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Intensity distributions in various transverse cross sections of a Bessel beam formed using a curveddgroove DBR laser.
Source publication
Broad-stripe edge-emitting semiconductor lasers have been used to obtain propagation-invariant (nondiffracting) light beams
with powers and diameters of the central ray acceptable for optical manipulation and tweezing. The results of investigations
of the propagation of Bessel beams generated from broad-stripe lasers with spectrally selective reson...
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Citations
... The Bessel beam can be effectively used for optical imaging [3], particle trapping and manipulation [4], terahertz photonics [5], material processing [6], and high-contrast light sheet microscopy [7]. Following demonstrations of Bessel beam generation by semiconductor lasers and LEDs [8,9], the possibility of their practical application has grown significantly. ...
We theoretically investigate droplet quasi-Bessel beams for different shapes of the round-tip axicon. Exact solutions for the Fresnel diffraction integrals describing the axial distribution of the electric field amplitude behind the axicon are demonstrated. The analysis of the exact solutions shows that the period of “light droplets” is not a constant value, but depends on the axial distance and on the deviation of the axicon surface from the conical shape far from the rounded region. The predicted effect can be applied for the reconstruction of the exact shape of the axicon surface without 3D scanning.
... The Bessel beam can be effectively used for optical imaging [3], particle trapping and manipulation [4], terahertz photonics [5], material processing [6], and high-contrast light sheet microscopy [7]. Following demonstrations of Bessel beam generation by semiconductor lasers and LEDs [8,9], the possibility of their practical application has grown significantly. ...
We theoretically investigate droplet quasi-Bessel beams for different shapes of the round-tip axicon. Exact solutions for the Fresnel diffraction integrals describing the axial distribution of the electric field amplitude behind the axicon are demonstrated. The analysis of the exact solutions shows that the period of {\guillemotleft}light droplets{\guillemotright} is not a constant value, but depends on the axial distance and on the deviation of the axicon surface from the conical shape far from the rounded region. The predicted effect can be applied for the reconstruction of the exact shape of the axicon surface without 3D scanning.
... Quasi-Bessel beams formed in this way can be effectively used to capture and manipulate microscopic objects [3], to implement optical visualization [4], to process materials [5], in light sheet microscopy [6] and THz photonics [7]. The possibilities of their practical use become considerably wider after the quasi-Bessel beam generation using semiconductor lasers and LEDs was demonstrated [8,9]. ...
We demonstrate the experimental study of the axial intensity distribution of a quasi-Bessel beam with a droplet structure of the central core, formed by an axicon with the round-tip, and the results of the theoretical calculations. We show that the period of droplet quasi-Bessel beam is determined by the shape of the surface rounding and the angle at the top of the axicon lens and depends on the distance to it. The analysis of this dependence makes it possible to restore the shape of the round-tip of the axicon without 3D scanning. Keywords: bessel beams, axicon, droplet beams.
... Формируемые таким образом квазибесселевы пучки могут быть эффективно использованы для захвата и манипулирования микрообъектами [3], оптической визуализации [4], обработки материалов [5], микроскопии плоскостного освещения [6] и терагерцевой фотоники [7]. Возможности их практического использования значительно расширились после демонстрации генерации квазибесселевых пучков при помощи полупроводниковых лазеров и светодиодов [8,9]. ...
We demonstrate the experimental study of the axial intensity distribution of a quasi-Bessel beam with a droplet structure of the central core, formed by an axicon with the round-tip, and the results of the theoretical calculations. We show that the period of ‘droplet’ quasi-Bessel beam is determined by the shape of the surface rounding and the angle at the top of the axicon lens and depends on the distance to it. The analysis of this dependence makes it possible to restore the shape of the round-tip of the axicon without 3D scanning.
... In the cross section, a Bessel beam is a bright spot surrounded by rings the intensities of which are described by the Bessel function of the first kind zero order. The cross-sectional size of such a spot can be considerably smaller than that using traditional focusing [4,7]. The Bessel beam also has the property of self-restoration upon encountering an obstacle [8]. ...
A method for generation of droplet quasi-Bessel beams using a conical lens with a rounded tip is demonstrated. The study of the longitudinal distribution of the intensity of the obtained quasi-Bessel beam showed that, due to the interference of two wavefronts that occurred as the generating beam passed through the rounded axicon, periodical intensity pulsations that looked like “drops” of light occurred in the resulting beam. These light beams can be used for micromanipulation of biological objects and in super-resolution microscopy. The application of an axicon with a rounded tip for generation of a droplet beam allows considerable simplification and miniaturization of the experimental setup, which paves the way for multiple practical applications.
... However, application of the laser diodes to the optical trapping is hindered by the low spatial quality of their beams [6] resulting in the high beam propagation parameter M 2 . The impact of the high M 2 values on the optical trap must be taken into account even for super-focused [7], non-diverging [8][9][10], and self-focused [11] laser diode beams and results in considerable reduction of the trapping force. On the other hand, if a particle is located in a wall-bounded flow, the particle drag coefficient can change in a wide range and the drag force can exceed the trapping force that leads to loss of trapping and escape of the particle from the laser beam. ...
We present results of numerical simulation of the drag force acting on a spherical micro-particle in a two-wall channel formed by parallel plates. Dependence of the drag force on the distance between the particle and the channel wall is studied for different channel heights. We show the drag force in a two-wall channel with the height of the order of the particle diameter to be significantly higher than that in the single-wall counterpart.
... Recently, the idea of 'superfocusing' for high-M 2 beams was proposed [11] and demonstrated experimentally [12]. Superfocusing relies on a technique developed for the generation of so-called Bessel beams from laser diodes using a cone-shaped lens (axicon) [13][14][15][16]. This type of non-diffracting beam (i.e. ...
Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of ‘interference’ superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with high-precision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser ‘needle’ beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an ‘ideal’ lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser ‘needle’ beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations
... Unfortunately, since the first demonstration, Bessel beams have generally been produced only by reconfiguring the output beams from solid-state or gas lasers and it was believed that the main condition for generation of non-diffracting light fields is the coherence of light. But recently it was shown that non-diffracting beams can be formed from low-coherent light sources [9] and that the spatial rather than the temporal coherence of the light source plays the crucial role in formation of Bessel beams [10]. This opens up new avenues for generation of Bessel beams from the semiconductor light sources which are nowadays by far the most compact, reliable and efficient. ...
In this paper, we demonstrate, for the first time to the best of our knowledge, utilization of Bessel beams generated from a semiconductor laser for optical trapping and manipulation of microscopic particles including living cells.
... Until recently, it was believed that only lasers exhibiting high coherence (gas or solid state lasers) could be used to produce Bessel beams. However, recent work has shown that Bessel beams can be produced from different semiconductor light sources, including light emitting diodes (LED) [5], edge-emitting laser diodes [5,6], vertical cavity surface emitting lasers (VCSEL) [5,7,8] and vertical external cavity surface emitting lasers (VECSEL) [7,8], and even from a halogen bulb [9] (the last with substantial aperturing). These reports open the way for 'direct' implementations of semiconductor lasers. ...
The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the ‘quality’ of laser beams is characterized by so-called ‘beam propagation parameter’ M2, which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M2 determines the ratio of the beam focal-spot size to that of the ‘ideal’ Gaussian beam focused by the same optical system. Typically, M2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of ‘superfocusing’ for high-M2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wavefronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M2. In contrast, the generation of a Bessel-type beam with an axicon relies on ‘self-interference’ of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M2 below 20 and an emission wavelength in ~1μm range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an ‘ideal’ lens of unity numerical aperture.
... The idea of the proposed approach (superfocusing) is based on the fact that, in the case of traditional focusing of multimode radia tion, different curvatures of the wave fronts of various modes lead to a shift of their foci along the optical axis and, hence, to an increase in the focal spot size with increasing M 2 value. The interference focusing of radi ation of the semiconductor source with the aid of a cone shaped lens (axicon) [3,4] leads to the forma tion of the common central lobe of a Bessel beam [5,6] for all modes (Fig. 1b). During the propagation of the Bessel beam formed from a collimated multi mode quasi Gaussian beam, the size of the central lobe gradually increases because of a considerable divergence of the initial beam, which limits the propa gation length z B of the resulting beam (Fig. 1c). ...
... Taking into account the roots of the zero order Bessel function of the first kind, one can write the expression for determining m and the central lobe size d 0 on a 1/e 2 level with good accuracy as follows: (4) where α is the apex angle of the axicon. Upon carrying out simple transformations and taking into account that, in practice, α exceeds 140°, one can write the above formula in a much more convenient form: (5) It should be noted that the difference between the val ues of (4) and (5) does not exceed 5% in the entire range of practical axicon angles. ...
The problem of focusing multimode radiation of high-power semiconductor lasers and light-emitting diodes (LEDs) has been studied. In these sources, low spatial quality of the output beam determines theoretical limit of the focal spot size (one to two orders of magnitude exceeding the diffraction limit), thus restricting the possibility of increasing power density and creating optical field gradients that are necessary in many practical applications. In order to overcome this limitation, we have developed a method of superfocusing of multimode radiation with the aid of interference. It is shown that, using this method, the focal spot size of high-power semiconductor lasers and LEDs can be reduced to a level unachievable by means of traditional focusing. An approach to exceed the theoretical limit of power density for focusing of radiation with high propagation parameter M
2 is proposed.
