Dan Cojoc - Academia.edu (original) (raw)

Papers by Dan Cojoc

2006 IEEE Ultrasonics Symposium, 2006

Here we present optical tweezers as a micromanipulation tool for the study of ultrasound contrast... more Here we present optical tweezers as a micromanipulation tool for the study of ultrasound contrast agent (UCA) microbubbles. Optical trapping and the resulting manipulation of individual and multiple microbubbles enables the study of their dynamics with controlled boundary conditions. The bubble response to ultrasound is recorded optically using the ultra high-speed Brandaris 128 camera. In our experiments, the amplitude of

Digest of Papers Microprocesses and Nanotechnology 2003. 2003 International Microprocesses and Nanotechnology Conference, 2003

In this paper, efficient optical coupling between a single mode fiber and a LiNbO3-APE waveguide ... more In this paper, efficient optical coupling between a single mode fiber and a LiNbO3-APE waveguide using a lens fabricated on the top of the fiber was demonstrated.

International Journal of Optomechatronics, 2011

We report a home built optical tweezers setup to investigate the mechanism of the membrane tether... more We report a home built optical tweezers setup to investigate the mechanism of the membrane tether formation from single cells in vitro. Using an optically trapped microbead as probe, we have determined the force-elongation curve during tether formation and ...

The Mie scattering of a Laguerre-Gaussian beam is studied. Applications to position detection in ... more The Mie scattering of a Laguerre-Gaussian beam is studied. Applications to position detection in optical tweezers are considered. The cross-talk between the position signals predicted by simulations is confirmed in experiments.

$Research paper thumbnail of Scanning x-ray microdiffraction of optically manipulated liposomes$

Applied Physics Letters, 2007

We show optical tweezers manipulation of individual micron-sized samples investigating at the sam... more We show optical tweezers manipulation of individual micron-sized samples investigating at the same time their inner nanostructure by synchrotron diffraction experiments. The validity of this technique is demonstrated for clusters of multilamellar liposomes trapped in single and multiple positions in the optical path of a microfocused x-ray beam and analyzed in a microscanning mode. The signal to background ratio of

$Research paper thumbnail of <title>Gaussian to rectangular laser beam shaping using diffractive optical elements</title>$

The design and fabrication of two binary phase diffractive optical elements is presented. We use ... more The design and fabrication of two binary phase diffractive optical elements is presented. We use iterative Fourier transform algorithms and a geometrical optics approach to design the diffractive elements. The outgoing beam shapes of the designed elements are compared by computer simulations. The advantages and disadvantages of each design are presented.

$Research paper thumbnail of <title>Spherical-based approach to design diffractive optical elements</title>$

A novel method to design diffractive optical elements, based on the spherical wave propagation an... more A novel method to design diffractive optical elements, based on the spherical wave propagation and superposition, is presented in this paper. Underlying theory, practical considerations, results and limitations of this method are presented based on computer simulation experiments. ...

Optical Trapping and Optical Micromanipulation III, 2006

Optical tweezers enable non-destructive, contact-free manipulation of ultrasound contrast agent (... more Optical tweezers enable non-destructive, contact-free manipulation of ultrasound contrast agent (UCA) microbubbles, which are used in medical imaging for enhancing the echogenicity of the blood pool and to quantify organ perfusion. The understanding of the fundamental dynamics of ultrasound-driven contrast agent microbubbles is a first step for exploiting their acoustical properties and to develop new diagnostic and therapeutic applications. In

Optical Trapping and Optical Micromanipulation, 2004

Trapping and manipulation of microparticles using optical tweezers is usually performed within a ... more Trapping and manipulation of microparticles using optical tweezers is usually performed within a sample cell formed by two parallel microscope cover slides. In this paper we discuss and demonstrate trapping and manipulation conditions when the cell has more complex configurations like microchannels or capillary tubes. The microchannels are fabricated on the surface of the cover slide by means of lithographic

$Research paper thumbnail of Fiber optic trapping of low-refractive-index particles - art. no. 608812$

Since the low index particles are repelled away from the highest intensity point, trapping them o... more Since the low index particles are repelled away from the highest intensity point, trapping them optically requires either a rotating Gaussian beam or optical vortex beams focused by a high numerical microscope objective. However, the short working distance of these microscope objectives puts a limit on the depth at which these particles can be manipulated. Here, we show that axicon

$Research paper thumbnail of Force trapping gradient using diffractive optical elements$

We discuss a new technique to generate force gradient in arrays of optical traps. The arrays can ... more We discuss a new technique to generate force gradient in arrays of optical traps. The arrays can be configured in two or three dimensions by means of phase diffractive optical elements displayed on a spatial light modulator. The design of the diffractive optical elements is based on the approach of spherical wave propagation and superposition, which enables to individually control

Nano- and Micro-Optics for Information Systems, 2003

In this paper we report results obtained in the design and fabrication of diffractive optical ele... more In this paper we report results obtained in the design and fabrication of diffractive optical elements (DOEs) with minimum feature size down to tens of nanometers by the use of e-beam and x-ray lithography. The DOEs are patterned using e-beam lithography and replicated by x-ray ...

Micromachining Technology for Micro-Optics and Nano-Optics V and Microfabrication Process Technology XII, 2007

In this paper we will discuss the use of the crossbeam ZEISS XB1540 applied to photonic structure... more In this paper we will discuss the use of the crossbeam ZEISS XB1540 applied to photonic structures and to obtain nano-imprinting templates. Some 1D Photonic Crystals (PhC) on silica based optical waveguides are shown as well as the realization of 3D optical structures curved directly on silica and used subsequently as a master for imprinting. Focused ion beam lithography (FIB)

$Research paper thumbnail of On a diffractive optical element$

2004 International Semiconductor Conference. CAS 2004 Proceedings (IEEE Cat. No.04TH8748), 2004

... Our methodology [5] consist of the following steps: Firstly by geometrical optics (ray tracin... more ... Our methodology [5] consist of the following steps: Firstly by geometrical optics (ray tracing) we determine the shape of a special lens (not spherical), called refractive optical element, that spreads out the incident Gaussian laser beam simmetricaly in respect to its initial direction ...

$Research paper thumbnail of <title>Design and implementation of optical tweezer arrays using diffractive optical elements</title>$

Although optical tweezers have been a valuable research tool since their invention in the 1980s, ... more Although optical tweezers have been a valuable research tool since their invention in the 1980s, they have remained limited for many years to trapping only one particle per laser beam. One of the most exciting developments in optical tweezers in recent years has ...

A strongly focused laser beam through an objective microscope with high NA allows the trapping of... more A strongly focused laser beam through an objective microscope with high NA allows the trapping of dielectric particles with micrometric sizes. The trapping force is proportional to the power of the laser, the relative refractive index (the ratio between the refractive index of the particle and the refractive index of the medium surrounding it) and the trapping geometry (shape of

Optical Trapping and Optical Micromanipulation II, 2005

Higher-order laser beams were demonstrated to enable optical manipulation of low-index-particles.... more Higher-order laser beams were demonstrated to enable optical manipulation of low-index-particles. In this work single-ringed Laguerre-Gaussian beams, obtained by means of phase-only diffractive optical elements, are used to perform manipulation of phospholipid-shelled gas microbubbles in water. Implementation of diffractive optical elements on a programmable spatial light modulator allows to generate also arrays of Laguerre-Gaussian traps. We show manipulation of low-index

2007 IEEE Ultrasonics Symposium Proceedings, 2007

We present time-resolved optical measurements of the coupled dynamics of two UCA microbubbles in ... more We present time-resolved optical measurements of the coupled dynamics of two UCA microbubbles in ultrasound. We isolate microbubble pairs using optical tweezers to move them away from confining walls and study purely the bubble-bubble interaction. The dynamics in ultrasound is recorded optically using the ultra-high speed camera Brandaris 128. Our measurements indicate that the viscous drag on a translating and

$Research paper thumbnail of Phase and intensity control through diffractive optical elements in X-ray microscopy$

Journal of Electron Spectroscopy and Related Phenomena, 2005

Diffractive optics now plays a major role in optical systems for the extreme ultraviolet and X-ra... more Diffractive optics now plays a major role in optical systems for the extreme ultraviolet and X-ray region. For example, zone plates in their different appearances are widely used for focusing X-rays, as monochromatizing condenser optics, and for high resolution imaging, particularly in X-ray microscopy. The idea in this paper is based upon a more general approach to solve optical problems