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Optical Manipulation of Cells
Published in Tuhin S. Santra, Microfluidics and Bio-MEMS, 2020
Srabani Kar, Pallavi Shinde, Moeto Nagai, Tuhin S. Santra
A single-beam optical trap uses a single laser beam. The simplest OT uses a single laser beam with a zero-order fundamental mode Gaussian intensity profile in the radial direction. However, this approach fails to trap particles more than a few micrometers in multiple locations of 3D space apart from the axial direction because the beam strongly diverges after the focal plane and the trapped object distorts the beam profile. Thus the performance is limited by depth, which allows single object trapping once at a time. To address this problem, a laser beam with a Bessel intensity profile has been proposed. Compared to the Gaussian beam, the Bessel beam contains concentric rings of light field patterns of decreasing intensity with a diffraction-less and self-healing nature, which can efficiently trap multiple spatially separated objects once at a time [34]. This approach has been successfully implemented to trap and manipulate multiple yeast cells in 3D traps [35]. Therefore, the use of different beam intensity profiles has a significant contribution to the development of OT techniques. Similarly, Laguerre–Gaussian beams with LG01 mode were used to trap and manipulate spermatozoa with reduced photodamage of the cells, without compromising the trapping efficiency, compared to TEM00 mode of the Gaussian beam [36].
Introduction
Published in Korotkova Olga, Random Light Beams, 2017
In Fig. 1.6 the intensity |U0(B)|2 of a J0-Bessel beam (left) and |U1(B)|2 of J1-Bessel beam (right) as functions of x and y (in millimeters). Unlike the J0- Bessel beam the higher-order Bessel beams possess the zero value of intensity at the optical axis. In addition, the higher-order Bessel beams carry the phase singularity at the origin, which is called the optical vortex.
Laser Beams
Published in Rajpal S. Sirohi, Introduction to OPTICAL METROLOGY, 2017
The zeroth-order Bessel beam has a bright core surrounded by a number of rings, whereas the higher-order Bessel beams have a phase singularity on axis and hence a black spot. One of the simplest ways to generate a zeroth-order Bessel beam is to diffract a laser beam at a ring aperture (circular slit). Other methods are to use a refractive axicon, and holographic or diffractive optical elements. The Bessel beams possess a remarkable property of healing, that is, if an obstacle is placed in its path, it regenerates itself past the obstacle. The J0 Bessel beam is well suited in applications requiring high pointing accuracy.
Refractive Bessel lattice in azobenzene liquid crystal
Published in Journal of Modern Optics, 2018
Varsenik Nersesyan, Tigran Dadalyan, Jeroen Beeckman, Filip Beunis, Kristiaan Neyts, Rafael Drampyan
Figure 1 demonstrates the experimental set-up for the induction of Bessel lattices. An axicon with apex cone angle of 175° (Del Mar Photonics AX-BK-7-175) is used in our experiments. In order to increase the number of rings in the overlapping zone of the Bessel beam, the diameter of the initial beam is enlarged before the axicon, using a two lens telescopic system LS1. When a linearly polarized Gaussian laser beam at 532 nm wavelength (Spectralus SP532 BFL) passes through the axicon, it is transformed into a Bessel beam. The overlapping zone of the axicon is measured to be Zovlp = 20 cm. This is the distance over which the refracted beams create bright and dark rings in the transverse plane of the initial beam propagation (Figure 1, zoomed part). Behind the overlapping zone, a ring pattern is formed in the far field. A fragment of the measured intensity distribution of the Bessel beam is shown in Figure 2(a), which shows nearly equidistant concentric rings except of a few central rings. The period of the Bessel rings is measured by beam profiler Thorlabs BP109-VIS and is equalled to 12 µm.
Generation of nondiffraction beam with arbitrary focusing direction using metasurface
Published in Electromagnetics, 2020
Figure 1 shows the generation principle of nondiffraction beam by axicon lens. The traditional axicon lens can transform the incident electromagnetic wave into a Bessel beam, because its thickness changes along the radial direction.