The UB Physical Optics Research Group

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Dynamic Holographic Optical Tweezers
Spatial Light Modulators and Digital Holography
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	Contact: UB Physical Optics Research Group Departament de Física Aplicada i Òptica Facultat de Fisica Universitat de Barcelona Martí i Franquès, 1 08028 Barcelona optics @ ub.edu

Recent Publications

Dynamic Holographic Optical Tweezers
Spatial Light Modulators and Digital Holography
Digital & Optical Image Processing
Topics on Physical Optics: Thin Films and Wave Propagation
Research on Education in Optics

PhD and Master Thesis

1. Dynamic Holographic Optical Tweezers

Interactive hologram design for multiple dynamic optical trapping, E. Pleguezuelos, A. Carnicer, J. Andilla, E. Martin-Badosa, M. Montes-Usategui, Submitted to CPC (November 2006)

Abstact
This work presents an application that generates interactive holograms to be displayed in a holographic optical tweezers setup, a technique which allows the manipulation of particles in the range from micrometers to nanometers. The software is written in Java, and implements the random binary masks method to generate the holograms. It allows customization of the parameters adapted to the experimental setup and the used hologram display, taking into account the specific characteristics of the device, such as the modulation or the presence of aberrations. The performance of the software is evaluated, achieving 12 fps at full display resolution when run on a Pentium IV HT, 3.2 GHz computer, which allows real time interaction with the sample. Experimental results of the manipulation of microspheres using this program are provided.

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Design of a low-cost interactive holographic optical tweezers system, E. Pleguezuelos, J. Andilla, A. Carnicer, E. Martín-Badosa, S. Vallmitjana, and M. Montes-Usategui, Proc of SPIE 6326, 63262Q (2006).

Abstract
The paper describes the design of an inexpensive holographic optical tweezers setup. The setup is accompanied by software that allows real-time manipulation of the sample and takes into account the experimental features of the setup, such as aberration correction and LCD modulation. The LCD, a HoloEye LCR-2500, is the physical support of the holograms, which are calculated using the fast random binary mask algorithm. The real-time software achieves 12 fps at full LCD resolution (including aberration correction and modulation) when run on a Pentium IV HT, 3.2 GHz computer.

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Algorithm for computing holographic optical tweezers at video rates, M Montes-Usategui, E Pleguezuelos, J Andilla, E Martín-Badosa, and I Juvells, Proc of SPIE 6326, 63262X (2006)

Abstract
Digital holography enables the creation of multiple optical traps at arbitrary three-dimensional locations and spatial light modulators permit updating those holograms at video rates. However, the time required for computing the holograms makes interactive optical manipulation of several samples difficult to achieve. We introduce an algorithm for computing holographic optical tweezers that is both easy to implement and capable of speeds in excess of 10 Hz when running on a Pentium IV computer. A discussion of the pros and cons of the algorithm, a mathematical analysis of the efficiency of the resulting traps, as well as results of the three-dimensional manipulation of polystyrene micro spheres are included.

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Mario Montes-Usategui, Encarnación Pleguezuelos, Jordi Andilla, and Estela Martín-Badosa "Fast generation of holographic optical tweezers by random mask encoding of Fourier components", Opt. Express 14, 2101-2107 (2006)

Full Text PDF: (external link)

http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-6-2101

Abstract
The random mask encoding technique of multiplexing phase-only filters can be easily adapted to the generation of holographic optical tweezers. The result is a direct, non-iterative and extremely fast algorithm that can be used for computing arbitrary arrays of optical traps. Additional benefits include the possibility of modifying any existing hologram to quickly add more trapping sites and the inexistence of ghost traps or replicas.

Fig3 E. Martín-Badosa, M. Montes-Usategui, J. Andilla,E. Pleguezuelos, I. Labastida, S. Vallmitjana, I. Juvells, A. Carnicer, "Generation of Holographic Optical Tweezers with Arbitrary Modulation Operating Curves" presented at Diffractive Optics 2005, September 2005, Warsaw (Poland).

Full Text: PDF

Abstract
This work pursues the study and development of a dynamic holographic optical tweezer (DHOT) [1]. Optical tweezers are strongly focused laser beams capable of trapping microscopic particles. When combined with holographic optical elements displayed on spatial light modulators (SLM), arrays of optical tweezers can be generated and dynamically controlled. Our work intends merging of both techniques to obtain dynamic, flexible and more usable optical manipulators.

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2. Spatial Light Modulators and Digital Holography

R Tudela, E Martín-Badosa, I Labastida, S Vallmitjana, I Juvells and A Carnicer, "Full complex Fresnel holograms displayed on liquid crystal devices", J. Opt. A: Pure Appl. Opt. 5, S189-S194 (2004).

Full Text: PDF (external link)
http://stacks.iop.org/JOptA/5/S189

Abstract.
We propose a method to display full complex Fresnel holograms by adding the information displayed on two analogue ferroelectric liquid crystal spatial light modulators. One of them works in real-only configuration and the other in imaginary-only mode. The Fresnel holograms are computed by backpropagating an object at a selected distance with the Fresnel transform. Then, displaying the real and imaginary parts on each panel, the object is reconstructed at that distance from the modulators by simple propagation of light. We present simulation results taking into account the specifications of the modulators as well as optical results. We have also studied the quality of reconstructions using only real, imaginary, amplitude or phase information. Although the real and imaginary reconstructions look acceptable for certain distances, full complex reconstruction is always better and is required when arbitrary distances are used.

Wavefront reconstruction by adding modulation capabilities of two liquid crystal devices, R Tudela, E Martín-Badosa, I Labastida, S Vallmitjana, A Carnicer, Opt. Eng. 43, 2650-2657 (2004)

Abstract
We analyze the behavior of complex information in the Fresnel domain, taking into account the limited capability to display complex values of liquid crystal devices when they are used as holographic displays. To do this analysis we study the reconstruction of Fresnel holograms at several distances using the different parts of the complex distribution. We also use the information adjusted with a method that combines two configurations of the devices in an adding architecture. The results of the error analysis show different behavior for the reconstructions when using the different methods. Simulated and experimental results are presented.

R. Tudela, I. Labastida, E. Martín-Badosa, S. Vallmitjana, I. Juvells and A. Carnicer, "Fresnel holograms on liquid crystal panels" Optics Communications, 214, 107-114 (2002)

Full Text: PDF (external link)
http://dx.doi.org/10.1016/S0030-4018(02)02173-9

Abstract
In this paper we present a method for reconstructing Fresnel holograms using two liquid crystal devices, one to display the amplitude information and the other to display the phase. The theoretical approach has been adapted to real configurations of VGA panels removed from a commercial video projector. The optical setup is based on the projection of the phase plane into the amplitude plane by means of an imaging lens. Simulated and experimental results are presented.

3. Digital & Optical Image Processing

A. Carnicer, M. Montes-Usategui, S. Arcos, and I. Juvells, "Vulnerability to chosen-cyphertext attacks of optical encryption schemes based on double random phase keys," Opt. Lett. 30, 1644-1646 (2005)

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(external link)

http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-13-1644

Abstract
We show how optical encryption methods based on double random phase keys are vulnerable to an organized attack of the chosen-ciphertext type. The decryption key can be easily obtained by an opponent who has repeated access to either the encryption or decryption machines. However, we have also devised a solution that prevents the attack. Our results cast doubts on the present security of these techniques.

J. Pérez-Tudela, I. Juvelis, M. Montes-Usategui, S. Vallmitjana, and A. Carnicer, "Reduction of the Effect of Aberrations in a Joint-Transform Correlator ," Appl. Opt. 43, 841-849 (2004)

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http://www.opticsinfobase.org/abstract.cfm?URI=ao-43-4-841

Abstract
We report the study of the influence of optical aberrations in a joint-transform correlator: The wave aberration of the optical system is computed from data obtained by ray tracing. Three situations are explored: We consider the aberration only in the first diffraction stage (generation of power spectrum), then only in the second (transformation of the power spectrum into correlation), and finally in both stages simultaneously. The results show that the quality of the correlation is determined mostly by the aberrations of the first diffraction stage and that we can optimize the setup by moving the cameras along the optical axis to a suitable position. The good agreement between the predicted data and the experimental results shows that the method explains well the behavior of optical diffraction systems when aberrations are taken into account.

E. Pleguezuelos, I. Labastida, M. Montes-Usategui, S. Vallmitjana, and A. Carnicer, "Generalization of the Jared and Ennis Method of Complex Transmittance Objects for the Generation of Synthetic Discriminant Function Filters," Appl. Opt. 43, 5647-5654 (2004)

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http://www.opticsinfobase.org/abstract.cfm?URI=ao-43-30-5647

Abstract
We present a simple method of constructing synthetic discriminant function filters optimized to take into account the modulation of liquid-crystal devices. This relaxation algorithm, a generalization of the Jared and Ennis method, is an iterative method that includes arbitrary modulations for both scene and filter, extending the problem to the complex plane. Simulated and experimental results obtained in a VanderLugt correlator are presented for a two-class recognition problem. The optimal number of images needed to describe an object in a filter generated in this way is discussed, and the influence of the spatial light modulation resolution on the correlation is studied.

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4. Topics on Physical Optics

Reply to commnet on 'Structure of the transverse profile of Gaussian-model non-paraxial electromagnetic beams', R Martínez-Herrero, P M Mejías, S Bosch and A Carnicer J. Opt. A: Pure Appl. Opt. 8 1025-1026 (2006)

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Structure of the transverse profile of Gaussian-model non-paraxial electromagnetic beams, R Martínez-Herrero, P M Mejías, S Bosch and A Carnicer J. Opt. A: Pure Appl. Opt. 8 524-530 (2006)

Abstract.
Starting from the (inexact) Gaussian beam model, and on the basis of a plane-wave spectrum representation of non-paraxial electromagnetic fields, three free-propagating exact solutions of the Maxwell equations are investigated. The transverse part of one of these solutions is shown to closely resemble both the beam profile irradiance and the polarization distribution of a typical Gaussian beam. A limit has also been established for the validity of the paraxial regime, particularly for focused beams whose size at the waist approaches the light wavelength.

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R. Martínez-Herrero, P. Mejías, S. Bosch, and A. Carnicer, "Non-paraxial transverse vector fields closest to non-polarized beams," J. Opt. A: Pure Appl. Opt.6 S64-S66 (2004)

Full Text PDF (external link)

http://stacks.iop.org/JOptA/6/S64

Abstract.
The concept of the so-called closest field to a given vector function is extended to the non-polarized case. Attention is focused on transverse field solutions of the Maxwell equations whose transverse character is preserved under free propagation. The coherence matrix of the non-paraxial transverse field that is closest to a paraxial unpolarized transverse beam is given. It is shown that the intensity matrix of this closest field can be written as the sum of the intensity matrices of a non-polarized field and a totally polarized beam.

R. Martínez-Herrero, P. Mejías, S. Bosch, and A. Carnicer, " Spatial width and power-content ratio of hard-edge diffracted beams ," J. Opt. Soc. Am. A 20, 388-391 (2003)

Full Text: PDF (external link)

http://www.opticsinfobase.org/abstract.cfm?URI=josaa-20-2-388

Abstract
On the basis of the intensity-moment formalism, certain analytical relationships are obtained for both the angular domain and the size of a transverse region of the beam that ensure a power content of at least 75% of the total power. As an illustrative application, the analytical results are compared with the exact values (numerically computed) of the amplitude of a lowest-order Gaussian beam diffracted by slits.

R. Martínez-Herrero, P. Mejías, S. Bosch, and A. Carnicer, "Vectorial structure of nonparaxial electromagnetic beams ," J. Opt. Soc. Am. A 18, 1678-1680 (2001)

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http://www.opticsinfobase.org/abstract.cfm?URI=josaa-18-7-1678

Abstract
A representation of the general solution of the Maxwell equations is proposed in terms of the plane-wave spectrum of the electromagnetic field. In this representation the electric field solution is written as a sum of two terms that are orthogonal to each other at the far field: One is transverse to the propagation axis, and the magnetic field associated with the other is also transverse. The concept of the so-called closest field to a given beam is introduced and applied to the well-known linearly polarized Gaussian beam.

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5. Research on Education in Optics

Understanding the concept of resolving power in the Fabry–Perot interferometer using a digital simulation, I Juvells, A. Carnicer, J. Ferré-Borrull, E. Martin-Badosa and m. Montes-Usategui Eur. J. Phys. 27 1111-1119 (2006)

Full Text: PDF (external link)

Abstract
The resolution concept in connection with the Fabry–Perot interferometer is difficult to understand for undergraduate students enrolled in physical optics courses. The resolution criterion proposed in textbooks for distinguishing equal intensity maxima and the deduction of the resolving power equation is formal and non-intuitive. In this paper, we study the practical meaning of the resolution criterion and resolution power using a computer simulation of a Fabry–Perot interferometer. The light source in the program has two monochromatic components, the wavelength difference being tunable by the user. The student can also adjust other physical parameters so as to obtain different simulation results. By analysing the images and graphics of the simulation, the resolving power concept becomes intuitive and understandable.

Applet A. Carnicer, S. Bosch, J.Ferre, I. Juvells, I. Labastida, E. Martin-Badosa, J. R. de F. Moneo, E. Pleguezuelos, R. Tudela, S, Vallmitjana, "On-line applet-based optics course for undergraduate students", Proc. SPIE Vol. 4829, p. 3-4 (2003)

Full Text: PDF (external link)

Abstract
We present an educational resource based in a virtual optical laboratory for undergraduate students. It consists in a web-based textbook with several applets to illustrate the theory and simplify the teaching tasks in the classroom. These programs can also be used as a method for self-learning in an on-line environment. Applets are written in Java language using the Java Network Launching Protocol (JNPL) for avoiding problems related with the use of specific browsers or Java interpreters versions.

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PhD and Master thesis

Phd Thesis