Position dispersion and optical limiting resulting from thermally induced nonlinearities in Chinese tea liquid

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Self-action of continuous laser radiation and Pearcey diffraction in a water suspension with light-absorbing particles

Water suspension of light-absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities favorable for optical treatment of organic and biological objects. We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the incident light, here being strongly sensitive to the medium position with respect to the focus. This technique, based on the complex spatial structure of both the incident and the diffracted fields, can be employed for the detection and measurement of weak non-linearities.

Wavelength dependent studies of nonlinear absorption in zinc meso-tetra(p-methoxyphenyl)tetrabenzoporphyrin (Znmp TBP) using Z-scan technique

We report here, our experimental results and theoretical analysis of the dispersion data of nonlinear absorption in zinc meso-tetra-(p-methoxyphenyl)tetrabenzoporphyrin (ZnmpTBP). Using a ns optical parametric oscillator (OPO) we obtain the open aperture Z-scan data over the visible region starting from 480 nm to 600 nm. We use a more general five-level model for evaluating the excited state parameters like excited state absorption coefficients, two-photon absorption coefficient, etc. Due to its large excited state absorption cross-sections this material acts as a very good candidate for a broadband optical limiter in the visible region.

Active chromatic control on the group velocity of light at arbitrary wavelength in benzocyclobutene polymer

A novel method is proposed to generate slow and fast lights at arbitrary signal wavelength in benzocyclobutene (BCB) polymer, which eliminates the requirement on the optical nonlinearity or the resonant effect at the signal wavelength with the help of the thermo-optic nonlinear effect induced by a control beam at a different but fixed wavelength. The signal group velocity can be precisely tuned simply by scanning the position of the BCB sample along the light propagation direction. Another advantage is the ability to control chromatically the group velocity of the signal beam by adjusting the control beam in the BCB sample, which, in essence, is to control the refractive index change experienced by the signal beam. This method provides an active chromatic control on the group velocity of light at arbitrary signal wavelength and therefore may have important potential applications in optical communication network and optical information processing.

High-efficiency multipass optical limiter

We report experimental results on a highly efficient optical limiter that uses a three-mirror, multipass ring configuration. The optical limiter's enhanced performance is based on the accumulative effect that is achieved when the laser beam passes through the sample several consecutive times. Its feasibility was demonstrated for media with different limiting action processes, namely, reverse saturable absorption, nonlinear scattering, and thermal lensing. We employed a frequency-doubled, Q-switched, 10-ns Nd:YAG laser operating at a 5-Hz repetition rate.

Nonlinear optical beam propagation for optical limiting

We implement numerical modeling of high-energy laser-pulse propagation through bulk nonlinear optical materials using focused beams. An executable program with a graphical user interface is made available to researchers for modeling the propagation of beams through materials much thicker than the diffraction length (up to 10(3) times longer). Ultrafast nonlinearities of the bound-electronic Kerr effect and two-photon absorption as well as time-dependent excited-state and thermal nonlinearities are taken into account. The hydrodynamic equations describing the rarefaction of the medium that is due to heating are solved to determine thermal index changes for nanosecond laser pulses. We also show how this effect can be simplified in some cases by an approximation that assumes instantaneous expansion (so-called thermal lensing approximation). Comparisons of numerical results with several Z-scan, optical limiting and beam distortion experiments are presented. Possible application to optimization of a passive optical limiter design is discussed.

Formation of steady-state cylindrical thermal lenses in dark stripes

Characteristic features of the formation of cylindrical laser-induced thermal steady-state lenses in the dark stripes associated with spatial dark-soliton propagation are analyzed and verified experimentally in an ethanol-dye solution. Positive focusing power perpendicular to the dark stripe is ensured by defocusing along the axis of this stripe and depends strongly on the shape of the light-beam profile and the orientation of the dark stripe within it.

Ray matrix for Gaussian beam propagation in a nonlinear medium: experimental results

The validity of a ray-matrix formulation of Gaussian beam propagation in a liquid nonlinear medium exhibiting self-defocusing is examined experimentally. By comparing the measured spot size of a Gaussian laser beam passing through the medium with the calculated spot size, it was found that the theory is consistent with the experimental results as long as the waist position of the input beam is not close to the exit surface of the medium.

Analysis of beam propagation in thick nonlinear media

We present a theoretical analysis of beam propagation in thick nonlinear media by using the Gaussian decomposition method and considering a thick medium as a stack of thin media. Simple analytic solutions of Z-scan characteristics and optical limiting with thick nonlinear media are obtained. Comparisons of these results with those obtained by use of a distributed-lens model and Gaussian-Laguerre mode decomposition are made. Good agreement is obtained with a distributed-lens model.

Ultrafast transient Kerr lens in solution detected by the dual-beam thermal-lens method

Time profiles of a transient lens on a subpicosecond time scale are observed by use of a dual-beam thermal-lens configuration. On this time scale and under nonresonant conditions the transient lens is composed mainly of the Kerr response. The electronic and nuclear responses are clearly separated by the polarization selection.