Nonlinear Nanocrystals Research Articles

Anisotropic PCL nanofibers embedded with nonlinear nanocrystals as strong generators of polarized second harmonic light and piezoelectric currents.

Using the electrospinning technique nanofibers consisting of organic nonlinear optical 3-nitroaniline (3NA, C6H6N2O2) nanocrystals embedded in poly-ε-caprolactone (PCL) polymer, 3NA@PCL nanofibers, were produced. Polarimetry optical second harmonic generation and X-ray diffraction studies show that 3NA push–pull molecules crystallize inside the polymer fibers with a strong preferential orientation giving rise to an alignment of the molecular dipole moments along the nanofibers longitudinal axis. This alignment strongly enhances the second order nonlinear optical response of the fibers. Intense second harmonic generation emission was observed from a single nanofiber, corresponding to an effective second order susceptibility of 80 pm V−1, four times greater than the largest second order susceptibility tensor element (21 pm V−1) associated with a macroscopic 3NA crystal. Moreover, when subjected to a modest periodically applied force of 3 N, a piezoelectric current of 70 nA generated by a 4 cm2 electrospun nanofiber mat amounted to 122 nW cm−2 of instantaneous density power, sufficient to power a LCD display. The results show that the electrospinning technique is a powerful technique to fabricate organic functional materials with oriented nanocrystals made of highly polarizable molecules, embedded in a polymer matrix.

Synthesis and properties of new infrared nonlinear optical Li2Ga2GeS6 crystal

IR Li 2 Ga 2 GeS 6 nonlinear crystals were directly obtained with the composition of 40GeS 2 - 30Ga 2 S 3 -30Li 2 S, by the conventional melt-quenching method. The high depth digital image indicated that the obtained Li 2 Ga 2 GeS 6 crystals showed a big size of 0.3 × 0.25 × 0.3 mm 3 . It was shown that the compound was very susceptive to H 2 O with second harmonic observation. Besides, the glass-forming region of GeS 2 -Ga 2 S 3 - Li 2 S system was further studied by the conventional melt-quenching method.GeS 2 -Ga 2 S 3 -Li 2 S glass-ceramics containing IR Li 2 Ga 2 GeS 6 nonlinear nanocrystals were obtained at a more carefully controlled heating rate.

Large third-order optical nonlinearity of ZnO–Bi2O3–B2O3 glass–ceramic containing Bi2ZnB2O7 nanocrystals

Homogeneous transparent optical glass–ceramics precipitated with unique nonlinear crystals are promising materials for photonic applications. We have utilized heat treatment method to prepare transparent ZnO–Bi 2 O 3 –B 2 O 3 glass–ceramic containing Bi 2 ZnB 2 O 7 nonlinear nanocrystals. A large third-order nonlinear susceptibility χ (3) of glass–ceramic is measured by Z-scan technique, which mainly attributed to unique [BiO 6 ] and [B 2 O 5 ] units in Bi 2 ZnB 2 O 7 crystal structure and the quantum size effect of nanoparticles. The discovery is of great potential in the application of nonlinear optical integrated devices.

IR Li2Ga2GeS6 nanocrystallized GeS2-Ga2S3-Li2S electroconductive chalcogenide glass with good nonlinearity.

GeS2-Ga2S3-Li2S electroconductive glasses were prepared by the conventional melt-quenching method through carefully controlling the heating rate. Comparing with the reference of glass-forming region, our investigated GeS2-Ga2S3-Li2S system was extended to the cation ratio of 0–20% Li with around 40% Ga. GeS2-Ga2S3-Li2S glass-ceramics containing IR Li2Ga2GeS6 nonlinear nanocrystals were obtained by the more carefully controlled heating rate. Its optical nonlinearity was investigated by the Maker fringe measurements, the maximum second harmonic intensity was observed to be 0.35 of the reference Z-cut quartz. IR Li2Ga2GeS6 nonlinear crystals were directly obtained at the composition of 40GeS2-30GaS1.5-30LiS0.5.

Selectively addressing optically nonlinear nanocrystals by polarization-shaped ultrafast laser pulses

A noncentrosymmetric nanocrystal can produce second-harmonic generation (SHG) and sum-frequency generation (SFG) upon interaction with a laser field. The SHG or SFG radiation depends on the orientation of the nanocrystal as well as the field polarization, which allows for modulating the second-order emission of an arbitrarily oriented nanocrystal by specially tailoring the field polarization. We theoretically study SHG and SFG signals produced by nanocrystals driven with broad-bandwidth laser pulses. Several simulations explore the influence of the field polarization and temporal pulse profile. The latter two factors are decoupled in their influence upon the SHG and SFG signals, and thus polarization and temporal shaping can be independently performed to modulate a nanocrystals’ second-order emission. We consider the possibility of enhancing (suppressing) the signal from one nanocrystal among others by choosing the appropriate polarization, thereby opening up the prospect of selectively addressing optically nonlinear nanocrystals.

New optical tools used for characterization of phase transitions in nonlinear nano-crystals. Exampleof Yb3+-doped BaTiO3

The main objective of this paper is to focus on the use of new techniques to specifically characterizeBaTiO3 nonlinear nano-crystals as a test case. We use the second harmonicgeneration (SHG) of an IR YAG:Nd pump laser and detection of theYb3+ ion pairs to investigate effect of doping and synthesis route (sol–gel between 700 and1200 °C)on both crystallite sizes (25–60 nm) and different phase symmetries (tetragonal, cubic, hexagonal) inYb3+-dopedBaTiO3. In nano-crystals, a higher intensity of SHG was observed in the acentrictetragonal phase, whereas the isotropic cubic phase was detected by theabsence of a SHG signal. Cooperative emission, indicating the presence ofYb3+ ion pairs, was easily detected in the cubic phase and not seen in the ferroelectric tetragonalstructure.

Second-harmonic and sum-frequency imaging of organic nanocrystals with photon scanning tunneling microscope

Second-harmonic generation and sum-frequency generation with photon scanning tunneling microscopy and shear-force detection are used to map the nonlinear optical response and the surface topograph of N-(4-nitrophenyl)-(L)-prolinol crystals with a subdiffraction-limited resolution. The domain-size dependence of the spatial feature is obtained, which shows the local orientational distribution of the optical near field radiated by nonlinear nanocrystals and reveals the difference between nanoscopic and macroscopic second-order optical nonlinearities of molecular crystals.