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11 pages, 1495 KiB

Open AccessArticle

Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection

by Bo-Wei Li, Min-Cheng Zhong and Feng Ji

Appl. Sci. 2020, 10(21), 7795; https://doi.org/10.3390/app10217795 - 3 Nov 2020

Cited by 10 | Viewed by 2281

Abstract

Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the [...] Read more.

Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation. Full article

(This article belongs to the Special Issue Optical Trapping)

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17 pages, 2012 KiB

Open AccessArticle

Optimization of Optical Trapping and Laser Interferometry in Biological Cells

by Yujiro Sugino, Masahiro Ikenaga and Daisuke Mizuno

Appl. Sci. 2020, 10(14), 4970; https://doi.org/10.3390/app10144970 - 19 Jul 2020

Cited by 6 | Viewed by 2812

Abstract

Optical trapping and laser interferometry enable the non-invasive manipulation of colloids, which can be used to investigate the microscopic mechanics of surrounding media or bound macromolecules. For efficient trapping and precise tracking, the sample media must ideally be homogeneous and quiescent whereas such [...] Read more.

Optical trapping and laser interferometry enable the non-invasive manipulation of colloids, which can be used to investigate the microscopic mechanics of surrounding media or bound macromolecules. For efficient trapping and precise tracking, the sample media must ideally be homogeneous and quiescent whereas such conditions are usually not satisfied in vivo in living cells. In order to investigate mechanics of the living-cell interior, we introduced (1) the in-situ calibration of optical trapping and laser interferometry, and (2) 3-D feedback control of a sample stage to stably track a colloidal particle. Investigating systematic errors that appear owing to sample heterogeneity and focal offsets of a trapping laser relative to the colloidal probe, we provide several important caveats for conducting precise optical micromanipulation in living cells. On the basis of this study, we further improved the performance of the techniques to be used in cells, by optimizing the position sensitivity of laser interferometry and the stability of the feedback simultaneously. Full article

(This article belongs to the Special Issue Optical Trapping)

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8 pages, 1652 KiB

Open AccessArticle

An Evaluation of the Zeeman Shift of the ⁸⁷Sr Optical Lattice Clock at the National Time Service Center

by Xiaotong Lu, Mojuan Yin, Ting Li, Yebing Wang and Hong Chang

Appl. Sci. 2020, 10(4), 1440; https://doi.org/10.3390/app10041440 - 20 Feb 2020

Cited by 9 | Viewed by 3050

Abstract

The Zeeman shift plays an important role in the evaluation of optical lattice clocks since a strong bias magnetic field is applied for departing Zeeman sublevels and defining a quantization axis. We demonstrated the frequency correction and uncertainty evaluation due to Zeeman shift [...] Read more.

The Zeeman shift plays an important role in the evaluation of optical lattice clocks since a strong bias magnetic field is applied for departing Zeeman sublevels and defining a quantization axis. We demonstrated the frequency correction and uncertainty evaluation due to Zeeman shift in the ⁸⁷Sr optical lattice clock at the National Time Service Center. The first-order Zeeman shift was almost completely removed by stabilizing the clock laser to the average frequency of the two Zeeman components of m_F = ±9/2. The residual first-order Zeeman shift arose from the magnetic field drift between measurements of the two stretched-state center frequencies; the upper bound was inferred as 4(5) × 10⁻¹⁸. The quadratic Zeeman shift coefficient was experimentally determined as –23.0(4) MHz/T² and the final Zeeman shift was evaluated as 9.20(7) × 10⁻¹⁷. The evaluation of the Zeeman shift is a foundation for overall evaluation of the uncertainty of an optical lattice clock. This measurement can provide more references for the determination of the quadratic coefficient of ⁸⁷Sr. Full article

(This article belongs to the Special Issue Optical Trapping)

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10 pages, 663 KiB

Open AccessArticle

Optical Trapping, Sizing, and Probing Acoustic Modes of a Small Virus

by Jeffrey Burkhartsmeyer, Yanhong Wang, Kam Sing Wong and Reuven Gordon

Appl. Sci. 2020, 10(1), 394; https://doi.org/10.3390/app10010394 - 4 Jan 2020

Cited by 27 | Viewed by 5226

Abstract

Prior opto-mechanical techniques to measure vibrational frequencies of viruses work on large ensembles of particles, whereas, in this work, individually trapped viral particles were studied. Double nanohole (DNH) apertures in a gold film were used to achieve optical trapping of one of the [...] Read more.

Prior opto-mechanical techniques to measure vibrational frequencies of viruses work on large ensembles of particles, whereas, in this work, individually trapped viral particles were studied. Double nanohole (DNH) apertures in a gold film were used to achieve optical trapping of one of the smallest virus particles yet reported, PhiX174, which has a diameter of 25 nm. When a laser was focused onto these DNH apertures, it created high local fields due to plasmonic enhancement, which allowed stable trapping of small particles for prolonged periods at low powers. Two techniques were performed to characterize the virus particles. The particles were sized via an established autocorrelation analysis technique, and the acoustic modes were probed using the extraordinary acoustic Raman (EAR) method. The size of the trapped particle was determined to be 25 ± 3.8 nm, which is in good agreement with the established diameter of PhiX174. A peak in the EAR signal was observed at 32 GHz, which fits well with the predicted value from elastic theory. Full article

(This article belongs to the Special Issue Optical Trapping)

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9 pages, 8437 KiB

Open AccessArticle

Optical Conveyor Belts for Chiral Discrimination: Influence of De-Phasing Parameter

by Luis Carretero, Pablo Acebal and Salvador Blaya

Appl. Sci. 2019, 9(7), 1304; https://doi.org/10.3390/app9071304 - 28 Mar 2019

Cited by 1 | Viewed by 1985

Abstract

A numerical analysis is carried out of the influence of the de-phasing parameter of an optical conveyor belt in the enantiomeric separation. The optical conveyor belt is obtained by the interference of a Laguerre Gaussian and a Gaussian beam with different beam waists, [...] Read more.

A numerical analysis is carried out of the influence of the de-phasing parameter of an optical conveyor belt in the enantiomeric separation. The optical conveyor belt is obtained by the interference of a Laguerre Gaussian and a Gaussian beam with different beam waists, which are temporally de-phased. In order to obtain the maximum separation distance between enantiomers, we calculate the optimum range of values of the de-phasing parameter. Full article

(This article belongs to the Special Issue Optical Trapping)

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12 pages, 1918 KiB

Open AccessArticle

Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective

by Min-Cheng Zhong, Ai-Yin Liu and Rong Zhu

Appl. Sci. 2018, 8(9), 1522; https://doi.org/10.3390/app8091522 - 1 Sep 2018

Cited by 7 | Viewed by 3396

Abstract

Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical [...] Read more.

Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers. Full article

(This article belongs to the Special Issue Optical Trapping)

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Review

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18 pages, 3775 KiB

Open AccessReview

From Far-Field to Near-Field Micro- and Nanoparticle Optical Trapping

by Theodoros D. Bouloumis and Síle Nic Chormaic

Appl. Sci. 2020, 10(4), 1375; https://doi.org/10.3390/app10041375 - 18 Feb 2020

Cited by 28 | Viewed by 4960

Abstract

Optical tweezers are a very well-established technique that have developed into a standard tool for trapping and manipulating micron and submicron particles with great success in the last decades. Although the nature of light enforces restrictions on the minimum particle size that can [...] Read more.

Optical tweezers are a very well-established technique that have developed into a standard tool for trapping and manipulating micron and submicron particles with great success in the last decades. Although the nature of light enforces restrictions on the minimum particle size that can be efficiently trapped due to Abbe’s diffraction limit, scientists have managed to overcome this problem by engineering new devices that exploit near-field effects. Nowadays, metallic nanostructures can be fabricated which, under laser illumination, produce a secondary plasmonic field that does not suffer from the diffraction limit. This advance offers a great improvement in nanoparticle trapping, as it relaxes the trapping requirements compared to conventional optical tweezers although problems may arise due to thermal heating of the metallic nanostructures. This could hinder efficient trapping and damage the trapped object. In this work, we review the fundamentals of conventional optical tweezers, the so-called plasmonic tweezers, and related phenomena. Starting from the conception of the idea by Arthur Ashkin until recent improvements and applications, we present the principles of these techniques along with their limitations. Emphasis in this review is on the successive improvements of the techniques and the innovative aspects that have been devised to overcome some of the main challenges. Full article

(This article belongs to the Special Issue Optical Trapping)

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15 pages, 2980 KiB

Open AccessReview

Plasmonic Tweezers towards Biomolecular and Biomedical Applications

by Xue Han and Changsen Sun

Appl. Sci. 2019, 9(17), 3596; https://doi.org/10.3390/app9173596 - 2 Sep 2019

Cited by 9 | Viewed by 3400

Abstract

With the capability of confining light into subwavelength scale, plasmonic tweezers have been used to trap and manipulate nanoscale particles. It has huge potential to be utilized in biomolecular research and practical biomedical applications. In this short review, plasmonic tweezers based on nano-aperture [...] Read more.

With the capability of confining light into subwavelength scale, plasmonic tweezers have been used to trap and manipulate nanoscale particles. It has huge potential to be utilized in biomolecular research and practical biomedical applications. In this short review, plasmonic tweezers based on nano-aperture designs are discussed. A few challenges should be overcome for these plasmonic tweezers to reach a similar level of significance as the conventional optical tweezers. Full article

(This article belongs to the Special Issue Optical Trapping)

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Other

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6 pages, 1721 KiB

Open AccessLetter

A High-Power and Highly Efficient Semi-Conductor MOPA System for Lithium Atomic Physics

by Hao Wu, Hongbo Zhu, Jianwei Zhang, Hangyu Peng, Li Qin and Yongqiang Ning

Appl. Sci. 2019, 9(3), 471; https://doi.org/10.3390/app9030471 - 30 Jan 2019

Cited by 1 | Viewed by 2132

Abstract

A compact and highly efficient 670.8-nm semi-conductor master oscillator power amplifier (MOPA) system, with a unique optical design, is demonstrated. The MOPA system achieves a continuous-wave (CW) output power of 2.2 W, which is much higher than commercial products using semi-conductor devices. By [...] Read more.

A compact and highly efficient 670.8-nm semi-conductor master oscillator power amplifier (MOPA) system, with a unique optical design, is demonstrated. The MOPA system achieves a continuous-wave (CW) output power of 2.2 W, which is much higher than commercial products using semi-conductor devices. By comparing solid state lasers and dye lasers, higher wall-plug efficiency (WPE) of 20 % is achieved. Our developed laser system also achieves spectral line-width of 0.3 pm (200 MHz) and mode-hop free tuning range of 49 pm (32.6 GHz), which is very suitable for experiments of lithium atomic physics at several-watt power levels, such as Bose-Einstein condensation (BEC) and isotope absorption spectroscopy. Full article

(This article belongs to the Special Issue Optical Trapping)

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