Pablo Vaveliuk

Limits of the paraxial approximation in laser beams

The validity of the paraxial approximation for laser beams in free space is studied via an integral criterion based on the propagation invariants of Helmholtz and paraxial wave equations. This approach allows one to determine the paraxial limit for beams with nondefined spot size and for beams described by more parameters in addition to typical longitudinal wavelength and transverse waist. As examples, the paraxiality of higher-order Hermite, Laguerre, and Bessel-Gaussian beams was completely determined. This method could be extended to nonlinear optics and Bose condensates.

Intensity-symmetric Airy beams

Theoretical, numerical, and experimental research on a novel family of Airy beams in rectangular coordinates having a symmetric transverse pattern of light intensity is presented. The intensity-symmetric Airy beams include both the symmetric Airy beam whose field amplitude is an even function of the transverse coordinates and the antisymmetric Airy beam whose field amplitude is an odd function of such coordinates. The theoretical foundations are based on the relationship of the symmetries of the spectral phase with the cosine and sine Fourier transforms. These beams are analyzed in a propagation range also including the region preceding the Fourier plane. These beams exhibit autofocusing, collapse, self-bending, and reversal propagation. Moreover, the intensity distribution is strongly asymmetric with respect to the Fourier plane. All these peculiar features were not reported for other classes of paraxial beams in a rectangular frame. The experimental generation of intensity-symmetric Airy beams is demonstrated supporting the theoretical predictions. Possible applications in planar waveguide writing and optical trapping are also discussed.

Shaping symmetric Airy beam through binary amplitude modulation for ultralong needle focus

Needle-like electromagnetic field has various advantages for the applications in high-resolution imaging, Raman spectroscopy, as well as long-distance optical transportation. The realization of such field often requires high numerical aperture (NA) objective lens and the transmission masks. We demonstrate an ultralong needle-like focus in the optical range produced with an ordinary lens. This is achieved by focusing a symmetric Airy beam (SAB) generated via binary spectral modulation with a digital micromirror device. Such amplitude modulation technique is able to shape traditional Airy beams, SABs, as well as the dynamic transition modes between the one-dimensional and two-dimensional (2D) symmetric Airy modes. The created 2D SAB was characterized through measurement of the propagating fields with one of the four main lobes blocked by an opaque mask. The 2D SAB was verified to exhibit self-healing property against propagation with the obstructed major lobe reconstructed after a certain distance. We further produced an elongated focal line by concentrating the SAB via lenses with different NAs and achieved an ultralong longitudinal needle focus. The produced long needle focus will be applied in optical, chemical, and biological sciences.

Comment on "Degree of paraxiality for monochromatic light beams".

This Comment shows that the parameter called the degree of paraxiality of a monochromatic beam [Opt. Lett.33, 1360 (2008)] was derived using misleading criteria and that the results in that Letter might lack physical meaning.

Squared-field amplitude modulus and radiation intensity nonequivalence within nonlinear slabs.

This paper presents an approach to wave propagation inside the Fabry-Pérot framework. It states that the time-averaged Poynting vector modulus can be nonequivalent to the squared-field amplitude modulus. This fact permits the introduction of a kind of nonlinear medium whose nonlinearity is proportional to the time-averaged Poynting vector modulus. Its transmittance is calculated and found to differ from that obtained for a Kerr medium, whose nonlinearity is proportional to the squared-field amplitude modulus. The latter emphasizes the nonequivalence of these magnitudes. A space-time symmetry analysis shows that the Poynting nonlinearity should be possible only in noncentrosymmetric materials.

Photophysical properties of corrphycenes.

The photophysical properties of the Zn salt of octaethylcorrphycene (compound 1) and the doubly protonated octaethylcorrphycene (compound 2) were determined in benzene solutions. Fluorescence spectra and fluorescence quantum yields of phiF (1) = 0.03+/-0.02 and PF (2) = 0.06+/-0.02 were measured. The triplet-triplet absorption spectra were obtained by means of flash-photolysis experiments. The triplet quantum yield values phiT (1) = 0.79+/-0.08 and phiT (2) = 0.82+/-0.08 were obtained by using laser-induced optoacoustic spectroscopy. The quantum yield of singlet molecular oxygen generation in air-saturated solutions, phidelta (1) = 0.55+/-0.07 and phidelta (2) = 0.38+/-0.05, were also measured using time resolved NIR luminescence.

Caustic beams from unusual powers of the spectral phase

Caustic optical beams arising from a spectral phase whose power lies in an unusual range of values less than two are presented. Unlike what happens for conventional phase powers greater than two, it is feasible to generate caustic structures having properties that do not follow the established sorting. For instance, an asymptotic cusp caustic beam having a cusp point at infinity is demonstrated. For the sake of completeness, the caustic beam properties are analyzed within the whole real range of the phase power. Accurate behavior rules between the symmetries of the beam spectral phase and its intensity distribution are found. These findings strengthen the fundamentals and engineering on caustic beams in diverse optical and physical branches.

Optical transmittance of plane-parallel-faces saturable nonlinear media

The transmittance of saturable nonlinear media under plane-wave excitation is analyzed for a Fabry-Perot geometry. The medium response is studied in terms of both a squared-field amplitude modulus and a time-averaged Poynting vector modulus. It was observed that both cases provide similar transmittance for the parameter range considered. For the nonlinearity proportional to the time-averaged Poynting vector modulus, a simple analytical expression for transmittance is derived as an Airy-type pattern. This allows us to perform a global analysis on the optical properties in terms of the nonlinear parameters and medium thickness. Several types of behavior were found at different parameter regions. Bistability happens only for excitation intensities around the saturation value. Finally, some possible implications of our results for bistable solitons are proposed.

Nonsymmetric curved beams within a symmetric caustic skeleton

Nonsymmetric curved beams having a symmetric caustic skeleton are presented. They arise from a finite jump in the symmetric spectral phase that breaks the symmetry of the beam intensity without altering its associated caustic curve. These nonsymmetric beams can be represented as a superposition of two caustic beams whose wave fields have well-defined even and odd symmetries with weight coefficients dependent on the phase jump. In this approach, the phase jump acts as a measure of the beam asymmetry degree that can be easily controlled in experiments. This scheme is a promising step towards optical cryptography and quantum optics applications.