Wave Mixing Method Research Articles

Detecting Localized Plastic Strain by a Scanning Collinear Wave Mixing Method

When the frequencies of a pair of collinear shear and longitudinal waves satisfy the resonant condition, mixing of these two primary waves generates a third, resonant shear wave that propagates in the direction opposite to the propagating direction of the primary shear wave. In this study, experiments were conducted to demonstrate that the acoustic nonlinearity parameter at the location of the mixing zone can be obtained by measuring the resonant shear wave. Since the location of the mixing zone can be controlled by adjusting the trigger time of the transducers that generate the primary waves, this collinear wave mixing technique enables the scanning of a bar sample to measure the distribution of acoustic nonlinearity along the bar. To demonstrate this scanning capability, bar samples with non-uniform acoustic nonlinearity parameters were fabricated by inducing localized plastic deformation at known locations. Scanning collinear wave mixing tests conducted on such bar samples clearly identified the locations of the plastic zone. These results show that collinear wave mixing is a promising method for scanning the test sample to map out the distribution of localized plastic deformation.

Multi-colour pulses from seeded free-electron-lasers: towards the development of non-linear core-level coherent spectroscopies

We report on new opportunities for ultrafast science thanks to the use of two-colour extreme ultraviolet (XUV) pulses at the FERMI free electron laser (FEL) facility. The two pulses have been employed to carry out a pioneering FEL-pump/FEL-probe diffraction experiment using a Ti target and tuning the FEL pulses to the M(2/3)-edge in order to explore the dependence of the dielectric constant on the excitation fluence. The future impact that the use of such a two-colour FEL emission will have on the development of ultrafast wave-mixing methods in the XUV/soft X-ray range is addressed and discussed.

Noncollinear wave mixing for measurement of dynamic processes in polymers: Physical ageing in thermoplastics and epoxy cure

Elastic wave mixing using an immersion method has shown effective monitoring and scanning capabilities when applied to thermoplastic ageing, epoxy curing, and non-destructive testing. In water, excitation and reception of waves do not require physical contact between the tools and the specimen, making the acquisition of high-resolution C-scans possible. The nonlinear material parameters exhibit a much higher sensitivity to the specimen state compared to linear ones. Thus, the nonlinear data for polymethyl methacrylate (PMMA) have a 40% difference between zones of “young” and “aged” material, while the linear data show no difference at all. Methodology and logistics of the immersion wave-mixing method are discussed in detail. Monitoring of epoxy curing has also revealed a good sensitivity of the method to this complex process including several characteristic stages, such as the time of maximal viscosity, the gel time, and the vitrification time. These stages are independently verified in separate rheometry measurements. The presented method allows for a number of possibilities: wave-mode and frequency separations, elimination of surrounding medium influence, “steering” (scanning) a scattered wave, controlling the location of the intersection volume, single-sided or double-sided measurements, and operation in detector mode.

Optical properties of oxazalone derivatives with and without DNA–CTMA

The oxazalone derivatives were synthesized and their optical properties were studied and the results are presented. Also the complex of DNA with a surfactant CTMA (DNA–CTMA) was also functionalized with the synthesized oxazalone derivatives. The third order nonlinear optical susceptibilities of studied compounds were investigated in solutions using the degenerate four wave mixing (DFWM) method at 532 nm wavelength. We found that the values of third order nonlinear optical susceptibilities ( χ 〈3〉) for oxazalone derivatives with DNA–CTMA are higher than for pure oxazalone derivatives.

Nonlinear Optical Effects in Polymeric Azoesters

The new photochromic polymers based on methacrylic azoesters were synthesized. The azobenzene side chains of obtained polymers contain different groups of both acceptor and donor nature as well as flexible alkyl spacer. The third order nonlinear optical susceptibilities (3) of the studied solutions were measured by degenerating four wave mixing (DFWM) method. As a result, the enhancement of the molecular conjugation and the high NLO chromophore concentration in the molecular chain contribute much to heightening the third-order NLO effect. The electronic effect of the substituent on the azobenzol group and the push–pull electronic structure contributes much to enhancing the NLO property

Fully and Partially Coherent Pathways in Multiply Enhanced Odd-Order Wave-Mixing Spectroscopy

Nuclear magnetic resonance spectroscopy relies on using multiple excitation pulses to create multiple quantum coherences that provide great specificity for chemical measurements. Coherent multidimensional spectroscopy (CMDS) is the optical analogue of NMR. Current CMDS methods use three excitation pulses and phase matching to create zero, single, and double quantum coherences. In order to create higher order multiple quantum coherences, the number of interactions must be increased by raising the excitation intensities high enough to create Rabi frequencies that are comparable to the dephasing rates of vibrational coherences. The higher Rabi frequencies create multiple, odd-order coherence pathways. The coherence pathways that involve intermediate populations are partially coherent and are sensitive to population relaxation effects. Pathways that are fully coherent involve only coherences and measure the direct coupling between excited quantum states. The fully coherent pathways are related to the multiple quantum coherences created in multiple pulse NMR methods such as heteronuclear multiple quantum coherence (HMQC) spectroscopy with the important difference that HMQC NMR methods have a defined number of interactions and avoid dynamic Stark effects whereas the multiply enhanced odd-order wave-mixing pathways do not. The difference arises because CMDS methods use phase matching to define the interactions and at high intensities, multiple pathways obey the same phase matching conditions. The multiple pathways correspond to the pathways created by dynamic Stark effects. This paper uses rhodium dicarbonyl chelate (RDC) as a model to demonstrate the characteristics of multiply enhanced odd-order wave-mixing (MEOW) methods. Dynamic Stark effects excite vibrational ladders on the symmetric and asymmetric CO stretch modes and create a series of multiple quantum coherences and populations using partially and fully coherent pathways. Vibrational quantum states up to v = 6 are excited. A series of spectra provides different two-dimensional cross sections through the multidimensional parameter space involving two excitation frequencies, the frequency of the output coherence, and the excitation pulse time delays. The spectra allow the identification of 18 different overtone and combination band states. Comparison with a local mode model with two anharmonic Morse oscillators with interbond coupling shows excellent agreement.

Asymmetric Energy Transfer in Photorefractive Polymer Composites Under Non-Electric Field

We prepared photorefractive composites using poly(methyl methacrylate) (PMMA) as a host material doped with 3-[(4-Nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzE) as an NLO chromophore. Photorefractive properties were characterized by means of a two beam coupling (2BC) and a degenerated four wave mixing (DFWM) methods performed at 632.8 nm and room temperature. We successfully observed asymmetric 2BC under non-electric field: photorefractive characteristics obtained are a net 2BC gain of 426 cm−1 and a diffraction efficiency of 35%. We could also demonstrate its high performance by DFWM image processing experiment. In order to reduce the glass transition temperature Tg of photorefractive composites we selected poly(ethyl methacrylate) (PEMA) as a host material. Photorefractive properties obtained are a net 2BC gain of 398 cm−1 and a diffraction efficiency of 40%.

Nonlinear Optical Effects In Polymeric Azoesters

The methacrylic monomers containing azobenzene moiety with flexible alkyl spacers of different lengths and groups of different nature are synthesized, and their physicochemical properties were determined by electronic absorption, 1H NMR spectroscopy, and element analysis. In the present work, the homopolymers built with the use of the free radical polymerization of methacrylic monomers incorporating an azobenzene side-group have been synthesized and structurally characterized. The results of photochemical and optical activities of the corresponding polymers are presented. Third-order nonlinear optical (NLO) properties of the azopolymer solutions are studied by the degenerate four wave mixing (DFWM) method.

Non-Electric Field Photorefractive Effect Using Polymer Composites

We prepared photorefractive composites using poly(3,4-ethylenedioxythiophene)-block-polyethylene glycol (PEDOT-block-PEG) as a key material doped with nonlinear optical chromophore ((S)-(-)-l-(4-Nitrophenyl)-2-pyrrolidinemethanol (NPP). To adjust the optical absorbancc PMMA was used as a matrix. Photorefractive properties were characterized by means of a two beam coupling (2BC) method and a degenerated four wave mixing (DFWM) method. We successfully observed asymmetric 2BC under non-electric field: Photorefractive characteristics obtained are a net 2BC gain of 175 cm−1, a diffraction efficiency of 49%, and a phase shift of 90°. Furthermore, we could demonstrate its high performance by DFWM image processing experiment.

Dependence of the Third Order Nonlinear Optical Susceptibility on Concentration and Peripheral Substituent of Metallophthalocyanines

Third order nonlinear optical properties of metallophthalocyanines (MPcs) were investigated using degenerate four wave mixing (DFWM) method. We also studied how the replacement of peripheral substituent around the MPcs cores correlates with nonlinear optical properties. Therefore third order nonlinear optical susceptibilities (χ<3>) of MPcs with liquid crystal (MPcs-LC) were investigated. We found that the χ<3> values of MPcs-LC increase in comparison with the corresponding values of MPcs. We supposed that this is caused by the increase of the charge transfer effects and change of the dipole moments of the molecule with the increase of molecules dimension.

New Methacrylic Oxazolone and Thiazolidinone Containing Polymers for Nonlinear OpticalApplications

Oxazalone and thiazolidinone derivatives were synthesized and their physicochemical properties are determined by absorption, HNMR spectroscopies. The third order nonlinear optical properties of oxazolone and thiazolidinone containing compounds were investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.

Nonlinear optical properties of thiazolidinone derivatives

Thiazolidinone derivatives were synthesized and their physicochemical properties are determined by absorption, H NMR spectroscopies. The third order nonlinear optical properties of thiazolidinone containing compounds were investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.

Nonlinear optical properties of Zn 1− xMg xSe and Cd 1− xMg xSe crystals

Nonlinear optical properties of Zn 1− x Mg x Se and Cd 1− x Mg x Se crystals have been studied using degenerate four wave mixing (DFWM), nonlinear transmission (NLT), second harmonic generation (SHG) and third harmonic generation (THG) methods by Nd:YAG laser operating at 532 nm and 1064 nm, respectively. The studied Zn 1− x Mg x Se and Cd 1− x Mg x Se crystals were grown from the melt by the modified high-pressure Bridgman method. The quadratic nonlinear optical properties of ternary crystals were investigated by second harmonic generation (SHG) technique. We found that the highest value of the second order nonlinear optical susceptibility was obtained for Cd 0.7Mg 0.3Se. In the case of cubic nonlinear optical properties we used third harmonic generation (THG) and degenerate four wave mixing (DFWM) methods. We found that the values of third order nonlinear optical susceptibility for Cd 1− x Mg x Se crystals are higher than for Zn 1− x Mg x Se ones.

Synthesis, polymerization ability, nonlinear optical properties of methacrylic monomers and polymers with benzylidene moiety

New methacrylic monomers, their polymers with benzylidene fragment were synthesized. Structures of all compounds were determined by HNMR, UV- spectroscopies. The third order nonlinear optical properties of oxazolone, thiazolidinone and thiohydantoin containing compounds were investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.

Synthesis and study of nonlinear optical properties of oxazolone containing polymers

The oxazolone derivatives were synthesized and their structures determined by UV- and H NMR-spectroscopies. The polymerization was carried out in DMF with AIBN as initiator. The products of polymerization were characterized by H NMR. The third-order nonlinear optical properties of oxazolone containing compounds have been investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.

Organic Photorefractive Composites Based on PEDOT-co-PEG

We prepared photorefractive composites using poly(3,4-ethylenedioxythiophene)-co-poly(ethyleneglycol) (PEDOT-co-PEG) as a key material doped with nonlinear optical chromophore (Coumarin 6). To adjust the optical absorbance PMMA was used as a matrix. Photorefractive properties were characterized by means of a two beam coupling (2BC) method and a degenerated four wave mixing (DFWM) method. We obtained a net 2BC gain of 146 cm−1, a diffraction efficiency of 9 %, a phase shift of 70° for PMMA/ PEDOT-co-PEG/ Coumarin 6/composite (Sample 2). These results were dramatically larger than traditional polyvinylcarbazole (PVCz) matrix systems.

Investigation of crystal structure and nonlinear optical properties of 2-methoxyanilinium nitrate

Single crystals of a new hybrid compound salt: 2-methoxyanilinium nitrate were prepared by slow evaporation at room temperature of diluted aqueous solutions containing 2-methoxyaniline with nitric acids. The compound crystallizes in a space group Pcab of orthorhombic system with cell parameters a=8.8784 (6) Å, b=10.6348 (7) Å, c=18.3045 (7) Å, V=1728.31 (17) Å3 at T=100 K and Z=8. The structure has been refined to an R-value of 0.044 for 1956 observed reflections using three-dimensional X-ray diffraction data. Third-order nonlinear optical susceptibility (χ〈3〉) was measured by degenerate four wave mixing (DFWM) method at 532nm. Third harmonic generation (THG) measurements at the 1064nm were carried out for the 2-methoxyanilinium nitrate crystal with the following dimensions: 4×9×0.5mm.

Influence of the central metal atom on the nonlinear optical properties of MPcs solutions and thin films

Third order nonlinear optical susceptibility ( χ 〈3〉) of metallophthalocyanines (MPcs, where M = Co, Cu, Zn, Mg) thin films and solutions was investigated by standard backward degenerate four wave mixing (DFWM) method at 532 nm. Third harmonic generation (THG) measurement at 1064 nm performed on MPcs thin films is also discussed. MPcs thin films were grown by conventional thermal evaporation in high vacuum and solution were dissolved in tetrahydrofuran (THF), in which the studied materials are soluble. In the case of microscopic nonlinearity, we calculated the second order hyperpolarizability ( γ) for MPcs solutions. We found that the χ 〈3〉 and the γ values are affected by the nature of the central metal atom. We also found that the χ DFWM 〈 3 〉 value is larger than that measured via THG experiment. The variation in χ 〈3〉 values occurs due to the different resonance contributions.

Multifunctional Block Copolymers for Organic Photorefractive Materials

Photorefractive active block copolymers were successfully synthesized via an atom transfer radical polymerization of acrylate containing liquid crystalline moiety and hole transporting carbazole moiety. Resulting copolymers were characterized by gel permeation chromatography, NMR, and DSC. Copolymers afforded the transparent films showing birefringent nature. Photorefractive characteristics of copolymers with 2 wt% of trinitro- fluorenone as a photosensitizer were investigated by four wave mixing and two-beam coupling methods with a He-Ne laser. For the block copolymer, higher diffraction efficiency and larger coupling gain were observed compared with the corresponding statistical random copolymer.

Structure and non-linear optical performance of TeO 2–Nb 2O 5–ZnO glasses

The non-linear optical performance and structure of TeO 2–Nb 2O 5–ZnO glasses was investigated as a function of ZnO content. The third-order non-linear optical susceptibility ( χ (3)) as measured by a Degenerate Four Wave Mixing (DFWM) method, initially increased with increasing ZnO content to about 8.2 × 10 −13 esu for a glass containing 2.5 wt% ZnO, and then decreased to 5.9 × 10 −13 esu as the ZnO content increased to 10 wt%. There was no noticeable change as the ZnO content increased from 10 to 15 wt%. The non-linear optical response time, which caused electron cloud deformation, was from 450 to 500 fs. The structure of these glasses as analyzed by Raman spectroscopy and FT-IR spectra, was affected by the addition of ZnO up to 5 wt%, when, it is believed, the Zn 2+ ions occupied the interstitial positions in the glass network by replacing the Nb 5+ ions. The replaced Nb 5+ ions occupied the network forming positions as the Te 4+ ions. Increasing ZnO > 5 wt% did not have any further effect on the glass structure.