Integrated calibration method and device for radiometric optical systems

Abstract

Integrated calibration method and device for radiometric optical systems The invention relates to a method for measuring the transmission of a light beam, and the associated radiometry device (3), the method comprising a propagation of the light beam (2), in a first configuration, comprising a transmission of the light beam (2), a number a of times by a first assembly (31) and a transmission of the beam, a number b of times by a second assembly (32) comprising an optical transmission element capable of being altered, a propagation of the beam (2), in a second configuration, comprising a transmission of the beam (2), a number c of times by the first assembly (31), and a transmission of the beam (2), a number d of times by the second assembly (32), the numbers a, b, c, d forming an invertible matrix,to independently determine the transmission by the first assembly (31) and / or the transmission linked to the optical transmission element. Figure for the abstract: Fig. 2.,

Description

Title of the invention: Integrated calibration method and device for radiometric optical systems Technical field

[0001] The present invention relates to a method for measuring the transmission of a beam by a radiometry device comprising at least one optical transmission element capable of being altered, and the associated radiometry device. Particularly advantageous applications relate to optical diagnostics of tokamak, measurements of optical transmissions of a medium such as air or water, for example by a transmissiometer. STATE OF THE ART

[0002] In many radiometric measurement applications, one seeks to measure the transmission efficiency of a light beam through a medium and / or an optical device. This is a calibration measurement.

[0003] These radiometry devices comprise a plurality of optical components arranged so that a light beam, emitted by a source, propagates through optical components and is measured after its propagation by a sensor. Knowing the power of the source, the transmission efficiency of the beam in the radiometry device can be determined. Knowing the transmission efficiency of the optical components of the radiometry device, it is possible to determine the transmission efficiency of the medium and / or the optical device.

[0004] The transmission efficiency of these optical components is in fact included with the measurement of the transmission efficiency of the beam by the radiometry device, during the measurement by the sensor. However, the optical components may have surfaces that are likely to be altered, for example dirty, in an uncontrolled manner and thus impact the measurement of the transmission efficiency. The transmission efficiency of the optical components of the radiometry device therefore varies, inducing uncertainty on the value that one seeks to measure.

[0005] This is the case, for example, of transmissiometers. It is known to use a transmissiometer to measure the transmission efficiency of an aquatic environment, for example an underwater environment. The optical surfaces in contact with the aquatic environment risk becoming dirty, for example due to various deposits and / or algae growth.

[0006] It is further known to use runway visual range transmissiometers to provide pilots and air traffic services units with information on runway visibility conditions during periods of low visibility. visibility, whether due to fog, rain, snow or sandstorms, for example. Optical surfaces in contact with the ambient air are likely to become dirty and therefore disrupt the visibility measurement.

[0007] To remedy this, there are solutions for calibrating and / or maintaining these radiometry devices. One preventive maintenance solution is to clean the dirty optical surfaces at regular intervals. However, these maintenance operations are costly. In addition, the fouling does not follow a predictable progression, which does not guarantee reliable measurement between maintenance operations.

[0008] Another solution is to install a calibrated light source at the location where the measurement is to be carried out. However, such an installation may be made impossible either because of the cramped conditions or access, or because of its viability or because its performance may be affected by the environment.

[0009] These alteration phenomena can concern many other applications.

[0010] For optical diagnosis of tokamak, measurement in transmission with a source Calibrated light transmission is difficult, if not impossible, due to the environment. To overcome this problem, one solution is to integrate a shutter equipped with a retroreflector that is configured to reflect a light beam from the tokamak optical line in a controlled manner towards a sensor. The shutter, and possibly other optical components, however, remain placed close to the plasma. Fouling by plasma sputtering and / or water vapor leakage can occur and impact the optical transmission efficiency of the system. While calibration solutions exist to eliminate these factors, they are not complete and can be particularly complex to implement. Indeed, setting up and maintaining precise and stable alignment over time of several combined optical paths represents a challenge in a tokamak environment.

[0011] There is therefore a need to carry out a transmission measurement reliably and independently of external conditions.

[0012] An objective of the present invention is therefore to improve the measurement of transmission by a radiometry device, and in particular independently of conditions external to the device. SUMMARY

[0013] To achieve this objective, according to a first aspect, a method for measuring the transmission of at least one light beam is provided, comprising the following steps: - a provision of a radiometry device comprising at least one sensor, a first optical assembly, a second optical assembly, the second assembly comprising at least one optical transmission element capable of being altered, the radiometry device having at least a first and a second propagation configuration of the at least one light beam, - a propagation of the at least one light beam in the first configuration along a first optical path, comprising a transmission of the at least one light beam, a first number a of times with a transmission T, by the first set and a transmission of the at least one light beam, a second number b of times with a transmission ¢, by the second set comprising the at least one optical transmission element, - a propagation of the at least one light beam in the second configuration along a second optical path at least partly different from the first optical path, comprising a transmission of the at least one light beam a third number c of times with a transmission T, by the first assembly, and the transmission of the at least one light beam a fourth number d of times with a transmission ¢, by the second assembly comprising the at least one optical transmission element, the numbers a, b, c, d forming the following invertible matrix:

[0014] [Math.l] ab\ CD / a plurality of measurements by the at least one sensor, comprising at least: • a measurement Ml of the light beam having propagated in the first configuration, • an M2 measurement of the light beam having propagated in the second configuration, • from the plurality of measurements, a determination of at least one of T and ¢, thus independently determining the transmission efficiency by the first set and / or the transmission efficiency linked to the at least one optical transmission element likely to be altered.

[0015] The beam propagation is therefore carried out according to two configurations, with a different number of transmissions between the two configurations. The method therefore makes it possible to make two separate measurements, one for each configuration.

[0016] Since the matrix of transmission numbers associated with these two configurations is invertible, there is a solution for the system of equations qualifying the propagation of light in the radiometry device to determine each of T and ¢. For example, T corresponds to the value that we are seeking to measure, and <e>understand the transmission efficiency by the optical transmission element(s) likely to be altered. The resolution of this system therefore makes it possible to know independently the transmission efficiency that one seeks to measure, for example the transmission efficiency of a medium and / or an optical device, and the transmission associated with the at least one optical transmission element potentially altered. It is therefore understood that the method allows an integrated calibration taking into account independently the transmission that one seeks to measure and the transmission associated with the at least one optical transmission element.

[0017] Therefore, the determination of the transmission efficiency that one seeks to measure is made reliable, since it can be determined independently of the alteration of the optical transmission element, for example fouling. Furthermore, the method allows a measurement of the transmission efficiency associated with this possible alteration. The determination of the transmission efficiency associated with this possible alteration is made accessible independently of the determination of the transmission efficiency of the first assembly. It is therefore possible to know this alteration in order, for example, to plan maintenance of the radiometry device.

[0018] The transmission efficiency that one seeks to measure, as well as the transmission efficiency linked to the alteration of the optical transmission element can be obtained simultaneously or not. With these two configurations, it is also not necessary to put a calibrated light source placed in “transmission”: that is to say the source arranged on one side of the radiometry device and the detector on the other side of the radiometry device. This solution is therefore compatible with constraints of cramped spaces and / or difficult access.

[0019] According to a second aspect, a radiometry device is provided comprising at least one optical transmission element capable of being altered and at least one sensor configured to measure a transmission of at least one light beam. Advantageously, the radiometry device comprises a first optical assembly and a second optical assembly, the second assembly comprising the at least one optical transmission element. The radiometry device has at least a first and a second propagation configuration of the at least one light beam such that: - in the first configuration and according to a first optical path, the first assembly is configured to transmit the at least one light beam a first number a of times with a transmission T, and the second assembly is configured to transmit the at least one light beam a second number b of times with a transmission ¢, - in the second configuration and according to a second optical path at least partly different from the first optical path, the first assembly is configured to transmit the at least one light beam a third number c of times with a transmission T, and the second assembly is configured to transmit the at least one light beam a fourth number d of times with a transmission ¢.

[0020] The numbers a, b, c, d form the following invertible matrix, so as to determine at least one of T and ¢, and thus to independently determine the transmission efficiency by the first set and / or the transmission efficiency of the optical transmission element likely to be altered:

[0021] [Math.2] / ab\ d /

[0022] The radiometry device therefore has two optical configurations, between which the transmissions of the light beam are different, to obtain the above invertible matrix. It is therefore understood that it is the architecture of the radiometry device, defining the optical path for each configuration, which makes it possible to obtain the above invertible matrix. The radiometry device therefore has the effects and advantages presented above with reference to the first aspect. BRIEF DESCRIPTION OF THE FIGURES

[0023] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0024] [Fig.l] [Fig.l] schematically represents the optical transmissions by a first assembly and an optical transmission element capable of being altered by a radiometry device.

[0025] [Fig.2] [Fig.2] schematically represents the optical transmissions by a radiometry device according to an exemplary embodiment.

[0026] [Fig.3] [Fig.3] represents steps of the transmission measurement method, according to several examples of achievement.

[0027] [Fig.4A] Figures 4A and 4B represent a schematic view of a radiometry device, according to two exemplary embodiments.

[0028] [Fig.4B]

[0029] [Fig.5] Figures 5 and 6 represent schematic views of a device for radiometry, in which the first set is a tokamak optical diagnostic line.

[0030] [Fig.6]

[0031] [Fig.7A] Figures 7A and 7B respectively represent a top view and a cross-sectional view of the first and second reflection modules, according to an exemplary embodiment.

[0032] [Fig.7B]

[0033] [Fig.8A] Figures 8A and 8B represent the measurement by a matrix sensor of the beams after their propagation in a radiometry device comprising the first and second reflection modules illustrated in Figures 7A and 7B, according to an exemplary embodiment.

[0034] [Fig.8B]

[0035] [Fig.9] [Fig.9] represents a schematic view of a radiometry device, the radiometry device being a transmissiometer according to an exemplary embodiment.

[0036] [Fig. 10] [Fig. 10] represents a time tracking between the emission and the measurements made by the sensor, in the device illustrated in [Fig.9] according to an exemplary embodiment.

[0037] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular the relative dimensions of the different optical elements and their distances between them are not representative of reality. DETAILED DESCRIPTION

[0038] Before commencing a detailed review of embodiments of the invention, optional features are set out below which may optionally be used in combination or alternatively.

[0039] According to one example, - during propagation of the light beam in the first configuration, the light beam passes through the first set and the second set, such that a resulting measurement Ml of the light beam by the sensor in the first configuration is proportional, and preferably equal, to the first equation: Ml= Qn.E. Your. 0>b + Q12.E. Tc. O", preferably to Ml= Qn.E. Ta. b + Qi2.E. Tc. <bd, et - during propagation of the light beam in the second configuration, the light beam passes through the first set and the second set, such that a resulting measurement M2 of the light beam by the sensor in the second configuration is proportional, and preferably equal, to the second equation: M2= Q21.E. Your. 0>b + Q22.E. Tc. O" preferably to M2= Q2[.E. Ta. b + Q22.E. Tc. <bd - avec E the power of a light source, • Qn a non-zero geometric parameter characterizing the first configuration, • Q22 a non-zero geometric parameter characterizing the second configuration, • Qn, Q21 geometric parameters characterizing a coupling between the first and second optical paths, • T the transmission of the first set, • <e>the transmission of the second set. - the determination of T and / or <e>includes solving a system of equations comprising the first and second equations.

[0040] The equation system associated with these two measurements M1, M2 can thus be solved to obtain T and ¢, to thus independently determine the transmission efficiency by the first set and / or the transmission efficiency linked to the at least one optical transmission element capable of being altered. The solution of this equation system may depend on whether or not there is optical coupling between the first and second configurations.

[0041] According to one example, the quantities Q[2. Tc. <e>d and Q2i. Ta. <e>b are zero or at least negligible compared to Qu. Ta. <e>b et Q22. Tc. <e>d. For example, reports (Q12. Tc. <bd) / (Qn. Ta. <bb) et (Q2i. Ta. Ob) / ( Q22. Tc. <bd) sont inférieurs ou égaux à 1 / 100. Il n’y a alors pas ou très peu de couplage optiqueentre les deux configurations.

[0042] When the optical coupling is negligible, the matrix of geometric parameters Q becomes diagonal. The resolution of the system of equations and therefore Indeterminacy of T and / or

[0043] According to an alternative example, the radiometry device having an optical coupling between the first and the second configuration, Q[2 and Q2i are uninterrupted, and the numbers Qn, Q22, Q12, Q21 form the following invertible matrix:

[0044] [Math.3] 11 ^12 21 ^22 ​

[0045] The determination of T and / or

[0046] An optical coupling between the two configurations is thus taken into account to determine T and / or ¢. In optics, due to the precisions, the probability that the above matrix is non-invertible is very low. However, the person skilled in the art is able / Q to choose the optical configurations making it possible to obtain an invertible matrix and minimizing the uncertainty on the values of T and / or ¢. For this, the person skilled in the art is in particular able to choose the optical configurations minimizing the optical coupling between the configurations.

[0047] According to one example, the second assembly further comprising a first reflection module and a second reflection module: ​- in the first configuration, the beam propagation includes: • a first propagation of the light beam in the first set and the second set, • a reflection of the light beam a number m of times by the first reflection module, • a second propagation of the light beam, in the first set and the second set, - in the second configuration, the beam propagation includes: • a first propagation of the light beam in the first set and the second set, • a reflection of the light beam a number p of times by the second reflection module, m being different from p, • a second propagation of the light beam, in the first set and the second set, so that the numbers a, b, c, d of times the light beam is transmitted form the invertible matrix:

[0048] [Math.4] the b\ \CD /

[0049] According to an example: - in the first configuration, the beam propagation includes: • a first propagation of the light beam in the first set and the second set, • a reflection of the light beam a number b of times by the first reflection module, • a second propagation of the light beam, in the first set and the second set, - in the second configuration, the beam propagation includes: • a first propagation of the light beam in the first set and the second set, • a reflection of the light beam a number of times by the second reflection module, • a second propagation of the light beam, in the first set and the second set.

[0050] The reflection by the first and second reflection modules thus makes it possible to create an optical path that is at least partly different between the first and second configurations, while maintaining a simplified architecture of the radiometry device. The numbers a, b, c, d can thus form the invertible matrix. The measurement of the reflections can be good without overly complicating the overall device. The reflectivity measurements of the reflection modules are obtained regardless of the variations in reflectivity of one and / or the other of the modules.

[0051] According to one example, the method further comprises emitting a beam primary light by a light source, the second assembly being configured to form, from said primary beam, a first light beam propagating in the first configuration and a second light beam propagating in the second configuration. It is therefore understood that part of the optical path may be common between the first and second configurations. The architecture of the radiometry device is thus simplified, as is the implementation of the method.

[0052] According to an example: - At the end of the first configuration, the light beam presents a first distribution of light, and - at the end of the second configuration, and in particular after its propagation in the second configuration, the light beam has a second light distribution, different from the first light distribution, so as to spatially separate the light beam propagating in the first and second configurations, so that at least the following matrix is invertible. [Math.5] {ab\ and preferably such that the following matrix is further invertible: [Math.6] Qn Q £2-1 j £2

[0053] Indeed, the difference between the light distributions of the first and second configurations makes it possible to spatially separate the optical paths of the first and second configurations and therefore to allow to measure Ml, M2 for the corresponding configuration. As the two beams are spatially separated, in practice the matrix of geometric parameters will be invertible. Preferably, the second set is configured to transmit the beam with a distinct light distribution between each configuration. Furthermore, the difference in light distribution can be chosen so that the optical coupling is negligible between the two configurations. When the optical coupling is negligible, the term (Q^.Q 21) becomes negligible compared to (Qn.Q22)- The matrix of geometric parameters Q therefore becomes diagonal. The resolution of the equation system and therefore the determination of T and / or <e>is thus simplified. The process and the device are made more reliable.

[0054] The light distribution corresponds to a light energy per unit of surface area and solid angle. This light distribution can be point or extended, uniform or not, with a convergent, parallel or divergent beam.

[0055] According to an alternative or additional example, the method comprises an emission of a first light beam and its propagation in the first configuration, the emission of the first light beam, and preferably its propagation in the first configuration, being followed by an emission of a second light beam and its propagation in the second configuration. It is thus possible to have a temporal separation between the propagation in the first and second configurations, which makes it possible to measure M1, M2 for the corresponding configuration. This also makes it possible to minimize the optical coupling between the two configurations. When the optical coupling is negligible, the resolution of the equation system and therefore the determination of T and / or <e>is simplified. The process and the device are made more reliable.

[0056] According to one example, the second assembly further comprising a first reflection module and a second reflection module: - in the first configuration, the propagation of the light beam includes: • a propagation of the primary beam in the first set and the second set, • a reflection of the primary beam a number m of times by the first reflection module, to form the first beam, • a propagation of the first beam, in the first set and the second set, - in the second configuration, the propagation of the light beam includes • a propagation of the primary beam in the first set and the second set, • a reflection of the primary beam a number p of times by the second reflection module, m being different from p, to form the second beam, • a propagation of the second beam, in the first set and the second set,

[0057] so that the numbers a, b, c, d of times the light beam is transmitted form the invertible matrix:

[0058] [Math.7] ia b\ \c dJ

[0059] Here again, the reflection by the first and second reflection modules thus makes it possible to create an optical path that is at least partly different between the first and second configurations, while maintaining a simplified architecture of the radiometry device. The implementation of the method is therefore simplified. The numbers a, b, c, d can thus form the invertible matrix.

[0060] According to one example, the propagation of the light beam in the first configuration and the propagation of the light beam in the second configuration are at least partly simultaneous. The determinations of T and can thus be made for the same optical arrangement, at a given time. The robustness and reliability of these determinations are further improved.

[0061] According to one example, the propagation of the light beam in the first configuration and the propagation of the light beam in the second configuration are separated temporally and / or spatially.

[0062] According to one example, the first set comprises a medium whose transmission T is to be measured. The method is thus advantageously adapted to measurements by a transmissiometer, for example to measure the extinction coefficient of a medium.

[0063] According to one example, the first assembly comprises an optical diagnostic device whose transmission T is to be measured, for example an optical diagnostic device of a tokamak.

[0064] According to one example, - in the first configuration, the first set and the second set are configured to transmit the light beam, such that a resulting measurement Ml of the light beam by the sensor is proportional to, and preferably equal to, Ml= Qn.E. Ta. 0>b + Q12.E. Tc. O", preferably Ml= Qn.E. Ta. b + Qi2.E. Tc. <bd, et in the second configuration, the first set and the second set are configured to transmit the light beam, such that a resulting measurement M2 of the light beam by the sensor is proportional, and preferably equal, to M2= Q21.E. Your. 0>b + Q22.E. Tc. <Ed preferably M2= Q21.E. Your. O1' + Q22.E. Tc. <Ed with • E the power of a light source, • Qnun non-zero geometric parameter characterizing the first configuration • Q22 a non-zero geometric parameter characterizing the second configuration • Qi2, Q2i geometric parameters characterizing a coupling between the first and second optical paths, • T the transmission of the first set, • <e>the transmission of the second set.

[0065] Here again, the equation system associated with these two measurements M1, M2 can thus be solved to obtain T and / or ¢, to thus independently determine the transmission efficiency by the first set and / or the transmission efficiency linked to the at least one optical transmission element capable of being altered.

[0066] According to an example, the radiometry device having an optical coupling between the first and the second configuration, the first set and the second set are configured so that, Q[2, Q2[ being uninterrupted, the numbers Qn, Q22, Q[2, Q2[ form the following invertible matrix:

[0067] [Math. 8] / Qn Q12\ ^22 /

[0068] An optical coupling between the two configurations is thus supported to determine T and / or ¢.

[0069] According to an example, the second assembly comprises a first reflection module configured to reflect the light beam a number m of times in the first configuration, and a second reflection module configured to reflect the light beam a number p of times in the second configuration, m being different from p. Here again, the reflection by the first and second reflection modules thus makes it possible to create an optical path that is at least partly different between the first and second configurations, while maintaining a simplified architecture of the radiometry device. The implementation of the method is therefore simplified. The numbers a, b, c, d can thus form the invertible matrix.

[0070] According to an example, the second assembly comprises a first reflection module configured to reflect a number b of times the light beam in the first configuration, and a second reflection module configured to so as to reflect the light beam a number of times in the second configuration.

[0071] According to an example, the first reflection module has a first shape configured to reflect the light beam with a first light distribution, and the second reflection module has a second shape different from the first shape and configured to reflect the light beam with a second light distribution, different from the first light distribution. In addition to the reflection, the different light distribution between the two configurations makes it possible to modulate the numbers a, b, c, d and the geometric parameters Q to form the invertible matrices. The intensities of the signals can be modulated in order to minimize, and preferably eliminate, optical coupling between the first and second configurations, in particular by choosing the relative optical dimensions of the first and second reflection modules.

[0072] According to an example, the first reflection module is a corner cube mirror and the second reflection module is a concave mirror, preferably a hyperboloid mirror. The hyperboloid mirror allows the beam to be distributed homogeneously and diffusely, while the corner cube mirror allows the beam to be distributed punctually. Advantageously, this embodiment can give negligible coupling between the two configurations. For example, Qn, Q2i can be negligible compared to Qu, Q22. The determination of T and / or <e>is thus simplified.

[0073] According to one example, the first reflection module and the second reflection module are made of the same material, so that their reflectivity is substantially equal.

[0074] According to one example, the first assembly is an optical diagnostic device, for example of a tokamak.

[0075] According to one example, the first set comprises a plurality of mirrors configured to transmit by successive reflection the at least one light beam.

[0076] According to one example, the second assembly comprises a shutter disposed downstream of the plurality of mirrors, along the first and second optical paths, and a retroreflector associated with the shutter, the retroreflector being configured to reflect the at least one light beam from the first assembly toward the first assembly.

[0077] According to one example, the retroreflector comprises a corner cube mirror and a concave mirror, preferably hyperboloid.

[0078] According to one example, the radiometry device is a transmissiometer, for example a runway visual range transmissiometer or a transmissiometer configured to measure the attenuation coefficient of an aquatic environment, the first assembly comprising a medium whose transmission is to be measured.

[0079] According to one example, the second set comprises: - a first optical transmission element upstream of said medium and a second optical transmission element downstream of said medium along the first and second optical paths, - a first reflection module placed downstream of the second optical transmission element along the first optical path and configured to reflect m times, preferably once, the at least one light beam coming from said medium to return it to said medium, and - a second reflection module placed downstream of the second optical transmission element along the second optical path and configured to reflect p times, m being different from p, preferably twice, the at least one light beam coming from said medium to return it to said medium.

[0080] According to an example, we have am=b and p=d.

[0081] According to an example, the second assembly further comprises a third reflection module placed downstream of the first optical transmission element along the second optical path and configured to reflect once the at least one light beam coming from said medium from the second reflection module, to return it towards said medium and towards the second reflection module.

[0082] According to one example, the device comprises a light source configured to emit the at least one light beam.

[0083] According to one example, the method comprises emitting the at least one light beam by a source.

[0084] In the remainder of the description, the term “on” does not necessarily mean “directly on”. Thus, when it is indicated that a part or member A is supported “on” a part or member B, this does not mean that the parts or members A and B are necessarily in direct contact with each other. These parts or members A and B may be either in direct contact or be supported on each other by means of one or more other parts.

[0085] In the detailed description which follows, use may be made of terms such as “horizontal”, “vertical”, “longitudinal”, “transverse”, “upper”, “lower”, “top”, “bottom”, “upstream”, “downstream”. These terms must be interpreted relatively in relation to the normal position of the radiometry device and the propagation of the light beams in this device. For example, an “upstream” element is an element of the device placed before another so-called “downstream” element following the direction of propagation of the light beams in the device. It is considered that the direction of propagation of the light beams in the device starts from the side of its emission, for example from the light source, and goes towards the sensor.

[0086] A reference will also be used whose longitudinal or rear / front direction corresponds to the x axis, the transverse or right / left direction corresponds to the y axis and the vertical or down / up direction corresponds to the z axis.

[0087] For the purposes of this disclosure, the expression "A and / or B" means (A), (B), or (A and B). For the purposes of this disclosure, the expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0088] Several embodiments of the invention implementing successive steps of the method are described below. Unless explicitly stated, the adjective “successive” does not necessarily imply, even if this is generally preferred, that the steps follow one another immediately, intermediate steps being able to separate them.

[0089] Furthermore, the term “step” means the carrying out of a part of the method, and can designate a set of sub-steps.

[0090] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may in particular be followed by actions linked to a different step, and other actions of the first step may be repeated subsequently. Thus, the term step does not necessarily mean unitary and inseparable actions in time and in the sequence of the phases of the process.

[0091] The term "transmission" is broadly understood as an optical action of an optical component or element on a beam. A transmission may include a reflection, for example on a mirror, a transmission of the beam through a component, for example a lens or a window, or a set of reflection(s) and transmission(s) through a component. A transmission may further include a sum of transmissions and / or reflections by one or more optical components or elements.

[0092] As illustrated in [Fig.l], the radiometry device may comprise a first assembly 31 having a transmission efficiency. At least one optical component forms an optical transmission element 320 capable of being altered, for example by contact with a fouling medium. Here, a diopter is considered as an optical element as a whole, this element being at least partly in contact with the environment. The optical transmission element is capable of being altered. This element may for example be a diopter, a mirror, a lens. The alteration of this transmission element may be fouling or a change in optical property (for example opacification). In the following, this optical transmission element is designated, without limitation, by the term diopter, and the alteration by fouling.

[0093] Fouling can be due to a multitude of phenomena. For example, for a 320 diopter in contact with outside air, dust particles or even bad weather can cause a deposit on the diopter 320. For a diopter 320 in contact with an aquatic environment, deposits and / or algae growth can occur on the diopter 320. A diopter 320 can also become dirty when exposed to reactions and / or products of physicochemical reactions. This is the case, for example, for a diopter placed at the level of an incineration stack or in optical diagnostic devices such as optical diagnostic devices for a tokamak. According to this last particular example, components can in fact be placed near the plasma generated in the tokamak. An uncontrolled deposit can then occur on the diopter(s) 320 formed by these components. Furthermore, it can also be envisaged that this fouling comes from a deliberate deposition of a layer on the diopter 320, for example in a manufacturing process.

[0094] During a transmission measurement by the radiometry device, at least one light beam 2 propagates in the device. The light beam 2 is emitted 11 by a light source 30. Generally, a radiometry device may comprise the source 30, or this source 30 may be external to the device.

[0095] After its propagation in the first assembly 31 and the diopter 320, the resulting light beam 2 can be measured by a sensor 33, and more particularly an optical detector, for example a camera.

[0096] In this measurement, the transmission efficiency T of the first set 31, or transmission T, and the transmission efficiency T is affected by the transmission loss of the diopter 320. We therefore obtain an overall transmission efficiency T. It is not possible to know independently the real contribution of each of these elements. In this measurement, we have 2 unknowns: E and T. since E is affected by the transmission of the diopter, it is not possible to know T and E independently and reliably. The signal M measured by the sensor 33 can be assimilated to M = QE T, with: - E the power of the source 30, for example which we can try to measure in fine, - T the overall transmission of the first set 31 and the diopter 320 - Q: a non-zero geometric parameter characterizing the architecture of the device. It is a geometric parameter linked for example to solid angles, to light losses, which is preferably constant over time.

[0097] The method 1 for measuring the transmission of at least one light beam 2 and the radiometry device 3 according to the invention are therefore described in more detail according to several exemplary embodiments with reference to FIGS. 2 to 10. [Fig. 3] represents an example of the method 1, in which optional steps indicated in dotted lines, and variants are described by parallel paths.

[0098] As illustrated for example by figures 2, 3, 4A and 4B, in the method 1 and the radiometry device 3 according to the invention, a first optical assembly 31 and a second optical assembly 32 are used, the second assembly 32 comprising at least one diopter 320 capable of fouling.

[0099] At least one light beam 2 propagates in the first assembly 31 and the second assembly 32, until it reaches the sensor 33. As seen previously, the radiometry device may comprise the source 30 emitting the beam 2, or this source 30 may be external to the device 3.

[0100] The device 3 has two distinct configurations for propagation of the light beam 2. These two configurations being distinct, the resulting measurement of the light beam 2 by the sensor 33 for each configuration can make it possible to independently determine the transmission T of the first assembly 31 and the transmission linked to fouling.

[0101] For this, the light beam 2 propagates 12 in the first configuration along a first optical path 20. The light beam 2 is transmitted a first number a of times with a transmission T, by the first set 31. The light beam 2 is transmitted a second number b of times with a transmission ¢, by the second set 32.

[0102] The light beam 2 propagates 13 in the second configuration along a second optical path 21, at least partly distinct from the first optical path 20. The first 20 and second 21 optical paths may have at least one common section. Alternatively, the first 20 and second 21 optical paths may be entirely distinct. In the second configuration, the light beam 2 is transmitted a third number c of times with a transmission T by the first assembly 31. The light beam 2 is transmitted a fourth number d of times with a transmission <e>by the second set 32.

[0103] Each transmission <e>includes in particular at least one transmission through the diopter 320.

[0104] The radiometry device 3 is configured so that the following matrix is invertible.

[0105] [Math.9] the b\ \cd /

[0106] It is therefore the number of transmissions by the first 31 and second 32 sets of the light beam 2 which are chosen so as to obtain an invertible matrix. We therefore have ad - bc 0.

[0107] After its propagation in the first 31 and second 32 sets, the resulting light beam 2 is measured 14 by at least one sensor 33, for example a optical detector, and for example a camera. We thus obtain a measurement M1 of the light beam 2 having propagated in the first configuration along the first optical path 20, and a measurement M2 of the light beam 2 having propagated in the second configuration along the optical path 21. The plurality of measurements can be obtained during the same acquisition by one or more sensor(s) 33, or during successive acquisitions, as will be detailed below.

[0108] The configuration of the device 3 being such that the above matrix is invertible, there exists a solution to a system of equations to determine 15 independently <e>and / or T, from the measurements M1 and M2. It is therefore possible to determine the transmission efficiency by the first set 31 and / or the transmission efficiency linked to the diopter 320.

[0109] If the transmission of the first set 31 changes over time, it is possible to measure it reliably, even if the transmission of the second set 32 and more particularly the diopter 320 changes over time due to fouling.

[0110] The two configurations may have optical coupling between them. A portion of the light beam intended to follow the first optical path 20 may therefore pass through a portion of the second optical path 21 to be measured at the sensor 33, and vice versa.

[0111] The measurements M1, M2 resulting from the sensor 33 can be proportional, and preferably equal to the following propagation equations: Ml= Qn.E. Ta. 0>b + Q12.ET O" M2= Q21.E. Your. 0>b + Q22.E. Tc. O" with - E the power of the light source 30, - Qnun non-zero geometric parameter characterizing the first configuration, - Q22 a non-zero geometric parameter characterizing the second configuration, - Q12, Q2i geometric parameters characterizing a coupling between the first 20 and second 21 optical paths, - T the transmission of the first set, - O the transmission of the second set.

[0112] The optical path of each configuration is therefore more particularly configured so that the measurement M1, M2 of the output beam corresponds to these equations.

[0113] With negligible optical coupling between the two configurations, and preferably without optical coupling, the quantities Q[2. Tc. O" and Q21. Your. b are zero or at least negligible compared to Qu respectively. Your. <e>b et Q22. Tc. <e>d. For example, reports (Q12. Tc. <e>d) / (Qn. Ta. <e>b) and (Q2b Yes. <e>b) / ( Q22. Tc. <e>d) are less than or equal to 1 / 100. The propagation equations associated with the measurements Ml, M2 can then be as follows: Ml=Qn.E. Ta. 0>b M2= Q22.E. Tc. O"

[0114] In this case, in order to determine T and / or ¢, only the matrix of numbers a, b, c, d must be invertible. The resolution of the system is further simplified, as seen later in more detail.

[0115] In the case of optical coupling, in practice, noise is added to the analysis and therefore to the measurement. From a metrology point of view, it is therefore interesting to limit the optical coupling as much as possible. When the optical coupling is negligible, the calibration uncertainties are reduced. The measurement method as well as the device are therefore made more reliable.

[0116] According to another example, the radiometry device 3 has an optical coupling between the first and the second configuration. We therefore have Qi 2, Q2i which are not harmed. In this case, the device can be configured so that Qu, Q22, Q[2, Q2[ form the following invertible matrix:

[0117] [Math. 10] । Q j 2 \ ^21 ^22 /

[0118] Since both matrices are invertible, there exists a solution to a system of equations of equation to determine 151 a solution for (Ta. <e>b) and (Tc. <e>d) then to determine T and / or ¢.

[0119] In the case of optical coupling, the following system of equations can be obtained. A resolution of this system is then given as an example. For two measurements M1, M2, we obtain, with In the natural logarithm.

[0120] [Math. 11] Tad)b-

[0121] [Math. 12] ~ E.(ü(]_%2-O.2l.fî12)

[0122] [Math. 13] aJn ( T ) + = In [ ]

[0123] [Math. 14] cJn(T) = \ / L iLAU; [.i222"^21~"3 2'

[0124] The solution can therefore be presented in the following form:

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] [Math. 15] T = exp [Math. 16] O = exp ad-cb r 1 ri ad-cb It should be noted that these solutions can be presented equivalently in other mathematical forms, for example in power form like the following. [Math. 17] • T* - n^MS-On-Ml t - £{£), / / ,-0, / 1,) J [Math. 18] According to the example in which the optical coupling is negligible between the two configurations, and preferably zero, the following system of equations can be obtained, to determine T and / or 150. Q and Q22 are not harmed Its resolution is then given as an example. In(Ml) = ln(Qn.E)+ a.ln(T)+ b.ln(0>) ln(M2) = ln(Q22.E)+ c.ln(T)+ d.ln(0>) The solution can therefore be presented in the following form: [Math. 19] T = ex PL------[uLh.....••••••• J [Math.20] These solutions can be presented in another mathematical form like the following. [Math.21]

[0138] [Math.22]

[0139] From the above solutions, it is understood that it is possible to determine, from the measurements M1 and M2, the transmissions T and / or <e>and not necessarily both sets. It is therefore possible to determine the transmission T of the first set 31 when desired, and independently determine the transmission to assess the fouling of the 320 diopter. The transmission to assess the fouling of the diopter 320 can for example be determined at regular intervals to plan maintenance. The determination of the transmission can for example be done at the same time as the nominal measurement of the transmission T, or alternatively separately. Any other scheme for determining T and / or can of course be considered by the person skilled in the art.

[0140] According to one example, the geometric parameters Qu, Q22, Qi2, Q2i can be determined theoretically and / or be obtained by a calibration step, preferably an initial calibration step. These parameters can for example be determined by the manufacturer of the device and provided for the implementation of the measurement method 1. Alternatively or additionally, the method 1 can comprise a calibration step prior to the propagations of the beam for the measurement of M1 and M2. The calibration step can comprise the measurement of at least one, and preferably each, of the parameters Qu, Q22, Q[2, Q2b. According to the example where the optical coupling is negligible, or even zero, between the 2 configurations, it is understood that only the parameters Qu, Q22 are to be provided and / or determined. Preferably, and in practice, these parameters are constant over time.A single supply and / or measurement of these parameters can therefore be made for several transmission measurements spread over time.

[0141] For example, when manufacturing the device 3, T and can be determined, knowing the optical components that compose them. E can be measured independently, by a power measurement for example. Calibration, for example when installing the device 3, can provide the parameters Q by the measurements M1 and M2, when the optics have not yet been dirty. For example, the optical paths can be modified so as to isolate each of Qu, Q22, Q[2, Q2L For this, for example, selective blocking masks can be used. Other means can be envisaged by those skilled in the art for isolating the optical paths so as to measure the parameters Q.

[0142] Concerning the matrix of geometric parameters Q, in practice, the probability of having a non-invertible matrix of parameters Q is tiny due to the precision of the optical assembly. On the other hand, if the equations are very close, then this risks leading to uncertainties in the values of T and / or ¢. For this reason, the skilled person is able to choose the optical configurations to minimize the coupling between the two configurations. By decreasing the optical coupling, the matrix of geometric parameters Q is modified. The terms Qi2. Tc. <e>d and Q2p Your. <e>b are become significantly lower in front of respectively Qu. Ta. <e>b et Q22. Tc. d. In the case of negligible optical coupling, the matrix of geometric parameters Q becomes diagonal with Qu and Q22 unaffected. The uncertainty in solving the equation system decreases.

[0143] [Fig. 2] illustrates by way of example two optical paths 20, 21 of the device 3, according to an exemplary embodiment. In this example, a source 30 emits a light beam 2, a part of the light beam 2 following the first optical path 20 and another part of the light beam 2 following the optical path 21.

[0144] Along the first optical path 20, the light beam 2 passes through the first assembly 31 twice and the second assembly 32 three times, before arriving at the sensor 33. Along the second optical path 21, the light beam 2 passes through the first assembly 31 twice and the second assembly 32 once, before arriving at the sensor 33.

[0145] We therefore obtain the following numbers: a = 2, b = 3; c = 2; d = 1, and the following invertible matrix:

[0146] [Math.23] p 3\ \2 1 /

[0147] It is therefore understood that the number of passages of the light beam 2 in the first set 31 and the second set 32 can be chosen to obtain an invertible matrix. The person skilled in the art is therefore able to choose the architecture of the device 3 to fulfill this condition.

[0148] Note that, as is known to those skilled in the art, the numbers a, b, c, d, and also m, p as detailed below, are not necessarily integers. Indeed, the transmission by an optical component may correspond to an average of an integer number of transmissions depending on where the beam is incident on the optical component, which gives a non-integer overall number. For example, a component may reflect one part of the beam twice and another part of the beam only once, giving an overall transmission number between 1 and 2.

[0149] As illustrated for example in [Fig.3], it is understood that the propagation 12 of the light beam 2 in the first configuration may be at least partly simultaneous with the propagation 13 of the light beam 2 in the second configuration. Alternatively, it may be provided that the propagation 12 of the light beam 2 in the first configuration is made upstream of the propagation 13 of the light beam 2 in the second configuration, and vice versa.

[0150] These two configurations can be obtained with numerous installations comprising for example the following optical elements: - one or a plurality of sensor(s), - a spatial separation of light in a pupil or in the field, - by refraction or diffraction, - by polarization separation, - by separation with anisotropic materials, - by temporal separation, for example with a pulsed source.

[0151] For example, the two configurations can be obtained in a removable manner. The device 3 may therefore comprise at least one module fixed in a removable manner and making it possible to induce the formation of the first 20 and second 21 optical paths. This may be particularly advantageous for applications where optimization or maximization of the optical power is required. As will be seen later, the generation of these two configurations may in fact induce a reduction in the optical power of the light beam 2 for each optical path, since the beam can be divided into two beams. It may be preferable to generate these two configurations when seeking to evaluate the transmission efficiency linked to the fouling state of the diopter 320. This can also be advantageous for applications where one seeks to make a transmission measurement without the second set, for example to make a "white" of the specular lights in the device during an initial calibration step. The accuracy of the calibration is thus increased. The method 1, and more particularly the supply 10 of the device 3, can therefore comprise the installation of at least one module configured to generate the two configurations.

[0152] As illustrated for example by Figures 4A and 4B, the second assembly 32 may comprise a first reflection module 321 and a second reflection module 322. The first 321 and second 322 reflection modules may be configured to reflect at least one incident light beam 2 and re-emit two beams 2b, 2c, each propagating in a given configuration. The first 321 and second 322 reflection modules may further be configured so as to to reflect respectively a number m and a number p of times the light beam 2, p being different from m, to generate the two configurations of the device 3. The reflection numbers m and p will directly influence the number of transmissions and in particular the coefficients b and d of the matrix. We therefore understand that the reflection number m, p can modulate the matrix of coefficients a, b, c, d. The coefficient b can be a multiple of m, and for example b = m, and the coefficient d can be a multiple of p and for example d = p.

[0153] The reflection by the first 321 and second 322 reflection modules thus makes it possible to create an optical path that is at least partly different between the first and second configurations, while maintaining a simplified architecture of the device 3. Furthermore, the use of reflection modules makes it possible to simply place them at the level of the second assembly 32, for example downstream of the diopter 320, to obtain the two configurations. These modules can be placed in a removable manner without impacting the architecture of the rest of the device 3.

[0154] According to the example illustrated in [Fig.4A], a primary light beam 2a can be emitted by a source 30. This primary beam 2a can propagate 120, 130 in the first assembly 31 and in the second assembly 32 comprising the diopter 320, until reaching the first 321 and second 322 reflection modules. The first and second optical paths 20, 21 can then be substantially identical. The first 321 and second 322 reflection modules can be configured to generate from the primary beam 2a, a first light beam 2b by a reflection Rm and a second light beam 2c by a reflection Rp.

[0155] The first light beam 2b can, from the first reflection module 321, propagate 121 again in the first assembly 31 then in the first assembly 32 before arriving at the sensor 33, along the first optical path 20. The second light beam 2c can, from the second reflection module 322, propagate 131 again in the first assembly 31 then in the first assembly 32 before arriving at the sensor 33, along the second optical path 21. Between the two configurations, the same sensor 33 can be used to measure the two beams 2b, 2c, or alternatively separate sensors 33 can be used.

[0156] The reflection numbers m, p being different, the first optical path 20 is therefore at least partly different from the second optical path 21. Furthermore, the propagations 121, 131, downstream of the first 321 and second 322 reflection modules can follow different optical paths 20, 21, as will be seen in the example later.

[0157] According to the example illustrated in [Fig.4B] it can be provided that the source 30 directly emits two beams 2a, 2b, propagating respectively in the first 20 or the second 21 optical paths. These two beams 2b, 2c can for example be spaced temporally and / or spatially.

[0158] In order to be able to measure Ml and M2, and therefore to obtain the system of equations, several solutions are possible. The measurements Ml, M2 can be separated spatially and / or temporally. According to a first example, the light distributions, or equivalently the light distributions, of the light beam are different between the first and second configurations. In particular, between the first and second configurations, the focusing state of the light beam can be different, so that at the end of the first and second configurations, the light distribution of the beams is different between the configurations. This makes it possible to spatially separate the optical paths of the first and second configurations and therefore to make it possible to measure Ml, M2 for the corresponding configuration, with a sensor for each measurement or a sensor matrix as with a camera.Since the two beams are spatially separated, in practice the geometric parameter matrix Q will be invertible. Furthermore, the difference in light distribution can be chosen so that optical coupling is negligible between the two configurations, as detailed later with reference to a particular example.

[0159] Alternatively or additionally, the method may comprise a temporal separation of the beams propagating in the first and second configurations. For this, the method may comprise an emission of a first light beam and its propagation in the first configuration. The emission of the first light beam, and preferably its propagation in the first configuration, may be followed by the emission of the second light beam and its propagation in the second configuration. Due to this temporal separation, it is possible to measure M1, M2 for the corresponding configuration.

[0160] As a non-limiting example, two successive emissions can be made with a first beam 2b emitted and a second beam 2c emitted, the beams 2b, 2c having a polarization difference of 90° from one another. For example, a quarter-wave plate can be inserted on the optical path, for example at the source, during the emission of one of the beams. It is possible to separate these beams for their propagation in a given configuration with a polarization splitter. Other optical solutions can be envisaged by those skilled in the art, for example a motorized mirror to orient a beam in one or other of the configurations.

[0161] A particular example of the device 3 and the method 1 is now described with reference to FIGS. 5 to 8B, for an application in a tokamak. It is understood that the characteristics described below can be applied to other application examples.

[0162] As for example illustrated by [Fig.5], the device 3 may comprise a light source 30, for example an optical fiber. The device 3 may comprise a sensor 33 configured to measure the light beam 2 after its propagation in the device 3. The first assembly 31 may comprise an optical diagnostic device 311 of an optical path of the tokamak. The tokamak may for example be the tokamak of the ITER project, or any other tokamak.

[0163] Radiometric optical diagnostic devices used in tokamaks are for example given below: - 55.El Core CXRS diagnostic, - 55.E4 / GE DIM (Divertor Impurity Monitor, which can be translated as divertor impurity detector, - 55.EB Motional Stark Effect, which can be translated as Stark effect of movement, 55.EC CXRS Edge, - 55.E6 VSRS (Visible Spectroscopy Reference System, which can be translate as Reference System for Visible Spectroscopy), - 55.G1: visible and infrared visualization system for equatorial ports, - 55.GA: visible and infrared viewing system for upper ports.

[0164] Note that this list is not exhaustive and that any radiometric optical diagnostic device may be covered by the invention.

[0165] According to one example, the first assembly 31 comprises a plurality of mirrors 312 configured to transmit the light beam 2 by successive reflections. The second assembly may comprise a shutter 320 arranged downstream of the plurality of mirrors 312. The light beam 2 may propagate through the plurality of mirrors 312 until it reaches the shutter 320. The device 3 may further comprise a plurality of lenses 300 and a mirror 330 to modulate the optical path of the light beam 2, in particular between the source 30 and the first assembly 31, and between the first assembly 31 and the sensor 33.

[0166] Typically, one seeks to measure the transmission efficiency T of the first assembly 31 comprising the plurality of mirrors 312. The rear of the shutter 320, on which the beam 2 is incident, may be diffusely reflective. This reflection is used in existing solutions to measure the transmission efficiency T of the mirrors 312. However, since the shutter 320 is arranged close to the plasma, its reflectivity as well as the diffusion angles may change over time.

[0167] The second assembly 32 further comprises a retroreflector comprising the first reflection module 321 and the second reflection module 322 introduced previously. The retroreflector may be configured to reflect the at least one light beam 2 from the first assembly 31 towards the first assembly 31, being associated with the shutter 320, preferably being placed at the back of the latter to reflect the beam 2 coming from the first assembly 31.

[0168] As illustrated in [Fig.5], during the transmission measurement by method 1, the light beam 2 propagates along the illustrated optical path, without requiring the addition of additional mirrors to form an additional optical path not passing through the mirrors 312. An optical path is therefore obtained allowing the transmission measurement by method 1. As illustrated by [Fig.6], a single optical path 30 can be connected to a light generation and analysis module 301, or equivalently a light emitter / receiver module. Method 1 and device 3 therefore make it possible to avoid the addition of components to form additional beamlines. This is particularly advantageous for an application in environments of high thermal and / or physicochemical stress, as is the case in a tokamak. The savings in terms of cost and risks are significant.

[0169] The retroreflector according to an exemplary embodiment is described with reference to FIGS. 7A and 7B. The first reflection module 321 may have a first shape 321a configured so as to reflect the light beam 2 m times with a first light distribution. In this case, am = b. The second reflection module 322 may have a second shape 322a different from the first shape 321a and configured so as to reflect the light beam 2 p times with a second light distribution. In this case, ap = d. For example, the light distribution may result from a state of focusing of the light beam passing through a configuration, and in particular following transmission by the second assembly, for example a state of focusing by the reflection module. This may be, for example, a homogeneous and diffuse light distribution, compared to a localized light distribution.This allows to modulate the numbers a, b, c, d as well as the geometric parameters Qu, Q2b Q[2, Q22 to form the invertible matrices.

[0170] At the sensor 33, the image of the beam 2b having propagated in the first configuration can thus be spatially distinct from the image of the beam 2c having propagated in the second configuration. An acquisition by the sensor 33 can therefore make it possible to access the measurements M1 and M2.

[0171] As for example illustrated by Figures 7A to 8B, the first reflection module 321 is a corner cube mirror 321 and the second reflection module 322 is a concave mirror, for example a hyperboloid mirror 322. The corner cube mirror 321 reflects the incident light beam 2, 2a three times on the three facets of the corner cube, to form the first beam 2b in a localized manner.

[0172] The hyperboloid mirror 322 reflects the incident light beam 2, 2a substantially once, to form the second beam 2c. The concavity of the mirror induces a modification of the light distribution of the beam 2c. It allows a distribution of light from the fiber 30 to the observation field of the sensor 33 and more particularly of a camera.

[0173] As illustrated in Figures 8A and 8B, the image of the first beam 2b at the sensor 33 may be substantially punctual and of higher intensity. The image of the second beam 2c at the sensor 33 may be a more or less uniform diffuse background, of lower intensity. An acquisition by the sensor 33 may then comprise the superposition of these two images and therefore a first zone corresponding to the measurement M1, and a second distinct zone corresponding to the measurement M2, as illustrated by Figures 8A, 8B, [Fig.8B] presenting a simulated example of measurement.

[0174] The measuring method 1 may comprise a closing of the shutter 320. The closing of the shutter 320 preferably induces the placement of the retroreflector on the optical path of the beam 2.

[0175] In the measurements, the signal contribution S32i of the corner cube mirror 321 can be formulated as follows, with (i,j) the coordinates of a pixel of a camera 33:

[0176] S32i(i,j) = Qi(i,j).T2. 3.E, because the light beam crosses the first one twice set 31 and is reflected three times by the corner cube mirror 321, with Qi(i,j) the solid angle factor per unit area of the detector (e.g. one pixel).

[0177] The signal contribution S322 of the hyperboloid mirror 322 can be formulated as follows, with (i,j) the coordinates of a pixel of a camera 33:

[0178] S322 (i,j) = Q2(i,j)T2. .E, because the light beam crosses the first one twice set 31 and is reflected once by the hyperboloid mirror 322 with fLli J) the solid angle factor per unit area of the detector (e.g. one pixel).

[0179] Preferably, the first reflection module 321 and the second reflection module 322 are made of the same material, so that their reflectivity is substantially equal.

[0180] On the camera 33, at the level of the first zone, the measured signal Ml can be proportional, and preferably equal to:

[0181] Ml^jû = S32i(ii,ji) + S322 (ii,ji) = Qi(ii,ji).T2. <D3.E + Q2(ii,ji).T2.<D.E

[0182] Indeed, the contribution of the corner cube mirror 321 is added to that of the hyperboloid mirror 322. We are therefore in an optical coupling condition for the ML measurement.

[0183] On the camera 33, at the level of the second zone, the measured signal M2 can be proportional, and preferably equal to:

[0184] M2(i2,j2) = S322 (i2,j2) = Q2(i2,j2).T2 <D.E

[0185] Only the contribution of the hyperboloid mirror 322 is observed. There is therefore no optical coupling for the M2 measurement.

[0186]

[0187]

[0188]

[0189]

[0190]

[0191]

[0192]

[0193]

[0194] A measurement 14 can be made for all or part of the pixels of the camera 33, so as to obtain M1 and M2. According to one example, during the fabrication of the device 3, T and $ are measured. E can be measured independently, by a power measurement. A calibration step, for example at the installation of the device 3, can provide Qi(i,j) and fWi J) by the measurements Ml and M2, when the optics have not yet been fouled. For example, a blocking mask can be placed on the corner cube so S32i = 0. Then, Ml(ii,ji) = S322 (i,j) = Q2(ii,ji).T2.RE and Q2(ii ji) can be directly measured. Qi(ii,ji) can then be inferred from a measurement without the blocking mask. When device 3 was used, a degradation of the reflectivity can be observed ( <P devient $ * avec $ *< d> ) and / or transmission (T becomes T* with T* <T). Selon les équations ci-dessus, pour chaque pixel on peut avoir un signal S égal à : Ml^jû = Q^jû.T*2 <P*3.E + Q2(ii,ji).T*2.<P*.E By selecting at least one pixel in the measurement area of Ml and at least one pixel in the measurement area of M2, we can obtain: Ml^jû = Qi(ii,ji).T*2. <P*3.E + Q2(ii,ji).T*2.<P*.E, et M2(i2,j2) = Q2(i2,j2).T2 <P.E And so: [Math.24] *2 ,3 4*2'ÜM 1(i3j 1 — 7 \ 7 '

[0195] [Math.25] ^2(>2jJ

[0196]

[0197] Which gives the following solutions: [Math.26]

[0198] = exp [Math.27] Ë / t +log ---4 —FT' T - exp H 3 log Ë - logl--------

[0199]

[0200] Or in another formulation: [Math.28]

[0201] [Math.29] *_ LI T ” P 02(1^0

[0202] According to one example, the contribution to the signal of the hyperboloid mirror 322 may be negligible compared to the contribution of the corner cube mirror 321, in terms of signal value. Therefore, we can have Qi(ii,ji).T*2.C>*3.E » Q2(ii ji)-T*2. <b*.E, par exemple la contribution du miroir hyperboloïde est au moins 50 fois, de préférence au moins 100 fois inférieure à la contribution du miroir coin cube. Dès lors, il est possible de considérer que S322 (ii,j 1) « 0 et donc Ml(ii,j 1) ~ S32i(ii,ji) = Qi(ii,ji).T*2. <1> *3.E

[0203] This simplifies the measurements and the resolution of the system of equations to determine T* and / or C>*. For example, the dimensions of the corner cube mirror relative to the hyperboloid mirror can be chosen to obtain this ratio.

[0204] Preferably, the retroreflector is removably mounted on the shutter. Thus, it is possible to make a measurement without the retroreflector so as to measure the specular light signals linked to the other optics of the device 3. This measurement, for example during an initial calibration, makes it possible to improve the accuracy of the calibration.

[0205] A second particular example is now described in which the radiometry device 3 is a transmissiometer, with reference to FIGS. 9 and 10. The device 3 can in particular be configured to measure the transmission (for example the attenuation coefficient) of a medium 310, for example ambient air (for example in the case of a runway visual range transmissiometer) or an aquatic medium.

[0206] According to this example, the first assembly 31 may comprise the medium 310 of which the transmission T is to be measured. The medium 310 may be framed by two windows, each forming a diopter 320a, 320b. The first diopter 320a may therefore be placed upstream of the medium 310 and the second diopter 320b may be placed downstream of the medium 310 along the first 20 and second 21 optical paths. In one example, when the device 3 is a runway visual range transmissiometer, the diopters 320a, 320b are spaced apart by a distance of the order of a few tens of meters, for example substantially between 15 and 70 m.

[0207] The second assembly may comprise, in addition to the first 320a and second 320b diopters, the first reflection module 321 and the second reflection module 322, and a third reflection module 323, configured to generate optical paths 20, 21 which are at least partly distinct to form the two configurations.

[0208] For this, the first reflection module 321 can be placed downstream of the second diopter 320b along the first optical path 20. The light beam 2 coming from the source 30 can therefore pass through the first diopter 320a then propagate through the middle 310 to the second diopter 320b before being reflected m times on the first reflection module 321, for example once. The first beam 2b resulting from this reflection Rm can again follow substantially the same optical path and recross the second diopter 320b, the middle 310, the first diopter 320a until reaching the sensor 33. The first reflection module 321 therefore forms the first configuration.

[0209] The second reflection module 322 can be placed downstream of the second diopter 320b along the second optical path 21. The second reflection module 322 can be arranged so as to reflect the light beam 2 p times, and for example twice. The light beam 2 from the source 30 can therefore pass through the first diopter 320a then propagate through the medium 310 to the second diopter 320b before being reflected p times on the second reflection module 322. The second beam 2c resulting from this reflection Rp can follow a spatially different optical path to re-cross the second diopter 320b, the medium 310, the first diopter 320a until reaching the third reflection module 323. The third reflection module can be configured to reflect the second beam 2c once.The second beam 2c is therefore returned to re-cross the device 3 by the same optical path to the second reflection module and then to reach the sensor 33. The second 322 and third 323 reflection modules thus form the second configuration.

[0210] The resulting measurements 14 Ml, M2 for each of the configurations can be proportional, and preferably equal, to:

[0211] Ml =^^.12.0)4, with Qi the geometric parameter associated with the first optical path 20, T the transmission of the medium 310, and <e>the transmission of the windows. The medium 317 is in fact crossed twice and each window is crossed twice which gives four transmissions ¢.

[0212] M2= Qz-T4®12 with Q2 the geometric parameter associated with the second optical path 21, T the transmission of the middle 310, and <e>the transmission of the windows. The middle 317 is in fact crossed four times, the window 320a is crossed four times and the window 320b is crossed eight times which gives twelve transmissions ¢.

[0213] The Qi Q2 parameters can be obtained during an initial calibration step, for example according to the methods previously described.

[0214] In this example, the optical coupling between the two configurations is negligible. We therefore obtain:

[0215] ln(Ml) = InCQJ +4 ln(0>)+ 2 ln(T)

[0216] ln(M2) = ln(Q2) +12 ln(0>)+ 4 ln(T)

[0217] and therefore the following solutions:

[0218] [Math.30] O = exp[|(log(^J -21og(^) )]

[0219]

[0220]

[0221]

[0222]

[0223]

[0224]

[0225] [Math.31] T = exp[E-log(^) +3log(^) ) ] Or in another formulation: [Math.32] 4 I ^2 M y 4¾ .Ml 2 [Math.33] T = lM1^ As illustrated for example in Figures 9 and 10, the length of the second optical path 21 is much longer than the length of the optical path 20. The measurement M1 is therefore temporally separable from the measurement M2. [Fig. 10] shows by way of example the beam 2a emitted by the source 30 at a time to, the reception of the first beam 2b by the sensor 33 during the measurement M1 at a time tb and the reception of the second beam 2c by the sensor 33 during the measurement M2 at a time t2. It is therefore understood that a single sensor 33 can be used as an alternative to the two sensors 33 illustrated in [Fig.9]. Reducing the number of sensors is preferable because, generally speaking, several sensors must be calibrated with each other to obtain a reliable measurement. This can be particularly advantageous when the windows 320a, 320b are spaced a long distance apart, in particular for runway visual range transmissiometer applications. In view of the foregoing description, it is clear that the invention provides a measuring method and a radiometry device improving the measurement of transmission by a radiometry device, and in particular independently of conditions external to the device. The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. The present invention is not limited to the examples previously described, and in particular to the optical architectures described. Many other variant embodiments are possible, for example by combining previously described characteristics, without departing from the scope of the invention. The characteristics described in relation to a particular exemplary embodiment can also be applied to other examples, and other applications. For example, a retroreflector as introduced previously can be used for applications other than tokamak optical diagnostics. In addition, the characteristics described in relation to one aspect of the invention can be combined with another aspect of the invention. In particular, the device can have any characteristics resulting from or allowing the implementation of a step of the method and conversely the method may include any step resulting from a characteristic of the device.< / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e>

Claims

Claims

1. Method (1) for measuring the transmission of at least one light beam (2) comprising the following steps: • a supply (10) of a radiometry device (3) comprising at least one sensor (33), a first optical assembly (31), a second optical assembly (32), the second assembly (32) comprising at least one optical transmission element (320) capable of being altered, the device (3) having at least a first and a second propagation configuration of the at least one light beam (2), • a propagation (12) of the at least one light beam (2) in the first configuration along a first optical path (20), comprising a transmission of the at least one light beam (2), a first number a of times with a transmission T, by the first set (31) and a transmission of the at least one light beam, a second number b of times with a transmission ¢, by the second set (32), • a propagation (13) of the at least one light beam (2) in the second configuration along a second optical path (21) at least partly different from the first optical path (20), comprising a transmission of the at least one light beam (2), a third number c of times with a transmission T, by the first assembly (31) and the transmission of the at least one light beam (2), a fourth number d of times with a transmission ¢, by the second assembly (32), the numbers a, b, c, d forming the following invertible matrix: ab\ cd) a plurality of measurements (14) by the at least one sensor (33), comprising at least: - a measurement Ml of the light beam having propagated in the first configuration, - a measurement M2 of the light beam having propagated in the second configuration, • From the plurality of measurements (14), a determination (15) of at least one of T and ¢, the determination comprising the resolution of a system of equations qualifying the propagation of light in the radiometry device from the plurality of measurements (14) and said invertible matrix, thus independently determining the transmission efficiency by the first set (31) and / or the transmission efficiency linked to the at least one optical transmission element (320) capable of being altered, method in which the propagation (12) of the light beam (2) in the first configuration and the propagation (13) of the light beam (2) in the second configuration are at least partly simultaneous.

2. Method (1) according to the preceding claim, in which: • during the propagation (12) of the light beam (2) in the first configuration, the light beam (2) passes through the first assembly (31) and the second assembly (32), so that the resulting measurement Ml of the light beam (2) by the sensor (33) in the first configuration is proportional, and preferably equal, to: Qn.E. Your. o” + q12.e. tc. o" • during the propagation (13) of the light beam (2) in the second configuration, the light beam (2) passes through the first assembly (31) and the second assembly (32), so that the resulting measurement M2 of the light beam (2) by the sensor (33) in the second configuration is proportional, and preferably equal, to: Q21.E. Ta. Ob + Q22.ET Od with - E the power of a light source (30), - Qn a non-zero geometric parameter characterizing the first configuration, - Q22 a non-zero geometric parameter characterizing the second configuration, - Qn, Q21 geometric parameters characterizing a coupling between the first (20) and second (21) optical paths, - T the transmission of the first set, - <e>the transmission of the second set, - the determination (15) of T and / or <e>includes solving a system of equations comprising the first and second equations.

3. Method (1) according to the preceding claim, in which, the radiometry device (3) having an optical coupling between the first and the second configuration, Q[2, Q21 are unnullified, and the numbers Qn, Q22, ^12, ^21 form the following invertible matrix: / £2|j £2^) y £221 £2921 and in which the determination (15) of T and / or <e>includes solving (151) a system of equations to determine a solution for (Ta. <bb) et (Tc. <bd) puis pour déterminer T et / ou ¢.

4. Method (1) according to any one of the two preceding claims, in which: • At the end of the first configuration, the light beam (2) has a first light distribution, and • At the end of the second configuration, the light beam (2) has a second light distribution, different from the first light distribution, so as to spatially separate the light beam (2) propagating in the first and second configurations, and so that the following matrices are invertible: (a M \c dJ [Math.36] / £2^ । £2| 2 \ ( £2-} £2^2 /

5. Method (1) according to any one of the preceding claims, wherein, the second assembly (32) further comprising a first reflection module (321) and a second reflection module (322): • in the first configuration, the propagation (12) of the beam (2) comprises: - a first propagation (120) of the light beam (2) in the first set (31) and the second set (32), - a reflection (Rm) of the light beam (2) a number m of times by the first reflection module (321), - a second propagation (121) of the light beam (2), in the first set (31) and the second set (32), • in the second configuration, the propagation (13) of the beam comprises: - a first propagation (130) of the light beam (2) in the first set (31) and the second set (32), - a reflection (Rp) of the light beam (2) a number p of times by the second reflection module (322), m being different from p, - a second propagation (131) of the light beam (2), in the first set (31) and the second set (32),so that the numbers a, b, c, d form the invertible matrix: (ab\ d / ,

6. Method (1) according to any one of claims 1 to 4, further comprising an emission (11) of a primary light beam (2a) by a light source (30), the second assembly (32) being configured to form, from said primary beam (2a), a first light beam (2b) propagating in the first configuration and a second light beam (2c) propagating in the second configuration.

7. Method (1) according to the preceding claim, wherein, the second assembly (32) further comprising a first reflection module (321) and a second reflection module (322): • in the first configuration, the propagation (12) of the light beam (2) comprises: - a propagation (120) of the primary beam (2a) in the first set (31) and the second set (32), - a reflection (Rm) of the primary beam (2a) a number m of times by the first reflection module (321), to form the first beam (2b), - a propagation (121) of the first beam (2b), in the first set (31) and the second set (32), • in the second configuration, the propagation (13) of the light beam (2) comprises - a propagation (130) of the primary beam (2a) in the first set (31) and the second set (32), - a reflection (Rp) of the primary beam (2a) a number p of times by the second reflection module (322), m being different from p, to form the second beam (2c), - a propagation (131) of the second beam (2c), in the first set (31) and the second set (32),so that the numbers a, b, c, d form the invertible matrix: (ab\ \cd),

8. Method (1) according to any one of the preceding claims, in which the first assembly (31) comprises a medium (310) of which the transmission T is to be measured.

9. Method (1) according to any one of claims 1 to 7, in which the first assembly (31) comprises an optical diagnostic device (311) of which the transmission T is to be measured, for example an optical diagnostic device (311) of a tokamak.

10. Radiometry device (3) comprising at least one optical transmission element (320) capable of being altered and at least one sensor (33) configured to measure a transmission of at least one light beam (2), characterized in that the radiometry device (3) comprises a first optical assembly (31) and a second optical assembly (32), the second assembly (32) comprising the at least one optical transmission element (320), and in that the radiometry device (3) has at least a first and a second propagation configuration of the at least one light beam (2) so that: • in the first configuration and along a first optical path (20), the first assembly (31) is configured to transmit the at least one light beam (2) a first number a of times with a transmission T, and the second assembly (32) is configured to transmit the at least one light beam (2) a second number b of times with a transmission ¢, the at least one sensor (33) being configured to perform at least one measurement Ml of the light beam having propagated in the first configuration, • in the second configuration and according to a second optical path (21) at least partly different from the first optical path (20), the first assembly (31) is configured to transmit the at least one light beam (2) a third number c of times with a transmission T, and the second assembly (32) is configured to transmit the at least one light beam (2) a fourth number d of times with a transmission ¢, the at least one sensor (33) being configured to carry out at least one measurement M2 of the light beam having propagated in the second configuration, the numbers a, b, c, d forming the following invertible matrix, so as to determine, from the at least one measurement Ml and from the at least one measurement M2, at least one of T and ¢, the determination comprising the resolution of a system of equations qualifying the propagation of light in the radiometry device from the at least one measurement Ml and from the at least one measurement M2 and said invertible matrix, and thus to determine independently the transmission efficiency by the first assembly (31) and / or the transmission efficiency of the optical transmission element (320) likely to be altered: [Math 40] / ab\, \cd! the device being configured so that the propagation (12) of the light beam (2) in the first configuration and the propagation (13) of the light beam (2) in the second configuration are at least partly simultaneous.

11. Radiometry device (3) according to the preceding claim, in which • in the first configuration, the first assembly (31) and the second assembly (32) are configured to transmit the light beam (2), so that the resulting measurement Ml of the light beam (2) by the sensor (33) is proportional, and preferably equal, to: Qn.E. Your. 0”. + Q12.E. Tc. O" • in the second configuration, the first assembly (31) and the second assembly (32) are configured to transmit the light beam (2), so that the resulting measurement M2 of the light beam (2) by the sensor (33) is proportional, and preferably equal, to: Q21.E. Your. 0>b + Q22.E. Tc. O" with - E the power of a light source (30), - Qnun non-zero geometric parameter characterizing the first configuration - Q22 a non-zero geometric parameter characterizing the second configuration - Qi2, Q21 geometric parameters characterizing a coupling between the first (20) and second (21) optical paths, - T the transmission of the first set (31), - <e>the transmission of the second set (32),

12. Radiometry device (3) according to any one of the two preceding claims, in which the second assembly (32) comprises a first reflection module (321) configured so as to reflect a number m of times the light beam (2) in the first configuration, and a second reflection module (322) configured so as to reflect a number p of times the light beam (2) in the second configuration, m being different from p.

13. Radiometry device (3) according to the preceding claim, in which the first reflection module (321) has a first shape (321a) configured so as to reflect the light beam (2) with a first light distribution, and the second reflection module (322) has a second shape (322a) different from the first shape (321a) and configured so as to reflect the light beam (2) with a second light distribution, different from the first light distribution.

14. Radiometry device (3) according to the preceding claim, wherein the first reflection module (321) is a corner cube mirror (321) and the second reflection module (322) is a hyperboloid mirror (322).

15. Radiometry device (3) according to any one of the five preceding claims, wherein the first assembly (31) is an optical diagnostic device (311) of a tokamak, the first assembly (31) comprising a plurality of mirrors (312) configured to transmit by successive reflection the at least one light beam (2), and wherein the second assembly (32) comprises a shutter (323) arranged downstream of the plurality of mirrors (312), along the first (20) and second (21) optical paths, and a retroreflector (321, 322) associated with the shutter (323), the retroreflector (321, 322) being configured to reflect the at least one light beam (2) from the first assembly (31) towards the first assembly (31), the retroreflector comprising a corner cube mirror (321) and a hyperboloid mirror (322).

16. Radiometry device (3) according to any one of claims 10 to 14, the radiometry device (3) being a transmissiometer, for example a runway visual range transmissiometer or a transmissiometer configured to measure the attenuation coefficient of an aquatic environment (310), the first assembly (31) comprising a medium (310) whose transmission is to be measured, and the second assembly (32) comprising: • a first optical transmission element (320a) upstream of said medium (310) and a second optical transmission element (320b) downstream of said medium (310) according to the first (20) and second (21) optical paths, • a first reflection module (321) placed downstream of the second optical transmission element (320b) along the first optical path (20) and configured to reflect once the at least one light beam (2) coming from said medium (310) towards said medium (310), and • a second reflection module (322) placed downstream of the second optical transmission element (320b) along the second optical path (21) and configured to reflect twice the at least one light beam coming from said medium (310) towards said medium (310). • a third reflection module (323) placed downstream of the first optical transmission element (320a) along the second optical path (21) and configured to reflect once the at least one light beam coming from said medium (310) from the second reflection module (322), towards said medium (310) and towards the second reflection module (322).< / e> < / e> < / e> < / e>

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