WO2022258554A1

WO2022258554A1 - Optical scalpel and method of manufacturing

Info

Publication number: WO2022258554A1
Application number: PCT/EP2022/065294
Authority: WO
Inventors: Roberto Caputo; Antonio Ferraro; Giuseppe Emanuele LIO
Original assignee: Universita' Della Calabria
Priority date: 2021-06-08
Filing date: 2022-06-06
Publication date: 2022-12-15

Abstract

The present invention relates to an optical scalpel, comprising: - A laser (7) designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm; - An optical fibre (11) defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser (7); - A transducer device (1) of light energy into thermal energy positioned on the first end of the optical fibre and comprising: o A first continuous layer of metallic material (3), with a thickness comprised between 5 nanometres and 150 nanometres; o A first layer of dielectric material (4), with a thickness comprised between 5 nanometres and 300 nanometres; o A second continuous layer of metallic material (5), with a thickness comprised between 5 nanometres and 150 nanometres.

Description

OPTICAL SCALPEL AND METHOD OF MANUFACTURING

The present invention relates to an optical scalpel using a photothermal transducer to transform energy deriving from an electromagnetic radiation into heat. The invention also relates to the method of operation of such a scalpel including a transducer.

It is well known in surgery to combine the presence of a traditional blade (that of the scalpel) with heat to prevent the wounds formed by the blade from bleeding. The fully-fledge blade has gradually become an "optional extra", as the heat itself was also able to form the cut. Typical examples of this type of application are, for example, electro-scalpels, which include two electrodes: a neutral electrode (neutral plate) placed on the patient and an active electrode, appropriately shaped, called a "handpiece" held in the surgeon's hands. At the tip of the active electrode, the current density is extremely high. At the point of contact between electrode and skin, the current develops, in a short time, a large amount of heat in the electrical resistance encountered at the contact. Depending on the shape of the active electrode, the speed at which it is moved, the intensity of the current used and its waveform, a cutting or clotting effect is obtained, or a cutting and clotting effect together.

Additionally, laser scalpels have recently been developed. The increasing success of laser surgery is linked to its ability to selectively and microscopically photocoagulate tissues, without electrical contact with the patient. For example, in pulsed emission, the diode laser vaporises superficial benign lesions with no anaesthesia nor stitches. It is used as a "scalpel" to totally remove lesions. The surgical field is bloodless and sterile due to the immediate coagulation of the haemolymphatic vessels.

However, there is a need to improve laser scalpels as the power required to generate the heat necessary for optimal cutting precision without damaging healthy tissues is relatively high. These lasers are also relatively expensive, increasing the overall cost of the scalpel.

The object of the present invention is to make available an optical laser scalpel that generates heat, which is used for cutting and/or coagulation. The scalpel requires a relatively low laser power. Furthermore, the scalpel is easy to make.

When an electromagnetic radiation hits a certain sample of material, part of the radiation may be absorbed by it. Due to absorption, there is a resulting change in the thermal state of the sample. The radiation absorbed and not missed causes heating. Heat increases the temperature thereby affecting the thermodynamic properties of the sample or of a suitable material adjacent thereto.

The theory underlying the operation of the device is known as thermo-plasmonics.

Plasmonics studies the interaction between electromagnetic radiation and metallic nanoparticles (NPs). When a nanoparticle, with a diameter smaller than the wavelength of the incident electromagnetic radiation, is irradiated by this electromagnetic radiation, the oscillating electric field induces a coherent oscillation of the conduction electrons and the formation of a dipole. This charge imbalance induces a return force causing the conduction electrons to oscillate. Such oscillation of electrons is called a "plasmon". The electrons oscillate in phase at a certain frequency, called the plasma frequency, which depends on the conduction electron density, actual electron mass, shape and size of the nanoparticle. When the plasma frequency is comparable to the frequency of the incident radiation, the phenomenon of plasmonic resonance occurs, resulting in the absorption of the radiation. In the case of the present invention, reference is made to localised surface plasmon (LSP). The LSP has two important effects: the electric fields near the surface of the particle are significantly increased and the optical absorption of the particle has a maximum at the plasmon resonance frequency.

A uniform or homogeneous layer of metal can be approximated to a system containing endless nanoparticles.

The polarizability of the nanoparticle is defined in Eq. (1), where R is the radius of the nanoparticle, e(w) is the complex permittivity of the NP immersed in a surrounding medium with a relative permittivity e(s) (where "s" stands for the medium around the nanoparticle - surrounding medium). It follows from the equation (1) that the resonance condition occurs when e(w) = -2 e(5).

The efficiency of these processes may be described by the absorption, scattering and extinction cross sections given in Equations (2), (3) and (4) respectively.

The oscillation of electrons, representing an electronic current in a metal, generates energy dissipation by the Joule effect. In order to study the effects of heat generation and thus of temperature increase, one starts from the energy balance equation, Equation (5), where Q_j e Q_eXt represent the rate of energy supplied by the heat induced by the electromagnetic radiation and heat dissipation to the outside, m, e C_{P i} are the mass and heat capacity of the components of the system under investigation, T is the temperature and t the time.

The above equation applies to both a nanoparticle system and a "layered" system of the MDM or DMD type (which is defined hereinafter).

The thermal energy due to the radiation of the electromagnetic radiation is given in Equation (6) where I is the power of the incident radiation, A the absorbance of the material hit by the electromagnetic radiation, and h the conversion efficiency of the absorbed electromagnetic radiation into thermal energy.

In a linear thermal system, the rate of energy leaving the system is given by Equation (7) where h is the heat transfer coefficient (dissipation) and S the area perpendicular to the heat conduction.

By grouping some terms and making a change of variable, T^*, the Equation (5) can be written in a simplified form as shown in Equation (8) where T^*=T-T₀ is the temperature difference of the irradiated sample with respect to the environment (T₀).

The coefficients A and B are given in Equations (9) and (10) where A (°C/s) is the rate of energy absorption and B (s ¹) is the constant rate of heat loss; m e C_p are the actual mass and heat capacity of the medium surrounding the thermo-plasmonic component.

The rate constant of the heat loss from the NP to an external tank (B) is determined by following the temperature decay to room temperature after the incident radiation is stopped. In this regime, the temperature profile is given by equation (11), where T_MAX is the temperature when the electromagnetic radiation source is stopped.

Equation (12) provides the steady-state temperature (T_ss) during excitation. The steady-state temperature within the NP is assumed to be uniform and unchangeable and is obtained when the rate of energy absorption equals the rate of heat loss.

The conversion efficiency is described by Equation (13).

Equation (14) describes the temperature profile of the irradiated sample after the radiation source is activated (i.e. after the sample is irradiated with electromagnetic radiation).

The transformation of light energy into thermal energy is useful in many applications. This transformation may be useful in thermal sutures as well as within a high-resolution local thermal-ablation of tissues or cells.

Generally, radiation-to-heat conversion in which the electromagnetic radiation has a wavelength in the ultraviolet-visible range is carried out using devices including metal nanoparticles (eg. Gold, Silver, Aluminium etc.). Such a solution requires significant production costs. Nanoparticles are generally dispersed on a substrate or in a solution. The radiation-to-heat conversion creates an increase in the temperature of the irradiated sample of a maximum of 50°C - 70°C. Moreover, nanoparticle devices only operate at specific wavelengths determined by the nature of the nanoparticles themselves. Engineering them to make them functional at other wavelengths is very difficult if not, in some cases, impossible. To partially overcome this problem, complex nanoscale structures are used. However, the performance and problems of these additional devices are almost identical to devices containing nanoparticles. Examples of such solutions are disclosed for example in: Palermo et All, Nanoscale 10 (35), 16556-16561 (2018); Baffou et All, Laser Photon. Rev. 7, 171-187 (2013); Richardson, Nano Lett. 9, 1139-1146 (2009); Jauffred et All, Chem. Rev. 119, 8087-8130 (2019).

In this specific field, a need is therefore perceived for a transducer device to transform light energy into thermal energy and a method for making the same that is easy to manufacture and implement. It is also desirable that such a device or method is easily scalable. With such a transducer device, better functioning, cheaper and higher performance scalpels can be realised.

According to a first aspect, the present invention relates to an optical scalpel, comprising:

A laser designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm;

An optical fibre defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser;

A transducer device of light energy into thermal energy positioned on the first end of the optical fibre and comprising: o A first continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres; o A first layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres; o A second continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres. This first transducer device comprised in the optical scalpel of the invention is hereinafter called for brevity's sake metal-dielectric-metal transducer or MDM transducer.

According to a second aspect, the present invention relates to an optical scalpel, comprising:

A transducer device of light energy into thermal energy positioned on the first end of the optical fibre and comprising: o A first layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres; o A first continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres; o A second layer of dielectric material with a thickness comprised between 5 nanometres and 300 nanometres.

This second transducer device comprised in the optical scalpel of the invention is hereinafter called for brevity's sake dielectric-metal-dielectric transducer or DMD transducer.

According to a third aspect, the present invention also relates to a method for manufacturing an optical scalpel, comprising:

Providing a laser designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm;

Providing an optical fibre defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser;

Making on the first end of the optical fibre a transducer device of light energy into thermal energy comprising the steps of: o Depositing a first continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres; o Depositing a first layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres; o Depositing a second continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres.

According to a fourth aspect, the present invention also relates to a method for manufacturing an optical scalpel, comprising: - Providing a laser designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm;

Making on the first end of the optical fibre a transducer device of light energy into thermal energy comprising the steps of: o Depositing a first layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres; o Depositing a first continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres; o Depositing a second layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres.

The optical scalpel of the invention comprises a transducer device. The transducer device is designed to transform the energy of an electromagnetic radiation ("light" energy) into thermal energy. The electromagnetic radiation useful for such a transformation in this context has a wavelength in the range from 300 nanometres to 1500 nanometres, i.e. from ultraviolet to near-infrared. Therefore, the optical scalpel of the present invention comprises a laser capable of emitting electromagnetic radiation in this wavelength.

The optical scalpel also includes a transducer device to transform the energy provided by the electromagnetic radiation provided by the laser into heat. Heat is therefore emitted by the scalpel. An optical fibre is used to carry the electromagnetic radiation from the laser to the transducer device. Preferably the optical fibre is standard in the field and not further detailed hereinafter.

The optical fibre includes a first end and a second end. One of the first and second ends receives the electromagnetic radiation emitted by the laser. On the other one of the first and second end, the transducer device of light energy into thermal energy is positioned. The transducer device of the invention is able to efficiently convert the light energy coming from the laser into thermal energy. The transducer device is at least a three-layered device that can be, as described above, of the metal-dielectric-metal (MDM) or dielectric-metal-dielectric (DMD) type, such that a dual metal/dielectric interface is present.

Hereinafter, when the layers of dielectric and/or metallic material are named without being preceded by the adjective "first" or "second", it means that what is written in that paragraph can be applied to the first as well as the second layer of dielectric and/or metallic material.

In detail, the transducer device of the invention is made up of at least three layers. It may have two configurations. A layer of metallic material may be interposed between two layers of dielectric material, or a layer of dielectric material may be interposed between two layers of metallic material. The device of the invention therefore contains two metal/dielectric interfaces.

The interfaces between the various layers, which are metal/dielectric interfaces, are preferably planar. In other words, the interface preferably defines a plane, called the interface plane, where the interface lies. Preferably, the two interfaces in the device define two interface planes that are parallel to each other.

The layer of metallic material of both the MDM and DMD device is a continuous layer. In other words, the metallic material does not have spatial discontinuities, such as are present in nanoparticles or nanostructures. The layer of metallic material, preferably in a direction parallel to the interfaces between the various layers constituting the device, is therefore continuous (it is obvious that at the atomic and/or molecular level, there is no continuity, but the dimensions involved here are at least nanometres and not picometres). There are no interfaces separating portions of metallic material in the same layer, as is instead the case with nanoparticles or nanostructures.

Preferably, this continuity is present throughout the thickness of the layer of metallic material, in other words, for any section parallel to the interface planes between a metallic layer and a dielectric layer, the layer of metallic material has such continuity.

In the case of the transducer device with MDM configuration, both the first and second layer of metallic material are continuous.

The layer of dielectric material is also preferably but not necessarily continuous. Furthermore, a layer of dielectric material means "at least one layer". In other words, each layer of dielectric material in either DMD or MDM configuration may include more than one layer, even of different dielectric materials.

In the case of the transducer device with DMD configuration, both the first and second layer of dielectric material are preferably but not necessarily continuous. Whatever the method of deposition or manufacturing of a layer of metallic material, it is impossible to completely avoid impurities or the possibility of oxidation on the upper surface of the layer when exposed to air, for example. Therefore, this layer continuity applies for 90%, more preferably 95% of the layer, in other words, there may be impurities in the layer that cause unintended interfaces, which are nevertheless undesired, and for a maximum of 10%, more preferably 5% of the layer. The most common impurities are, for example, spontaneous oxide formation on the metal.

Preferably, in the MDM transducer, the first layer of metallic material is first deposited, e.g. on a substrate, the first layer of dielectric material is deposited on the first layer of metallic material, and finally the second layer of metallic material is deposited on the first layer of dielectric material.

Preferably, in the DMD transducer, the first layer of dielectric material is first deposited, e.g. on a substrate, the first layer of metallic material is deposited on the first layer of dielectric material, and finally the second layer of dielectric material is deposited on the first layer of metallic material.

The electromagnetic radiation incident on the MDM or DMD transducer may be monochromatic radiation, such as a laser beam, i.e. carrying a single wavelength, or it may be polychromatic. Of course, the wavelength or wavelengths that "count", i.e. that cause the transformation from light energy to heat energy, are only those that are absorbed by the transducer device of the invention and cause a plasmonic resonance (see below).

The electromagnetic radiation emitted by the laser is conveyed through the optical fibre and hits the transducer device so as to convert the light energy (at predetermined wavelengths) into thermal energy. The electromagnetic radiation preferably hits the device in the case of the MDM configuration in the first layer or in the second layer made of metallic material. Alternatively, in the DMD case, the radiation hits the device in the first layer or in the second layer made of dielectric material.

The MDM or DMD device may also include a substrate. Thus in this case the first metallic layer of the MDM device or the first dielectric layer of the DMD device is in contact with (e.g. deposited on) a substrate. The electromagnetic radiation may also irradiate the substrate if it is transparent to the wavelength (or wavelengths) of interest that are absorbed by the transducer device.

The response of the transducer device depends on the wavelengths of the incident electromagnetic radiation that are most absorbed by the transducer device.

The angle of incidence of the radiation on the device (on the first layer or second layer of metallic material in the MDM transducer, or on the first layer or second layer of dielectric material in the DMD transducer, or on the substrate in both transducers) is irrelevant. Figures 1 to 4 show, respectively, two simulations

(Figures 1 and 2) and two experimental measurements (Figures 3 and 4) of the transducer absorption as a function of the wavelength (abscissa) and angle of incidence of the electromagnetic radiation (the transducer in question here is an MDM transducer where an additional layer of dielectric material has been deposited on the second metallic layer. The transducer therefore has these characteristics: first layer of metallic material: 30-nanometre-thick silver first dielectric layer: 80-nanometre ITO second layer of metallic material: 30-nanometre silver additional (second) dielectric layer: 20-nanometre ITO). Figures 1 and 3 are for a polarised electromagnetic radiation P and Figures 2 and 4 are for a polarised electromagnetic radiation S. As visible, the electromagnetic radiation is absorbed at a specific wavelength and the angle of incidence and polarisation are irrelevant for the absorption thereof (i.e. the absorption does not vary with the angle of incidence of the electromagnetic radiation).

The MDM or DMD transducer device is placed on one end of the optical fibre so that the electromagnetic radiation can properly reach it. The positioning is such that the first layer of metallic material in the case of the MDM transducer or the first layer of dielectric material in the case of the DMD transducer rests on one end of the optical fibre so that the electromagnetic radiation is incident on it. In case the DMD or MDM transducer rests on a substrate, the substrate rests on one end of the optical fibre.

The laser-emitted electromagnetic radiation entering the optical fibre so as to hit the first layer (be it metallic or dielectric) of the transducer, preferably has a power of at least 10 mW for a 1 mm diameter beam. Flowever, smaller beams are also possible.

The first continuous layer of metallic material and the second continuous layer of metallic material in the MDM-type transducer preferably have a thickness of between 5 nanometres and 150 nanometres; more preferably between 10 nanometres and 100 nanometres; even more preferably between 20 nanometres and 30 nanometres. The first layer and the second layer do not necessarily have to be of the same thickness, but can be made of different thicknesses. Additionally, the first layer and the second layer of metallic material may be made of different metals.

The first layer of dielectric material in the MDM-type transducer preferably has a thickness comprised between 5 nanometres and 300 nanometres; more preferably between 40 nanometres and 150 nanometres, even more preferably between 60 nanometres and 80 nanometres.

The first continuous layer of metallic material in the DMD-type transducer preferably has a thickness comprised between 5 nanometres and 150 nanometres; more preferably between 10 nanometres 100 nanometres, even more preferably between 20 nanometres and 30 nanometres. The first layer of dielectric material and the second layer of dielectric material in the DMD-type transducer preferably have a thickness comprised between 5 nanometres and 300 nanometres; more preferably between 40 nanometres and 150 nanometres, even more preferably between 60 nanometres and 80 nanometres. The first layer and the second layer of dielectric material do not necessarily have to be of the same thickness, but can be made of different thicknesses. Additionally, the first layer and the second layer of dielectric material may be made of different dielectric materials.

The theory underlying the light-to-thermal energy transducer used in the scalpel of the invention is as follows.

When there are layers of material with a thickness of the order of nanometres (even hundreds of nanometres) and there is a further interface between a metal and a dielectric, various phenomena can occur if an electromagnetic radiation hits them. For example, due to the electromagnetic radiation incident on the structure forming a metal/dielectric interface, a polariton may form, the polariton being an electromagnetic wave coupled to a polarised excitation in the structure. When this coupled excitation occurs at the interface between two media, we speak of a surface polariton. The latter is an evanescent electromagnetic wave propagating along the interface, with an amplitude decaying exponentially in the two materials forming the interface. When the materials are, as in this case, a metal and a dielectric, the propagating waves are referred to as surface plasmonic polaritons (SPP).

It is particularly interesting in addition the situation wherein two interfaces are present, i.e. two metallic/dielectric interfaces, as in the DMD or MDM transducer of the present invention. Such dual interface systems behave like an optical nanocavity and allow efficient concentration and confinement of the electromagnetic energy. It is therefore possible to excite, between the two interfaces, an electromagnetic wave (the polariton) resonating in the cavity defined by the two interfaces. The excitation of this resonant electromagnetic wave therefore allows the electromagnetic energy to be "concentrated" and thus transformed into heat. Therefore, the MDM or DMD structure is made in such a way that the transmission to another object is possible. In fact, the heat emitted must be transmitted to the outside so that it may be used as a "heat beam" in the scalpel. In the cavity formed between the two metallic/dielectric interfaces of the MDM or DMD transducer, electrons excited by the incident electromagnetic radiation are put back together.

In the case of the DMD configuration, the dielectric layers select the wavelength, in other words, they select the wavelength range that the electromagnetic radiation hitting the transducer must have in order for the resonant plasmonic wave to be excited. The thickness and type of the metallic layer between the two dielectric layers, on the other hand, acts as a "filter", i.e. it determines how wide the band wherein this excitation is possible is (depending on the thickness of the metal, this band is wider or narrower). Additionally, both in case of both MDM and DMD, the thickness of the metal layer (or layers) determines the absorption of the transducer. If the metal layers are too thick, transmission becomes almost impossible and thus heat cannot be transmitted to another object. Therefore, depending on the absorption (determined by the thickness of the metal layers or of the metal layer if only one is present), a greater or lesser conversion of the incident electromagnetic radiation into heat is possible.

The combination of the layers of metallic material and dielectric material, with their respective thicknesses, contribute to determine the wavelength and absorption band of the electromagnetic radiation whose energy is transformed into heat, both in the MDM and DMD transducers.

By varying the parameters of the thicknesses of the metallic and/or dielectric material layers of each MDM or DMD device, it is possible to establish the resonance/absorption band as well as the wavelength generated by this transformation of optical energy into thermal energy. Therefore, the scalpel according to the invention is easily "adaptable" to a desired band and wavelength (e.g. it can adapt to different types of available lasers). Additionally, the scalpel according to the invention may be made cost-effectively given the production process and the materials involved. The production process involves techniques used in the industrial field. Furthermore, always due to the production process and materials involved, it can easily be manufactured in different sizes, i.e. scalpels with transducers covering a very small area, in the order of micrometres, or a large area, such as several centimetres.

Additionally, it is possible to consider making a "stack" of several MDM or DMD transducer devices on top of each other. Different wavelengths of incident radiation can be thereby selected, creating different resonant plasmons within the structure, each one at a different wavelength. It is therefore possible, for example, to have a resonant wave in the green at the same time as a resonant wave in the blue. Therefore, the scalpel may be particularly versatile and may couple with different lasers and emit heat if radiation at different wavelengths is used.

Moreover, the energy conversion of the device is particularly efficient.

Preferably, in each MDM or DMD transducer, the layer of metallic material is in direct contact with the dielectric material layer that is part of the same transducer. Direct contact means that there are no other layers or intermediate elements between the layer of metallic material and the layer of dielectric material belonging to the same transducer.

For example, the layer of metallic material may be deposited directly on the layer of dielectric material, or vice versa the layer of dielectric material may be deposited directly on the layer of metallic material.

The layers in both MDM and DMD transducers are preferably parallel to each other. The layers are therefore arranged on planes parallel to each other. The thickness of the layer is measured in a direction perpendicular to the parallel planes defined by the various layers. The height of the transducer device is given by the sum of the thicknesses of all its layers.

Preferably, the thickness of the layer (whether metallic or dielectric) is constant throughout the layer.

Preferably, the transducer comprises a first and a second end. The first and second ends are defined along the direction in which the height of the device is calculated. In a DMD device, the two ends are defined by the layers of dielectric material, whereas in the MDM device by the two layers of metallic material. Additional layers in the number of N with N > 1 may be present in the transducer device in addition to the three MDM or DMD layers. The additional layers are preferably all alternated in the same way, i.e. the alternation of the layers is always j-th layer of dielectric material followed by the j+lth layer of metallic material and so on. Having called A the dielectric layer and B the metallic layer, an alternation ABABAB... or the alternation can be of the type BABABA... may be obtained.

Preferably, the metallic material forming the first metallic layer and the metallic material forming the second metallic layer are the same metallic material.

Preferably, the dielectric material forming the first metallic layer and the dielectric material forming the second dielectric material are the same dielectric material.

The transducer device is preferably made on a substrate. In contact with the substrate there may be the first layer of metallic material in the MDM device, or the first layer of dielectric material in the DMD device. In other words, the transducer device may be made, from the bottom upwards, starting with the substrate on which the first layer of metallic material is made, then the first layer of dielectric material, and finally the second layer of metallic material. Alternatively, the device may be made, from the bottom upwards, starting with the substrate on which the first layer of dielectric material is made, then the first layer of metallic material, and finally the second layer of dielectric material.

The substrate may be made of one or more of: glass, silicon, polymeric or composite materials. The substrate may be rigid or flexible.

In the case of an MDM device, it is preferable to deposit an additional (second) layer of dielectric material on the second layer of metallic material to protect it from oxidation. Preferably, the second layer of dielectric material is deposited directly onto the second layer of metallic material of the MDM transducer.

Preferably, the metallic material making up the first metallic layer and/or the second metallic material of the DMD transducer device or MDM transducer device comprises one of: silver, gold, aluminium, copper, platinum, titanium, vanadium, chrome, iron. The choice of metal depends on the optical properties thereof, ease of deposition and environmental and biological compatibility. Preferably, the dielectric material making the first dielectric layer and/or the second dielectric layer of the DMD transducer device or the MDM transducer device comprises one of: zinc oxide (ZnO), titanium oxide (Ti0₂), aluminium oxide (Al₂0₃), indium tin oxide (ITO), aluminium doped zinc oxide (AZO), copper oxide (CuO, Cu₂0 e Cu₂0₃), silicon oxide (Si0₂) or composites thereof. Additionally, the dielectric material making up the first dielectric layer and/or the second dielectric layer of the DMD transducer device or MDM transducer device preferably comprises a polymeric material. The polymeric material is preferably one of: polyvinylpyrrolidone (PVP), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA). Additionally, the dielectric material of the first and/or second layer of the DMD transducer device or MDM transducer device may be silicon, germanium, and oxides or alloys thereof. The choice of the dielectric material depends on which losses are acceptable (low optical losses are preferable) and which are resistant to the temperature rise that occurs when the optical energy is converted into heat.

Preferably, depositing the first layer of metallic material and/or the second layer of metallic material and/or the first layer of dielectric material and/or the second layer of dielectric material includes depositing the first and/or the second layer of dielectric material and/or the first layer of metallic material and/or the second layer of metallic material by one of: direct current cathodic vaporization deposition (DC sputtering); physical vapour deposition (PVD); chemical vapour deposition (CVD); atomic layer deposition (ALD); ion beam assisted deposition; electron-beam physical vapour deposition.

All these deposition techniques make it possible to create layers of dielectric and/or metallic material of the required thickness. They are also now industrially used and are capable of producing layers with a surface area of easily a few square metres.

Furthermore, in case the first layer of dielectric material and/or the second layer of dielectric material of the DMD transducer device or MDM transducer device includes a polymeric material, depositing the first layer of dielectric material and/or the second layer of dielectric material includes one of: cold plasma deposition; spin coating deposition.

The polymers used to make the first and/or second dielectric layer of the DMD transducer device or MDM transducer device are generally liquid prior to deposition, and therefore liquid deposition techniques are preferred. In this case as well, the deposition techniques are well known and allow to create layers of uniform and controlled thickness. Moreover, the surface covered by the layer is easily variable.

Preferably, the electromagnetic radiation is emitted by a laser. As mentioned, the polarisation of the laser electromagnetic radiation is irrelevant to the operation of the device. The electromagnetic radiation emitted by the laser may be continuous or pulsed. The beam may be collimated or focused.

The present invention will be better shown in detail with non-limiting reference to the following drawings wherein:

Figures 1 and 2 are numerical simulations of the absorption of a transducer device according to the invention with an electromagnetic radiation having a certain wavelength incident at various angles of incidence;

Figures 3 and 4 are equivalent to Figures 1 and 2, but experimentally obtained;

Figure 5 is a schematic perspective view of a scalpel according to the present invention;

Figure 5a is an enlarged detail of the scalpel of Figure 5;

Figure 6 is a schematic side view of a transducer, part of the scalpel of Figures 5 and 5a;

Figure 7 is a graph of three experimental measurements of temperature as a function of the incident intensity for a laser having a wavelength of 532 nm at three different powers on a transducer device according to the invention;

Figure 8 is a thermal map of a surrounding region of the transducer of Figure 6 after 30 seconds of irradiation by electromagnetic radiation;

Figure 9 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first metal layer, in this case Silver, in an MDM-type transducer configuration as in Figure 6;

Figure 10 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first dielectric layer, in this case Silver, in an MDM-type transducer configuration as in Figure 6;

Figure 11 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first metal layer, in this case Silver, in a DMD-type transducer configuration;

Figure 12 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first and second dielectric layers, in this case Silver, in a DMD-type transducer configuration;

Figure 13 represents the absorption map obtained through numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first metallic layer, in this case

Gold, in a DMD-type transducer configuration; Figure 14 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first and second dielectric layers, in this case Gold, in a DMD-type transducer configuration; and

Figure 15 represents the absorption map obtained by numerical simulations as a function of the electromagnetic radiation wavelength and the thickness of the first and second dielectric layers, in this case Gold, in a DMD-type transducer configuration, wherein gold is twice as thick as in the simulation of Figure 14.

Referring initially to Figures 5 and 5a, 100 globally denotes a scalpel made according to the present invention.

The scalpel 100 includes a transducer device 1 of light energy into thermal energy, better detailed in Figure 6.

The device 1 is preferably made on a substrate 2. The device 1 comprises three layers deposited on the substrate with the following characteristics.

The first layer 3 is made of metallic material with a thickness comprised between 5 and 150 nm, the second layer is of dielectric material 4 (called the first dielectric layer) with a thickness comprised between 5 and 300 nm, followed by a new metallic layer 5 with a thickness (second metallic layer) comprised between 5 and 150 nm, and the device is closed with a second dielectric layer 6 with a thickness of between 5 and 50 nm. The second dielectric layer is optional, and is for protecting the second layer of metallic material.

Figure 6 represents one of the two possible configurations for making the transducer device, called MDM transducer; a second configuration not shown is the configuration with first layer of dielectric/layer of metallic material/second layer of dielectric. The configuration is identical to that presented in Figure 6, considering the first layer 3 as made of dielectric material with a thickness comprised between 5 and 300 nm, the second layer is made of metallic material 4 (called the first metallic layer) with a thickness comprised between 5 and 150 nm, followed by a new dielectric layer 5 with a thickness (second dielectric layer) comprised between 5 and 300 nm. In this case the layer 6 is not present.

The layers of metallic material mainly determine the resonance/absorption bandwidth, i.e. as the thickness of the layers increases, the band becomes narrower. The resonance/absorption wavelength is instead determined almost exclusively by the thickness of the first dielectric layer.

In order to convert light energy into thermal energy via the device 1, the scalpel 100 includes an electromagnetic radiation source, such as a laser 7 (depicted schematically as a rectangle in Figure 5), by means of which the transducer device 1 is irradiated. The scalpel 100 also comprises an optical fibre 11 to transport the electromagnetic radiation from the laser 7 to the first layer of the transducer device 1. The angle of incidence between radiation and the first layer is not relevant.

Additionally, the scalpel 100 includes an endoscope 12. In order to be able to engineer the plasmon resonance at the desired wavelength and to obtain a light-heat transducer 1 with maximum efficiency to be used in the scalpel 100, it is necessary to take into account the following dispersion relation which is equally valid for the MDM and DMD transducer 1 configurations:

where

m and d denote metal and dielectric (also insulator) respectively, and s_d and s_m are the permittivity of the dielectric and metal, respectively. /?is the complex wave vector of the wave propagating inside the cavity (cavity, as said, defined by the two metal/dielectric interfaces). The thickness of the layer of interest is indicated by t, so tcav = t (thickness) of the first metallic layer in the DMD configuration or tcav = t (thickness) of first dielectric layer in the MDM configuration.

In the specific case of dielectric or metallic cavity with a thickness comprised between 5 nm and 300 nm (i.e. when the metallic layer between two dielectrics, or the dielectric layer between two metals has a thickness in this range), the approximation tanh(x ) * 1 - 2e²*can be applied.

Thereby, the dispersion relation for a gap surface plasmon (GSP) can be derived:

Where

And in turn

From the above equations, the role of cavity thickness can easily be traced ( t_cav ).

By contrast, the relationship for polaritonic surface plasmons (SPPs) is calculated according to the following dispersion relation:

So the dispersion relation for a GSP becomes:

Proceeding in this way, it is possible to derive the following explanatory equation that allows us to derive the wavelength of the plasmonic resonance for a given mode "n" tcavbgsp — fl · Tΐ f

Leaving aside the phase shifting term f, given the possibility of cavities that do not introduce it, we find that the single mode "n=l" for which the incident light is fully transformed into heat is directly related to the cavity thickness as follows: tcav — bgsp ^{' n p}

It is also possible to proceed in a more analytical way by calculating the modal curve, i.e. the number of modes present in the realised structure, from the following relation: n — ·oanb 5r! ^p

An analytical but also graphical way to easily establish the existence of the single mode as a function of the cavity thickness and resonance wavelength is to use a transfer matrix method (TMM) and derive absorption maps.

Therefore, the choice of materials for the transducer device 1 and the thicknesses of each layer, in both MDM and DMD configurations, makes use of finite element models or coded in matlab, C++ or python. These models make it possible to assess, depending on the dielectric dispersion curves of metals/dielectrics/semiconductors or alloys/composites thereof, which is the best thickness to increase absorption and identify the resonant mode for the resonance of the cavity defined between the two dielectric/metal interfaces. Having identified the metal thickness for which there is a good absorption value and that this coincides with the required wavelength, it is possible to proceed in a similar manner to select the thickness of the dielectric cavity that will then guarantee maximum light-to-heat conversion.

Example 1 In this case, simulations carried out in a Metal-Dielectric-Metal (MDM) configuration are reported, as shown in Figure 6. Absorption maps are reported as a function of the wavelength of electromagnetic radiation incident on the transducer device and the thickness of the layer of metallic material, Fig. 9, whereas in Figure 10 as a function of the thickness of the dielectric material layer.

The first and second layers of metallic material are made of Silver. The first dielectric layer is made of ITO.

Regarding the results in Figure 9, the first and second metal layers (Silver) vary simultaneously (i.e. in Figure 9, the thickness of the first metal layer is always equal to the thickness of the second metal layer) while the thickness of the first dielectric layer (ITO) remains unchanged and is 80 nm.

As far as the results in Figure 10 are concerned, the thickness of the first dielectric layer, consisting of ITO, varies, while the thicknesses of the first and second layers of metallic material, consisting of Silver, of 20 nm each, remain unchanged.

It is therefore possible to see the variation of the transducer absorption as the wavelength and dielectric or metal thicknesses vary.

The procedure mainly used to derive optimal values for making the device 1 is based on the transfer matrix method (TMM).

The procedure may be summarised as follows: a) Start b) The material characteristics (complex refractive index) are introduced c) The values of the thicknesses of the layers of dielectric and metallic material are input. Thicknesses can be fixed or variable (preferably the range of variation is 0-300 nm) d) The calculation of the results is done according to the rules of the Global Scattering Matrix Method (SMM), here the polarisation of the incident electromagnetic radiation (which can be p, s, user- defined, unpolarised) is imposed e) based on the results of the SMM, the Fresnel complex coefficients are calculated f) TMM extracts the results of reflectance (R), transmittance (T) and absorbance (1-T-R) as a function of the wavelength (l) and the thickness of each layer of the transducer 1.

If the best thickness must be found to maximise a given optical response, the TMM is repeated, producing the maps of Figures 9 and 10 for the various thicknesses. The same maps may be repeated as the material changes.

Example 2

Absorption maps are reported as a function of the wavelength and thickness of the first and only metal layer and the thickness of the first and second dielectric layers in a Dielectric-Metal-Dielectric DMD configuration. Figure 11 reports the results of simulations carried out as in Example 1 wherein the thickness of the first metal layer, i.e. Silver, varies, while the dielectric layers, ITO, remain unchanged with thicknesses of 50 nm each.

Figure 12, on the other hand, reports the results of the simulations carried out as in Example 1 wherein the thicknesses of the first and second dielectric layers (ITO) (which have the same thickness) vary and the thickness of the first metal layer, Silver, with a thickness of 20 nm remains unchanged.

The absorption spectra shown in Figures 11 and 12 are repeated by changing the type of metal, instead of silver as in the example of Figures 11 and 12, gold is used in Figures 13 and 14. As it can be seen, the choice of the materials greatly affects the optical response.

Figure 13 reports the results where the thickness of the first metal layer, Gold in this case, varies, while the first and second dielectric layers, ITO, remain unchanged with thicknesses of 50 nm each.

In Figure 14, on the other hand, the thicknesses of the first and second dielectric layers (ITO) with equal thickness vary, while the metal layer, gold, with a thickness of 20 nm remains unchanged.

Figure 15 is similar to Figure 14, but with a gold layer with a thickness of 40 nm.

Example 3 Experimental examples for making the transducer of Figure 6 are hereinafter reported.

The MDM device 1 (to which the second layer of dielectric is also added to cover the second layer of metal) is made up of the following 4 layers: Silver 30 nm, ITO 80 nm, Silver 30 nm, ITO 20 nm.

Deposition takes place by DC sputtering in a deposition chamber at a temperature of approximately 25°C. For the polymers, a solution of 5 wt% poly vinyl pyrrolidone in ethanol deposited by spin coating was used (Trade name: Calctec FR10KPA) at 3000 RPM.

For the first and second silver layer, the parameters are: power 20 W, Argon pressure 4.5c10^L-2 mbar for a time of 120 seconds. For the first dielectric layer (ITO), the parameters are: power 40 W, Argon pressure 4.5c10^L-2 mbar for a time of 420 seconds.

For the second dielectric layer (ITO), the parameters are: power 40 W, Argon pressure 4.5c10^L-2 mbar for a time of 100 seconds.

The device 1 is irradiated by a laser with a wavelength centred in the absorption band of the device 1, in this case l=532 nm. The laser beam produced by the laser has a diameter of 5 mm with a power of 100 mW (corresponding to 5 mW/mm²). The temperature acquisition as a function of time was carried out using a FUR thermal imaging camera (model E40) equipped with a data acquisition and processing software.

At time t = 0, the laser 7 is switched off.

The laser 7 is switched on (and thus emits electromagnetic radiation against the transducer 1) at a time t = 3 seconds

The beam is then switched off at t = 38 seconds, so after 35 seconds of irradiation Example 4

Similar to Example 1, but the device is irradiated by a laser beam with a power of 400 mW (equivalent to 20 mW/mm²). Example 5

Similar to Example 1, but the device is irradiated by a laser beam with a power of 1500 mW (equivalent to 75 mW/mm²) and the beam is switched off at t = 63 seconds, i.e. after 60 seconds of irradiation.

Figure 7 shows the graph of the temperature trend measured on the surface of transducer 1 where the electromagnetic radiation is incident as a function of time for the three examples outlined above (Example 3, Example 4 and Example 5, i.e. same transducer, but three different laser powers). The temperature difference shown is the difference between the temperature before irradiation and the temperature after irradiation.

It can be seen that, for the highest power, the temperature difference is higher than 500°C, although the intensity of the laser irradiation is only 75 mW/mm². This maximum temperature difference is reached after about 30 seconds of continuous irradiation and is represented in the thermal map in Figure 8 where the transducer 1 is irradiated by the electromagnetic radiation produced by the laser 7 for 30 seconds. The maximum temperature reached is 570°C.

Example 6 With the transducer of Example 3 - 5, a scalpel 100 is made as shown in Figures 5 and 5a. In order to perform the tests, samples of animal meat were irradiated with a laser having a wavelength of 532 nm and an intensity of 71 mW/mm² or 140 mW/mm² for 60 seconds.

By moving the meat sample, well-defined stripes of burnt meat may be seen.

Claims

1. An optical scalpel (100), comprising:

A laser (7) designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm;

An optical fibre (11) defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser (7);

A transducer device (1) of light energy into thermal energy positioned on the first end of the optical fibre and comprising: o A first continuous layer of metallic material (3), with a thickness comprised between 5 nanometres and 150 nanometres; o A first layer of dielectric material (4), with a thickness comprised between 5 nanometres and 300 nanometres; o A second continuous layer of metallic material (5), with a thickness comprised between 5 nanometres and 150 nanometres.

2. An optical scalpel (100), comprising:

An optical fibre (11) defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser;

A transducer device (1) of light energy into thermal energy positioned on the first end of the optical fibre and comprising: o A first layer of dielectric material (3), with a thickness comprised between 5 nanometres and 300 nanometres; o A first continuous layer of metallic material (4), with a thickness comprised between 5 nanometres and 150 nanometres; o A second layer of dielectric material (5) with a thickness comprised between 5 nanometres and 300 nanometres.

3. Optical scalpel (100) according to claim 1 or 2, comprising an endoscope (12).

4. Optical scalpel (100) according to one or more of the preceding claims, wherein the metallic material making up the first metallic layer and/or the second layer of metallic material consists of at least 90% pure metal.

5. Optical scalpel (100) according to one or more of the preceding claims, wherein the first layer of metallic material is in direct contact with the first layer of dielectric material and/or the first layer of metallic material is in direct contact with the second layer of dielectric material.

6. Optical scalpel (100) according to one or more of the preceding claims, wherein the metallic material making up the first layer of metallic material and/or the second layer of metallic material comprises one of: silver, gold, aluminium, copper, platinum, titanium, vanadium, chromium, iron.

7. Optical scalpel (100) according to one or more of the preceding claims, wherein the dielectric material making up the first layer of dielectric material and/or the second layer of dielectric material comprises one of: zinc oxide (ZnO), titanium oxide (Ti0₂), aluminum oxide (AI203), indium tin oxide (ITO), aluminum doped zinc oxide (AZO), copper oxide (CuO, Cu₂0 and Cu₂0₃), silicon oxide (Si0₂) or composites thereof; polyvinylpyrrolidone (PVP), polymethylmethacrylate (PMMA), polyvinyl alcohol (PVA), Silicon, Germanium and oxides or alloys thereof.

8. Method for manufacturing an optical scalpel (100), comprising:

Providing a laser (7) designed to emit an electromagnetic radiation with a wavelength comprised between 300 nm and 1500 nm;

Providing an optical fibre (11) defining a first and a second end, the optical fibre being designed to guide the electromagnetic radiation emitted by the laser;

Making on the first end of the optical fibre a transducer device (1) of light energy into thermal energy comprising the steps of: o Depositing a first continuous layer of metallic material (3), with a thickness comprised between 5 nanometres and 150 nanometres; o Depositing a first layer of dielectric material (4), with a thickness comprised between 5 nanometres and 300 nanometres; o Depositing a second continuous layer of metallic material (5), with a thickness comprised between 5 nanometres and 150 nanometres.

9. Method for manufacturing an optical scalpel (100), comprising:

Making on the first end of the optical fibre a transducer device (1) of light energy into thermal energy comprising the steps of: o Depositing a first layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres; o Depositing a first continuous layer of metallic material, with a thickness comprised between 5 nanometres and 150 nanometres; o Depositing a second layer of dielectric material, with a thickness comprised between 5 nanometres and 300 nanometres.

10. Method according to claim 9, wherein the first layer of metallic material is deposited on the first layer of dielectric material, and the second layer of dielectric material is deposited on the first layer of metallic material.

11. Method according to claim 8, wherein the first layer of dielectric material is deposited on the first layer of metallic material, and the second layer of metallic material is deposited on the first layer of dielectric material.

12. Method according to one or more of claims 8 to 11, wherein depositing the first layer of metallic material and/or the second layer of metallic material and/or the first layer of dielectric material and/or the second layer of dielectric material includes depositing the first and/or second layer by one of: cathodic vaporization deposition with direct current; physical vapour deposition; chemical vapour deposition; atomic layer deposition; deposition by ion gun; deposition by electron gun.

13. Method according to any one or more of claims 8 to 12, wherein the first layer of dielectric material and/or the second layer of dielectric material includes a polymeric material, and depositing the first layer of dielectric material and/or the second layer of dielectric material includes one of: cold plasma deposition; deposition by rotation coating.

14. Method according to claim 8, wherein depositing the first layer of metallic material includes depositing the first layer of metallic material on a substrate.

15. Method according to claim 9, wherein depositing the first layer of dielectric material includes depositing the first layer of dielectric material on a substrate.