Peigen Ni

Second-harmonic generation in two-dimensional periodically poled lithium niobate using second-order quasiphase matching

Two-dimensional nonlinear photonic crystals of lithium niobate with square lattices were fabricated. In these crystals, efficient quasiphase-matched second-harmonic generation was demonstrated by using second-order quasiphase matching. As a mode-locked Nd:yttritium–aluminum–garnet laser at 1064 nm with 35 ps pulse was used, we obtained an average power of 0.86 mW at 532 nm with 2.73 mW input, which corresponds to 42% internal conversion efficiency. The variations of second-harmonic output with crystal temperature and incident angle were measured. In addition, the relation between the second-harmonic output and reversed duty cycle was studied. All the experimental results are well consistent with simulations.

More direct evidence of the fcc arrangement for artificial opal

We present a scanning electron microscopy (SEM) investigation of artificial opals prepared by the sedimentation of suspension with sub-micrometer silica spheres. An analysis of the SEM images confirms that the fcc stacking is the most stable phase for the artificial crystals. Optical diffraction and transmission spectrum indicate a good alignment of the top (111) crystal plane. We also show that defects and dislocations of opal crystals are caused mainly by the irregular spheres. Slow sedimentation and uniform size of silica spheres may be the key factors for growing high quality opal crystals.

Quasiphase matched harmonic generation in a two-dimensional octagonal photonic superlattice

We have fabricated LiNbO3 nonlinear photonic crystals with a two-dimensional octagonal quasilattice. The effective collinear quasiphase matched second-harmonic orange and green lights, with conversion efficiencies of ∼38% and 23%, were realized. The noncollinear harmonic processes at multiple wavelengths were also observed with the conversion efficiency of around 5%. All the-same results can be obtained when the crystal is rotated by the integral multiples of π∕4.

Inverse opal with an ultraviolet photonic gap

Photonic crystals composed of TiO2 and air voids fabricated by the template method exhibit an ultraviolet photonic stop band (∼380 nm) in the Γ–L direction. Scanning electron microscopy images show that the inverse opal possesses face-centered-cubic symmetry with a lattice constant of 240 nm. The transmission spectra show that the change in transmittance is one order of magnitude in the gap, which is in accord with the reflection spectrum.

Transmission modulation in the passband of polystyrene photonic crystals

The periodic disturbance in transmittance of polystyrene photonic crystal is detected in our experiment. The peak-to-peak intervals of the periodic disturbance vary with the wavelength. It is attributed to the propagation of the whispering gallery mode in polystyrene spheres. The results show that the periodically arrayed particles may affect light transfer outside the gap band, which implies the possibility in applications of photonic crystal films.

Preparation of higher-quality SiO2 opals using a new submicrospheres selection technique

Monodisperse colloidal SiO2 submicrospheres were prepared by hydrolysis and condensation of tetraethoxysilane. We measured various relative settle velocities of different aggregated submicrospheres and then developed a submicrospheres selection technique separating single spheres from aggregated spheres. Monodispersity Of SiO2 submicrospheres was improved by this submicrospheres selection technique. Higher-quality SiO2 opals were fabricated from selected submicrospheres., (C) 2002 Elsevier Science B.V. All rights reserved.

Multi-color coherent radiation in a two-dimensional nonlinear photonic crystal with rectangular lattices

The temperature dependence of the magnetic field-induced strain (MFIS) and the field-controlled shape memory effect in Ni52Mn16.4Fe8Ga23.6 single crystals were investigated by measuring the MFIS and measuring the magnetic field-enhanced transformation strain with a field bias applied in the [001] and [010] directions of the parent phase, respectively. The results show that such material combined with the martensitic transformation can product large field-enhanced transformation strain and large MFIS. The strain accompanying the martensitic transformation is -1.61% in zero field and can be enhanced to -3.30% by a field of 960 kA/m. A MFIS of 1.04% has been induced along [001] in unstressed crystals with saturated magnetic field of 600 Win applied along the same direction at near martensitic transformation temperature. It was found that the MFIS is almost temperature independent; the maximum decrease of the saturated MFIS is less than 10%, from 265 K to 100 K. This well-behaved temperature response makes this alloy particularly valuable for industrial and military smart actuators and transducers. Furthermore, it was found that the direction in which the MFIS has the largest value is always the [001], namely, the growth direction of the crystals.

Effect of Different Quasi-Phase Matchings in Two-Dimensional Nonlinear Photonic Crystal

The second-harmonic generations (SHGs) of nanosecond pulses using first- and second-order quasi-phase matching (QPM) were realized in a two-dimensional periodically poled LiNbO3 with square lattice. Maximum conversion efficiency of 35% and 14% was achieved respectively at the fundamental wavelengths of 1.352 µm and 1.064 µm. In addition, the SHG of 1.064 µm picosecond laser using second-order QPM was also studied in this crystal. Based on the comparison between the SHGs excited by nanosecond and picosecond pulses, it may be concluded that if second-order QPM is used, the incident laser with higher peak power is necessary.

Silica Colloidal Crystals with Ethanol Solvent

We have prepared a silica colloidal crystal with ethanol, which has a face-centered cubic structure and a corresponding photonic band gap located in the visible region, determined by Kossel ring analysis and the transmission spectra. A special feature is an apparent variation of its lattice constant, as well as the gap frequency, with sample height. The Raman scattering induced by a picosecond laser at different heights of the colloidal crystal has been measured. It is found that the intensity of the Raman scattering is not related sensitively to the photonic gap, even though the Raman-Stokes wavelength is inside the gap.

Intensity-invariable Raman scattering in an ethanol-silica photonic crystal with a varying pseudogap

We have measured the Raman scattering intensities, which are induced by a picosecond intense laser, of an ethanol-silica photonic crystal (ESPC) with a pseudogap varying with the height (up from the inner bottom of the cuvette) of the ESPC. We find that, although the center wavelength of Raman signals (RSs) generated within the ESPC is almost in the pseudogap, the total intensity of the RSs is not reduced relative to the total intensity generated at other positions. It is also found that, although the transmission of an incident beam with the wavelength of the RSs is greatly dependent on the height of the ESPC, the intensity of the RSs generated within the ESPC does not change with this height. Both anti-intuitive phenomena, we think, can be demonstrated using the different propagation mechanisms between the incidental laser and inner light sources inside a PC.