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Single crystals of pure and various amount of L-lysine doped KDP crystals were grown from aqueous solution. The doping of L-lysine was confirmed by CHN analysis and FT-IR spectroscopy. Powder XRD was carried out to assess the single phase nature of the samples. The effect of doping on thermal stability of the crystals was carried out by TGA and the kinetic and thermodynamic parameters of dehydration were evaluated. It was found that as the amount of doping of amino acid, L-lysine, increased the thermal stability of the grown crystals decreased. However, the second-harmonic generation (SHG) efficiency of Nd:YAG laser and UV-vis spectroscopy studies indicated that as the L-lysine doping increased in KDP crystals the SHG efficiency and optical transmission percentage increased. The dielectric constant and the dielectric loss of L-lysine doped KDP crystals are lower than the pure KDP crystals. Hence L-lysine doped KDP crystals are found to be more beneficial from an application point of view as compared to pure KDP crystals. The results are discussed.

Two major reasons limit porphyrins photonic applications: (i) the difficulty of handling them in liquid solutions and (ii) their degradation with long exposure to light. This necessitates the use of appropriate solid matrices to host the porphyrin compounds such as Nafion (117), a stable and inert ion exchange polymer. The first part of this publication confirms such a possibility. In addition to their effective NLO properties, an enhancement of the Soret and Q-bands' absorbance width have been observed by blending three different porphyrin molecules in the Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. The second part of this contribution reports on the self-assembly/molecular recognition of a specific class of porphyrins giving rise to tubular nano-systems with potential THG nonlinear properties.

The advancement of crystal growth and characterization methods allows us to investigate new substances with excellent nonlinear optical characteristics. To synthesize nonlinear optical material L-histidine hydrochloride hydrate (L-HHCLH), the gradual evaporation process was used. The produced samples were characterized by single-crystal X-ray crystallography, Fourier transform infrared (FTIR) and Raman spectroscopy, UV–visible (UV–Vis) spectroscopy, second harmonic generation (SHG) test, dielectric, and mechanical investigations. The L-HHCLH sample was crystallized in an orthorhombic structure with the P2₁2₁2₁ space group, as verified by the crystallographic data. FTIR and Raman spectroscopy were applied to examine the molecular vibrations and availability of the functional groups of the compound. The L-HHCLH is significantly transparent across the UV and visible ranges, as shown by the UV–Vis spectra measurements. The bandgap of L-HHCLH is 5.45 eV. The SHG test showed that the L-HHCLH crystals produced a significant amount of SHG output thrice that of the potassium dihydrogen phosphate (KDP) sample. The frequency dependences of the dielectric parameters were investigated in the dielectric tests. With increasing frequency, both the dielectric constant and loss dropped exponentially. The crystal hardness was determined using a microhardness test.

2-methylimidazole (2MI) single crystal has been successfully grown by slow evaporation solution technique (SEST) by using water as a solvent. The synthesized 2MI crystal was purified by repetitive recrystallization. Various other characterizations were carried out for the grown 2MI single crystal, such as powder X-ray diffraction (PXRD), FTIR, UV–Visible NIR, Microhardness, Photoluminescence, SEM, Piezoelectric, and SHG. The 2MI crystal was subjected to PXRD to endorse the crystalline quality of the material. The vibrational assignments and their functional groups were identified from the FTIR analysis. The UV–Visible NIR study exposes the transparency and cut-off wavelength of the 2MI crystal. The mechanical strength was investigated by Vickers microhardness tester. The surface investigation of the 2MI crystal was analyzed by a scanning electron microscope technique to obtain the presence of defects and surface texture in the developed 2MI crystal. The photoluminescence spectrum confirmed the green light emission of the crystal. The value of the piezoelectric d${}_{33}$ coefficient is measured using piezoelectric analysis. Kurtz powder’s second harmonic generation test reveals that the frequency conversion efficiency of 2MI is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal.

The development of crystal fabrication and characterization approaches makes it possible to study novel materials with enhanced linear and nonlinear optical properties. The solution growth method was adopted in the present investigation to create Barium thiourea chloride (BTCL), a metal–organic single crystal. Structural, optical, and thermal characteristics of the BTCL crystals were evaluated by XRD analysis, Fourier transform infrared spectroscopy, UV–Vis spectrometry, photoluminescence, SHG, and thermal analyses. The XRD method was applied to investigate the structural characteristics of the BTCL, which is related to the monoclinic structure. The FT-IR spectral investigation was conducted to observe the vibrational modes in BTCL. The optical measurements showed the transmittance in the near-UV and visible spectrums. Optical characteristics include bandgap, refractive index, extinction coefficient, optical, and electrical conductivities, and dielectric constants were obtained. The PL curve showed two notable emission peaks at 482.5nm and 491nm. The ability to generate second harmonics was investigated using the Kurtz and Perry method, and the SHG was more than 1.79 times the KDP sample. The thermal behavior of the BTCL was evaluated by TGA/DTA measurements. The Coats–Redfern relation was used to estimate the activation energy of the thermal system and the value was determined to be 9.48KJ/mol. The findings indicate that the BTCL crystals possess excellent optical transparency, higher SHG potency, and good thermal stability, which are suitable for use in photonic structures.

We have developed a two-photon fluorescence microscope capable of imaging up to 4mm in turbid media with micron resolution. The key feature of this instrument is the innovative detector, capable of collecting emission photons from a wider surface area of the sample than detectors in traditional two-photon microscopes. This detection scheme is extremely efficient in the collection of emitted photons scattered by turbid media which allows eight fold increase in the imaging depth when compared with conventional two-photon microscopes. Furthermore, this system also has in-depth fluorescence lifetime imaging microscopy (FLIM) imaging capability which increases image contrast. The detection scheme captures emission light in a transmission configuration, making it extremely efficient for the detection of second harmonic generation (SHG) signals, which is generally forward propagating. Here we present imaging experiments of tissue phantoms and in vivo and ex vivo biological tissue performed with this microscope.

The cyano and nitro groups were chosen as acceptor groups, and the substituent amino or ether groups as donor groups to the matrix. Polyurethane (PU) was modified by glycerol to increase the content of chromophore and to improve the stability of the nonlinearity. T_g and T_m were raised and solubility, film-forming ability and other physical properties were improved. The average functional groups of the reactant can be adjusted to ≥ 2 with polygroups and monogroups mixture. These poled polymers show high second-order optical nonlinearity and would have potential application in frequency-doubling or electro-optical controlling devices.

Here, we propose a novel plasmonic structure, called asymmetric plasmonic nanocavity grating (APNCG), which is shown to dramatically enhance nonlinear optical process of second harmonic generation (SHG). The proposed structure consists of two different metals on both sides of lithium niobate and a thin layer of graphene. By using two different metals the nonlinear susceptibility of the waveguide would be increased noticeably causing to increase SHG. On the other hand, it consists of two identical gratings on one side. By two identical gratings, the pump beam is coupled to two opposing SPP waves, which interfere with each other and result in SPP standing wave in the region between the two gratings. The distance between two gratings will be optimized to reach the highest SHG. It will be shown that by optimizing the geometry of proposed structure and using different metals, field enhancement in APNCG waveguides can result in large enhancement of SHG.