Marcelo David Iturbe-Castillo

Nonlinear common-path interferometer: an image processor

A single-lens optical setup with a nonlinear medium placed in its geometrical focal plane is used to contrast a phase disturbance. This setup blends the robustness of phase-contrast methods with an optical nonlinear intensity-dependent medium and the usefulness of traditional interferometric techniques. We show that the ratio of the total illumination area to the phase-object area determines an adequate phase-disturbance contrast.

Neither Kerr Nor Thermal Nonlinear Response of Dye Doped Liquid Crystal Characterized by the Z-Scan Technique

In the experimental characterization of the nonlinear optical properties of dye-doped liquid crystals by the Z-scan technique with CW lasers it is rather common to assign it a Kerr or thermal nonlinear response. In this work, we demonstrate that neither of them correctly describes all features of the Z-scan obtained in planar samples of methyl red doped 5CB liquid crystal using He-Ne CW illumination, where a strong nonlinear optical response is observed. The Z-scan curves depend strongly on the input polarization of the beam obtaining negative and positive nonlinear response for polarizations parallel and orthogonal to the director vector. We discuss and compare the effect of an additional incoherent linearly-polarized beam and plain heating source on Z-scan experiments. A theoretical model, valid for small and large phase modulation, is proposed based on the assumption that the sample can be considered as a thin lens with a photoinduced focal length dependent on the Gaussian beam radius ω m (where m is an integer), obtaining good agreement with the experimental curves for m = 3, which is neither a Kerr nor thermal nonlinearity.

Multiple beam Michelson-based interferometer

We present a modification to the classic Michelson interferometer that allows the interference of multiple beams with equal amplitude. The proposed architecture presents the same advantages and simplicity as those of a classic Michelson interferometer. The basic unit of the device consists of a beamsplitter and two mirrors arranged as in a Michelson interferometer. To increase the number of interfering beams, the mirrors are replaced by a basic unit. In order to demonstrate the type of interference patterns that can be obtained, we present interferograms corresponding to three to eight interfering beams. The system can be used to optically induce photonic lattices.

Nonlinear phase contrast microscope

Phase contrast microscopy, is a technique that can be used to produce high-contrast images of transparent objects. The technique employs a phase mask, at the object Fourier transform plane, to create a synthetic reference wave that interferes with the object wave at the image plane. However, the fabrication and alignment of these masks is an expensive and delicate process. In this work, we present a nonlinear phase contrast microscope that can be implemented with a conventional optical microscope using a low power CW coherent light source to illuminate the specimen. An intensity dependent refractive index material is used to photoinduce the filter. Therefore, the aligning procedure is greatly simplified. The nonlinear material is a thin cell of dye doped liquid crystal where it is possible to produce a tunable phase delay depending on the incident light intensity, the light polarization, and the temperature. Due to these characteristics the resulting setup is relatively inexpensive, easy to implement, and extremely robust.

Splitting after collision of high-order bright spatial solitons in Kerr media

We study numerically the asymmetric collision of high order bright spatial solitons with a fundamental one. It is demonstrated the splitting of the high-order soliton under some separation distances and angles between the solitons

Analytical expression for the z-scan normalized transmittance of a thin nonlocal nonlinear media

Starting from a phenomenological model which takes into account the nonlocal character of a nonlinear interaction, an analytical expression for the z-scan normalized transmittance of a thin nonlocal nonlinear media was obtained.

Asymmetric collision of two bright spatial solitons in a Kerr media

We study numerically the asymmetric collision of spatial solitons and their waveguide properties. We demonstrated that the amount of energy confined by each waveguide is function of the initial angle and separation between the solitons

Nonlinear refractive and absorptive response of a thin nonlocal media

A model to describe both nonlinear refractive and absorptive response of a thin nonlocal media is proposed. The model is used to obtain the far field intensity of the close or open aperture z-scan technique

Polarization-dependent nonlinear phase contrast by using dye-doped nematic liquid crystals

Nonlinear phase contrast microscopy is an optical technique that uses an intensity-dependent refractive index material to produce high-contrasted images of transparent specimens. Earlier proposal of liquid crystals as phase filters for phase contrast applications used optically addressed spatial light modulators fabricated with photoconductive film. Here, we propose the use of a simpler planar nematic liquid crystal cell doped with 1% wt methyl red. Owing to their polarization dependent enhancement factor a tunable phase filter can be photoinduced efficiently. Thus, images of different degree of contrast (and even contrast reversal) can be obtained either by rotating the polarization vector. All optical real-time imaging of dynamic events can be performed and image processing such as edge enhancement is demonstrated.

General theory for self-healing beams applied to a caustic field

We present a general theory of self-healing beams and demonstrate that caustic optical fields generated by an axicon illuminated with a cylindrical wavefront are self-healing when they are partially obstructed by an opaque object.