EP2297745A1 - Device for trapping particles - Google Patents

Device for trapping particles

Info

Publication number
EP2297745A1
EP2297745A1 EP09753842A EP09753842A EP2297745A1 EP 2297745 A1 EP2297745 A1 EP 2297745A1 EP 09753842 A EP09753842 A EP 09753842A EP 09753842 A EP09753842 A EP 09753842A EP 2297745 A1 EP2297745 A1 EP 2297745A1
Authority
EP
European Patent Office
Prior art keywords
thin layer
laser beam
optical
layer
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09753842A
Other languages
German (de)
French (fr)
Inventor
Delphine Neel
Stéphane Getin
Bérangère HYOT
Salim Mimouni
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Commissariat a lEnergie Atomique CEA, Commissariat a lEnergie Atomique et aux Energies Alternatives CEA filed Critical Commissariat a lEnergie Atomique CEA
Publication of EP2297745A1 publication Critical patent/EP2297745A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/32—Micromanipulators structurally combined with microscopes

Definitions

  • the invention relates to a device for trapping particles.
  • the device of the invention finds applications, for example, in the field of nanotechnologies (manipulation and assembly of micro and nanoparticles, dielectrics, semiconductors and metals, nanowires or nanotubes), biology
  • an optical trap forming device comprises a laser source which emits a laser beam and means of focusing the laser beam which strongly concentrate the laser beam with the aid of a microscope objective whose opening numeric is greater than 1.
  • FIGS. 1A and 1B illustrate the known principle of trapping a particle P with the aid of an optical clamp.
  • a particle P is placed in a liquid L.
  • a laser beam F emitted by a laser source (not shown in the figure) is focused in the liquid L and has a central zone of smaller diameter W, commonly called “waist”.
  • W central zone of smaller diameter W
  • the particle P has a refractive index greater than that of the liquid medium L surrounding it and if it is placed in the vicinity of the beam, it enters, under the effect of forces commonly called “forces of gradient "in the field of the beam F (see Figure IA). In fact, these forces attract the particle P towards the maximum intensity of the beam, that is to say at waist level. The particle then stops in the center of the waist (see Figure IB).
  • the particle thus trapped is then displaced by relative displacement of the beam F and the medium containing the particle (displacement of the medium containing the particle P with respect to the beam, displacement of the beam F relative to the medium, mutual displacement of the beam and the medium).
  • the diameters of the trapped particles range from ten microns to ten nanometers.
  • the particles can be of different types: dielectric, metallic, semiconductive, biological, polymeric, etc.
  • a major disadvantage of the particle trapping method described above is that the trapping volume of the clamp is limited by diffraction at the objective.
  • the trapping volume depends on the size of the waist of the beam, which is related to the wavelength used, the numerical aperture of the objective and the middle index in which the lens is immersed. .
  • the positioning accuracy by an optical clamp of this type is several hundred nanometers, even micron, which is not a good accuracy.
  • Optical traps of this type exhibit strong spatial confinement of the electromagnetic field and thus allow a more precise location of the object.
  • the positioning accuracy is of the order of ten nanometers.
  • FIG. 2 A first example of this type of optical trap is given in FIG. 2.
  • a metal mask M provided with nano-openings 0 is deposited on a structure T.
  • the structure T is transparent to the wavelength of the laser beam F which must trap the particles.
  • the laser beam F propagates in the structure T in a direction substantially perpendicular to the flat surface on which the mask M is deposited.
  • the laser beam F then passes through all the openings 0 which thus constitute so many traps for the particles. It is then possible, for example, to trap a latex particle of 200 nm in diameter in a nano-opening of 500 nm in diameter.
  • the disadvantages of such an optical clamp are, on the one hand, the number of steps related to the manufacture of nano-openings is important and, on the other hand, that the particles are not trapped in a free space but in a hole.
  • FIG. 3 represents a schematic diagram of such a point Pt placed in a laser beam and the distribution of the intensity of the electromagnetic field around the tip. Intensity levels are increasing as you get closer to the tip (darker and darker areas in Figure 3).
  • FIGS. 4A and 4B relate to another known device for optical trapping with an optical near-field effect.
  • This other known device comprises a photonic crystal array Ph in which a cavity Q is formed.
  • the photonic crystal array Ph is fixed on a transparent substrate T.
  • a laser beam F passes through the substrate T to reach the photonic crystal array Ph.
  • an overcurrent is generated at the cavity Q.
  • FIG. 4B illustrates the presence of this overcurrent.
  • FIG. 4B represents the normalized power R which is radiated, at the level of the cavity Q, by the device of FIG. 4A.
  • the normalized power curve R is plotted as a function of the normalized wave wavelength ⁇ of the wave propagation in the device ( ⁇ is expressed in multiples of the period "a" of the photonic crystal array). It appears, at a given wavelength A 0 , an overcurrent of the optical power in the network. This overcurrent is used for particle trapping.
  • the disadvantages of such a device are the large number and complexity the various technological steps necessary for the fabrication of the photonic crystal array, the cost of the tunable laser source necessary for the proper functioning of the device and the tuning of the tuning wavelength A 0 which depends on the size, the shape and the nature of the particles.
  • FIG. 5 Another optical near-field optical trapping device is also known from the prior art. This other device is shown in FIG. 5. It comprises a Pr pr pr transparent to the wavelength of use on which are deposited a glass plate V and a thin layer of gold f. A laser beam F passes through the prism and the glass slide V until it reaches the gold layer f on which it is reflected to create the reflected beam Fr. The direction of the laser beam F must imperatively deviate from the normal to the glass slide (ie the angle of incidence ⁇ of the beam on the glass slide must be non-zero). The coupling of the laser light in the metal layer f leads to the formation of a plasmon on the surface of the gold layer f and the appearance of an evanescent electromagnetic field Ev on this surface.
  • the particles are trapped in an annular arrangement that results from two contributions: a) the optical forces attract the objects towards the center of the beam; b) the thermophoretic forces expel the particles from the beam.
  • a disadvantage of this device is its complexity due, among other things, to the use of a prism.
  • the invention does not have the disadvantages mentioned above.
  • the invention relates to a device for trapping particles contained in a liquid placed in a tank, characterized in that it comprises a transparent substrate at a working wavelength, a thin layer of material with no optical properties. -linear reversible at the working wavelength fixed on a first face of the transparent substrate and forming all or part of at least one wall of the vessel in contact with the liquid, a near field effect optical trap forming device lens which comprises a laser source which emits a laser beam at the working wavelength and means for forming a waist of the laser beam, said means being positioned relative to the transparent substrate so that the laser beam is incident on a second face of the transparent substrate located opposite the first face and that the waist of the laser beam is formed in the thin layer, an electromagnetic field evanes This is formed as an extension of the laser beam waist on the surface of the thin layer.
  • the device for trapping particles comprises an optical mask provided with openings deposited on the thin layer.
  • the particle trapping device comprises an optical mask provided with openings placed between the thin layer and the first face of the substrate.
  • a light modulator modulates the phase of the laser beam so that a plurality of elementary laser beams are formed under the action of the light modulator, each elementary laser beam participating in the formation of the laser beam. an evanescent field at the surface of the thin layer.
  • each evanescent field at the surface of the thin layer is capable of trapping a particle.
  • an additional layer having an antireflection or mirror function is placed between the thin layer and the substrate.
  • a negative refractive index lens is placed on the surface of the thin layer, in contact with the liquid.
  • the negative index lens comprises a stack of metal / dielectric bilayers.
  • the thin layer is covered with a treatment layer capable of controlling the wettability of the surface of the thin layer which is in contact with the liquid.
  • the treatment layer is hydrophobic.
  • the thin layer constitutes a light intensity mask that moves with the laser beam.
  • the device of the invention does not necessarily have to include complex nanostructure to precisely locate small or large objects (typical dimensions ranging from 10 nm to more than 1 ⁇ m), as is the case with the devices of the art. prior.
  • FIGS. 1A and 1B illustrate the principle of trapping a particle using an optical clamp according to the known art
  • FIG. 2 represents a first example of an optical near field effect optical trap forming device according to the prior art
  • FIG. 3 represents a second example of an optical near field effect optical trap forming device according to the prior art
  • FIGS. 4A and 4B illustrate a third example of an optical near field effect optical trap forming device according to the prior art
  • FIG. 5 represents a fourth example of an optical near field effect optical trap forming device according to the prior art
  • FIG. 6 represents an optical near-field optical trap forming device according to the invention
  • FIGS. 7A and 7B respectively represent a first variant and a second variant of a first improvement of the optical near field effect optical trap forming device of the invention
  • Fig. 8 shows a second improvement of the optical near field effect optical trap forming device of the invention
  • FIG. 9 represents a particle trapping device which comprises an optical trap forming device according to the device represented in FIG. 6;
  • FIG. 10 represents a first improvement of the particle trapping device represented in FIG. 9;
  • FIG. 11 represents a second improvement of the particle trapping device represented in FIG. 9;
  • FIG. 12 represents a third improvement of the particle trapping device shown in FIG. 9;
  • FIG. 13 shows a particle trapping device which comprises an optical trap forming device according to the device shown in FIG. 7;
  • FIG. 14 represents a particle trapping device which comprises an optical trap forming device according to the device represented in FIG. 8.
  • FIG. 6 represents an optical near-field optical trap forming device according to the invention.
  • the device comprises an objective 3 which focuses a laser beam F coming from a laser source (not shown in the figure), a support 2 transparent to the wavelength of the laser beam and a thin layer 1 of material with non-optical properties.
  • "Material with reversible non-linear optical properties" means a material whose refractive index changes as a function of the illumination it receives, the number of photons arriving on this material being taken per unit of solid angle, and returning to its initial value after the illumination has ceased.
  • the material with reversible nonlinear optical properties is, for example, a III-V type semiconductor material with a small bandgap (for example InSb, GaAs, InAs, InP, GaP, CdTe, ZnS, CdS, etc.) or weakly doped (for example In x Sb y Te z ), or a material composed of KDP, or KH 2 PO 4 , or LiNbO 3 , or LiTaO 3 , or BaTiO 3 , or KNbO 3 , or BiI 2 SiO 2 O, or BiI 2 TiO 2 O, or KTP, or a phase change material such as, for example , a calcine.
  • a III-V type semiconductor material with a small bandgap for example InSb, GaAs, InAs, InP, GaP, CdTe, ZnS, CdS, etc.
  • weakly doped for example In x Sb y Te z
  • the objective 3 focuses the laser beam F so that the waist W of the beam is located in the thin layer 1.
  • the thin layer 1 changes the electronic structure of the as observed during super-resolution phenomena in optical recording (see Pichon et al., "Multiphysics Simulation of Super-Resolution BD ROM Optical Disk Readout", pages 206-208, ODS 2006).
  • the laser beam is then confined, inside the thin layer 1, in a zone z of dimensions smaller than the diffraction limit in this layer and leaves the thin layer 1 in the form of an evanescent electromagnetic field Ev very concentrated. This very concentrated evanescent electromagnetic field allows high performance optical trapping of particles.
  • FIG. 7A represents a first variant of a first improvement of the optical near-field optical trap forming device according to the invention.
  • the optical trap comprises an optical mask M such as that mentioned above with reference to FIG. 2.
  • the mask M is placed on the face of the layer 1.
  • the mask M advantageously creates a local overcurrent which, combined with the overcurrent created by the thin layer 1, leads to an even greater concentration of the evanescent field. It is then advantageously possible to use a laser beam of lower power than in the configuration without mask while obtaining identical results in terms of concentration of the evanescent field.
  • the optical mask M is placed under the face of the thin layer 1, that is to say between the thin layer 1 and the transparent support 2.
  • FIG. 7B illustrates this second variant.
  • Fig. 8 shows a second improvement of the optical trap forming device of the invention.
  • the device represented in FIG. 8 comprises a mod spatial light modulator, for example a liquid crystal screen, and a computer or a personal computer PC which controls the spatial modulator. of light Mod.
  • a particle surrounded by several elementary laser beams can to be kept in the center of these beams by repulsion.
  • Other means than a liquid crystal display can be used for forming multi-beam clamps such as, for example, an interferometer or a diffraction grating, or a hologram.
  • FIG. 9 represents a particle trapping device which is associated with the optical near-field optical trap forming device represented in FIG. 6.
  • the particles P evolve in a liquid L contained in a tank 4 whose bottom wall is made by the thin layer 1.
  • the very concentrated evanescent electromagnetic field Ev traps any particle located in its vicinity. To make a displacement of a particle thus trapped, a relative displacement of the laser beam F and the structure consisting of the elements 1, 2 and 4 is performed.
  • the thickness of the thin layer 1 can vary, for example, from 5 nm to 100 nm.
  • the laser beam F may be a continuous or pulsed beam in a frequency range from Hz to THz.
  • the following table illustrates some examples, without limitation:
  • the substrate 2 transparent at the wavelength of use is made, for example, of silicon
  • FIG. 10 represents a first improvement of the particle trapping device represented in FIG. 9.
  • the device of FIG. 10 comprises, between the substrate 2 and the layer 1, an additional layer. 5 which has an optical function, for example antireflection / mirror.
  • the layer 5 is formed of a single layer or a set of layers.
  • the thickness of the layer or of the set of layers constituting the layer 5 is typically between 10 nm and 10 ⁇ m.
  • the transfer of the layer 5 between the substrate 2 and the layer 1 is carried out by sol-gel, PVD (PVD for "Physical Vapor Deposition"), IBS (IBS for "Ion Beam Sputtering", spraying, CVD (CVD for "Chemical Vapor Deposition ”) ).
  • the material (s) which constitutes (s) the layer 5 is (are) chosen from among the dielectrics such as, for example, SiO 2 , HgO 2 , Ta 2 O 5 , TiO 2 , ZrO 2 , Al 2 O 3 , YF 3 , LaF , Ta 2 O 6 .
  • the layer 5 constitutes a heat sink which makes it possible to avoid the heating of the liquid L, which heating can occur under the effect of the laser beam.
  • the material or materials that constitute the layer 5 are then chosen from metals (for example, copper, aluminum, etc.), oxides, or nitrides (for example Si 3 N 4 ).
  • Fig. 11 shows a second improvement of the particle trapping device of the invention.
  • the thin layer 1 is covered with a treatment for controlling the wettability of the surface on the portion of the stack in contact with the liquid L.
  • a hydrophobic treatment is carried out with a layer of polytetrafluoroethylene commonly known as teflon or by grafting appropriate organic molecules to form, for example, a silane layer.
  • the hydrophobic layer advantageously makes it possible to prevent the particles P from sticking to the thin layer 1.
  • Fig. 12 shows a third improvement of the particle trapping device of the invention.
  • the device comprises, above the layer 1, a negative refractive index lens 6.
  • the negative refractive index lens consists of a stack of metal / dielectric bilayers.
  • each bilayer of the stack of bilayers is produced by a layer silver (Ag) covered by a layer of silica (SiO 2 ) •
  • the lens 6 advantageously makes it possible to image, on the surface of the lens, the confined beam at the surface of the layer 1 while maintaining its lateral dimension.
  • FIG. a particle trapping device which comprises an optical trap forming device according to the device shown in Figure 7A.
  • the device of FIG. 13 comprises a tank 4 situated above the layer 1. All the variants of the particle trapping devices represented in FIGS. 9-12 apply, if necessary, to particle trap device shown in FIG. 13.
  • FIG. 14 shows a particle trap device which comprises an optical trap forming device according to the device shown in FIG. 8. In addition to the elements represented in FIG. 8, the device of FIG. FIG.
  • the optical near-field optical trap forming device forms the bottom of the tank. More generally, the invention relates to other embodiments in which the optical near-field optical trap forming device constitutes all or part of any wall of the tank, the term "wall" in front of 'hear like any element of the tank in contact with the liquid and which delimits the inside of the outside of the tank (side wall, cover, bottom).
  • a silica substrate for example of Hérasil Hl type
  • a layer of InSb of 30 nm thickness is deposited by a sputtering method
  • annealing is carried out for two hours with an oven heated to 200 ° C.
  • a liquid solution is prepared containing 300 nm diameter latex beads which are injected into the tank by a micropipette;
  • vat is covered by a coverslip
  • the assembly thus constituted is placed on a sample holder of the optical system constituted by an inverted microscope construct which includes a lens digital aperture of, for example, 1.2 and into which is injected a laser beam from a laser diode emitting, for example, at the wavelength 405 nm, a modulated wave at 1 GHz and 50 mW power.
  • the sample holder is moved to trap the latex beads using the optical trap.
  • particle is used to refer generally to an object or nanoobject capable of being trapped using the optical trap forming device of the invention.
  • the term "nano-object" must of course not be understood as an object whose dimensions are exclusively of the order of a few nanometers.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
  • Microscoopes, Condenser (AREA)

Abstract

The invention relates to a device for trapping particles contained in a liquid (L) placed in a tank (4), characterized in that it comprises a substrate (2) that is transparent at a working wavelength, a thin layer (1) of material with non-linear optical properties that are reversible at the working wavelength and which is fixed to a first face of the transparent substrate (2) to form all or part of at least one wall of the tank (4), a device for forming an optical trap which comprises a laser source which emits a laser beam and means for forming a waist of the laser beam, the laser beam being incident upon that face of the transparent substrate that lies on the opposite side to the first face and the waist of the laser beam being formed in the thin layer (1), an evanescent electromagnetic field forming at the surface of the thin layer (1).

Description

DISPOSITIF DE PIEGEAGE DE PARTICULES DEVICE FOR TRAPPING PARTICLES
DESCRIPTIONDESCRIPTION
Domaine technique et art antérieur L' invention concerne un dispositif de piégeage de particules.TECHNICAL FIELD AND PRIOR ART The invention relates to a device for trapping particles.
Le dispositif de l'invention trouve des applications, par exemple, dans le domaine des nanotechnologies (manipulation et assemblage de micro et nanoparticules diélectriques, semi-conductrices et métalliques, nanofils ou nanotubes) , de la biologieThe device of the invention finds applications, for example, in the field of nanotechnologies (manipulation and assembly of micro and nanoparticles, dielectrics, semiconductors and metals, nanowires or nanotubes), biology
(manipulation de macromolécules telles que protéines,(manipulation of macromolecules such as proteins,
ADN) et de la chimie organique (macromolécules, polymères ou organométalliques) . Selon l'art connu, un dispositif de formation de piège optique comprend une source laser qui émet un faisceau laser et des moyens de focalisation du faisceau laser qui concentrent fortement le faisceau laser à l'aide d'un objectif de microscope dont l'ouverture numérique est supérieure à 1.DNA) and organic chemistry (macromolecules, polymers or organometallics). According to the known art, an optical trap forming device comprises a laser source which emits a laser beam and means of focusing the laser beam which strongly concentrate the laser beam with the aid of a microscope objective whose opening numeric is greater than 1.
Les figures IA et IB illustrent le principe connu du piégeage d'une particule P à l'aide d'une pince optique. Une particule P est placée dans un liquide L. Un faisceau laser F émis par une source laser (non représentée sur la figure) est focalisé dans le liquide L et possède une zone centrale de plus faible diamètre W, communément appelée « waist ». Si la particule P a un indice de réfraction supérieur à celui du milieu liquide L qui l'environne et si elle se trouve placée au voisinage du faisceau, elle entre, sous l'effet de forces communément appelées « forces de gradient », dans le champ du faisceau F (cf. figure IA) . De fait, ces forces attirent la particule P vers le maximum d'intensité du faisceau, c'est-à-dire au niveau du waist. La particule s'immobilise alors au centre du waist (cf. figure IB) .FIGS. 1A and 1B illustrate the known principle of trapping a particle P with the aid of an optical clamp. A particle P is placed in a liquid L. A laser beam F emitted by a laser source (not shown in the figure) is focused in the liquid L and has a central zone of smaller diameter W, commonly called "waist". If the particle P has a refractive index greater than that of the liquid medium L surrounding it and if it is placed in the vicinity of the beam, it enters, under the effect of forces commonly called "forces of gradient "in the field of the beam F (see Figure IA). In fact, these forces attract the particle P towards the maximum intensity of the beam, that is to say at waist level. The particle then stops in the center of the waist (see Figure IB).
La particule ainsi piégée est alors déplacée par déplacement relatif du faisceau F et du milieu contenant la particule (déplacement du milieu contenant la particule P par rapport au faisceau, déplacement du faisceau F par rapport au milieu, déplacement mutuel du faisceau et du milieu) . Les diamètres des particules piégées vont de la dizaine de microns à une dizaine de nanomètres. Les particules peuvent être de différentes natures : diélectrique, métallique, semi-conductrice, biologique, polymérique, etc.The particle thus trapped is then displaced by relative displacement of the beam F and the medium containing the particle (displacement of the medium containing the particle P with respect to the beam, displacement of the beam F relative to the medium, mutual displacement of the beam and the medium). The diameters of the trapped particles range from ten microns to ten nanometers. The particles can be of different types: dielectric, metallic, semiconductive, biological, polymeric, etc.
Un inconvénient majeur du procédé de piégeage de particules décrit ci-dessus est que le volume de piégeage de la pince est limité par la diffraction au niveau de l'objectif. Le volume de piégeage dépend en effet de la taille du waist du faisceau, laquelle est liée à la longueur d'onde utilisée, à l'ouverture numérique de l'objectif ainsi qu'à l'indice du milieu dans lequel baigne l'objectif. La précision de positionnement par une pince optique de ce type est de plusieurs centaines de nanomètres, voire du micron, ce qui n'est pas une bonne précision.A major disadvantage of the particle trapping method described above is that the trapping volume of the clamp is limited by diffraction at the objective. The trapping volume depends on the size of the waist of the beam, which is related to the wavelength used, the numerical aperture of the objective and the middle index in which the lens is immersed. . The positioning accuracy by an optical clamp of this type is several hundred nanometers, even micron, which is not a good accuracy.
Pour améliorer la localisation de la particule, il est connu d'utiliser une catégorie de pièges optiques qui reposent sur des effets de champ proche optique. Les pièges optiques de ce type présentent un fort confinement spatial du champ électromagnétique et permettent ainsi une localisation plus précise de l'objet. La précision de positionnement est de l'ordre de la dizaine de nanomètres.To improve the localization of the particle, it is known to use a category of optical traps that rely on optical near-field effects. Optical traps of this type exhibit strong spatial confinement of the electromagnetic field and thus allow a more precise location of the object. The positioning accuracy is of the order of ten nanometers.
Un premier exemple de ce type de piège optique est donné en figure 2. Un masque métallique M muni de nano-ouvertures 0 est déposé sur une structure T. La structure T est transparente à la longueur d' onde du faisceau laser F qui doit piéger les particules. Le faisceau laser F se propage dans la structure T selon une direction sensiblement perpendiculaire à la surface plane sur laquelle est déposée le masque M. Le faisceau laser F traverse alors l'ensemble des ouvertures 0 qui constituent ainsi autant de pièges pour les particules. Il est alors possible, par exemple, de piéger une particule de latex de 200nm de diamètre dans une nano- ouverture de 500nm de diamètre. Les inconvénients d'une telle pince optique sont, d'une part, que le nombre d'étapes liées à la fabrication des nano-ouvertures est important et, d'autre part, que les particules ne sont pas piégées dans un espace libre mais dans un trou.A first example of this type of optical trap is given in FIG. 2. A metal mask M provided with nano-openings 0 is deposited on a structure T. The structure T is transparent to the wavelength of the laser beam F which must trap the particles. The laser beam F propagates in the structure T in a direction substantially perpendicular to the flat surface on which the mask M is deposited. The laser beam F then passes through all the openings 0 which thus constitute so many traps for the particles. It is then possible, for example, to trap a latex particle of 200 nm in diameter in a nano-opening of 500 nm in diameter. The disadvantages of such an optical clamp are, on the one hand, the number of steps related to the manufacture of nano-openings is important and, on the other hand, that the particles are not trapped in a free space but in a hole.
Il est également connu de l'art antérieur d'utiliser la technologie SNOM pour réaliser un piège optique (SNOM pour « Scanning Near-field Optical Microscope », à savoir la technologie qui utilise les microscopes optiques en champ proche optique) . Le piège optique est alors réalisé, par exemple, à l'aide d'une pointe en or placée dans un faisceau laser. C'est la surintensité du champ électromagnétique qui apparaît à l'extrémité de la pointe qui piège la particule. Une pointe en or de rayon d'apex 5nm est alors apte à piéger une particule de latex de lOnm de diamètre placée dans de l'eau. La figure 3 représente un schéma de principe d'une telle pointe Pt placée dans un faisceau laser et la distribution de l'intensité du champ électromagnétique autour de la pointe. Les niveaux d' intensité sont croissants au fur et à mesure que l'on se rapproche de la pointe (zones de plus en plus foncées sur la figure 3) . Les inconvénients d'un tel dispositif sont dans son coût d'exploitation et dans le fait qu'il est difficilement parallélisable . Les figures 4A et 4B concernent un autre dispositif connu de piégeage optique à effet de champ proche optique. Cet autre dispositif connu comprend un réseau à cristaux photoniques Ph dans lequel est formée une cavité Q. Le réseau à cristaux photoniques Ph est fixé sur un substrat transparent T. Un faisceau laser F traverse le substrat T pour atteindre le réseau à cristaux photoniques Ph. Pour une longueur d'onde donnée du faisceau laser F, il se crée une surintensité au niveau de la cavité Q. La figure 4B illustre la présence de cette surintensité. La figure 4B représente la puissance normalisée R qui est rayonnée , au niveau de la cavité Q, par le dispositif de la figure 4A. La courbe de la puissance normalisée R est tracée en fonction de la longueur d'onde normalisée Λ de propagation de l'onde dans le dispositif (Λ est exprimée en multiples de la période « a » du réseau à cristaux photoniques) . Il apparaît, à une longueur d'onde donnée A0, une surintensité de la puissance optique dans le réseau. Cette surintensité est utilisée pour le piégeage des particules. Les inconvénients d'un tel dispositif sont le grand nombre et la complexité des différentes étapes technologiques nécessaires pour la fabrication du réseau à cristaux photoniques, le coût de la source laser accordable nécessaire au bon fonctionnement du dispositif et le réglage de la longueur d'onde d'accord A0 qui dépend de la taille, de la forme et de la nature des particules.It is also known from the prior art to use the SNOM technology to make an optical trap (SNOM for Scanning Near-field Optical Microscope, namely the technology that uses optical microscopy near-field optical). The optical trap is then made, for example, using a gold tip placed in a laser beam. It is the overcurrent of the electromagnetic field that appears at the end of the tip that traps the particle. A gold tip with apex radius 5 nm is then able to trap a latex particle of 10 nm in diameter. placed in water. FIG. 3 represents a schematic diagram of such a point Pt placed in a laser beam and the distribution of the intensity of the electromagnetic field around the tip. Intensity levels are increasing as you get closer to the tip (darker and darker areas in Figure 3). The disadvantages of such a device are in its operating cost and in the fact that it is difficult to parallelize. FIGS. 4A and 4B relate to another known device for optical trapping with an optical near-field effect. This other known device comprises a photonic crystal array Ph in which a cavity Q is formed. The photonic crystal array Ph is fixed on a transparent substrate T. A laser beam F passes through the substrate T to reach the photonic crystal array Ph. For a given wavelength of the laser beam F, an overcurrent is generated at the cavity Q. FIG. 4B illustrates the presence of this overcurrent. FIG. 4B represents the normalized power R which is radiated, at the level of the cavity Q, by the device of FIG. 4A. The normalized power curve R is plotted as a function of the normalized wave wavelength Λ of the wave propagation in the device (Λ is expressed in multiples of the period "a" of the photonic crystal array). It appears, at a given wavelength A 0 , an overcurrent of the optical power in the network. This overcurrent is used for particle trapping. The disadvantages of such a device are the large number and complexity the various technological steps necessary for the fabrication of the photonic crystal array, the cost of the tunable laser source necessary for the proper functioning of the device and the tuning of the tuning wavelength A 0 which depends on the size, the shape and the nature of the particles.
Un autre dispositif de piégeage optique à effet de champ proche optique est également connu de l'art antérieur. Cet autre dispositif est représenté en figure 5. Il comprend un prisme Pr transparent à la longueur d'onde d'utilisation sur lequel sont déposées une lame de verre V et une fine couche d'or f. Un faisceau laser F traverse le prisme et la lame de verre V jusqu'à atteindre la couche d'or f sur laquelle il se réfléchit pour créer le faisceau réfléchi Fr. La direction du faisceau laser F doit impérativement s'écarter de la normale à la lame de verre (i.e. l'angle d'incidence θ du faisceau sur la lame de verre doit être non nul) . Le couplage de la lumière laser dans la couche métallique f conduit à la formation d'un plasmon en surface de la couche d' or f et à l'apparition d'un champ électromagnétique évanescent Ev sur cette surface. Les particules sont alors piégées selon une disposition annulaire qui résulte de deux contributions : a) les forces optiques attirent les objets vers le centre du faisceau ; b) les forces thermophorétiques expulsent les particules du faisceau. Un inconvénient de ce dispositif est sa complexité due, entre autres, à l'utilisation d'un prisme .Another optical near-field optical trapping device is also known from the prior art. This other device is shown in FIG. 5. It comprises a Pr pr pr transparent to the wavelength of use on which are deposited a glass plate V and a thin layer of gold f. A laser beam F passes through the prism and the glass slide V until it reaches the gold layer f on which it is reflected to create the reflected beam Fr. The direction of the laser beam F must imperatively deviate from the normal to the glass slide (ie the angle of incidence θ of the beam on the glass slide must be non-zero). The coupling of the laser light in the metal layer f leads to the formation of a plasmon on the surface of the gold layer f and the appearance of an evanescent electromagnetic field Ev on this surface. The particles are trapped in an annular arrangement that results from two contributions: a) the optical forces attract the objects towards the center of the beam; b) the thermophoretic forces expel the particles from the beam. A disadvantage of this device is its complexity due, among other things, to the use of a prism.
L' invention ne présente pas les inconvénients mentionnés ci-dessus.The invention does not have the disadvantages mentioned above.
Exposé de l'inventionPresentation of the invention
En effet, l'invention concerne un dispositif de piégeage de particules contenues dans un liquide placé dans une cuve, caractérisé en ce qu'il comprend un substrat transparent à une longueur d'onde de travail, une couche mince de matériau aux propriétés optiques non-linéaires réversibles à la longueur d'onde de travail fixée sur une première face du substrat transparent et formant tout ou partie d'au moins une paroi de la cuve au contact du liquide, un dispositif de formation de piège optique à effet de champ proche optique qui comprend une source laser qui émet un faisceau laser à la longueur d'onde de travail et des moyens pour former un waist du faisceau laser, lesdits moyens étant positionnés par rapport au substrat transparent de telle sorte que le faisceau laser soit incident sur une deuxième face du substrat transparent située à l'opposé de la première face et que le waist du faisceau laser se forme dans la couche mince, un champ électromagnétique évanescent se formant dans le prolongement du waist de faisceau laser, en surface de la couche mince.Indeed, the invention relates to a device for trapping particles contained in a liquid placed in a tank, characterized in that it comprises a transparent substrate at a working wavelength, a thin layer of material with no optical properties. -linear reversible at the working wavelength fixed on a first face of the transparent substrate and forming all or part of at least one wall of the vessel in contact with the liquid, a near field effect optical trap forming device lens which comprises a laser source which emits a laser beam at the working wavelength and means for forming a waist of the laser beam, said means being positioned relative to the transparent substrate so that the laser beam is incident on a second face of the transparent substrate located opposite the first face and that the waist of the laser beam is formed in the thin layer, an electromagnetic field evanes This is formed as an extension of the laser beam waist on the surface of the thin layer.
Selon une caractéristique supplémentaire de l'invention, le dispositif de piégeage de particules comprend un masque optique muni d' ouvertures déposé sur la couche mince.According to a further characteristic of the invention, the device for trapping particles comprises an optical mask provided with openings deposited on the thin layer.
Selon une autre caractéristique supplémentaire de l'invention, le dispositif de piégeage de particules comprend un masque optique muni d' ouvertures placé entre la couche mince et la première face du substrat.According to another additional characteristic of the invention, the particle trapping device comprises an optical mask provided with openings placed between the thin layer and the first face of the substrate.
Selon encore une autre caractéristique supplémentaire de l'invention, un modulateur de lumière module la phase du faisceau laser de telle sorte que plusieurs faisceaux laser élémentaires se forment sous l'action du modulateur de lumière, chaque faisceau laser élémentaire participant à la formation d'un champ évanescent en surface de la couche mince.According to yet another additional characteristic of the invention, a light modulator modulates the phase of the laser beam so that a plurality of elementary laser beams are formed under the action of the light modulator, each elementary laser beam participating in the formation of the laser beam. an evanescent field at the surface of the thin layer.
Selon encore une autre caractéristique supplémentaire de l'invention, chaque champ évanescent en surface de la couche mince est apte à piéger une particule .According to yet another additional characteristic of the invention, each evanescent field at the surface of the thin layer is capable of trapping a particle.
Selon encore une autre caractéristique supplémentaire de l'invention, une couche supplémentaire ayant une fonction antireflet ou de miroir est placée entre la couche mince et le substrat.According to yet another additional characteristic of the invention, an additional layer having an antireflection or mirror function is placed between the thin layer and the substrate.
Selon encore une autre caractéristique supplémentaire de l'invention, une lentille à indice de réfraction négatif est placée en surface de la couche mince, au contact du liquide.According to yet another additional characteristic of the invention, a negative refractive index lens is placed on the surface of the thin layer, in contact with the liquid.
Selon encore une autre caractéristique supplémentaire de l'invention, la lentille à indice négatif comporte un empilement de bicouches métal/diélectrique . Selon encore une autre caractéristique supplémentaire de l'invention, la couche mince est recouverte d'une couche de traitement apte à contrôler la mouillabilité de la surface de la couche mince qui est au contact du liquide.According to yet another additional characteristic of the invention, the negative index lens comprises a stack of metal / dielectric bilayers. According to yet another additional characteristic of the invention, the thin layer is covered with a treatment layer capable of controlling the wettability of the surface of the thin layer which is in contact with the liquid.
Selon encore une autre caractéristique supplémentaire de l'invention, la couche de traitement est hydrophobe .According to yet another additional characteristic of the invention, the treatment layer is hydrophobic.
De façon très avantageuse, la couche mince constitue, du fait du caractère réversible de la non- linéarité créée dans cette couche par le faisceau laser, un masque d'intensité lumineuse qui se déplace avec le faisceau laser. Le dispositif de l'invention n'a donc pas à nécessairement comprendre de nanostructure complexe pour localiser avec précision des objets petits ou gros (dimensions typiques allant de lOnm à plus de lμm) , comme c'est le cas des dispositifs de l'art antérieur.Very advantageously, because of the reversible nature of the non-linearity created in this layer by the laser beam, the thin layer constitutes a light intensity mask that moves with the laser beam. The device of the invention does not necessarily have to include complex nanostructure to precisely locate small or large objects (typical dimensions ranging from 10 nm to more than 1 μm), as is the case with the devices of the art. prior.
D'autres caractéristiques et avantages de l'invention apparaîtront dans la description qui va suivre, faite en référence aux figures jointes, parmi lesquelles :Other features and advantages of the invention will appear in the description which follows, with reference to the appended figures, among which:
- Les figures IA et IB illustrent le principe de piégeage d'une particule à l'aide d'une pince optique selon l'art connu ;FIGS. 1A and 1B illustrate the principle of trapping a particle using an optical clamp according to the known art;
- La figure 2 représente un premier exemple de dispositif de formation de piège optique à effet de champ proche optique selon l'art antérieur ;FIG. 2 represents a first example of an optical near field effect optical trap forming device according to the prior art;
- La figure 3 représente un deuxième exemple de dispositif de formation de piège optique à effet de champ proche optique selon l'art antérieur ; - Les figures 4A et 4B illustrent un troisième exemple de dispositif de formation de piège optique à effet de champ proche optique selon l'art antérieur ;FIG. 3 represents a second example of an optical near field effect optical trap forming device according to the prior art; FIGS. 4A and 4B illustrate a third example of an optical near field effect optical trap forming device according to the prior art;
- La figure 5 représente un quatrième exemple de dispositif de formation de piège optique à effet de champ proche optique selon l'art antérieur ;FIG. 5 represents a fourth example of an optical near field effect optical trap forming device according to the prior art;
- La figure 6 représente un dispositif de formation de piège optique à effet de champ proche optique selon l'invention ; - Les figures 7A et 7B représentent respectivement une première variante et une deuxième variante d'un premier perfectionnement du dispositif de formation de piège optique à effet de champ proche optique de l'invention ; - La figure 8 représente un deuxième perfectionnement du dispositif de formation de piège optique à effet de champ proche optique de 1' invention ;FIG. 6 represents an optical near-field optical trap forming device according to the invention; FIGS. 7A and 7B respectively represent a first variant and a second variant of a first improvement of the optical near field effect optical trap forming device of the invention; Fig. 8 shows a second improvement of the optical near field effect optical trap forming device of the invention;
- La figure 9 représente un dispositif de piégeage de particules qui comprend un dispositif de formation de piège optique conforme au dispositif représenté en figure 6 ;FIG. 9 represents a particle trapping device which comprises an optical trap forming device according to the device represented in FIG. 6;
- La figure 10 représente un premier perfectionnement du dispositif de piégeage de particules représenté en figure 9 ;FIG. 10 represents a first improvement of the particle trapping device represented in FIG. 9;
- La figure 11 représente un deuxième perfectionnement du dispositif de piégeage de particules représenté en figure 9 ;FIG. 11 represents a second improvement of the particle trapping device represented in FIG. 9;
- La figure 12 représente un troisième perfectionnement du dispositif de piégeage de particules représenté en figure 9 ; - La figure 13 représente un dispositif de piégeage de particules qui comprend un dispositif de formation de piège optique conforme au dispositif représenté en figure 7 ; - La figure 14 représente un dispositif de piégeage de particules qui comprend un dispositif de formation de piège optique conforme au dispositif représenté en figure 8.FIG. 12 represents a third improvement of the particle trapping device shown in FIG. 9; FIG. 13 shows a particle trapping device which comprises an optical trap forming device according to the device shown in FIG. 7; FIG. 14 represents a particle trapping device which comprises an optical trap forming device according to the device represented in FIG. 8.
Description détaillée de modes de réalisation préférentiels de l' inventionDETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
La figure 6 représente un dispositif de formation de piège optique à effet de champ proche optique selon l'invention. Le dispositif comprend un objectif 3 qui focalise un faisceau laser F provenant d'une source laser (non représentée sur la figure), un support 2 transparent à la longueur d'onde du faisceau laser et une couche mince 1 de matériau aux propriétés optiques non linéaires réversibles à la longueur d'onde de travail déposée sur le support 2. Par « matériau aux propriétés optiques non linéaires réversibles », il faut entendre un matériau dont l'indice de réfraction change en fonction d'un éclairement qu'il reçoit, le nombre de photons arrivant sur ce matériau étant pris par unité d'angle solide, et revient à sa valeur initiale après que l' éclairement a cessé. Le matériau aux propriétés optiques non linéaires réversibles est, par exemple, un matériau semi-conducteur de type III-V à faible bande interdite (par exemple InSb, GaAs, InAs, InP, GaP, CdTe, ZnS, CdS, etc.) ou faiblement dopé (par exemple InxSbyTez) , ou un matériau composé de KDP, ou KH2PO4, ou LiNbO3, ou LiTaO3, ou BaTiO3, ou KNbO3, ou BiI2SiO2O, ou BiI2TiO2O, ou KTP, ou un matériau à changement de phase tel que, par exemple, un calcogénure. L'objectif 3 focalise le faisceau laser F de façon que le waist W du faisceau se trouve situé dans la couche mince 1. Sous l'effet de la lumière laser concentrée au niveau du waist, la couche mince 1 change de structure électronique de la façon constatée lors des phénomènes de super-résolution en enregistrement optique (cf. Pichon et al. « Multiphysics Simulation of Super-Resolution BD ROM Opical Disk Readout », pages 206-208, ODS 2006) . Le faisceau laser est alors confiné, à l'intérieur de la couche mince 1, dans une zone z de dimensions inférieures à la limite de diffraction dans cette couche et sort de la couche mince 1 sous la forme d'un champ électromagnétique évanescent Ev très concentré. Ce champ électromagnétique évanescent très concentré permet un piégeage optique très performant de particules.FIG. 6 represents an optical near-field optical trap forming device according to the invention. The device comprises an objective 3 which focuses a laser beam F coming from a laser source (not shown in the figure), a support 2 transparent to the wavelength of the laser beam and a thin layer 1 of material with non-optical properties. linear reversible to the working wavelength deposited on the support 2. "Material with reversible non-linear optical properties" means a material whose refractive index changes as a function of the illumination it receives, the number of photons arriving on this material being taken per unit of solid angle, and returning to its initial value after the illumination has ceased. The material with reversible nonlinear optical properties is, for example, a III-V type semiconductor material with a small bandgap (for example InSb, GaAs, InAs, InP, GaP, CdTe, ZnS, CdS, etc.) or weakly doped (for example In x Sb y Te z ), or a material composed of KDP, or KH 2 PO 4 , or LiNbO 3 , or LiTaO 3 , or BaTiO 3 , or KNbO 3 , or BiI 2 SiO 2 O, or BiI 2 TiO 2 O, or KTP, or a phase change material such as, for example , a calcine. The objective 3 focuses the laser beam F so that the waist W of the beam is located in the thin layer 1. Under the effect of the concentrated laser light at the waist, the thin layer 1 changes the electronic structure of the as observed during super-resolution phenomena in optical recording (see Pichon et al., "Multiphysics Simulation of Super-Resolution BD ROM Optical Disk Readout", pages 206-208, ODS 2006). The laser beam is then confined, inside the thin layer 1, in a zone z of dimensions smaller than the diffraction limit in this layer and leaves the thin layer 1 in the form of an evanescent electromagnetic field Ev very concentrated. This very concentrated evanescent electromagnetic field allows high performance optical trapping of particles.
La figure 7A représente une première variante d'un premier perfectionnement du dispositif de formation de piège optique à effet de champ proche optique selon l'invention. Le piège optique comprend un masque optique M tel que celui mentionné précédemment en référence à la figure 2. Le masque M est placé sur la face de la couche 1. Le masque M crée avantageusement une surintensité locale qui, combinée avec la surintensité créée par la couche mince 1, conduit à une encore plus grande concentration du champ évanescent. Il est alors avantageusement possible d'utiliser un faisceau laser de moindre puissance que dans la configuration sans masque tout en obtenant des résultats identiques en terme de concentration du champ évanescent . Selon une deuxième variante du premier perfectionnement de l'invention, le masque optique M est placé sous la face de la couche mince 1, c'est-à- dire entre la couche mince 1 et le support transparent 2. La figure 7B illustre cette deuxième variante. La figure 8 représente un deuxième perfectionnement du dispositif de formation de piège optique de l'invention. En plus des éléments du dispositif de l'invention représenté en figure 6, le dispositif représenté en figure 8 comprend un modulateur spatial de lumière Mod, par exemple un écran à cristaux liquides, et un calculateur ou un ordinateur personnel PC qui commande le modulateur spatial de lumière Mod. De façon connue en soi, en fonction des commandes qui lui sont appliquées à partir du calculateur, le modulateur de lumière Mod module la phase du faisceau laser F issu de la source Lz de telle sorte que n faisceaux laser élémentaires se forment sous l'action du modulateur de lumière, n étant un entier supérieur ou égal à 2 (n=3 sur la figure 8) . Chaque faisceau laser élémentaire crée, en surface de la couche 1, un champ évanescent élémentaire Ev1 (i=l, 2, ..., n) qui est apte à capter une particule. Il est ainsi possible de manipuler jusqu'à n particules en même temps. Dans le cas particulier où apparaissent d' importants effets thermophorétiques dans la couche 1, une particule entourée de plusieurs faisceaux laser élémentaires peut être maintenue au centre de ces faisceaux par répulsion. D'autres moyens qu'un écran à cristaux liquides peuvent être utilisés pour la formation de pinces multi-faisceaux comme, par exemple, un interféromètre ou un réseau de diffraction, ou un hologramme .FIG. 7A represents a first variant of a first improvement of the optical near-field optical trap forming device according to the invention. The optical trap comprises an optical mask M such as that mentioned above with reference to FIG. 2. The mask M is placed on the face of the layer 1. The mask M advantageously creates a local overcurrent which, combined with the overcurrent created by the thin layer 1, leads to an even greater concentration of the evanescent field. It is then advantageously possible to use a laser beam of lower power than in the configuration without mask while obtaining identical results in terms of concentration of the evanescent field. According to a second variant of the first improvement of the invention, the optical mask M is placed under the face of the thin layer 1, that is to say between the thin layer 1 and the transparent support 2. FIG. 7B illustrates this second variant. Fig. 8 shows a second improvement of the optical trap forming device of the invention. In addition to the elements of the device of the invention shown in FIG. 6, the device represented in FIG. 8 comprises a mod spatial light modulator, for example a liquid crystal screen, and a computer or a personal computer PC which controls the spatial modulator. of light Mod. In a manner known per se, as a function of the commands applied to it from the computer, the light modulator Mod modulates the phase of the laser beam F coming from the source Lz so that n elementary laser beams are formed under the action of the light modulator, n being an integer greater than or equal to 2 (n = 3 in Figure 8). Each elementary laser beam creates, on the surface of the layer 1, an elementary evanescent field Ev 1 (i = 1, 2, ..., n) which is able to capture a particle. It is thus possible to handle up to n particles at the same time. In the particular case where there are important thermophoretic effects in layer 1, a particle surrounded by several elementary laser beams can to be kept in the center of these beams by repulsion. Other means than a liquid crystal display can be used for forming multi-beam clamps such as, for example, an interferometer or a diffraction grating, or a hologram.
La figure 9 représente un dispositif de piégeage de particules qui est associé au dispositif de formation de piège optique à effet de champ proche optique représenté en figure 6. Les particules P évoluent dans un liquide L contenu dans une cuve 4 dont la paroi inférieure est réalisée par la couche mince 1. Le champ électromagnétique évanescent très concentré Ev piège toute particule située à sa proximité. Pour effectuer un déplacement d'une particule ainsi piégée, un déplacement relatif du faisceau laser F et de la structure constituée des éléments 1, 2 et 4 est effectuée .FIG. 9 represents a particle trapping device which is associated with the optical near-field optical trap forming device represented in FIG. 6. The particles P evolve in a liquid L contained in a tank 4 whose bottom wall is made by the thin layer 1. The very concentrated evanescent electromagnetic field Ev traps any particle located in its vicinity. To make a displacement of a particle thus trapped, a relative displacement of the laser beam F and the structure consisting of the elements 1, 2 and 4 is performed.
L'épaisseur de la couche mince 1 peut varier, par exemple, de 5nm à lOOnm. Le faisceau laser F peut être un faisceau continu ou impulsionnel dans une gamme de fréquences allant du Hz au THz. Pour ce qui concerne les particules susceptibles d'être piégées par une pince optique de l'invention, le tableau ci-dessous en illustre quelques exemples, à titre non limitatif : The thickness of the thin layer 1 can vary, for example, from 5 nm to 100 nm. The laser beam F may be a continuous or pulsed beam in a frequency range from Hz to THz. With regard to the particles capable of being trapped by an optical clamp of the invention, the following table illustrates some examples, without limitation:
Le substrat 2 transparent à la longueur d' onde d'utilisation est réalisé, par exemple, en siliciumThe substrate 2 transparent at the wavelength of use is made, for example, of silicon
(Si), en polycarbonate, en verre, en silice, etc. La figure 10 représente un premier perfectionnement du dispositif de piégeage de particules représenté en figure 9. En plus des éléments mentionnés en référence à la figure 9, le dispositif de la figure 10 comprend, entre le substrat 2 et la couche 1, une couche supplémentaire 5 qui a une fonction optique, par exemple antireflet/miroir. La couche 5 est formée d'une seule couche ou d'un ensemble de couches. L'épaisseur de la couche ou de l'ensemble de couches qui constituent la couche 5 est typiquement comprise entre lOnm et lOμm. Le report de la couche 5 entre le substrat 2 et la couche 1 est effectuée par sol-gel, PVD (PVD pour « Physical Vapor Déposition), IBS (IBS pour « Ion Beam Sputtering », pulvérisation, CVD (CVD pour « Chemical Vapor Déposition »)...) . Dans une première variante de l'invention, le (les) matériau (x) qui constitue (nt) la couche 5 est (sont) choisi (s) parmi les diélectriques tels que, par exemple, Siθ2, HgO2, Ta2O5, TiO2, ZrO2, Al2O3, YF3, LaF, Ta2O6. Dans une autre variante de l'invention, la couche 5 constitue un puits thermique qui permet d'éviter l' échauffement du liquide L, lequel échauffement peut survenir sous l'effet du faisceau laser. Le ou les matériaux qui constituent la couche 5 sont alors choisis parmi les métaux (par exemple, cuivre, aluminium, etc.), les oxydes, ou les nitrures (par exemple Si3N4) .(Si), polycarbonate, glass, silica, etc. FIG. 10 represents a first improvement of the particle trapping device represented in FIG. 9. In addition to the elements mentioned with reference to FIG. 9, the device of FIG. 10 comprises, between the substrate 2 and the layer 1, an additional layer. 5 which has an optical function, for example antireflection / mirror. The layer 5 is formed of a single layer or a set of layers. The thickness of the layer or of the set of layers constituting the layer 5 is typically between 10 nm and 10 μm. The transfer of the layer 5 between the substrate 2 and the layer 1 is carried out by sol-gel, PVD (PVD for "Physical Vapor Deposition"), IBS (IBS for "Ion Beam Sputtering", spraying, CVD (CVD for "Chemical Vapor Deposition ") ...). In a first variant of the invention, the material (s) which constitutes (s) the layer 5 is (are) chosen from among the dielectrics such as, for example, SiO 2 , HgO 2 , Ta 2 O 5 , TiO 2 , ZrO 2 , Al 2 O 3 , YF 3 , LaF , Ta 2 O 6 . In another variant of the invention, the layer 5 constitutes a heat sink which makes it possible to avoid the heating of the liquid L, which heating can occur under the effect of the laser beam. The material or materials that constitute the layer 5 are then chosen from metals (for example, copper, aluminum, etc.), oxides, or nitrides (for example Si 3 N 4 ).
La figure 11 représente un deuxième perfectionnement du dispositif de piégeage de particules de l'invention. La couche mince 1 est recouverte d'un traitement permettant de contrôler la mouillabilité de la surface sur la partie de l'empilement en contact avec le liquide L. On réalise, par exemple, un traitement hydrophobe par une couche de polytétrafluoroéthylène communément appelé téflon ou par greffage de molécules organiques appropriées pour former, par exemple, une couche de silane. La couche hydrophobe t permet avantageusement d'éviter que les particules P ne se collent sur la couche mince 1.Fig. 11 shows a second improvement of the particle trapping device of the invention. The thin layer 1 is covered with a treatment for controlling the wettability of the surface on the portion of the stack in contact with the liquid L. For example, a hydrophobic treatment is carried out with a layer of polytetrafluoroethylene commonly known as teflon or by grafting appropriate organic molecules to form, for example, a silane layer. The hydrophobic layer advantageously makes it possible to prevent the particles P from sticking to the thin layer 1.
La figure 12 représente un troisième perfectionnement du dispositif de piégeage de particules de l'invention. Le dispositif comprend, au dessus de la couche 1, une lentille à indice de réfraction négatif 6. De façon connue en soi, la lentille à indice de réfraction négatif est constituée d'un empilement de bicouches métal/diélectrique. A titre d'exemple non limitatif, chaque bicouche de l'empilement de bicouches est réalisée par une couche d'argent (Ag) que recouvre une couche de silice (SiO2) • La lentille 6 permet avantageusement d' imager, en surface de la lentille, le faisceau confiné en surface de la couche 1 tout en conservant sa dimension latérale. Dans le cas où la lentille est suffisamment épaisse, par exemple comprise entre 3nm et lOOnm, elle peut avantageusement constituer un puits thermique et ainsi permettre d'éviter l' échauffement du liquide L sous l'effet du faisceau laser Fe. La figure 13 représente un dispositif de piégeage de particules qui comprend un dispositif de formation de piège optique conforme au dispositif représenté en figure 7A. En plus des éléments représentés en figure 7A, le dispositif de la figure 13 comprend une cuve 4 située au dessus de la couche 1. Toutes les variantes des dispositifs de piégeage de particules représentées aux figures 9-12 s'appliquent, si nécessaire, au dispositif de piégeage de particules représenté en figure 13. La figure 14 représente un dispositif de piégeage de particules qui comprend un dispositif de formation de piège optique conforme au dispositif représenté en figure 8. En plus des éléments représentés en figure 8, le dispositif de la figure 14 comprend une cuve 4 située au dessus de la couche 1. Toutes les variantes des dispositifs de piégeage de particules représentées aux figures 9-12 s'appliquent, si nécessaire, au dispositif de piégeage de particules représenté en figure 14. Sur l'ensemble des figures qui illustrent les dispositifs de piégeage de particules munis d'une cuve de l'invention, le dispositif de formation de piège optique à effet de champ proche optique constitue le fond de la cuve. De façon plus générale, l'invention concerne d'autres modes de réalisation dans lesquels le dispositif de formation de piège optique à effet de champ proche optique constitue tout ou partie d'une paroi quelconque de la cuve, le terme « paroi » devant s'entendre comme tout élément de la cuve au contact du liquide et qui délimite l'intérieur de l'extérieur de la cuve (paroi latérale, couvercle, fond) .Fig. 12 shows a third improvement of the particle trapping device of the invention. The device comprises, above the layer 1, a negative refractive index lens 6. In a manner known per se, the negative refractive index lens consists of a stack of metal / dielectric bilayers. By way of nonlimiting example, each bilayer of the stack of bilayers is produced by a layer silver (Ag) covered by a layer of silica (SiO 2 ) • The lens 6 advantageously makes it possible to image, on the surface of the lens, the confined beam at the surface of the layer 1 while maintaining its lateral dimension. In the case where the lens is sufficiently thick, for example between 3 nm and 100 nm, it may advantageously constitute a heat sink and thus make it possible to avoid the heating of the liquid L under the effect of the Fe laser beam. FIG. a particle trapping device which comprises an optical trap forming device according to the device shown in Figure 7A. In addition to the elements shown in FIG. 7A, the device of FIG. 13 comprises a tank 4 situated above the layer 1. All the variants of the particle trapping devices represented in FIGS. 9-12 apply, if necessary, to particle trap device shown in FIG. 13. FIG. 14 shows a particle trap device which comprises an optical trap forming device according to the device shown in FIG. 8. In addition to the elements represented in FIG. 8, the device of FIG. FIG. 14 comprises a tank 4 located above layer 1. All variants of the particle trapping devices shown in FIGS. 9-12 apply, if necessary, to the particle trapping device shown in FIG. set of figures that illustrate the devices for trapping particles with a tank of the invention, the optical near-field optical trap forming device forms the bottom of the tank. More generally, the invention relates to other embodiments in which the optical near-field optical trap forming device constitutes all or part of any wall of the tank, the term "wall" in front of 'hear like any element of the tank in contact with the liquid and which delimits the inside of the outside of the tank (side wall, cover, bottom).
Un exemple de procédé de réalisation de dispositif de formation de piège optique de l'invention conforme à la figure 6 est donné ci-dessous :An exemplary embodiment of optical trap forming device of the invention according to Figure 6 is given below:
• Sur un substrat de silice (par exemple de type Hérasil Hl), on dépose une couche d' InSb de 30 nm épaisseur par un procédé de pulvérisation cathodique ;• On a silica substrate (for example of Hérasil Hl type), a layer of InSb of 30 nm thickness is deposited by a sputtering method;
• Afin de faire passer cette couche de l'état amorphe à l'état cristallin, on opère un recuit pendant deux heures avec un four chauffé à 2000C ;In order to pass this layer from the amorphous state to the crystalline state, annealing is carried out for two hours with an oven heated to 200 ° C.
• On reporte, par exemple par collage, des parois verticales sur la couche 1 afin de former la cuve ;• It is reported, for example by gluing, vertical walls on the layer 1 to form the vessel;
• On prépare une solution liquide contenant des billes de latex de 300nm de diamètre que l'on injecte dans la cuve par une micropipette ;• A liquid solution is prepared containing 300 nm diameter latex beads which are injected into the tank by a micropipette;
• On recouvre la cuve par une lamelle couvre objet ;• The vat is covered by a coverslip;
• On place l'ensemble ainsi constitué sur un porte-échantillon du système optique constitué par un bâtit de microscope inversé qui comporte un objectif d'ouverture numérique de, par exemple, 1,2 et dans lequel on injecte un faisceau laser issu d'une diode laser émettant, par exemple, à la longueur d'onde 405 nm, une onde modulée à 1 GHz et de 50 mW de puissance. On déplace le porte-échantillon pour piéger les billes de latex à l'aide du piège optique. Il est à noter que, pour des raisons de commodité, dans la description ci-dessus, le terme «particule» est utilisé pour désigner, de façon générale, un objet ou un nano- objet susceptible d'être piégé à l'aide du dispositif de formation de piège optique de l'invention. Comme cela apparaît clairement dans le tableau établi précédemment, le terme « nano-objet » ne doit bien sûr pas s'entendre comme un objet dont les dimensions sont exclusivement de l'ordre de quelques nanomètres. The assembly thus constituted is placed on a sample holder of the optical system constituted by an inverted microscope construct which includes a lens digital aperture of, for example, 1.2 and into which is injected a laser beam from a laser diode emitting, for example, at the wavelength 405 nm, a modulated wave at 1 GHz and 50 mW power. The sample holder is moved to trap the latex beads using the optical trap. It should be noted that, for the sake of convenience, in the above description, the term "particle" is used to refer generally to an object or nanoobject capable of being trapped using the optical trap forming device of the invention. As it is clear in the table previously established, the term "nano-object" must of course not be understood as an object whose dimensions are exclusively of the order of a few nanometers.

Claims

REVENDICATIONS
1. Dispositif de piégeage de particules contenues dans un liquide (L) placé dans une cuve (4), caractérisé en ce qu'il comprend un substrat (2) transparent à une longueur d'onde de travail, une couche mince (1) de matériau aux propriétés optiques non-linéaires réversibles à la longueur d'onde de travail fixée sur une première face du substrat transparent (2) et formant tout ou partie d'au moins une paroi de la cuve (4) au contact du liquide, un dispositif de formation de piège optique à effet de champ proche optique qui comprend une source laser qui émet un faisceau laser à la longueur d'onde de travail et des moyens pour former un waist du faisceau laser, lesdits moyens étant positionnés par rapport au substrat transparent (2) de telle sorte que le faisceau laser soit incident sur une deuxième face du substrat transparent située à l'opposé de la première face et que le waist du faisceau laser se forme dans la couche mince (1), un champ électromagnétique évanescent se formant dans le prolongement du waist de faisceau laser, en surface de la couche mince (1) .1. Device for trapping particles contained in a liquid (L) placed in a tank (4), characterized in that it comprises a substrate (2) transparent at a working wavelength, a thin layer (1) material with non-linear optical properties reversible to the working wavelength fixed on a first face of the transparent substrate (2) and forming all or part of at least one wall of the tank (4) in contact with the liquid, an optical near field effect optical trap forming device which comprises a laser source which emits a laser beam at the working wavelength and means for forming a waist of the laser beam, said means being positioned relative to the substrate transparent (2) so that the laser beam is incident on a second face of the transparent substrate located opposite the first face and that the waist of the laser beam is formed in the thin layer (1), an electromagnetic field evanes escent forming in the extension of the laser beam waist on the surface of the thin layer (1).
2. Dispositif selon la revendication 1, dans lequel un masque optique (M) muni d' ouvertures est déposé sur la couche mince (1) .2. Device according to claim 1, wherein an optical mask (M) provided with openings is deposited on the thin layer (1).
3. Dispositif selon la revendication 1, dans lequel un masque optique (M) muni d'ouvertures est placé entre la couche mince (1) et la première face du substrat .3. Device according to claim 1, wherein an optical mask (M) provided with openings is placed between the thin layer (1) and the first face of the substrate.
4. Dispositif selon l'une quelconque des revendications précédentes, dans lequel un modulateur de lumière (Mod) module la phase du faisceau laser (F) de telle sorte que plusieurs faisceaux laser élémentaires se forment sous l'action du modulateur de lumière, chaque faisceau laser élémentaire participant à la formation d'un champ évanescent en surface de la couche mince (1) .4. Apparatus according to any one of the preceding claims, wherein a light modulator (Mod) modulates the phase of the laser beam (F) so that a plurality of elementary laser beams are formed under the action of the light modulator, each elementary laser beam involved in the formation of an evanescent field at the surface of the thin layer (1).
5. Dispositif selon la revendication 4, dans lequel chaque champ évanescent en surface de la couche mince (1) est apte à piéger une particule.5. Device according to claim 4, wherein each evanescent field at the surface of the thin layer (1) is capable of trapping a particle.
6. Dispositif selon l'une quelconque des revendications précédentes, dans lequel une couche supplémentaire (5) ayant une fonction antireflet ou de miroir est placée entre la couche mince (1) et le substrat (2) .6. Device according to any one of the preceding claims, wherein an additional layer (5) having an antireflection or mirror function is placed between the thin layer (1) and the substrate (2).
7. Dispositif selon l'une quelconque des revendications précédentes, dans lequel une lentille à indice de réfraction négatif (6) est placée en surface de la couche mince (1), au contact du liquide.7. Device according to any one of the preceding claims, wherein a negative refractive index lens (6) is placed on the surface of the thin layer (1), in contact with the liquid.
8. Dispositif selon la revendication 7, dans lequel la lentille à indice négatif (6) comporte un empilement de bicouches métal/diélectrique. 8. Device according to claim 7, wherein the negative index lens (6) comprises a stack of metal / dielectric bilayers.
9. Dispositif selon l'une quelconque des revendications 1 à 5, dans lequel la couche mince (1) est recouverte d'une couche de traitement (t) apte à contrôler la mouillabilité de la surface de la couche mince qui est au contact du liquide.9. Device according to any one of claims 1 to 5, wherein the thin layer (1) is covered with a treatment layer (t) adapted to control the wettability of the surface of the thin layer which is in contact with the liquid.
10. Dispositif de piégeage de particules selon la revendication 9, dans lequel la couche de traitement (t) est hydrophobe . The particle trapping device of claim 9, wherein the treatment layer (t) is hydrophobic.
EP09753842A 2008-05-26 2009-05-25 Device for trapping particles Withdrawn EP2297745A1 (en)

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