Samira Ebrahimi - Academia.edu (original) (raw)

Papers by Samira Ebrahimi

Expert Systems with Applications

Optics Letters, 2021

In this Letter, a very simple, stable, and portable lensless digital holographic (DH) microscopy ... more In this Letter, a very simple, stable, and portable lensless digital holographic (DH) microscopy method is presented relying on the Fresnel diffraction (FD) of light from a phase discontinuity (PD). A phase plate in the transmission or a physical step in the reflection can be employed in the path of the divergent beam of a coherent light source as a component imposing the PD. The recorded diffraction pattern in the vicinity of the PD is a hologram produced by off-axis overlapping of two diffracted waves in both sides of the boundary region with adjustable fringe modulation. To validate the method, measurements are performed on the amplitude and phase specimens as well as on the dynamic processes of water evaporation and 3D tracking of floating cells. A reflective configuration of FD from a physical step can be used as a powerful platform for lensless DH microscopy using high-energy electromagnetic radiation, e.g., x-ray and UV sources for the high-resolution imaging of moving samples.

Optics and Photonics Society of Iran, 2017

Optical imaging through turbid and scattering layers is a challenge in optical microscopy. The li... more Optical imaging through turbid and scattering layers is a challenge in optical microscopy. The light passing through the inhomogeneous samples including biological cells is scattered and speckle pattern appears. In this paper, a method is introduced based on Fourier-domain shower-curtain effect for imaging of objects and resolution enhancement of the recorded images in scattering media. The information of the object can be reconstructed from the autocorrelation of speckle patterns by a phase retrieval algorithm.

Journal of Industrial and Systems Engineering, 2018

In this paper, an incentive contract is proposed to coordinate the environmental and social decis... more In this paper, an incentive contract is proposed to coordinate the environmental and social decisions in a manufacturer-duopolistic retailers green supply chain.The manufacturer invests in newtechnology to enhance the green level of the products and two retailers invest in the corporate social responsibility (CSR). The investigated supply chain is modeled under three decision-making structures. In the decentralized model, a manufacturer-Stackelberg game under the two different game behaviors of retailers (Cournot and Collusion) is investigated. Afterward, the centralized model as a benchmark is established. Then, an environmental and social cost sharing contract is developed to encourage the supply chain members to participate in the coordination model. Under the coordination model, the surplus profit is shared among the members based on the members’ bargaining power. Results demonstrate that the proposed coordination contract not only improves the profitability of entire supply cha...

Optics and Photonics Society of Iran, 2017

In this paper, a method based on Fresnel diffraction from a parallel phase plate is presented for... more In this paper, a method based on Fresnel diffraction from a parallel phase plate is presented for the phase study of micronsized transparent samples. If a transparent plate is located in the path of a monochromatic beam of laser light, the diffraction fringes appear due to an abrupt change in the optical path length (OPL) difference between the part of the incoming light passing through the plate and the other propagating in the air. Now, if another phase sample is located in the path of the incoming light to the plate, the diffraction fringe pattern changes. the phase information of the sample can be extracted within the fringes by different fringe analysis methods. The presented setup is simple in comparison with complex interferometry techniques and the fringe pattern is stable against any mechanical and optical vibrations. Also, the accuracy of phase measurement is comparable with other common methods in which anti-vibration tables and high precision optical elements are require...

Journal of the Operational Research Society, 2020

A coordination model in a reverse supply chain (RSC) considering product acquisition management a... more A coordination model in a reverse supply chain (RSC) considering product acquisition management and competition of third-party collectors is developed. Motivated by a case study of plastic recycling, collectors not only compete on the return incentives paid to consumers but also control the quality level of returned products delivered to the remanufacturer. A triparty two-part tariff mechanism is introduced to coordinate the links between competing collectors and the remanufacturer. We analyze the retail and acquisition prices, and the quality level decisions under decentralized, centralized, and coordination systems. The results demonstrate that the coordination model not only significantly enhances both the quantity and quality of items received by the remanufacturer but also provides a win-win-win situation for members.

Optics and Lasers in Engineering, 2020

Digital holographic (DH) microscopy is a nondestructive quantitative method for studying micron-s... more Digital holographic (DH) microscopy is a nondestructive quantitative method for studying micron-sized samples with a special application in medicine, biology and materials science. Off-axis geometry of this method generates high-quality quantitative phase images employing beam-splitters, mirrors, condensers and magnifying lenses, which greatly increase the cost, size and sensitivity of the system against mechanical noise effects. The essential aim of recently proposed common-path configurations is to make viable approaches which minimize the mechanical and optical noises. Here we present a lensless DH microscopy system based on a common-path geometry using a Fresnel biprism for formation of off-axis geometry. The system comprises a lens for producing two spherical waves and by carefully choosing its parameters, we can construct a 3D imaging microscope with desired fringe spacing and overlapping region which is employed for studying many samples with different sizes, shapes and confluences. The system is compact, lightweight and robust versus mechanical vibrations. The ability to image amplitude and phase samples has been tested using standard test samples, living cells and water droplets.

Journal of Cleaner Production, 2020

Coordination of dual-function acquisition price and corporate social responsibility in a sustaina... more Coordination of dual-function acquisition price and corporate social responsibility in a sustainable closed-loop supply chain, (2019),

Journal of the Operational Research Society, 2019

In supply chain (SC) context, many SC members make sustainability effort not only to help the env... more In supply chain (SC) context, many SC members make sustainability effort not only to help the environment but also promote the market demand. Under such a situation, effective strategies should be adopted to coordinate the members' sustainability decisions such as carbon emission reduction and green effort decisions. This article makes contributions to the literature on SC coordination by proposing a novel model for coordinating sustainable supply chain (SSC) under competition. In this investigation, a manufacturer invests to reduce the carbon emissions and two retailers compete on investing in the green effort. Firstly, the profit of SSC members and optimal decisions are determined under the decentralised and centralised systems. Then, a three-party compensation-based contract is proposed for coordinating the SSC decisions and a Nash bargaining model is proposed to fairly share the surplus profit. The results indicate that the proposed contract not only improves the whole SSC profit and its members compared to the decentralised system, but also improves the whole SSC performance regarding sustainability. Therefore, the coordination contract is applicable and efficient from both economic and sustainability viewpoints.

Applied Physics Letters, 2019

The structural complexity and instability of many interference phase microscopy methods are the m... more The structural complexity and instability of many interference phase microscopy methods are the major obstacles toward high-precision phase measurement. In this vein, improving more efficient configurations as well as proposing methods are the subjects of growing interest. Here, we introduce Fresnel diffraction from a phase step to the realm of quantitative phase imaging. By employing Fresnel diffraction of a divergent (or convergent) beam of light from a plane-parallel phase plate, we provide a viable, simple, and compact platform for three-dimensional imaging of micrometer-sized specimens. The recorded diffraction pattern of the outgoing light from an imaging system in the vicinity of the plate edge can be served as a hologram, which would be analyzed via the Fourier transform method to measure the sample phase information. The period of diffraction fringes is adjustable simply by rotating the plate without the reduction of both the field of view and fringe contrast. The high stab...

Applied Physics Letters, 2019

Phase-shifting digital holography is widely considered to be a groundbreaking method to quantitat... more Phase-shifting digital holography is widely considered to be a groundbreaking method to quantitatively investigate the phase distribution of specimens, such as living cells. The main flaws of this method, however, are that the requirement for several sequential phase-shifted holograms eliminates the possibility of single-shot imaging and complex configurations would also increase the temporal noise. The present paper aims to validate a single-shot, common-path, phase-shifting digital holographic microscopy, employing a self-referencing geometry. A Ronchi ruling, located in the Fourier plane of a standard microscopic imaging system, produces multiple replicas of sample information in the image plane. The phase retrieval algorithm is performed by superposition of the sample-free portion of each replica with the object information, and requires at least three adjacent diffraction orders. To evaluate the performance of the proposed method, the phase distribution of silica microspheres a...

Information Sciences, 2019

In the information age, demand disruptions are challenging for supply chain (SC) systems. This st... more In the information age, demand disruptions are challenging for supply chain (SC) systems. This study explores a reverse supply chain (RSC) system dealing with demand disruptions in its online channel. The disruptions hurt the company's revenue since a fraction of the online channel demand will be lost. It is also important to determine the level of investment in sustainability to meet both the cap-and-trade rule imposed by the government on the company and the customers' expectations about the sustainability level of products. In the reverse channel, the company collects the used products through a collector whose efforts increase the collection volume. Since the earnings of the reverse channel highly depend on the collection volume, finding an effective strategy to entice the collector to collect a desirable number of used products is critically important for the company. In order to find a proper strategy for resolving these challenges, we analytically develop an RSC model and derive the optimal pricing, sustainability level, and corporate social responsibility (CSR) decisions under demand disruptions for both the decentralized and centralized RSCs. We then propose a combination scheme by using the combined two-part-tariff (CTPT) contract. We find that the proposed coordination scheme is efficient because it not only improves the profits of the RSC and its members but also enhances the environment. Moreover, the CTPT contract can properly allocate the SC surplus among the RSC members based on their bargaining powers.

International Journal of Machine Learning and Cybernetics, 2017

In a decentralized supply chain (SC), each member individually makes decisions according to its p... more In a decentralized supply chain (SC), each member individually makes decisions according to its personal objectives while these decisions impact on the other SC actors. The promotional effort made by retailers is one of the main factors that largely impacts on the market demand of a commodity, which in turn boosts the profitability of the whole SC members. In this paper, we investigate coordination of promotional effort and replenishment decisions in a two-echelon SC including single supplier and single retailer. The investigated SC faces a stochastic demand influenced by the retailer's promotional effort. To replenish items, the retailer uses a periodic review inventory system and decides on the review period, order-up-to-level and promotional effort. On the other side, the supplier employs a periodic review lot-for-lot strategy and determines its replenishment cycle multiplier. Firstly, we model the SC under the decentralized and centralized decision-making models. Exact solution procedures are presented using mathematical and concavity analysis to obtain the decentralized and centralized optimal solutions. Afterwards, a coordination model based on delay in payment contract is proposed to motivate the retailer to participate in the joint decision-making model. To create a more realistic model, in the proposed models we assume that the SC members' rates of return on investment are different. The minimum and maximum length of credit period which are acceptable to both members are determined. Finally, numerical examples and sensitivity analysis are conducted to investigate the performance and applicability of the developed models. The results show that the proposed coordination scheme considerably improves the profitability of both SC members and the whole SC in comparison with the decentralized setting.

Applied Physics Letters, 2018

Digital holographic (DH) microscopy has grown into a powerful nondestructive technique for the re... more Digital holographic (DH) microscopy has grown into a powerful nondestructive technique for the real-time study of living cells including dynamic membrane changes and cell fluctuations in nanometer and sub-nanometer scales. The conventional DH microscopy configurations require a separately generated coherent reference wave that results in a low phase stability and a necessity to precisely adjust the intensity ratio between two overlapping beams. In this work, we present a compact, simple, and very stable common-path DH microscope, employing a self-referencing configuration. The microscope is implemented by a diode laser as the source and a Fresnel biprism for splitting and recombining the beams simultaneously. In the overlapping area, linear interference fringes with high contrast are produced. The frequency of the interference pattern could be easily adjusted by displacement of the biprism along the optical axis without a decrease in fringe contrast. To evaluate the validity of the ...

Optics and Photonics Society of Iran, Feb 15, 2014

Optical tweezers is one of the most effective methods for manipulating micron and sub-micron size... more Optical tweezers is one of the most effective methods for manipulating micron and sub-micron sized particles nondestructively. In this paper a tapered fiber optical tweezers is calibrated using power spectrum analysis of the trapped particle motions. We utilized a high-speed CMOS camera with 500 frames per second for particle position detection. As validation experiment, using this setup, stretching of a multilamellar lipid bilayer is demonstrated.

Optics Letters, 2014

We present an integrated optical system for three-dimensional (3D) imaging of micrometer-sized sa... more We present an integrated optical system for three-dimensional (3D) imaging of micrometer-sized samples, while immobilizing and manipulating the samples by means of an optical fiber trap. Optical traps allow us to apply and measure pico-Newton-sized forces, and perform detailed measurements of micrometer-sized dielectric systems in the field of biology. The integrated 3D system can be used as a major tool in the field of biophysics. The trap is built using a tapered optical fiber to enhance the effective numerical aperture of the fiber. The trapping system is mounted on a conventional microscope, in which the two eyepieces' output ports are used as the paths of an off-axis self-referencing digital holographic microscopy (DHM) setup. The trap is calibrated using a high-speed camera, and trap stiffness is determined through the power spectrum method. The compact setup provides an elegant apparatus for temporally stable DHM for 3D imaging of optically controlled samples. Three-dimensional information and quantitative phase contrast images of the trapped samples are obtained by postprocessing the recorded digital holograms. Experiments were performed on lipids and red blood cells. Quantitative phase contrast images and temporal evolution of optical thickness of trapped samples are presented.

Sensors, 2021

Pulsed thermography is a commonly used non-destructive testing method and is increasingly studied... more Pulsed thermography is a commonly used non-destructive testing method and is increasingly studied for the assessment of advanced materials such as carbon fibre-reinforced polymer (CFRP). Different processing approaches are proposed to detect and characterize anomalies that may be generated in structures during the manufacturing cycle or service period. In this study, matrix decomposition using Robust PCA via Inexact-ALM is investigated as a pre- and post-processing approach in combination with state-of-the-art approaches (i.e., PCT, PPT and PLST) on pulsed thermography thermal data. An academic sample with several artificial defects of different types, i.e., flat-bottom-holes (FBH), pull-outs (PO) and Teflon inserts (TEF), was employed to assess and compare defect detection and segmentation capabilities of different processing approaches. For this purpose, the contrast-to-noise ratio (CNR) and similarity coefficient were used as quantitative metrics. The results show a clear improve...

Expert Systems with Applications

Optics Letters, 2021

In this Letter, a very simple, stable, and portable lensless digital holographic (DH) microscopy ... more In this Letter, a very simple, stable, and portable lensless digital holographic (DH) microscopy method is presented relying on the Fresnel diffraction (FD) of light from a phase discontinuity (PD). A phase plate in the transmission or a physical step in the reflection can be employed in the path of the divergent beam of a coherent light source as a component imposing the PD. The recorded diffraction pattern in the vicinity of the PD is a hologram produced by off-axis overlapping of two diffracted waves in both sides of the boundary region with adjustable fringe modulation. To validate the method, measurements are performed on the amplitude and phase specimens as well as on the dynamic processes of water evaporation and 3D tracking of floating cells. A reflective configuration of FD from a physical step can be used as a powerful platform for lensless DH microscopy using high-energy electromagnetic radiation, e.g., x-ray and UV sources for the high-resolution imaging of moving samples.

Optics and Photonics Society of Iran, 2017

Optical imaging through turbid and scattering layers is a challenge in optical microscopy. The li... more Optical imaging through turbid and scattering layers is a challenge in optical microscopy. The light passing through the inhomogeneous samples including biological cells is scattered and speckle pattern appears. In this paper, a method is introduced based on Fourier-domain shower-curtain effect for imaging of objects and resolution enhancement of the recorded images in scattering media. The information of the object can be reconstructed from the autocorrelation of speckle patterns by a phase retrieval algorithm.

Journal of Industrial and Systems Engineering, 2018

In this paper, an incentive contract is proposed to coordinate the environmental and social decis... more In this paper, an incentive contract is proposed to coordinate the environmental and social decisions in a manufacturer-duopolistic retailers green supply chain.The manufacturer invests in newtechnology to enhance the green level of the products and two retailers invest in the corporate social responsibility (CSR). The investigated supply chain is modeled under three decision-making structures. In the decentralized model, a manufacturer-Stackelberg game under the two different game behaviors of retailers (Cournot and Collusion) is investigated. Afterward, the centralized model as a benchmark is established. Then, an environmental and social cost sharing contract is developed to encourage the supply chain members to participate in the coordination model. Under the coordination model, the surplus profit is shared among the members based on the members’ bargaining power. Results demonstrate that the proposed coordination contract not only improves the profitability of entire supply cha...

Optics and Photonics Society of Iran, 2017

In this paper, a method based on Fresnel diffraction from a parallel phase plate is presented for... more In this paper, a method based on Fresnel diffraction from a parallel phase plate is presented for the phase study of micronsized transparent samples. If a transparent plate is located in the path of a monochromatic beam of laser light, the diffraction fringes appear due to an abrupt change in the optical path length (OPL) difference between the part of the incoming light passing through the plate and the other propagating in the air. Now, if another phase sample is located in the path of the incoming light to the plate, the diffraction fringe pattern changes. the phase information of the sample can be extracted within the fringes by different fringe analysis methods. The presented setup is simple in comparison with complex interferometry techniques and the fringe pattern is stable against any mechanical and optical vibrations. Also, the accuracy of phase measurement is comparable with other common methods in which anti-vibration tables and high precision optical elements are require...

Journal of the Operational Research Society, 2020

A coordination model in a reverse supply chain (RSC) considering product acquisition management a... more A coordination model in a reverse supply chain (RSC) considering product acquisition management and competition of third-party collectors is developed. Motivated by a case study of plastic recycling, collectors not only compete on the return incentives paid to consumers but also control the quality level of returned products delivered to the remanufacturer. A triparty two-part tariff mechanism is introduced to coordinate the links between competing collectors and the remanufacturer. We analyze the retail and acquisition prices, and the quality level decisions under decentralized, centralized, and coordination systems. The results demonstrate that the coordination model not only significantly enhances both the quantity and quality of items received by the remanufacturer but also provides a win-win-win situation for members.

Optics and Lasers in Engineering, 2020

Digital holographic (DH) microscopy is a nondestructive quantitative method for studying micron-s... more Digital holographic (DH) microscopy is a nondestructive quantitative method for studying micron-sized samples with a special application in medicine, biology and materials science. Off-axis geometry of this method generates high-quality quantitative phase images employing beam-splitters, mirrors, condensers and magnifying lenses, which greatly increase the cost, size and sensitivity of the system against mechanical noise effects. The essential aim of recently proposed common-path configurations is to make viable approaches which minimize the mechanical and optical noises. Here we present a lensless DH microscopy system based on a common-path geometry using a Fresnel biprism for formation of off-axis geometry. The system comprises a lens for producing two spherical waves and by carefully choosing its parameters, we can construct a 3D imaging microscope with desired fringe spacing and overlapping region which is employed for studying many samples with different sizes, shapes and confluences. The system is compact, lightweight and robust versus mechanical vibrations. The ability to image amplitude and phase samples has been tested using standard test samples, living cells and water droplets.

Journal of Cleaner Production, 2020

Coordination of dual-function acquisition price and corporate social responsibility in a sustaina... more Coordination of dual-function acquisition price and corporate social responsibility in a sustainable closed-loop supply chain, (2019),

Journal of the Operational Research Society, 2019

In supply chain (SC) context, many SC members make sustainability effort not only to help the env... more In supply chain (SC) context, many SC members make sustainability effort not only to help the environment but also promote the market demand. Under such a situation, effective strategies should be adopted to coordinate the members' sustainability decisions such as carbon emission reduction and green effort decisions. This article makes contributions to the literature on SC coordination by proposing a novel model for coordinating sustainable supply chain (SSC) under competition. In this investigation, a manufacturer invests to reduce the carbon emissions and two retailers compete on investing in the green effort. Firstly, the profit of SSC members and optimal decisions are determined under the decentralised and centralised systems. Then, a three-party compensation-based contract is proposed for coordinating the SSC decisions and a Nash bargaining model is proposed to fairly share the surplus profit. The results indicate that the proposed contract not only improves the whole SSC profit and its members compared to the decentralised system, but also improves the whole SSC performance regarding sustainability. Therefore, the coordination contract is applicable and efficient from both economic and sustainability viewpoints.

Applied Physics Letters, 2019

The structural complexity and instability of many interference phase microscopy methods are the m... more The structural complexity and instability of many interference phase microscopy methods are the major obstacles toward high-precision phase measurement. In this vein, improving more efficient configurations as well as proposing methods are the subjects of growing interest. Here, we introduce Fresnel diffraction from a phase step to the realm of quantitative phase imaging. By employing Fresnel diffraction of a divergent (or convergent) beam of light from a plane-parallel phase plate, we provide a viable, simple, and compact platform for three-dimensional imaging of micrometer-sized specimens. The recorded diffraction pattern of the outgoing light from an imaging system in the vicinity of the plate edge can be served as a hologram, which would be analyzed via the Fourier transform method to measure the sample phase information. The period of diffraction fringes is adjustable simply by rotating the plate without the reduction of both the field of view and fringe contrast. The high stab...

Applied Physics Letters, 2019

Phase-shifting digital holography is widely considered to be a groundbreaking method to quantitat... more Phase-shifting digital holography is widely considered to be a groundbreaking method to quantitatively investigate the phase distribution of specimens, such as living cells. The main flaws of this method, however, are that the requirement for several sequential phase-shifted holograms eliminates the possibility of single-shot imaging and complex configurations would also increase the temporal noise. The present paper aims to validate a single-shot, common-path, phase-shifting digital holographic microscopy, employing a self-referencing geometry. A Ronchi ruling, located in the Fourier plane of a standard microscopic imaging system, produces multiple replicas of sample information in the image plane. The phase retrieval algorithm is performed by superposition of the sample-free portion of each replica with the object information, and requires at least three adjacent diffraction orders. To evaluate the performance of the proposed method, the phase distribution of silica microspheres a...

Information Sciences, 2019

In the information age, demand disruptions are challenging for supply chain (SC) systems. This st... more In the information age, demand disruptions are challenging for supply chain (SC) systems. This study explores a reverse supply chain (RSC) system dealing with demand disruptions in its online channel. The disruptions hurt the company's revenue since a fraction of the online channel demand will be lost. It is also important to determine the level of investment in sustainability to meet both the cap-and-trade rule imposed by the government on the company and the customers' expectations about the sustainability level of products. In the reverse channel, the company collects the used products through a collector whose efforts increase the collection volume. Since the earnings of the reverse channel highly depend on the collection volume, finding an effective strategy to entice the collector to collect a desirable number of used products is critically important for the company. In order to find a proper strategy for resolving these challenges, we analytically develop an RSC model and derive the optimal pricing, sustainability level, and corporate social responsibility (CSR) decisions under demand disruptions for both the decentralized and centralized RSCs. We then propose a combination scheme by using the combined two-part-tariff (CTPT) contract. We find that the proposed coordination scheme is efficient because it not only improves the profits of the RSC and its members but also enhances the environment. Moreover, the CTPT contract can properly allocate the SC surplus among the RSC members based on their bargaining powers.

International Journal of Machine Learning and Cybernetics, 2017

In a decentralized supply chain (SC), each member individually makes decisions according to its p... more In a decentralized supply chain (SC), each member individually makes decisions according to its personal objectives while these decisions impact on the other SC actors. The promotional effort made by retailers is one of the main factors that largely impacts on the market demand of a commodity, which in turn boosts the profitability of the whole SC members. In this paper, we investigate coordination of promotional effort and replenishment decisions in a two-echelon SC including single supplier and single retailer. The investigated SC faces a stochastic demand influenced by the retailer's promotional effort. To replenish items, the retailer uses a periodic review inventory system and decides on the review period, order-up-to-level and promotional effort. On the other side, the supplier employs a periodic review lot-for-lot strategy and determines its replenishment cycle multiplier. Firstly, we model the SC under the decentralized and centralized decision-making models. Exact solution procedures are presented using mathematical and concavity analysis to obtain the decentralized and centralized optimal solutions. Afterwards, a coordination model based on delay in payment contract is proposed to motivate the retailer to participate in the joint decision-making model. To create a more realistic model, in the proposed models we assume that the SC members' rates of return on investment are different. The minimum and maximum length of credit period which are acceptable to both members are determined. Finally, numerical examples and sensitivity analysis are conducted to investigate the performance and applicability of the developed models. The results show that the proposed coordination scheme considerably improves the profitability of both SC members and the whole SC in comparison with the decentralized setting.

Applied Physics Letters, 2018

Digital holographic (DH) microscopy has grown into a powerful nondestructive technique for the re... more Digital holographic (DH) microscopy has grown into a powerful nondestructive technique for the real-time study of living cells including dynamic membrane changes and cell fluctuations in nanometer and sub-nanometer scales. The conventional DH microscopy configurations require a separately generated coherent reference wave that results in a low phase stability and a necessity to precisely adjust the intensity ratio between two overlapping beams. In this work, we present a compact, simple, and very stable common-path DH microscope, employing a self-referencing configuration. The microscope is implemented by a diode laser as the source and a Fresnel biprism for splitting and recombining the beams simultaneously. In the overlapping area, linear interference fringes with high contrast are produced. The frequency of the interference pattern could be easily adjusted by displacement of the biprism along the optical axis without a decrease in fringe contrast. To evaluate the validity of the ...

Optics and Photonics Society of Iran, Feb 15, 2014

Optical tweezers is one of the most effective methods for manipulating micron and sub-micron size... more Optical tweezers is one of the most effective methods for manipulating micron and sub-micron sized particles nondestructively. In this paper a tapered fiber optical tweezers is calibrated using power spectrum analysis of the trapped particle motions. We utilized a high-speed CMOS camera with 500 frames per second for particle position detection. As validation experiment, using this setup, stretching of a multilamellar lipid bilayer is demonstrated.

Optics Letters, 2014

We present an integrated optical system for three-dimensional (3D) imaging of micrometer-sized sa... more We present an integrated optical system for three-dimensional (3D) imaging of micrometer-sized samples, while immobilizing and manipulating the samples by means of an optical fiber trap. Optical traps allow us to apply and measure pico-Newton-sized forces, and perform detailed measurements of micrometer-sized dielectric systems in the field of biology. The integrated 3D system can be used as a major tool in the field of biophysics. The trap is built using a tapered optical fiber to enhance the effective numerical aperture of the fiber. The trapping system is mounted on a conventional microscope, in which the two eyepieces' output ports are used as the paths of an off-axis self-referencing digital holographic microscopy (DHM) setup. The trap is calibrated using a high-speed camera, and trap stiffness is determined through the power spectrum method. The compact setup provides an elegant apparatus for temporally stable DHM for 3D imaging of optically controlled samples. Three-dimensional information and quantitative phase contrast images of the trapped samples are obtained by postprocessing the recorded digital holograms. Experiments were performed on lipids and red blood cells. Quantitative phase contrast images and temporal evolution of optical thickness of trapped samples are presented.

Sensors, 2021

Pulsed thermography is a commonly used non-destructive testing method and is increasingly studied... more Pulsed thermography is a commonly used non-destructive testing method and is increasingly studied for the assessment of advanced materials such as carbon fibre-reinforced polymer (CFRP). Different processing approaches are proposed to detect and characterize anomalies that may be generated in structures during the manufacturing cycle or service period. In this study, matrix decomposition using Robust PCA via Inexact-ALM is investigated as a pre- and post-processing approach in combination with state-of-the-art approaches (i.e., PCT, PPT and PLST) on pulsed thermography thermal data. An academic sample with several artificial defects of different types, i.e., flat-bottom-holes (FBH), pull-outs (PO) and Teflon inserts (TEF), was employed to assess and compare defect detection and segmentation capabilities of different processing approaches. For this purpose, the contrast-to-noise ratio (CNR) and similarity coefficient were used as quantitative metrics. The results show a clear improve...