EP1774568A1

EP1774568A1 - Light source with electron cyclotron resonance

Info

Publication number: EP1774568A1
Application number: EP05763741A
Authority: EP
Inventors: Pascal Sortais; Xavier Pellet
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-29
Filing date: 2005-04-28
Publication date: 2007-04-18
Also published as: US20070273262A1; CN1950926A; WO2005117069A1; FR2869719B1; JP2007535103A; WO2005117069A8; FR2869719A1

Abstract

The invention relates to a light source comprising an emitter (4) which, by means of at least one antenna (3), creates a high-frequency electromagnetic wave in a sealed chamber (1) and which powers the lamp. According to the invention, the chamber (1) is equipped with a wall that is transparent to the light and contains a low-pressure gas. A permanent magnet (2) creates a static magnetic field inside the chamber (1). The respective values of the static magnetic field and the frequency of the electromagnetic wave are determined such as to cause an electron cyclotron resonance inside the chamber (1). Moreover, the emitter (4), the antenna (3) and the magnet (2) are disposed in relation to the chamber (1) such as to clear a solid angle of at least 2 Π steradians for the light. The antenna (3) can be disposed inside the chamber (1) and, optionally, can comprise the magnet (2). The magnet is essentially sheathed by the chamber (1).

Description

Light source with cyclotron electron resonance

Technical field of the invention

The invention relates to a light source powered by ultra high frequency, comprising a transmitter creating, via at least one antenna, an ultra high frequency electromagnetic wave in a sealed enclosure, having a wall transparent to light and containing a gas at low pressure, the source comprising magnetic means intended to create a static magnetic field inside the enclosure, the respective values of the static magnetic field and the frequency of the electromagnetic wave being predetermined, so as to cause inside the enclosure a cyclotron resonance of electrons.

State of the art

Light sources, visible or ultraviolet (UV), powered by ultra high frequency conventionally include a transmitter creating an ultra high frequency electromagnetic wave in a sealed enclosure, transparent to light and containing a gas at low pressure. An ultra high frequency discharge ionizes the gas and accelerates the electrons. The energetic electrons ionize the gas, so as to create a stationary plasma. During collisions between electrons and ions, light radiation is emitted. The document GB2375603 describes a UV light source comprising control means making it possible to optimize the intensity of the UV radiation emitted, in particular in the UVC band of the ultraviolet spectrum.

The document US Pat. No. 6,657,206 describes a system for generating UV radiation comprising a microwave chamber in which a plasma lamp is arranged. A microwave generator is coupled to the microwave chamber to excite the plasma in the plasma lamp which thereby emits UV radiation.

UV light is used, for example, for characterization, imaging, photolithography, disinfection or for the production of ozone. In most applications, high gloss is desired. However, known sources often have a low yield and / or have significant costs due to a limited lifespan.

Furthermore, conventional light sources, based on gas discharges, include electrodes in contact with the plasma. The wear of the electrodes, due to bombardment by plasma ions, limits the life of the light sources.

Document GB1020224, for example, describes an ultraviolet lamp with electron cyclotron resonance intended to create a particular plasma at high temperature and far ultraviolet radiation. The plasma is created in a discharge tube containing a gas at low pressure. Two electrodes are placed inside the tube to create the plasma by means of a low frequency subsidiary discharge. Two coils surround the outer periphery of the discharge tube and create an axial magnetic field limiting the plasma essentially to the central axis of the tube. The tube passes through side walls of a waveguide coupled to a high frequency source, so as to project electromagnetic radiation into the plasma, perpendicular to the magnetic field. A beam of parallel ultraviolet rays is emitted through an opening arranged in the center of one of the electrodes. This lamp is difficult to implement.

The document US Pat. No. 3,911,318 describes a method and an apparatus for generating high power UV and visible electromagnetic radiation. The device is powered by a radio frequency generator creating a radio frequency field inside a quartz or fused silica plasma tube allowing UV radiation to escape. The gas pressure in the tube is sufficient to support the generation of a plasma by microwave. The device comprises Helmholz coils creating inside the tube a static magnetic field. A mesh screen serving as a waveguide makes it possible to confine the radiofrequency radiation. The device allows to illuminate only in a limited solid angle. In addition, the device is bulky.

Subject of the invention

The object of the invention is to remedy these drawbacks and, in particular, to make it possible to produce a light source without an electrode, and in particular a compact UV source, providing a high light intensity and having a high efficiency.

According to the invention, this object is achieved by the appended claims and, in particular, by the fact that the magnetic means consist of at least one permanent magnet substantially enveloped by the enclosure and by the fact that the emitter, the antenna and the magnet are arranged relative to the enclosure so as to release for light a solid angle of at least 2π steradians.

Brief description of the drawings

Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples and represented in the appended drawings, in which:

Figures 1 to 5 show, in section, five particular embodiments of a light source according to the invention.

FIG. 6 represents, as a function of time, three particular embodiments of the radiofrequency power supplying the light source according to the invention.

Description of particular embodiments

The light source shown in Figure 1 comprises an enclosure 1, having substantially the shape of a sealed bulb, having an outer wall transparent to light. The enclosure 1 contains a low pressure gas, for example one or more rare gases at a total pressure of 2 μbar, deuterium or a metal vapor, for example sodium, zinc or mercury.

When the gas is a mercury vapor, the pressure in the enclosure 1 can be the vapor pressure of the mercury at ambient temperature which is of the order of 2 μbar. The wall of the enclosure 1 can be transparent only in one desired spectral band, for example in a visible band or in a UV band. Typically, the materials used for the light sources have a cut-off wavelength situated in the UV band of the electromagnetic spectrum, for example at 150 nm.

In FIG. 1, a single permanent magnet 2 and an antenna 3 connected to a transmitter 4 penetrate, in a sealed manner, into the enclosure 1. The permanent magnet 2 and the antenna 3 are then partially arranged inside. of enclosure 1 and partly outside of enclosure 1. The parts disposed outside of enclosure 1 are arranged in a housing 5, in which the transmitter 4 is also housed. may, for example, be a magnetron or a transmitter based on transistors, of the type used in portable telephones, capable of operating at low voltage, for example at 3V. The transmitter has, for example, a power between 1 Watt and 300W, depending on the type of transmitter.

The magnet 2 creates, inside the enclosure 1, a static magnetic field. The emitter 4 enables the light source to be supplied by an ultra high frequency electromagnetic wave created in the enclosure 1. The ultra high frequency electromagnetic wave makes it possible to ionize the gas and accelerate the electrons. The frequency of the ultra high frequency electromagnetic wave is between 300MHz and 300GHz.

In the static magnetic field, the electrons are subjected to a force perpendicular to their speed. The trajectories of the electrons are then substantially circular or in the form of spirals which are characterized, in a known manner, by a radius of gyration, inversely proportional to the magnetic field, and by a cyclotron frequency which is proportional to the field magnetic. The electrons are then confined by the static magnetic field.

The radius of gyration and the cyclotron frequency are, in principle, defined only in a uniform field, while the magnetic field created by a magnet 2 whose dimensions are of the order of those of enclosure 1, in fact presents a gradient in enclosure 1. However, the radius of gyration and the cyclotron frequency make it possible to estimate certain orders of magnitude, in particular the respective values of the static magnetic field and the frequency of the electromagnetic wave. These values are predetermined so as to cause a cyclotron resonance of electrons inside the enclosure, at least in a resonance zone arranged in the enclosure.

The magnetic field must be strong enough so that the radius of gyration is less than the dimension of the enclosure 1. A magnetic field of the order of

0.1 Tesla, for example, makes it possible to confine the electrons in an enclosure 1 having dimensions of a few decimeters, which corresponds to the typical dimension of a light source. The cyclotron frequency in a field of 0.1 Tesla is of the order of 2 GHz.

When the frequency of the ultra high frequency electromagnetic wave corresponds to the cyclotron frequency, a resonance effect is obtained. The resonance relationship between the static magnetic field B and the frequency f of the ultra high frequency electromagnetic wave, B = f.2.π.m / e, depends only on the ratio of mass m and charge e of l 'electron. When the static magnetic field is 0.1 Tesla, the frequency of the ultra high frequency electromagnetic wave is then about 2 GHz. One thus obtains a cyclotronic resonance of electrons inside the enclosure. Preferably, the static magnetic field is 0.0875 Tesla and the frequency of the ultra high frequency electromagnetic wave is 2.45 GHz, which is a frequency usually used in ultra high frequency sources. The static magnetic field having a gradient, the resonance conditions are not necessarily fulfilled in the entire space of the enclosure. The maximum resonance zone can take any shape, defined by the distributions of the static magnetic field and the ultra high frequency electromagnetic wave. The shape of the enclosure is preferably adapted to the distribution of the field of the magnet 2 used and the antenna 3 is arranged so that all the space delimited by the enclosure 1 receives the electromagnetic wave. ultra high frequency.

It should be noted that the electrons can, a priori, gain or lose energy under the effect of the electromagnetic wave, according to the orientation of their speed compared to the electric field of the wave. In addition, the electrons collide with the plasma ions in the resonance zone. However, the electrons being confined by the static magnetic field, it turns out that after a large number of passages in the zone subjected to the electromagnetic wave, the energy balance of the electrons is positive and can be between 1 electronvolt and a few tens of electronvolts per electron, for example 50eV. This balance determines the energy supply of the light source. The energy is then emitted during radiative inelastic collisions with the ions, in the visible spectrum and, in particular, in the UV spectrum.

The light efficiency of the light source, greater than 100 lumens per Watt, is significantly higher than that of known light sources, which makes it possible to obtain a predetermined brightness at very low power supply. During a start-up phase of the light source, the accelerated electrons further ionize the gas, so as to increase the electron density. However, in known manner, a plasma serves as a screen for frequencies below the plasma cutoff frequency, which depends on the square root of the electron density in the plasma. As the density increases during the start-up phase, the cutoff frequency increases correspondingly until the cutoff frequency reaches the value of the frequency of the injected ultra high frequency electromagnetic wave. The plasma then reaches an electronic saturation density, typically after a few tens of microseconds. The minimum pressure required for starting is around 0.4 μbar.

In the light source represented in FIG. 1, the emitter 4, the antenna 3 and the magnet 2 are arranged, with respect to the enclosure 1, so as to release for light a large solid angle of illumination, greater than 2π steradians. In fact, in FIG. 1, the light L is emitted all around an axis of rotation R. Only the housing 5 limits the solid angle of illumination of the light source. This gives a large field of illumination. This light source has the advantage of being able to operate at low temperature, for example at room temperature. However, maximum intensity is obtained at a higher temperature, for example of the order of 40 ° C.

In Figure 1, the enclosure 1 substantially envelops the magnet 2 and the antenna 3 which allows the gas disposed in the enclosure to absorb the electromagnetic radiation emitted by the antenna 3 very effectively. In addition, the resonance zone arranged in the enclosure 1 automatically constitutes a radiation screen making it possible to limit the ultra high frequency electromagnetic radiation outside the light source. The light source provides radiation in the visible spectrum and in the UV spectrum, corresponding to emission lines of the atoms and ions of the gas. The 254nm line of the non-ionized mercury atom can reach ten times the brightness of a standard UV lamp. The emission lines of ions with wavelengths less than 200nm are particularly intense. The once-ionized mercury lines, having wavelengths of 164.9nm and 194.2nm, are about five times more intense than the line at 254nm of the non-ionized mercury atom. The choice of gas and pressure in the enclosure makes it possible to adapt the spectrum of the source to its use, in particular to the desired UV regime. For example, the higher the pressure, the more dominated the lines emitted at long wavelengths, that is to say emission lines of non-ionized atoms. Knowledge of the atomic spectra of the atoms constituting the gas and of the ion spectra of the atoms ionized one or more times thus makes it possible to obtain the desired radiation. The radiation created is characterized by the corresponding atomic and ionic lines.

To constitute a visible light source, the enclosure 1 can comprise, as shown in FIG. 1, a fluorescent coating 6 transforming an ultraviolet radiation into visible radiation.

In the light source shown in FIG. 2, the magnet 2 simultaneously constitutes the antenna 3 of the transmitter 4. The enclosure 1 comprises an external housing 7 for the magnet 2. Thus, the magnet 2 is arranged in all outside the enclosure 1 and is not subjected to the action of the plasma during the operation of the light source. The enclosure 1 substantially enveloping the magnet 2 constituting the antenna 3, the light is always emitted in a large solid angle. The light source shown in Figure 2 has a mesh 8 end of protection against ultra high frequency radiation, which allows to meet safety standards even in the case of operation at high power of the transmitter 4. Such a grid 8 can also be provided in the embodiment of FIG. 1 and in the other embodiments described below. The fine mesh 8 can be placed outside the enclosure 1, as shown in FIG. 2, or inside the enclosure 1, so as to surround the resonance zone in which the antenna 3 is placed. .

In the particular embodiment represented in FIG. 3, the magnet 2 and the antenna 3 of the transmitter 4 are disposed entirely inside the enclosure 1. Thus, the magnet 2 and the antenna 3 are completely surrounded by the gas and do not imitate the solid angle at which the source radiates. Only the housing 5 limits the field of illumination. In FIG. 3, the enclosure 1 comprises a transparent conductive coating 9 on an internal face or an external face of the wall of the enclosure 1, surrounding the antenna 3 and thus constituting a radiation protection screen at ultra high frequency.

In the particular embodiment shown in Figure 4, the enclosure 1 has a tubular shape and four magnets 2 are arranged at the ends of the tubular enclosure 1, in the enclosure 1, on either side of the central axis of the enclosure, so as to create a magnetic trap for the electrons and ions of the plasma. To constitute such a trap, at least two magnets 2 are necessary. In the particular embodiment shown, the antenna 3 is arranged along the enclosure 1, on one side of the latter. The tubular enclosure 1 makes it possible to obtain light in a large solid angle, at least equal to 2π steradians.

The light source according to the invention can be of any dimensions and very particularly of very small dimensions if the wavelength of the injected electromagnetic wave and the static magnetic field are adapted to source dimensions. Thus, the source shown in Figures 1 to 3, for example, can have dimensions of the order of a centimeter, the frequency of the electromagnetic wave being of the order of 30 GHz and the static magnetic field being of the order of 1 Tesla. The ultra high frequency transmitter 4 may, for example, include a microelectronic circuit providing a power less than or equal to 1 Watt. A plurality of light sources can, for example, be grouped in the form of an array.

The lifespan of the source is limited by the lifespan of the emitter 4 which is typically significantly greater than the lifespan of a conventional light source, for example that of an incandescent or fluorescent bulb.

The efficiency of the coupling of the ultra high frequency electromagnetic wave and the plasma is very high thanks to the cyclotronic resonance of electrons.

The light efficiency of the source is therefore very good. The energy of the ultra high frequency electromagnetic wave is mainly transferred to the electrons, not to the ions, and is therefore directly useful for radiative and ionizing collisions, without heating the plasma, which allows the light source to be used at low consumption.

It is also possible to carry out a modulation of the power P of the radiofrequency wave injected into the enclosure 1, for example in the form of pulses of any shape and frequency. These pulses are preferably rectangular as shown in FIG. 6. The three curves P1, P2 and P3 correspond to the same average power Pmn and, thus, to the same average light intensity. Indeed, according to the curve P1 a predetermined continuous power is injected into the enclosure 1. The continuous power (P1) is equal to the average power Pmn. The average power Pmn injected is preferably between 10 and 1000W. Curve P2 represents rectangular pulses with maximum power Pmax2, for example with a frequency of 50Hz, and having a duty cycle such that the average power Pmn injected into the enclosure 1 is the same as that of the curve P1. The curve P3 has a frequency two times lower than that of the curve P2 (in the example 50 Hz) and a maximum power Pmax3 of the rectangular pulses twice as high as that of the curve P2. Thus, the average power Pmn of the curves P2 and P3 is effectively equal. However, the maximum powers of the curves P1, P2 and P3 being different, the curves P1, P2 and P3 correspond to different light spectra.

The series of rectangular pulses is not necessarily periodic. Indeed, it is possible to envisage injecting a series of pulses each having a duration of the order of a microsecond, for example. The duration of a pulse and / or the time difference between two successive pulses can be adjusted. Thus, the light signal obtained makes it possible to code information, for example of the Morse type.

The shape of the enclosure 1 can, for example, be a tubular shape (Figure 4), a hollow cylinder, an ovoid (Figures 1 to 3) or a swollen tube comprising the magnet 2 and / or the antenna 3 to inside or outside the space filled with gas. When the magnet 2 is placed outside the space filled with the gas, it is still substantially enveloped by the enclosure 1, for example by placing the magnet 2 in an external housing, as shown in the Figure 2. An external housing can also be envisaged for other forms of the enclosure 1, for example for a tubular enclosure. Another example is shown in Figure 5, where the magnet 2 is arranged in the center of the enclosure 1 which has the shape of a hollow cylinder. The assembly constituted by the enclosure 1 and the magnet 2 is preferably surrounded by a grid 8 of protection against ultra high frequency radiation. Unlike the Helmholz coils, the permanent magnet 2 can in particular be arranged so that the enclosure 1 envelops the magnet, that the magnet 2 is placed inside the enclosure 1 (Figures 1 and 3 ) or outside the enclosure 1 in an external housing (Figure 2), while being enveloped by the enclosure 1. Thus, a large solid angle can be released for the light L. In addition, when the enclosure 1 comprises a fine protective mesh 8, the magnet 2 can then be placed inside the mesh 8 (FIG. 2), while, the mesh constituting a resonance cage, the Helmholz coils could not be disposed inside the mesh because of the incompatibility of the coils and the radiofrequency field. However, the minimum dimensions of the resonance cage are determined by the resonance frequency. For example, for a resonance frequency of 2.45 GHz, the resonance cage must have minimum dimensions between 6cm and 10cm. The use of a permanent magnet then makes it possible to reduce the dimensions of the entire light source to the dimensions of the resonance cage, while the Helmholz coils would be added to the dimensions of the resonance cage.

In addition, Helmholz coils require additional electrical connections. This improves the compactness of the light source, which is particularly necessary in the case of a portable light source or for the integration of the source in other devices.

The invention is not limited to the particular embodiments shown in the figures. The fine protective mesh may cover the enclosure and / or the assembly formed by the enclosure and the antennas and possibly the magnets. The operation of the light source is independent of the geometric shape of the magnet and the enclosure.

Claims

claims

1. Light source powered by ultra high frequency, comprising a transmitter (4) creating, via at least one antenna (3), an ultra high frequency electromagnetic wave in a sealed enclosure (1), having a transparent wall in the light and containing a gas at low pressure, the source comprising magnetic means intended to create inside the enclosure (1) a static magnetic field, the respective values of the static magnetic field and the frequency of the electromagnetic wave being predetermined, so as to cause inside the enclosure a cyclotronic resonance of electrons, source characterized in that the magnetic means consist of at least one permanent magnet (2) enveloped substantially by the enclosure ( 1) and in that the emitter (4), the antenna (3) and the magnet (2) are arranged relative to the enclosure (1) so as to release for light a solid angle of at least minus 211 steradians.

2. Light source according to claim 1, characterized in that the antenna (3) is arranged inside the enclosure (1).

3. Light source according to one of claims 1 and 2, characterized in that the magnet (2) constitutes the antenna (3).

4. Light source according to any one of claims 1 to 3, characterized in that the magnet (2) is arranged inside the enclosure (1).

5. Light source according to any one of claims 1 to 3, characterized in that the magnet (2) is arranged outside the enclosure (1).

6. Light source according to claim 5, characterized in that the enclosure (1) comprises an external housing (7) for the magnet (2).

7. Light source according to claim 1, characterized in that the magnet (2) and the antenna (3) penetrate into the enclosure (1) in a sealed manner.

8. Light source according to any one of claims 1 to 7, characterized in that the enclosure (1) comprises a fluorescent coating (6) transforming ultraviolet radiation into visible radiation.

9. Light source according to any one of claims 1 to 8, characterized in that the enclosure (1) comprises a transparent conductive coating (9).

10. Light source according to any one of claims 1 to 9, characterized in that the source comprises a grid (8) end of protection against ultra high frequency radiation.

11. Light source according to any one of claims 1 to 10, characterized in that the enclosure (1) has a shape chosen from tubular shapes, hollow cylinders and ovoids.