemical reagents and hence avoids the inclusion of reagent byproducts to the reaction mixture, toxicity, and environmental or chemical contamination. Optical and morphological characterizations were performed to substantiate the successful anchoring of Au nanoparticles (Au NPs) on the GO sheets. Remarkably, these photon-generated nano-hybrids can act as an excellent surface enhanced Raman spectroscopy (SERS) platform for the sensing/detection of the 4-mercaptobenzoic acid (4-MBA) with a very low detection limit of 1 × 10−12 M and preserves better reproducibility also. In addition, these hybrid materials were found to act as an effective catalyst for the reduction of 4-nitrophenol (4-NP). Thus, this is a rapid, mild, efficient and green synthesis approach for the fabrication of active organometallic sensors and catalysts.

Improved second harmonic performance in periodically poled LNOI waveguides through engineering of lateral leakage.

In this contribution, we investigate the impact of lateral leakage for linear and nonlinear optical waveguides in lithium niobate on an insulator (LNOI). Silicon nitride (SiN) loaded and direct patterned lithium niobate cross-sections are investigated. We show that lateral leakage can take place for the TE mode in LNOI ridge waveguides (X-cut lithium niobate), due to the birefringence of the material. This work gives guidelines for designing waveguides in LNOI that do not suffer from the lateral leakage effect. By applying these design considerations, we avoided the lateral leakage effect at the second harmonic wavelength of a nonlinear optical waveguide in LNOI and demonstrate a peak second harmonic generation conversion efficiency of ~1160% W-1cm-2.

Study of laser-induced-plasma parameters for molybdenum targets

Molybdenum targets were irradiated with 2-ns 300-mJ pulses from an Nd:YAG laser at its second harmonic wavelength of 532 nm at a repetition rate of 10 Hz in open air. The radiation emitted from laser-induced plasma from the Mo target in the Local Thermal Equilibrium (LTE) state was analyzed. The temperature of the plasma was calculated using a Boltzmann-plot method. The electron density was determined from the Stark broadening via the comparison of the electron densities of different neutral molybdenum lines (465.5, 498, 517 and 550 nm) with hydrogen Hα-line (656.3 nm). We studied the variation of electron density and electron temperature as a function of μs-delay times and laser fluencies at different distances from the target surface. It was found that the neutral molybdenum lines suffer from self-absorption. The self-absorption changes the values of the electron density and the electron temperature due to the decrease in the line intensity and the increase in the line width and hence leads to the distortion in the line shape. The Mo I lines were corrected against self-absorption and the corrected values of the temperature and the electron density were obtained.

An open-path sensor for simultaneous atmospheric pressure detection of CO and CH4 around 2.33 μm

A compact open-path sensor for simultaneous atmospheric pressure detection of trace gases carbon monoxide (CO) and methane (CH4) has been developed by using a single-mode, distribution feedback (DFB) laser operating at ∼ 2.33 μm. A novel spectral interference eliminating approach based on second harmonic wavelength modulation spectroscopy (WMS) detection technique and an approximation method was adopted to solve the problem of interference between adjacent spectral absorption lines at atmospheric pressure and to increase the detection sensitivity and resolution. The relative concentration error of CO was calculated to be less than +/−3.17%, and the detection limit of 0.58 parts per million by volume (ppmv) for CO and 0.4 ppmv for CH4 was achieved at 1-s averaging time, which proves the effectiveness of the proposed approach. A one-week field continuous measurement was performed to demonstrate the stability of the reported sensor system.