Nikolai A. Khilo

Bessel-like beams with z-dependent cone angles.

The conventional means of generating Bessel-Gauss beams by axicons in the laboratory results in the distinct disadvantage of an abrupt change in intensity at the boundary of the non-diffracting region. We outline theoretically and then demonstrate experimentally a concept for the creation of Bessel-like beams that have a z-dependent cone angle, thereby allowing for a far greater quasi non-diffracting propagation region.

Propagation of high-order circularly polarized Bessel beams and vortex generation in uniaxial crystals

We investigate the generation and transformation of Bessel beams through linear and nonlinear optical crystals. We outline the gen- eration of high-order vortices due to propagation of Bessel beams along the optical axis of uniaxial crystals and expand this to the nonlinear regime by outlining a new phase-matching process (full conical phase matching) in second harmonic generation of vector Bessel beams for various sym- metries in uniaxial crystals. We demonstrate the principles experimentally in a uniaxial BBO crystal and find excellent agreement between the ex- perimental and theoretical results. The results imply a coupling of the intrinsic and extrinsic optical angular momentum of the resulting fields, which may have importance in studies involving quantum entanglement of the angular momentum basis of light. C 2011 Society of Photo-Optical Instru-

Intra-cavity generation of Bessel-like beams with longitudinally dependent cone angles

We report on two resonator systems for producing Bessel-like beams with longitudinally dependent cone angles (LDBLBs). Such beams have extended propagation distances as compared to conventional Bessel-Gauss beams, with a far field pattern that is also Bessel-like in structure (i.e. not an annular ring). The first resonator system is based on a lens doublet with spherical aberration, while the second resonator system makes use of intra-cavity axicons and lens. In both cases we show that the LDBLB is the lowest loss fundamental mode of the cavity, and show theoretically the extended propagation distance expected from such beams.

Vortex structure of elongated speckles

A novel type of quasi-nondiffracting (elongated) speckle fields having the vortex structure of individual speckles is investigated. A physical mechanism of forming the elongated vortex fields is established. Two optical schemes for forming such fields are proposed and realized.

Formation of TH- and TE-polarized Bessel light beams at acousto-optic diffraction in anisotropic crystals

The task has been solved of acoustooptic interraction of Bessel light beams (BLB) in uniaxial crystal with plane acoustic wave. The process has been calculated of isotropic scattering of BLBs without change of the polarization state. The diffraction efficiency has been found out, and it has been shown to be closely one hundred percent. The studied acoustooptical process can be taken as a principle of the method of TH- and TE-polarized Bessel light beams obtaining, which differs by the possibility of manipulation in time by the polarization state.

Generation and propagation of high-order Bessel vortices in linear and non-linear crystals

Linear and nonlinear processes of transferring optical singularities from anisotropic crystals onto the wavefront of Bessel light beams (BLBs) are investigated. The generation of high-order vortices at the propagation of BLBs along the optical axes of crystals was studied. Particularly, a nonlinear frequency doubling of Bessel vortices in the conditions of new type synchronism (full conical phase-matching) is considered. This scheme of three-wave interactions of BLBs based on that the spatial frequency cones of BLBs coincide with phase-matching cones of uniaxial crystals. New type of frequency doubling of Bessel vortices has been experimentally realized in uniaxial crystals.

Bessel-like beams with z-dependent cone angles

A new type of Bessel-like optical beams, which is distinguished by the dependence on the cone angle from the longitudinal coordinate, is investigated. Such beams have the properties of Bessel beams (ring-spatial spatial spectrum) as well as Gaussian beams (keeping the transverse profile at any distances). This new type of beams can be obtained in optical system composed of lens axicon doublet and conical lens. An experimental set-up for producing such beams is realized. It is shown that depending on its parameters the scheme allows one to produce z-dependent Bessel-like beams, whose spatial spectra change from Bessel function to shifted Gaussian one. It is establish theoretically and confirmed experimentally that on-axial intensity of z-dependent Bessel-like beam could be higher than that of incident Gaussian beam.

Focusing Bessel Beams by a Lens with Strong Spherical Aberrations

We have carried out the calculation and experimental measurement of the field formed by optical schemes composed of an axicon and lens with strong spherical aberrations. The calculation is performed by the methods of geometrical optics and diffraction integral. A mechanism is revealed, which is responsible for increasing the intensity in the near-axial focus of the doublet. It is shown that the formed bottle beam has a small length and the field at the periphery is of two types: oscillating and smooth ones. The changeover of the field from the bottle beam to a -dependent Bessel beam is traced. The last beam is characterized, in particular, by the Bessel-type structure of its Fourier spectrum.

Investigation of local spatial spectra of Bessel light-beams

The spectrum of spatial frequencies (SFS) of Bessel beams properties emerging at their spatial localization is investigated. The case, when limiting aperture has a circular shape and a center at any distance from the optical axis, was studied. The Bessel beam local SFS was discovered to be radically changing at shifting the localization zone. Namely, a full ring transforms into a light arcs pair and its angular dimensions monotonically decreases as shift growth. The axis orientation of the spectrum maximal intensity coincides with the diaphragm shifting direction. The numerical modeling results agree well with the experiments.

Conical beam -based laser profilometer for testing roller bearings

In the last years the investigations in the area of optics of Bessel and their associated conical beams are being shifted from the domain of scientific research to the one of practical applications. This is appreciably due to new potentialities of the practical use of these light fields, which are not realizable in the framework of traditional optics of Gaussian beams. The spatio-angular properties of conical light beams are optimal to control the form and quality of surfaces close to cylindrical and conical ones. This is related to the fact that a conical light beam enables one to realize the longitudinally uniform illumination at a certain angle. The grazing-incidence geometry of illumination permits one to significantly reduce the speckle noise in the field reflected and to extract, thereby, information on the macroscopic shape of the surfaces. In this work we develop two optical profilometers intended for non-destructive testing of objects having the form close to the cylindrical one. In particular, a new scheme of vibration-proof laser profilometer based on using the superposition of two conical beams is proposed. A laboratory optical setup of the profilometer is designed. The developed device includes two ring diaphragm as a basic element for crating two conical light beams. One of these beams serves as a reference beam and the second - as an object one. As a result, the independent reference arm has been removed and a single-arm scheme has been realized. The conical beams are spatially separated so that one beam illuminates the cylindrical surface and another beam is freely propagates. Due to a single-arm configuration, this profilometer is noted for a high mechanical stability. The experimental testing of the laboratory setup has confirmed this property of the device. The methods of eliminating the systematic errors and the misalignment aberrations are developed. The conical beam - based profilometer applies to controlling various cylindrical and conical samples including the roller bearings. It is shown that the single-arm profilometer is suitable for testing the roller bearings, because it is vibration-proof and also provides an enough measuring accuracy. Besides, this type of profilometers is not time consuming, which allows the online control of bearings.