Bessel Light Beams Research Articles

Formation of Bessel light beams with a subwavelength diameter of the axial maximum for diagnostics and nonlinear photolithography of semiconductor materials

Formation of Bessel light beams with a subwavelength diameter of the axial maximum for diagnostics and nonlinear photolithography of semiconductor materials

Bessel light beam for a surgical laser focusing telescope-a novel approach.

As the demand for CO[Formula: see text] laser surgeries continues to grow, the quality of their main instrument, the laser micromanipulator, becomes increasingly important. However, in many surgery systems, a large ratio of the laser power is wasted due to the reflection from the mirror of a telescopic system, like a Cassegrain telescope, back to the laser side, which not only decreases the system's efficiency but can also damage the system itself. In this article, we introduce a new design of the micromanipulator telescope for CO[Formula: see text] laser surgery, which employs a Bessel beam to improve the system efficiency. As in the propagation of a Bessel beam, the power of the light beam can be transferred from the center to a ring shape, the whole power reflected from the first mirror can reach the second mirror and no power goes back to the second mirror hole. The micromanipulator telescope design and optimization are carried out using Zemax Optics Studio, and the integration of the Bessel beam into the system is implemented using MATLAB. Our simulation results show that by applying the appropriate Bessel beam, the system efficiency can reach more than 96%, and the normalized peak irradiance can increase by 40 to 73% for various working distances. In addition to increasing the system efficiency and normalized peak irradiance, resulting in a sharper surgical blade, the use of the Bessel beam enhances the depth of focus, making the system less sensitive to depth misalignment.

Influence of the Nonideality of the Axicon and Input Gaussian Beam on the Quality Parameters and Fourier Spectrum of the Generated Bessel Light Beam

Influence of the Nonideality of the Axicon and Input Gaussian Beam on the Quality Parameters and Fourier Spectrum of the Generated Bessel Light Beam

Cross polarization in Gaussian and Bessel light beams

Cross Polarization is explicitly obtained in the two cases Gaussian and Bessel light beams using the elegant Mukunda–Simon–Sudarshan rule for transition from scalar optics to vector wave optics. Unlike other studies, we obtain the results without solving the Maxwell equations.

The formation of Bessel light beams at large distances from annular fields

In this work, the process of transformation of an annular beam in a Bessel-like field due to diffraction during propagation in a free space over long distances and due to the focusing effect is investigated. A number of models of annular fields are considered, including an analytical model in the form of a polynomial function in a bounded region of space, as well as an experimentally implemented model based on a scheme with two axicons. A comparison is made of the transverse and longitudinal intensity distributions for these models, and a high degree of stability of the structure of the longitudinal distribution of the axial intensity to a change in the model of the annular field is found. This distribution is characterized by the presence of an intense maximum with an asymmetric profile, the appearance of which is not connected with lens focusing. In the initial region of the pointed maximum, the process of formation of a Bessel beam from an annular beam arises, and a sharp increase in intensity takes place. It is also established that the focusing of an annular field at large distances essentially differs from focusing at short distances. In the case of large distances, the increase of the axial intensity does not take place in the vicinity of the focal plane, but much closer to the transmitter, and here the great increase of intensity caused by direct focusing is not identified. The transverse profile of a Bessel-like beam is calculated at large distances. It is shown that this profile is characterized by a small number of lateral rings, and the axial maximum and the first ring contain more than 90% of the light power. The problem of generation of a model annular field by a Fourier-type resonator with a special transparency mirror is considered.

Determination of the Bessel light beam cone parameter by Fourier analysis of the diametral distribution of the intensity

Power spectral density (PSD) of the intensity distribution of an ideal Bessel light beam (BLB) expressions are obtained. It is shown that the PSD of the intensity distribution of an ideal BLB is limited and the upper boundary of the PSD is equal to the doubled cone parameter (the product of the wave number and the sine of the half angle of the cone of wave vectors), and the number of zeros in the PSD of an ideal BLB located in the interval from zero frequency to the upper boundary of the spectrum, is equal to the order of the beam. A technique is proposed for estimating the cone parameter of BLBs by analysing the PSD estimates of diametral distributions – one-dimensional intensity distributions obtained in the transverse plane of the beam along a line passing through the beam axis from transverse two-dimensional BLB intensity distributions recorded in the form of digital computer images. The influence of clipping (the end of the distribution at the boundary of the sensitive sensor), Gaussian and cosine modulations of the diametral distribution on the shape of the spectrum and, in case of clipping, the error in the cone parameter estimation using the proposed method is investigated. The technique is tested on the example of the analysis of experimental BLBs of different orders (BLBm, m = 0, 1, 2). The proposed technique can be used to assess the quality parameters of the BLB. The results of the analysis of the influence of cosine modulation on the shape of the PSD can be used to assess the magnitude of the rounding of the apex of the axicon forming the BLB for control the quality of the axicon manufacturing.

Forming of Bessel beams from annular fields on large distances

Bessel light beam formation from annular fields is important for many applications related to laser remote sensing and also for the free-space laser communication. Annular beams have a few advantages, such as optimal combination with optical projectors based on mirror telescopes, self-healing property after passing around obstacles including stability in the atmospheric turbulence in some cases, and also large focal range. In the paper a process of annular beam transformation into a Bessel-type field by the free-space propagation diffraction is investigated. The transverse Bessel beam profile at large propagation distances is calculated. It is shown that the profile contains small number of rings, the on-axis maximum and the first ring contain more than 90% of light power.

Collinear acousto-optical filtration of polychromatic Bessel light beams in lithium niobate crystals

The features of collinear acousto - optical filtration of quasi - diffractive Bessel light beams of o- and e-type in uniaxial crystals are investigated. Using the method of overlap integrals, an expression is found for the diffraction efficiency depending on the parameters of the acousto-optical interaction, as well as on the values of the overlap integrals. It is shown that for the zero-order mode of a Bessel light beam for a lithium niobate crystal under conditions of transverse phase synchronism and in the optical spectrum range of 0.4-0.7 μm, the filter bandwidth of ∼0.2 nm is achievable; with an increase in the order of the mode m≥1, the increase in the bandwidth is insignificant and is ∼0.23 -0.24 nm.

Triple Bragg Diffraction of Bessel Light Beams by Ultrasound in Uniaxial Crystals

Triple Bragg Diffraction of Bessel Light Beams by Ultrasound in Uniaxial Crystals

Bessel-like light beams formed by the two-component scheme consisting of an axicon and a spherical lens

The combination in an optical scheme of rather different elements such as axicons and spherical lenses allows forming light fields that differ by a variety of properties. The simplest example of such a scheme consists of an axicon and a spherical lens spatially separated from it. Though this scheme was investigated earlier, the region of so-called secondary focusing located behind the well-known annular focus has not been studied yet. In this paper, the analytical and numerical analysis of a light field in the region of secondary focusing is conducted. The boundaries of this region are determined, and the longitudinal and transverse distribution of the light intensity is calculated. It is shown that the near field region of secondary focusing is formed in the regime of abrupt autofocusing of the annular field. It is established that in a general case the transverse intensity distribution in the far field region is a superposition of an annular field and an oscillating axialtype field. The distance between the axicon and the lens is determined when the annular component of the field practically disappears. It is shown that in this case the light field in the region of the secondary focusing is a locally Bessel light beam. The peculiarity of this beam is that its cone angle depends on the longitudinal component, namely, decreases in inverse proportion while the distance z increases. The important feature of such z-dependent Bessel beams is the absence of their transformation into annular fields, as it occurs for ordinary Bessel or Bessel-Gaussian beams in the far field region. This opens the prospect for application of z-dependent Bessel beams for optical communication in free space and remote probing, which is why such beams are perspective for application in different systems of remote probing.

Is laser repetition rate important for two-photon light sheet microscopy?

We demonstrate the thermal advantages of using low repetition rate, high peak power lasers for imaging in two-photon light sheet microscopy using a Bessel light beam. We compare the use of two ultrashort pulsed lasers in such an imaging system: a high repetition rate source operating at 80 MHz and a low repetition rate source operating at 1 MHz. The low repetition rate laser requires approximately one order of magnitude lower average power than the high repetition rate source to yield the same fluorescent signal. These lasers are used to image Zebrafish larvae and record their heart rates. The data show heart rate values 30% in excess of the ground truth baseline value when imaged with the high repetition rate source due to deleterious heating, whereas the low repetition rate source yields data only a few percent above this ground truth value.

Manifestation of extremely high-Q pseudo-modes in scattering of a Bessel light beam by a sphere

The exact analytical solution of Maxwell equations for a Bessel light beam scattered by a sphere is found. Scattered power, stored energy, and a generalized Q factor as a function of frequency, the sphere radius, permittivity, and the Bessel beam angle are found. On the basis of this solution, modes and pseudo-modes of a dielectric sphere are extracted by calculation of the generalized Q factor. It is shown that an appropriate choice of Bessel beam parameters can provide excitation of a single given mode and an unlimited value of the radiative Q factor of pseudo-modes.

Photopolymerization with high-order Bessel light beams.

We study photopolymerization with high-order Bessel light beams with phase singularities on-axis. Self-trapping and self-focusing of propagation-invariant light beams in a photopolymer allow the fabrication of extended helical microfibers with a length scale of a centimeter, which is more than an order of magnitude larger than the propagation distance of the Bessel light beams. We show the evolution of microfibers rotating at a rate proportional to the incident optical power, while the periodicity of the helical structures remains constant, irrespective of the laser power. This suggests that optical momentum transfer plays a predominant role in the growth and rotation of such fiber structures.

Photothermal Transformation of Bessel Light Beams in Periodically Polarized Nonlinear Crystals

A mechanism of the formation of a photodeflection response in a periodically polarized nonlinear crystal illuminated by a Bessel light beam (BLB) is considered. The thermal-field distribution is found, and the exact solution of the system of heat-conduction equations is obtained using the Fourier–Bessel and Laplace integral transforms for a three-layer system consisting of a nonlinear crystal, a substrate, and environment. A method for controlling the amplitude of the photodeflection signal is proposed based on the application of axicons with an adjustable taper angle or optical schemes providing a change in the conicity of BLBs.

Formation of two-dimensional photopolymer diffractive optical elements for converting light beams with two-beam interactions taken into account

Bessel light beams are used in many fields, such as nonlinear optics, optical metrology, design of atmospheric wireless telecommunication lines, nanoscale objects manipulating, etc. Bessel beams do not diffract, they have restoration properties, they retain high intensity in the axial region at large distances. Thus, the search for an affordable method of forming such beams seems very relevant. In this paper, we study the process of two-dimensional diffractive optical elements (DOEs) holographic formation in photopolymer materials (PPM) with allowance for two-beam interactions. DOEs is intended for converting light beams with a Gaussian distribution into a Bessel-like ones.

Some features of acousto-optic interaction of optical and acoustic Bessel beams in transversely isotropic optically positive crystals

Some basic properties of acousto-optical (AO) diffraction involving Bessel light and acoustic beams in anisotropic crystals are investigated. Hexagonal symmetry crystals are considered and are optically uniaxial and positive and acoustically transversely isotropic. It is shown that, unlike the case of AO diffraction of plane waves, the transition to Bessel beams allows one to realize a number of new diffraction channels having specific configurations of the wave vectors of interacting waves while maintaining the axial symmetry of the optical scheme as a whole. The diffraction channels for anisotropic scattering are classified and the main parameters of the scattered Bessel light beam and the parameters of the Bessel acoustic beam are calculated for each of them. The possibility of implementing the isotropic-type diffraction was revealed, which makes it possible to increase the efficiency of AO conversion. The parameters of this-type diffraction are determined for two scattering channels, namely, for scattering by a direct Bessel acoustic beam and by a backward propagating acoustic beam.Due to the appearance of a set of scattering channels and with regard to the fact that Bessel light and acoustic beams have helical wave front dislocations, as well as suppressed diffraction spreading, the study of the features of AO diffraction of such beams in optically positive crystals has both a scientific and practical interest.

Peculiarities of the acousto-optical interactions of Bessel light beams in crystals

The noncollinear acousto-optical filtration of diffracted Bessel light beams in uniaxial paratellurite crystals has been investigated. With the use of the method of overlap integrals it is shown that independently on the order of Bessel light beams in the conditions of transverse phase-matching of diffracted waves in the range of optical spectrum of 0.4-1.1 nm in paratellurite crystals the bandwidth of transmission of ∼0.52 nm is reached due to detuning from Bragg’s synchronism only. It is shown that in uniaxial gyrotropic crystals polarization-independent diffraction of Bessel light beams is possible, i.e. Bragg diffraction efficiency is independent of the polarization state of the incident beam. It has been stated that the physical reason of such diffraction is simultaneous realization of two processes of anisotropic scattering under which the Bragg synchronism conditions are realized for the orthogonally polarized elliptical Bessel beams.

Transformation of Evanescent Bessel Light Beams into Propagating Quasi-Nondiffracting Beams in Epsilon-Near-Zero Hyperbolic Metamaterials

In this paper, we show the possibility of rebuilding of the structure of wave vector surface and the appearance of its local parts with near zero curvature for epsilon-near-zero hyperbolic metamaterials. It is established that when evanescent Bessel light beam falls in special directions related to these local parts, it is transformed into propagating one. The features of transformed beam are analyzed.

Double Bragg Diffraction of Bessel Light Beams on Ultrasound in Uniaxial Gyrotropic Crystals

Noncollinear double acousto-optical diffraction of Bessel light beams on ultrasound in uniaxial gyrotropic crystals is studied theoretically and experimentally. It is found that when a Bessel light beam propagates along the optic axis of a crystal, the diffracted light beams of the ±1 order are symmetric relative to the incident beam and have roughly the same intensity. Double Bragg diffraction is also observed when a Bessel light beam is incident at the Bragg angle and near the optic axis, but the intensities of the +1 and +2 order diffracted beams are significantly different.

Noncollinear Acousto-Optic Filtering of Polychromatic Bessel Light Beams in Uniaxial Crystals

We have studied the features of noncollinear acousto-optic filtering of quasi-nondiffracting Bessel light beams in uniaxial crystals. We have obtained coupled wave equations for the vector amplitudes of an incident ordinary (o-type) Bessel beam and an extraordinary (e-type) diffracted beam for different modes. We have found an expression for the diffraction efficiency as a function of the parameters of interacting ordinary and extraordinary Bessel beams, and also as a function of the values of the overlap integrals. Using the overlap integral method, we have shown that regardless of the mode order for the Bessel light beam, under transverse phase matching conditions for ordinary and extraordinary diffracted Bessel beams in the optical spectral range 0.4–1.1 μm we can achieve a filter transmission bandwidth of ~0.6 nm in paratellurite crystals .