Journal of Nonlinear Optical Physics & Materials

The recent theoretical predictions and experimental observations of discrete surface solitons propagating along the interface between a one- or two-dimensional continuous medium and a one- or two-dimensional waveguide array are reviewed. These discrete solitons were found in second order (periodically poled lithium niobate) and third order nonlinear media, including AlGaAs, photorefractive media and glass, respectively.

We have reviewed mechanisms for the efficient conversion of the broadband terahertz (THz) pulses from ultrafast laser pulses propagating in semiconductor electro-optic materials. By measuring the behaviors of the THz output versus the pump beam in terms of incident angle, polarization, and azimuthal angle, we have demonstrated that we can precisely determine the contributions made by optical rectification and photocurrent surge. When a material is pumped below its bandgap, optical rectification is always the mechanism for the THz generation. Above the bandgap, however, these two mechanisms often compete with each other, depending on the material characteristics and pump intensity. At a sufficiently high pump intensity, optical rectification usually becomes the dominant mechanism for a second-order nonlinear material. Our analysis indicates that second-order nonlinear coefficients can be resonantly enhanced when a material is pumped above its bandgap. In such a case, the THz output power and normalized conversion efficiency can be greatly enhanced. We have also analyzed how the THz generation is affected by some competing processes such as two-photon absorption.

In this paper, we review our recent work on broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy in supercontinuum optical trap.

Cholesteric liquid crystals (CLCs) which possess a periodicity in the visible portion of the spectra, exhibit selective reflection of circularly polarized light. The ability to modulate this color through a variety of means has been explored, including work which incorporated azobenzene LCs. Two types of systems have recently been explored utilizing wavelength-specific cis-trans isomerization processes, which enable unprecedented photosensitivity. The first system exhibits large blue or red-shifted changes in reflection wavelength upon visible irradiation. The second system exploits the metastable, long-lived photoinduced isotropic state, whose return to the reflective Grandjean texture can be induced by wavelength-specific radiation. We demonstrate nonlinear transmission from both types of systems, starting with submicrowatt power levels and spanning over four orders of magnitude dynamic range. The power dependence and temporal evolution of this effect (10–100 ms) is documented here for red or green laser wavelengths. The effect for the former case is due to bandgap auto-tuning, when the laser beam is tuning the CLC Bragg reflection band to its own wavelength. For the latter case, autonomous, optical feedback due to bandgap restoration is the cause of the nonlinear transmission properties.

The four-wave mixing (FWM) effect in a so-called left-handed material (LHM) with a third-order nonlinear response is studied. The theoretical models for the wavelength conversion (WC) and parametric amplification (PA) based on the FWM in the LHM are established when the signal falls in the frequency range of backward or forward wave. Analytical formulas for the WC efficiency and PA gain are derived. The influences of the pump powers, the phase mismatch, and the interaction length on the performances of the WC and PA are analyzed. The phase-match dependence of the performance is reduced by carefully controlling the pump powers.

High quality unintentionally doped n-type GaN layers were grown on Si (111) substrate using AlN (about 200 nm) as buffer layer by radio frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (MBE). This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as-grown GaN. Metal–semiconductor–metal (MSM) photodiode was fabricated on the samples. For as-grown GaN-based MSM, the detector shows a sharp cut-off wavelength at 362 nm, with a maximum responsivity of 0.254 A/W achieved at 360 nm. For porous GaN MSM detector, a sharp cut-off wavelength at 360 nm with a maximum responsivity of 0.655 A/W was achieved at 359 nm. Both the detectors show a little decrease in responsivity in the UV spectral region. The MSM photodiode based on porous GaN shows enhanced (2×) magnitude of responsivity relative to the as-grown GaN MSM photodiode. Enhancement of responsivity can be attributed to the relaxation of tensile stress and reduction of surface pit density in the porous sample.

N,N′-bis(5-bromosalicylidene)propane-1,2-diamine-O,O′,N,N′)-manganese(III) chloride transition metal complex has been synthesized and characterized by elemental analysis and UV-vis spectroscopy. Its crystal structure has been determined using X-ray diffraction analysis. To provide an insight into the optical limiting (OL) behavior of the title compound, the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of the time-dependent Hartree–Fock (TDHF), AM1 and configuration interaction (CI) methods, respectively. According to ab initio calculation results, the examined molecule exhibits second hyperpolarizabilities (γ) with non-zero values at the positions of TPA peaks, implying microscopic third-order optical nonlinearity. The maximum OPA wavelengths recorded by linear optical experiment and quantum mechanical computations are estimated in the UV region to be shorter than 400 nm, showing good optical transparency to the visible light. The TPA cross-sections (δ(ω)) at values indicate that the synthesized compound might possess OL phenomena, which are in accord with the experimental observations on the manganese complexes in the literature.

The polarized spectra of the intensity and gain of the amplified spontaneous emission (ASE) have been measured for two glycerin solutions of a laser dye Rhodamine-640 (RhA and RhB with concentrations of 3 × 10^-4 and 3 × 10^-3 M/L, respectively). The solutions were pumped by the linearly polarized light. The ASE polarization ratio r strongly depends on the pump pulse energy, which is continuously increasing up to one for RhA and saturating at the level of r ≈ 0.8 for RhB. The gain spectra have been measured by variation of the amplification length for ASE. With increasing pump beam energy, the maximum gain continuously grows for RhA and saturates for RhB, reaching the values of 14–15 and 6 cm^-1 for both materials for the polarization parallel to the pump beam polarization. At a particular spectral point, the gain coefficient has also been measured by the direct amplification of the probe beam of a microlaser on a cholesteric liquid crystal.

The dispersion of nanoparticles in a nematic liquid crystal host medium provides an efficient way of designing tunable optical metamaterials that respond from the visible to the Terahertz and microwave regime. As studied in this article, these systems exhibit much larger birefringence than the nematic host and possess sub-unity, zero, and even negative refractive indices with unique reflection and transmission properties. These tunable optical metamaterials will enable a wide range of application possibilities in next-generation reflective, transmissive, modulation and switching elements and devices.