Journal of Nonlinear Optical Physics & Materials

We relate on a series of optical nonlinear propagation phenomena, mediated by photorefraction, present in ferroelectric crystals heated above the Curie point, in proximity of the critical regime. In particular, we discuss centrosymmetric screening solitons, diffusion-driven anisotropic nonlinear diffraction, ellipticity locking, diffusion-driven solitons, and spatial beam head-on collisions.

Photoluminescence of semiconductor quantum wells is studied using a fully quantized theory for the light-matter interaction. Quantum fluctuations of the light field lead to direct coupling between a coherent excitation and luminescence in other directions. Numerical results for the time evolution of the luminescence spectrum and emission intensity dynamics after a femtosecond pulse excitation are presented.

Several practical all-solid-state tunable ultraviolet subnanosecond laser sources have been developed based on Ce³⁺:LiLuF₄ (Ce:LLF) and Ce³⁺:LiCaAlF₆ (Ce:LiCAF) active media pumped by the fifth and fourth harmonics of a regular Q-switched 10-ns Nd:YAG laser, respectively. The demonstrated tuning range of the Ce:LiCAF oscillator providing reproducibly-single-pulse output was 282 nm to 314 nm with the maximum output energy of 1 mJ. Tunable laser output from 223 nm to 232 nm was obtained by sum-frequency-mixing Ce:LiCAF laser output with fundamental output of a Q-sw Nd:YAG laser. The maximum subnanosecond Ce:LiCAF single-pulse output of 14 mJ was obtained in a "master oscillator-power amplifier" (MOPA) configuration.

Second-harmonic cross-correlation is used to selectively detect the weak contribution remaining coherent with the incident field among the randomly de-phased contributions to an optical field that propagated through a scattering medium. It is shown to allow detection of opaque (reflecting) objects immersed in (located beyond) highly turbid media.

We report significant enhancement of THz radiation from InAs under magnetic field irradiated with femtosecond pulses. The THz-radiation power is significantly enhanced and reaches sub-mW level in a 1.7-T magnetic field with 1.5-W excitation power. The THz-radiation power is related almost quadratically both to the magnetic field and excitation laser power. Furthermore, the radiation spectrum is found to be controlled by the excitation pulsewidth, chirp direction of the excitation pulse, and the magnetic field. Additionally, we have demonstrated a new method to generate THz radiation from a saturable Bragg reflector in a magnetic field.

We present in this article the recent development of the measurement technique for coherent free-space THz field and applications in the mid-infrared range. The technique is based on the second-order nonlinear optical interaction both for the generation and for the detection of THz pulse. Particularly the detection process based on free-space electro-optic sampling gives us a possibility to timely trace directly the ultrabroad band coherent THz field unparalleled by other technique. Using an ultrashort laser pulse our measurement system is feasible to measure the ultrashort THz pulse with a bandwidth up to 40 THz. We present a detailed comparative study on the generation and detection using different nonlinear material. We demonstrate applications of the coherent THz technique for time-resolved semiconductor spectroscopy, time-domain imaging with high spatial resolution and broad band refractive and absorptive characterization of material in the mid-infrared range.

The observation of photorefractive gratings in new crosslinked polymer-stabilized liquid crystals (PSLCs) is discussed and compared to previous PSLCs. The PSLCs easily incorporate reduced or oxidized molecules that are present in a nematic liquid crystal at a concentration of 2 mol%. The PSLCs that are crosslinked provide improved photo-refractive grating resolution, due to their improved functionality as an immobile electron trap. These materials are capable of functioning well into the Bragg diffraction regime. Photoconductivity experiments that support the photorefractive mechanism and a different charge transport mechanism than neat liquid crystals are also performed.

The fundamental physical mechanism responsible for the self-focussing, filamentation, supercontinuum generation and conical emission of a powerful ultrashort laser pulse in a transparent optical medium is reviewed. The propagation can be described by the model of moving focus modified by the defocussing effect of the self-induced plasma through multiphoton interaction with the medium. Spatial and temporal self-phase modulation in both the neutral Kerr medium and the plasma transform the pulse into a chirped (elongated) and strongly deformed pulse both temporally and spatially. The manifestation of the deformation is supercontinuum generation and conical emission. A new phenomenon of refocussing was observed. It is due to the diffraction of the trailing part of the pulse by the plasma that results in a ring structure of positive index changes surrounding the plasma column. This ring structure refocuses the pulse partially. The measured coherence lengths of the various frequencies components of the supercontinuum are independent of the optical media used and are essentially equal to that of the pump laser pulse when compared to an incoherent white light source. We thus justify that such a deformed pulse with a very broad spectrum could be called a chirped white light laser pulse.

In this paper, the progress of the application of photorefractive fiber and waveguide crystal gratings to a narrow band, fast speed, tunable filter is presented. This novel filter is based on tunable Bragg grating. It uses the diffraction effect of Bragg grating to select the wavelength and the electro-optic effect of the grating to tune the effective grating period. Several approaches of fabricating this type of tunable Bragg grating based filter are discussed and some preliminary results are provided. It is shown that the tuning speed of this type of filter can be in the ns range and the bandwidth can be as narrow as 0.01 nm.

We solve by means of the coupled amplitude-phase formulation the derivative nonlinear Schrödinger equation (DNLS) for an optical fiber and we find fundamental soliton solutions in both the anomalous and normal dispersion regimes. Considering the general complex form of the solution it is very simple to see that bright solitons are also possible in the normal dispersion region.

We consider the self-consistent pulses which can propagate in a periodic fiber with alternating linear (β₂≠0, n₂=0) and nonlinear (β₂=0, n₂≠0) sections. The repeating breathing eigen pulse of the wave guide is derived.