Periodic domain-inversion of lithium niobate without a planar inverted layer

The spatial distribution of the second harmonic generation (SHG) efficiency of a high-average-power laser in a large-aperture potassium dihydrogen phosphate (KDP) crystal under spatially non-uniform deformation is investigated. A theoretical model is developed to investigate the SHG efficiency distribution based on local deformation at each position within the crystal aperture. The areas corresponding to different SHG efficiency intervals are calculated, and the calculation accuracy is analyzed through a case study. The results demonstrate that non-uniform deformation of the KDP crystal induces spatial non-uniformity in the SHG efficiency through deformation-induced incidence angle variations affecting phase mismatch, and the efficiency distribution is primarily governed by spatial variations in the deformation. This study provides a novel approach to investigate the dependence of SHG efficiency distribution on non-uniform deformation in large-aperture nonlinear optical crystals.

The effect of pressure to ∼90 kbar has been measured on the second harmonic generation (SHG) efficiency for the monoclinic crystals 4-aminobenzophenone (ABP), 4-Br-4'-methoxychalcone (BMC), and 2-methyl-4-nitroaniline (MNA). In ABP and BMC the SHG efficiency increases by 2−3 orders of magnitude with some dependence on orientation. The results can be explained qualitatively in terms of a decrease in Δk, the mismatch between the coupled fields, i.e., by pressure tuning of Δk. Powdered samples give much smaller increases in SHG efficiency but a clearer indication of first-order phase transitions, probably between point groups of the monoclinic structure. MNA crystal exhibits a very sharp increase in SHG efficiency by a factor ∼20 at pressures below 10 kbar. At pressures above ∼30 kbar self-absorption by the sample becomes dominant.

Motivated by the need to increase the second harmonic generation (SHG) efficiency of nonlinear optics with large apertures, a novel mounting configuration with active adjusting function on the SHG efficiency is proposed and mechanically and optically studied. The adjusting effects of the mounting force on the distortion and stress are analyzed by the finite element methods (FEM), as well as the contribution of the distortion and stress to the change in phase mismatch, and the SHG efficiency are theoretically stated. Further on, the SHG efficiency is calculated as a function of the mounting force. The changing trends of the distortion, stress, and the SHG efficiency with the varying mounting force are obtained, and the optimal ones are figured out. Moreover, the mechanism of the occurrence of the optimal values is studied and the adjusting strategy is put forward. Numerical results show the robust adjustment of the mounting force, as well as the effectiveness of the mounting configuration, in increasing the SHG efficiency.

Exploring a photonic quasi-crystal fiber for enhancing the efficiency of second harmonic generation: Modeling and analysis

Crystal growth is an important branch of solid state physics and material science. The Growth of Nonlinear Optical (NLO) materials crystals receives much importance nowadays because NLO materials have various applications in modern technologies like Laser technology, optoelectronics, and fiber optics, etc. Potassium dihydrogen phosphate (KDP) is a well known nonlinear optical (NLO) material with different applications. Since most of the amino acids exhibit NLO property, it is of interest to dope them in KDP. In the present study, amino acid L-Phenylalanine doped KDP crystals have been grown by slow evaporation solution growth technique. In present study powder XRD analysis was carried out which show that pure and L-Phenylalanine doped KDP crystals have tetragonal symmetry. The doping of L-Phenylalanine was confirmed by FT-IR and paper chromatography. Thermal analysis has been performed on the grown crystals.The SHG efficiency of L-Phenylalanine doped KDP crystals was found to be increasing with a doping concentration of L-Phenylalanine. Introduction. The demand for high quality large size KDP single crystal increases due to its application as frequency conversion crystal in inertial confinement fusion [1, 2]. KDP belongs to scalenohedral (twelve faced) class of tetragonal crystal system [3]. With the aim of improving the second harmonic generation (SHG) efficiency of KDP, researchers have attempted to modify KDP crystals by doping different types of impurities. The non-linear optical (NLO) and other properties of the crystal have been improved by doping of organic impurities [4-9]. KDP doped with amino acids like L-glutamine acid, L-gistidine, and L-valine was reported [10]. Kumaresan et al. [11] has reported the thermal dielectric properties of amino acids such as L-glutamic acid, L-histidine and L-valine doped KDP crystals. They found improved NLO properties of the KDP crystal and modifications in the structural, optical, mechanical, and electrical properties, too. Parikh [12] has reported the SHG efficiency of L-arginine doped KDP crystal. Kumaresan et al. [13] has also reported the effect of metal ion and amino acid doping on the optical properties of KDP crystal. Muley et al. [5] has studied thermal, NLO properties of KDP crystal doped with L-arginine and L-alanine. Suresh Kumar and Rajendrababu [6] studied the effects of L-arginine, L-histidine and glycine on the growth of KDP single crystals and observed that addition of amino acid enhances transparency, thermal stability and NLO efficiency of KDP crystals. Amino acid family crystals are playing an important role in the field of non-linear optical organic molecular crystal. Among them L-Phenylalanine (LPA) with chemical formula (C6H5CH2CH(NH2)COOH) is the α-amino acid with a non-reactive hydrophobic benzyl side chain. The physical, chemical and non-linear optical properties of KDP are enhanced by adding optically active amino acids as dopants.The growth and characterization of Single crystals of KDP doped with amino acids namely glycine, arginine, alanine, tryptophan, histidine have been reported earlier [5-8]. In the present work, single crystals of Potassium dihydrogen phosphate (KDP) added

Multiphoton microscopy (MPM) has become an important tool for high-resolution and non-invasive imaging in biological tissues. However, the efficiencies of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) are relatively low because of their nonlinear nature. Therefore, it is critical to optimize laser parameters for most efficient excitation of MPM. Reducing the pulse duration can increase the peak intensity of excitation and thus potentially increase the excitation efficiency. In this paper, a multiphoton microscopy system using a 12 fs Ti:Sapphire laser is reported. With adjustable dispersion pre-compensation, the pulse duration at the sample location can be varied from 400 fs to sub-20 fs. The efficiencies of TPEF and SHG are studied for the various pulse durations, respectively. Both TPEF and SHG are found to increase proportionally to the inverse of the pulse duration for the entire tested range. To transmit most of the SHG and TPEF signals, the spectral transmission widow of the detection optics needs to be carefully considered. Limitation from phase-matching in SHG generation is not significant because the effective interaction length for SHG is less than 10 μm at the focal depth of the objectives. These results are important in improving MPM excitation efficiency using ultrashort pulses. MPM images from human artery wall are also demonstrated.

\Ve present a new heterodyne technique for detecting weak signals beyond the standard shot-noise limit by employingamplitude-squeezed light as the local oscillator (LO) field. The amplitude-squeezed LO field at 428.8 nm is generated from ahighly efficient (up to 60% conversion efficiency) single-pass second-harmonic generation in a nonlinear crystal (KNbO3)pumped by femtosecond (130 fs) pulses at 857.7 nm. The weak signal field is introduced from the entrance port ofthe crystalto combine with the generated squeezed LO field. An enhancement of 0.7 dB (1.4 dB inferred) in signal-to-noise ratiobeyond the shot-noise limit is directly observed for this new heterodyne detection scheme. Practical applications of proposedtechnique in laser radar systems are discussed.Keywords: second harmonic generation, squeezed light 1. INTRODUCTION Second harmonic generation (SHG) is one of the nonlinear frequency conversion methods used as a means to extend coherentlight sources to shorter wavelengths. Having at the input of the nonlinear medium a fundamental field at a given frequency(no, one can obtain a field at doubled frequency 2wo with a quite high conversion efficiency, especially in case of pulse lasersbeing used as the fundamental field for pumping. The efficiency of the SHG conversion process is dependent on suchparameters as the input pump power, traveled distance inside the nonlinear medium, and the values of the medium's nonlinearcoefficients.i When one considers SHG from ultrashort pulses (such as pulse widths below half of a picosecond) in certainnonlinear media (such as KNbO3) processes like group velocity dispersion have to be taken into account.2One of the attractive features of SHG is the resulting suppression of the amplitude noise of the generated light. Amplitude-squeezed states of light have less quantum fluctuations in photon numbers of the light field than those of the coherent field(such as lasers).3 Unlike squeezed vacuum states of light, amplitude squeezed states of light can have intense optical power4,which allows direct replacement of coherent lasers in precision optical measurements where quantum shot-noise associatedwith the laser field needs to be suppressed.It has been observed that the degree of squeezing is proportional to the efficiency of SHG process,56 where the efficiency isdefined as the ratio of the generated second-harmonic light power to the input fundamental power. Therefore, configurationsof highly efficient SHG processes are very desirable for the generation of squeezed light. Using short pulse laser to pumpSHG process has a main advantage, which is the gain of its high peak power. Since the input power is one of the parametersthat the efficiency of SHG depends on, the high peak intensities that can be reached in short laser pulses contribute to theachievement of high conversion efficiencies in the nonlinear crystal. Recently, single-pass traveling-wave (TW) SHG hasbeen proposed and experimentally demonstrated in a bulk crystal7 and in quasi-phase-matched nonlinear waveguide8.Conversion efficiencies up to 60% were obtained in the experiments with nonlinear waveguides, and O.35-dB squeezing inthe generated second harmonic light was observed. We have shown that conversion efficiencies higher than 60% andamplitude squeezing of more than 1.0 dB could be obtained in a conceptually simple system of type I TW SHG in a bulkcrystal .

Non‐covalent interactions [Te‐‐‐X (X=Cl, Br, I, O, S)], secondary bonds, and C‐H‐‐‐X (X=O, I) hydrogen bonds induced supramolecular associations of organotelluriums have been synthesised and X‐ray characterised. The immediate coordination geometry around a central tellurium atom is a pseudotrigonal bipyramidal with a stereochemically active electron lone pair. Tetraorganotelluroxanes, charge transfer (CT) complexes and bis (ferrocenyl carboxylato) telluranes, possibly useful in material science, have been synthesised and X‐ray characterised. Select organotellurium derivatives have been tested for their second harmonic generation (SHG) efficiency. Cyclic voltammetric studies of ferrocenyl carboxylato derivatives show that they may be useful for two‐electron redox catalysis.

Effect of Co-60 gamma radiation on optical, dielectric and mechanical properties of strontium L-ascorbate hexahydrate NLO crystal

Synthesis, growth, structural, spectroscopic, crystalline perfection, second harmonic generation (SHG) and thermal studies of 2-aminopyridinium picrate (2APP): A new nonlinear optical material

Quasi-phase-matched (QPM) LiNbO3 waveguides are at present the most efficient device for second-harmonic- generation (SHG). They require the periodic inversion of the ferroelectric domains and the fabrication of annealed- proton-exchanged (APE) waveguides. In order to work at a wavelength of interest for telecommunications, 1300nm, we realized an APE waveguide, single-mode at such wavelength, on a periodically-poled substrate with a period of 11.7 micrometers . Domain inversion was obtained by Ti-indiffusion. The sample was linearly characterized. For the nonlinear experiment, a tunable Nd:YAG-pumped OPA was used as the light source. The maximum efficiency for SHG was found around 1300nm, within a few nanometers from the expected wavelength. The ratio among the output power of the second harmonic and of the fundamental guided mode was 56 percent. Together with the SH, the third harmonic was generated as the result of a (chi) 2 cascading process. On the basis of the result obtained, the problems connected with the design and fabrication of QPM devices will be discussed, with particular attention to the tolerance sin waveguide fabrication. It is worth noting that the two wavelengths were generated simultaneously, using a single laser source. This opens the possibility of generating multicolor output in diode-pumped QPM-waveguides.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We theoretically investigate second-harmonic generation (SHG) efficiency in a waveguide-side-coupled photonic nanocavity using coupled-mode-theory-based equations. Using an additional condition for the critical input power, we investigated SHG efficiencies at a very low input power and the critical power. At a very low input power, the SHG efficiency is enhanced by the increase in various Q factors for fundamental and SHG light. Conversely, the maximum SHG efficiency at the critical input power is determined by the Q factors for fundamental light and increases up to 50% in a waveguide-side-coupled photonic nanocavity. Our results provide a design rule for waveguide-side-coupled photonic nanocavities for developing highly efficient SHG devices.

Strategic improvement of second and third harmonic generation in multifunctional Cu-Sn-S3 ternary semiconducting thin films

The introduction of chirality into organic–inorganic hybrid perovskites (OIHPs) is expected to achieve excellent photoelectric and nonlinear materials related to circular dichroism. Owing to the existence of asymmetric center and intrinsic chirality in the chiral OIHPs, the different efficiencies of second harmonic generation (SHG) signal occurs when the circularly polarized light (CPL) with different phases passes through the chiral crystal, which is defined as second harmonic generation circular dichroism (SHG‐CD). Here, the SHG‐CD effect is developed in bulk single crystals of chiral one‐dimensional (1D) [(R/S)‐3‐aminopiperidine]PbI4. It is the first time that CPL is distinguished using chirality‐dependent SHG‐CD effect in OIHPs bulk single crystals. Such SHG‐CD technology extends the detection range to near infrared region (NIR). In this way, the anisotropy factor (gSHG‐CD) through SHG‐CD signal is as high as 0.21.

In this paper, noise characteristics of second-harmonic generation (SHG) in periodically poled lithium niobate (PPLN) using the quasi-phase-matching (QPM) technique are studied experimentally. In the experiment, a 0.78-mm second-harmonic (SH) wave was generated when a 1.55-mm fundamental wave passed through a PPLN crystal (bulk or annealed proton-exchanged waveguide). The fundamental and SH waves were then separated through a beam splitter and sent to two photodetectors, respectively. The time-domain and frequency-domain characteristics of the fundamental and SH waves were analyzed. By using the pump-probe method, the noise characteristics were studied further when 532-nm irradiation light co-propagated with the 1.55-mm fundamental light in the PPLN crystals. It is found that for the bulk and waveguides of PPLN crystals, the SH wave has a higher relative noise level than the corresponding fundamental wave. For the same fundamental wave, the SH wave has lower noise in a bulk crystal than in a waveguide, and in MgO-doped PPLN than in undoped PPLN. In addition, the photorefractive effect incurred by the irradiation light can influence the SHG noise.