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Optimal condition for optical trapping of large particles: Tuning the laser power and numerical aperture of the objective
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3053-3059 ; 07403224 (ISSN) ; Nader, S ; Reihani, S ; Sharif University of Technology
OSA - The Optical Society
2019
Abstract
A Gaussian laser beam tightly focused through a high-numerical-aperture objective lens, so-called optical tweezers, is widely used for piconewton-range force spectroscopy. Utilizing a proper value for parameters such as bead size, numerical aperture of the objective, and power of the laser is always a challenge. Here, we show which set of values for the parameters can maximize lateral trapping efficiency. Our results show that for a high-numerical-aperture force spectroscopy, a bead with a diameter of 4–5 µm is suitable, and that for manipulation using large beads, utilizing a proper value for laser power and numerical aperture of the objective is crucial. We present a practical method for...
Optimal condition for optical trapping of large particles: Tuning the laser power and numerical aperture of the objective
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3053-3059 ; 07403224 (ISSN) ; Nader, S ; Reihani, S ; Sharif University of Technology
OSA - The Optical Society
2019
Abstract
A Gaussian laser beam tightly focused through a high-numerical-aperture objective lens, so-called optical tweezers, is widely used for piconewton-range force spectroscopy. Utilizing a proper value for parameters such as bead size, numerical aperture of the objective, and power of the laser is always a challenge. Here, we show which set of values for the parameters can maximize lateral trapping efficiency. Our results show that for a high-numerical-aperture force spectroscopy, a bead with a diameter of 4–5 µm is suitable, and that for manipulation using large beads, utilizing a proper value for laser power and numerical aperture of the objective is crucial. We present a practical method for...
Crosstalk elimination in the detection of dual-beam optical tweezers by spatial filtering
, Article Review of Scientific Instruments ; Volume 85, Issue 5 , May , 2014 ; ISSN: 00346748 ; Reihani, S. N. S ; Oddershede, L. B ; Sharif University of Technology
Abstract
In dual-beam optical tweezers, the accuracy of position and force measurements is often compromised by crosstalk between the two detected signals, this crosstalk leading to systematic and significant errors on the measured forces and distances. This is true both for dual-beam optical traps where the splitting of the two traps is done by polarization optics and for dual optical traps constructed by other methods, e.g., holographic tweezers. If the two traps are orthogonally polarized, most often crosstalk is minimized by inserting polarization optics in front of the detector; however, this method is not perfect because of the de-polarization of the trapping beam introduced by the required...
Simulation of three different double-fiber probes for reflection sensing
, Article Journal of Applied Sciences ; Volume 10, Issue 1 , 2010 , Pages 20-28 ; 18125654 (ISSN) ; Golnabi, H ; Sharif University of Technology
Abstract
In this study simulation results for three double-fiber optical designs for the reflection measurements are reported. Modeling is perused for three cases namely Equal Fibers (EF), transmitter fiber shorter (TS) and receiver fiber shorter (RS) designs. By proper modeling and written programs the operations of such symmetric double-fiber probes are simulated and the role of different crucial parameters such as fiber-to-fiber distance (t), fiber core radius (r) and fiber Numerical Aperture (NA) are investigated. In the second study simulation results for the transmitter fiber shorter and receiver fiber shorter designs are investigated for different fiber length differences (w). Finally...
Optimal in-depth trapping by tuning the correction collar of a dry objective lens
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 39, Issue 12 , 2022 , Pages 3209-3215 ; 07403224 (ISSN) ; Mahdavi, S. M ; Reihani, S. N. S ; Sharif University of Technology
Optica Publishing Group (formerly OSA)
2022
Abstract
Optical tweezers are proven and indispensable micro-manipulation tools. It is very common to use an immersion-assisted high NA objective for optical trapping of micrometer-sized beads. However, such objectives suffer from low working depth range. Here we show, both by theory and experiment, that a dry objective can be utilized for optimal trapping of even sub-micrometer objects. For the first time, to the best of our knowledge, we were able to stably trap polystyrene beads with radii of 270 and 175 nm in 3D using an objective with numerical aperture of 0.9. © 2022 Optica Publishing Group
Theoretical Calculation of Optimal Trapping Conditions for Particles with Nanometer to Micrometers Sizes Using Generalized Lorenz-Mie Theory
, M.Sc. Thesis Sharif University of Technology ; Seyed Reihani, Nader (Supervisor)
Abstract
Optical tweezers consist of a tightly focused laser beam. Particle with refractive index grater than that of the surrounding medium are eligible for optical trapping. This device is used for measuring forces from pico-newton to nano-newton, and displacements from nanometer to micrometer. In biopolymers, for example, it is used for studying the elasticity of DNA molecules, mechanical properties of cell membrane; and also in Microfluidics, it can is used for mixing two liquids flowing in a micro-channel by rotating a trapped particle. In general, physics of optical tweezers (or interaction of the trapped particle with the tightly focused laser beam) is treated in three different regimes:1)...
Optimization and Accurate Measurement of the Force Acting on the Spherical Nano/micro Particles Trapped by Optical Tweezers: Theoretical and Experimental Study
, Ph.D. Dissertation Sharif University of Technology ; Seyed Reihani, Nader (Supervisor) ; Mahdavi, Mohammad (Supervisor)
Abstract
In this thesis, the optical force acting on the spherical polystyrene particle trapped by optical tweezers is calculated. The calculation is based on the generalized Lorenz-Mie theory. The effect of various parameters on the optical force is also investigated. It is shown that, tuning the different parameters, one can significantly enhance the optical force acting on the trapped particle. Besides, one can achieve a stable 3D trap of a sub-micron particle somewhere far deep inside the sample chamber. Our results indicate that: (1) By obstructing the central region of the incident Gaussian laser beam at the back focal plane of the objective lens, the trap stiffness, the maximum linear force,...
Fiber output beam shape study using imaging technique
, Article Journal of Applied Sciences ; Volume 10, Issue 4 , 2010 , Pages 312-318 ; 18125654 (ISSN) ; Golnabi, H ; Sharif University of Technology
Abstract
In this study the output beam profiles of the single mode and multimode optical fibers are investigated by the cross sectional imaging technique. Different experiments are performed for the single mode and multimode fibers and the captured images are compared. The relative near field intensity distribution and their relative changes with respect to the distance is examined and some fiber parameters are obtained. A similar pattern in the real-time image is observed for the two type fibers and major differences are discussed. Using this method it is possible to determine the numerical aperture of the illuminated fiber, which is about 0.22 for the tested fiber. The effect of coherency of the...
Power modulation in axial and lateral fiber displacements in a fiber-to-fiber design
, Article Optics and Lasers in Engineering ; Volume 48, Issue 10 , 2010 , Pages 987-993 ; 01438166 (ISSN) ; Kargaran, A ; Heidari, F ; Sharif University of Technology
2010
Abstract
In this study power transmission modulation for different fibers in a fiber-to-fiber design using two different light sources is reported. A fiber-to-fiber arrangement is used in which the source light is directly coupled to the first fiber and the second fiber delivers the light to a power meter. Arrangements with three sets of different type fibers are tested in this study and output powers are monitored with the white lamp or red LED as illumination light sources. Using this arrangement the variations of the power as a result of axial (Z-direction) and lateral (X- and Y-direction) displacements of the second fiber are monitored. Theoretical models are also used to evaluate the power...