Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/2889—Rapid scan spectrometers; Time resolved spectrometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/47—Scattering, i.e. diffuse reflection
  • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/59—Transmissivity

Definitions

• the present invention relates to a method and a device for impulse spectrophotometry.
• the invention applies to the analysis of media which are not clear and finds applications in various fields, in particular:
• the present invention makes it possible to determine the first, second and nth partial derivatives of the photon fluxes measured with respect to the wavelength and time, in addition to the information that these known techniques make it possible to obtain.
• Such imagery gives access to spectral and temporal distributions, which are specific to the analysis of decay times of fluorescence with several components.
• the single photo-electron counting mode is as powerful as for 'spectro-temporal fluorescence imaging because it measures photon fluxes not in arbitrary units but in event counting units. This also allows for greater measurement dynamics.
• the counting mode is achieved by binarization of the image by thresholding. This binarization causes the noise of the detection chain to be zeroed. This non-linear thresholding operation allows the use of an integration window over a very long time (which can exceed several hours). This mode makes it possible to count rare events linked to unabsorbed photons having stayed for a long time in the study environment.
• this document is oriented towards the “two-dimensional single-photon counting” in light emission by fluorescence or in any other emission at another wavelength than the initial source but never in transmittance and in particular in transmittance of a pulsed white laser.
• the present invention provides a method and a device for analyzing a non-clear medium.
• the invention aims to measure globally and in situ concentrations, or variations in concentrations, of absorbers and diffusers in a non-clear medium.
• the present invention relates to a spectrophotometry method differential, to analyze a non-limpid medium, this process being characterized in that:
• the non-limpid medium is illuminated by at least one light pulse allowing the subsequent use of the partial derivative, as a function of the wavelength, of at least one spectro-temporal transmission image acquired from the medium thus illuminated , one acquires, through at least one light collector, from the medium thus lit, at least one spectro-temporal image of transmission in counting mode allowing the subsequent use of the partial derivatives of the image as a function of the length d wave and time of flight of the light pulse, and the image and its partial derivatives are processed as a function of the wavelength and the time of flight to acquire information on the non-limpid medium.
• hyperdiffusive photons not absorbed by the medium over a wide spectral range allowing the use of the derivative operators, these hyperdiffusive or survivor photons being emitted by the medium during the illumination thereof.
• the time of flight of the light pulse and spectral data are used jointly to establish an identity card of the non-limpid medium and the associated partial derivatives.
• identity card of the non-limpid medium and the associated partial derivatives.
• the judicious exploitation of the statistical nature of this identity card makes it possible to qualify the scales and the modes of homogenization of the medium probed with respect to the contents of absorbers and diffusers.
• the non-limpid medium can be illuminated by a single broad spectrum light pulse.
• the partial derivatives linked to the variations in time of flight and in spectrum of the diffusive and ergodic photons not absorbed over a wide spectral range by the medium are emitted by the medium during the illumination of the latter.
• the partial derivatives linked to the time of flight of the light pulse and to the spectral data can be used jointly to establish a spectro-temporal identity card of the non-limpid medium.
• the collector can be illuminated without probing the medium and at the same time the non-limpid medium by one or more light pulses allowing spectro-temporal imaging derivable with respect to the wavelength and time, with two peaks simulating a double beam.
• the present invention also relates to a differential spectrophotometry device, for analyzing a non-clear medium, this device being characterized in that it comprises: a pulsed light source for illuminating the non-limpid medium and allowing the subsequent use of the partial derivative, as a function of the wavelength, of a spectral and temporal transmission image acquired from the medium thus illuminated, means acquisition, from the medium thus lit, of a spectral and temporal image of transmission, with or without spectral scanning, in counting mode, and with a step in wavelength and a step in time allowing the use subsequent partial derivatives of the image as a function of the wavelength and time of flight of the light pulse, and - means for processing this image, considered to be the zero order moment, and of its derivatives partial as a function of wavelength and time, to acquire information on this medium.
• a pulsed light source for illuminating the non-limpid medium and allowing the subsequent use of the partial derivative, as a function of the wavelength, of a spectral and temporal
• the pulse light source comprises means of non-linear generation of femtosecond or picosecond or nanosecond light pulses allowing the use of the partial derivative as a function of the length of wave.
• the pulse light source comprises means for generating and amplifying a femtosecond or picosecond or nanosecond continuum of a continuum, the continuum allowing directly (without scanning) the use of the partial derivative according to the wavelength.
• the acquisition means may comprise a scanning camera with slot in counting mode or a scanning camera with a single photoelectron counting slot, in single shot operating mode or in synchro-scan operating mode or in analog mode.
• a spectrophotometry method is also proposed which conforms to the method which is the subject of the invention and which allows the establishment of a real optical identity card of the volume probed, that is to say of a faithful signature of statistical nature. of the medium with respect to the more or less homogeneous contents of the diffusers and the absorbers, this optical identity card being in the form of one or more spectro-temporal images allowing to have access simultaneously to the temporal distributions for a window given spectral, to the spectral distributions for a given time interval, to the partial derivatives of these two distributions as well as to their integrals.
• a spectrophotometry and tomography method is also proposed in accordance with the method which is the subject of the invention, in which the partial derivatives, with respect to wavelength, time of flight and space, of spectro- temporal and single-point modes with spatial scanning or multi-point switched modes of injection zones and / or collection zones of the light, the use of partial derivatives of the space type then being possible and making it possible to treat certain cases of non-constant density in the volume probed, this tomography process with spectral and temporal image differentials allowing, on the one hand, a identification of a singularity of the concentration of absorbers and / or diffusers and, on the other hand, a molecular identification of these absorbers, the injections and collections of light being able to be carried out either on the surface or within the volume .
• a differential spectrophotometry method is also proposed in accordance with the method which is the subject of the invention, in which the partial derivatives, with respect to wavelength and time, of spectro-temporal transmittance imaging and the mode are used jointly. counting by binarization of the image then detection of a pixel area attributable to a photo-electron and reduction of this area to a single lit pixel, or to a subpixel scale, in order to increase the dynamics and to qualify the measurement in single photo-electron.
• the partial derivatives in time and in wavelength of the time queue linked to the photons are used. ergodic scattered by the medium when it is illuminated. It is possible to use, with a view to measuring or homogenizing the contents of absorbers and / or diffusers, spectro-temporal imagery and the operators d / dt, cP / dt 2 , d / d ⁇ , d 2 / d ⁇ 2 , d 2 / dtd ⁇ to higher orders, these operators applying to the spectro image -temporelle.
• spectro-temporal imagery used in the present invention provides access to operators of the type d n / dt m d ⁇ 'm with m ⁇ n.
• the present invention it is possible to use jointly the fluctuations of the spectro-temporal transmittance images and the associated operators (for the fluctuations over a macroscopic time for example at the second scale, the operator d / dt macroS copigue and the nth derivatives) in order to carry out dynamic measurements of opacimetry, colorimetry and granulometry.
• FIG. 1 is a schematic view of a device according to the invention
• - Figure 2 schematically illustrates the spectro-temporal image of transmission by recording the white pulse before the media to be probed and at the same time the pulse transmitted by these media with the device of FIG. 1
• FIG. 3 schematically illustrates the spectro-temporal transmission image provided by the display means which the device of FIG. 1 comprises
• FIG. 4 schematically illustrates examples of the statistical nature of two-phase media which are can study with the invention
• FIG. 5 is a schematic view of an example of the device of the invention.
• the invention notably consists in extending this approach to non-transparent media, for example industrial sludge, media containing suspensions, milk, cheese, meat, biological tissues, and more generally to turbid media. that is to say diffusing and absorbing media.
• the invention can be considered as a generalization of classical continuous spectrophotometry; it can be presented as a technique of colorimetry and opacimetry of complex media. It also makes it possible to qualify the degree of homogeneity of a medium surveyed and to discern when the quantities of average concentration of absorbers and / or diffusers have a meaning for the volume of interest (volume considered of the medium).
• the invention exploits in particular the hyperdiffusive photons not absorbed over a wide spectral range, ranging from ultraviolet to infrared, and over a wide time of flight domain, to detect a singularity of absorption and / or diffusion in a volume made of materials, for example granular, porous or fractured.
• the rare counting events of such photons, constituting the ergodic photons carry important information of volume average value whose statistical sense can in particular be compared with the survival rates. It should be noted that the absorption properties are measured by photons which are not absorbed and which therefore survive.
• the partial derivatives with respect to the wavelength make it possible to separate the characters of different monotony between absorption and diffusion.
• the partial derivatives with respect to the time of flight determine objective and sensitive criteria on the nature of the coupling between the diffusive modes linked to the macroscopic and mesoscopic organization of the medium and on the molecular absorptions.
• the crossed partial derivatives make it possible to remove the uncertainties of conjunction between the various propagations and absorptions.
• the invention makes it possible to detect very small variations in absorption due to the increase in the paths and the probability of absorption which correspond to the photons considered.
• the invention makes it possible to detect small variations in diffusion.
• the invention is based on obtaining and analyzing spectro-temporal transmission imagery without spectral scanning with a view to using operators of the partial derivative type.
• This dif erential spectro-temporal imaging is obtained by the coupling of a pulse light source with a broad spectrum, going from ultraviolet to infrared, and a streak camera in "streak camera” mode. counting or in analog mode.
• the impulse response of a volume of interest gives access to the optical transfer function in the form of an image in a reference frame whose first axis is a spectral window and whose second axis is a time window which corresponds to a deflection time.
• the joint use of time of flight of light and spectral data and their derivatives allows the establishment of a true "optical identity card" of the volume surveyed, that is to say a true signature of the statistical nature of the medium vis-à-vis the more or less homogeneous contents of diffusers and absorbers.
• the counting device is at a certain known distance from this stage. Between this observation point and the stadium are the environments to be studied, which, in a very colorful and almost two-dimensional way, can be a complex city.
• the observer counts the number of walkers according to their colors and he accumulates his counts for a time window for example every 2ps over a time interval of for example 960ps (2ps / pixel * 480pixels). This series of 480 points is directly used to approximate the partial derivatives as a function of the transport time.
• the pictorial example of the city is actually a case where the dimension of the workspace is understood between 1 and 3 if the places of transport are all on the same surface.
• FIG. 2 schematically illustrates the spectro-temporal image of transmission by recording the white pulse before the media to be probed and at the same time the pulse transmitted by these media.
• the wavelength ⁇ of the light (in nanometers) is plotted on the abscissa and the time jt on the ordinate (typically in picoseconds per pixel).
• FIG. 3 schematically illustrates the spectro-temporal transmission image provided by the display means 6, with the recording of only the instrumental function or only the optical response through the media surveyed.
• the wavelength ⁇ (in nanometers) is plotted on the abscissa and the time (typically in picoseconds per pixel) on the ordinate. It is specified that the image a corresponds, in the example shown, to the counting of photo-electrons in analog mode.
• I 0 1 be the intensity of the incident light which will pass through volume V, according to the conventional notation used in Beer-Lambert spectrophometry in clear media. In this non-pulse spectrometry, it is very common to have devices with two beams, one passing through the colored tank and the other allowing this I 0 to be measured.
• the invention also makes it possible to carry out a "two-stroke" spectro-temporal imaging thanks to the impulse nature: the measurement of I 0 or of the instrumental function is carried out, that is to say of the convolution of the output of the stage and detection without the media to be studied, vis-à-vis photon flight time analyzes. It is specified that the measurement of I 0 can be carried out thanks to a light leak, before propagation in the volume V, or in a sequential manner.
• the energy sent is contained in a pulse of equivalent length less than 0.3 mm in vacuum.
• nanosecond pulses can be used like those provided by hydrogen flash lamps, and deflection times of a hundred nanoseconds.
• the invention is especially useful for probing volumes of less than ten m 3 up to volumes of
• the lower limit of the volume that can be probed depends only on the performance of the deflection system of the streak camera, to which we will come back later, because broad spectrum sources (and which correspond to ultra sources -shorts of a few fs) are already known.
• broad spectrum sources and which correspond to ultra sources -shorts of a few fs
• an ultrashort pulse with very broad spectrum in the window constituted by the ultraviolet, visible and near-infrared domains.
• the most well-known examples of this type of pulse are the ultrashort broad spectrum pulses at the oscillator output, the pulses resulting from the generation of a femtosecond or picosecond continuum and / or from the amplification of a continuum.
• the injection and collection of light can be carried out either in single-point mode or in multi-point mode with or without automatic displacement.
• the use of a stack of spectro-temporal images with this kind of displacement allows a optical tomography that is to say (1) identification of a singularity of the concentration of absorbers and (2) molecular identification of these absorbers.
• the collection can be carried out either on the surface or within the volume.
• the collected light is analyzed by a diffracting element (grating spectrograph
• Essential aspects of the invention are the use of this image and its partial derivatives as a means qualifying and quantifying all of the optical properties of an object and the arrival at various degrees of formation of volume average or the decision not to form a volume average.
• a fourth class is also considered, namely the class of hyper-diffusive or ergodic photons. Despite their long contact time with the environment (or long flight time), those that were measured were not absorbed like the other 3 classes.
• the invention concentrates on partial derivatives as a function of wavelength and time of flight and on counting mode.
• SPE hyperdiffusive single photoelectrons
• the z axis in SPE units is very important. Spectro-temporal imagery in counting mode has great potential because it reaches the limits of these optical techniques vis-à-vis the measurement dynamics, especially for counting and accumulating these ergodic photons.
• the image of walkers is dangerous.
• the propagation of light in a dense medium is considered as a disturbance of an electric induction field and a magnetic induction field, both oscillating with a period of 1 to 3 femtoseconds (for example for window 300-900nm).
• the propagation of light is then carried out by dipoles, of molecular sizes, which re-induce an electromagnetic field in a damped manner.
• the structure of the dense medium at supramolecular scales induces different diffusion / diffraction regimes (Rayleigh, Mie, Fraunhofer).
• diffusion phenomena take place but only cause a change in direction (law of refraction).
• the standard deviation of this direction depends on local fluctuations in the density and damping of the dipoles, i.e. the distribution of the refractive index n which can often be approximated by a Dirac distribution.
• n is 1.4.
• the secondary waves that is to say transmitted by the oscillating dipoles, no longer interfere constructively to favor a direction.
• ergodic photons means that they can be considered as residual waves with a very strong phase shift or an enormous delay. These measured ergodic photons were in fact re-emitted by numerous non-absorbent oscillating dipoles.
• those which carry the most information with respect to the volume probed are the last classes, that is to say those of long times.
• the invention is not limited to the joint use of the transmission spectrum and the distribution of the flight time and their partial derivatives. It also relates to the use of a displacement of the points of impact and / or collection in order to carry out a tomography (implementing partial derivatives of space type). With these additional degrees of freedom, the spectral distributions and temporal allow to better qualify and locate in a volume the singularities of content of absorbers and / or diffusers.
• spectro-temporal imagery gives access to the operator d 2 / dtd ⁇ and to higher orders, with the sampling comb function (for example 480 pixels for 1.1 ns and 640 pixels for I80nm, it being understood that this can change depending on the polychromator and the camera used at the end of the acquisition chain).
• spectro-temporal imagery proposed in the present invention provides an optical and empirical identity map of the media. surveyed. The statistical study of its variations by means of partial derivatives makes it possible to directly qualify the variabilities of the environments explored. In addition, the exploitation of hyperdiffusive photons allows the passage from the spectro-temporal image to quantified information about the volume studied.
• These training courses are either geometric in nature (tomography, singularity detection) or chemical in nature (chemometry, quantification of concentration).
• the invention is thus situated on two levels:
• optical identity card we seek to analyze the path of hyperdiffusive photons to homogenize the contents of the absorbers and / or diffusers or decide to establish an average.
• the concentration of absorbers and diffusers makes sense and is quantifiable. Let us return in more detail to one of the problems which the present invention solves. It is desired to make a global and in situ measurement of the concentrations or variations in the concentration of absorber and diffuser in a non-limpid medium. In addition, the invention aims to know when it is valid to speak of average concentration and makes it possible to test the hypothesis of homogenization.
• a concentration of dye in a turbid medium for example the endogenous flavins in milk, or measuring dyes in a suspension
• Spectral chemometry methods can be applied to many fields, in particular in biology.
• the present invention provides spectral and temporal chemometry in pulse and differential mode.
• the light paths are no longer comparable to a distribution approximated by a Dirac distribution.
• the paths of the electromagnetic wave form a more or less complex distribution which is most often an unknown.
• any scattering medium is a multiphase system with dimensions close to the wavelength of the light with which the medium is illuminated.
• FIG. 4 This example is schematically illustrated by FIG. 4 where the two phases are respectively constituted by a matrix I and by an element II.
• F element more diffusing than the matrix and stronger absorption than the matrix.
• the goal is to carry out a tomography, in particular to locate one or sub-volumes whose optical properties are very different from those of the matrix.
• the exploitation of spectro-temporal imagery and its partial derivatives then requires displacements between the point of impact of the measurement laser beam and detection allowing the use of partial derivatives of the space type.
• the measurement leads to a spectro-temporal image which describes two types of distributions:
• the unit is an integer number of single photoelectrons or in arbitrary unit (lit pixels).
• turbid media absorbent and very diffusing
• the analysis of these time distributions is often based on the approximation of the diffusion.
• the spectral distribution classes depend mainly on the absorption spectra of the dyes. Calculation programs in quantum chemistry make it possible to obtain the absorption spectra of fairly simple molecules. Alternatively, databases of ultraviolet-visible-near infrared spectra can be used.
• One aspect of the invention is the search for integration windows (spectral and temporal distributions) making it possible to optimize the signal-to-noise ratio and to involve the dynamics between counting diffusive photons and ergodic photons.
• integration windows spectral and temporal distributions
• the pulse source at least two technical choices are possible: a) a source of ultrashort femtosecond pulses in themselves (ultra-short oscillator), and b) means of generating femtosecond or picosecond continuum and / or parametric amplification of a monofilament continuum.
• the detector is a scanning camera of slot. At least two operating modes are possible: i) synchronous scan mode or synchro-scan mode ii) single shot mode.
• FIG. 5 schematically illustrates an example corresponding to case b) -i).
• the device of FIG. 5 successively comprises: a femtosecond laser 8,
• a slit scanning camera 18 which captures the light coming from the polychromator 16 and operates in synchronous scanning mode, subsequently authorizing the derivations as a function of. wavelength and flight time, - electronic and computer means
• the time of flight is defined as the time of propagation of the light pulse between the point of entry into the volume 11 studied and the point of entry into the streak camera 18.
• the device of FIG. 5 provides imagery on, for example, 640 ⁇ 480 pixels and the image of which is derivable in wavelength and in time of flight.
• each pixel is coded on 8 bits then stored on 16 or 32 bits. This integer represents the number of single photo-electrons or of lit pixels which are counted during a certain measurement time called integration time.
• the analog mode is also usable but the counting mode in "camera streak" mode is more advantageous, in particular because of the great dynamics and the high signal / noise ratio which it makes it possible to obtain.
• spectro-temporal fluorescence imaging known in the state of the art, for example of the kind which has been developed by the company Hamamatsu, gives access to spectral and temporal distributions which are specific to the analysis of the decline times of multicomponent fluorescence.
• Spectro-temporal transmission imagery which is implemented in the present invention, gives access to spectral and temporal distributions and their partial derivatives, which are specific to the analysis of propagation modes / absorption in non-clear media.
• the problem of studying enlargement by increasing the diffusion of the transmitted pulse and enlargement by decreasing the absorption of the transmitted pulse and in particular the falling edge is also of a statistical nature.
• spectroscopic imaging transmission time presents more complex distributions.
• the laser 8 used has the following characteristics: Ti oscillator: Sa800nm 78MHz 500mW; chain CPA (Chirp Camille Amplification) Ti: Sa pumped by a YLF 10W, allowing to obtain 0.7W, IKHz, 150fs at 800nm; continuum generation.
• the cadence is 1000 pulses per second.
• a streak camera 18 can be used for which the time of each image is an integration over 33 ms, which corresponds to 33 laser shots.
• This second mode requires an adapted counting.
• D ⁇ (x) exp (- ((x-320) / 100) 2 ) where x is the pixel number.
• a stack of differentiable images was obtained: a first image constituted by a set of points in a reference number of SPEs (in an interval of wavelengths, for example 700nm- 725nm) as a function of Time ( ps) and Macroscopic Time (s), a second image constituted by a set of points in a frame Number of SPEs as a function of Wavelength (in nm), and Macroscopic Time (s), - a third so-called fundamental image, constituted by a set of points (number of SPEs) in a Wavelength (in nm) - Time (in ps) coordinate system.
• Beer-Lambert spectrometry Let us now consider the generalization of Beer-Lambert spectrometry. In general, it is necessary to establish a mathematical model of the structure of the medium to be probed. The simplest case consists of considering the measurement object as a model homogeneous isotropic suspension. In this case, many mathematical models (in addition to Monte-Carlo type methods) have already been proposed and are mainly based on the diffusion approximation and, more generally, on the theory of radiative transfer.
• the granulometry methods often use a dilution process to return to the linear case of simple diffusion where the Mie theory remains applicable.
• it is proposed to treat very loaded and colored suspensions, which allow measurements in situ, without contact and without dilution.
• the generalization of Beer-Lambert spectrophotometry applies to absorbers with the proposed imaging techniques.
• the invention thus makes it possible to measure the average of the concentration of these endogenous dyes over a volume of a few cm 3 in the example proposed.
• the pulse and differential spectrophotometry used in the invention makes it possible to measure a concentration of absorber in a non-limpid medium. It also makes it possible to measure concentrations of diffusers. In addition, it makes it possible to quantify the quality of the direction of the average of these concentrations (formation of an average or non-homogenization).
• the invention makes it possible to carry out derivable spectro-temporal imaging with a single laser-white pulse, which is impossible with a tunable scanning system.
• the invention has the advantage of being a contactless technique, allowing global measurement in situ and online. For example, online measurement of yogurt pots or diffusing objects can be done in their own container.
• the invention also makes it possible to acquire information on the volume of each object (and on absorbent sub-volumes, for example pieces of fruit), on the quality of the fermentation and on the visual quality.
• the invention constitutes a rapid and reliable technique in the case of an approach empirical.
• the invention can be considered as a generalization of Beer-Lambert spectrophotometry of non-limpid media, but without scanning and in pulse mode, the spectrophotometry of the invention being further differential.
• the impact-detection length should be adapted as a function of the importance of the diffusion and of the absorption. However, this adaptation is not necessary if the light source or the collector are displaced.
• u (r, t) is the density of photons (number of photons / mm 3 or in J / mm 3 ).
• the medium surveyed is reduced to 2 quantities
• ⁇ a is homogeneous at a time
• ⁇ a is the absorption coefficient in mm- 1 .
• ⁇ s ' is the reduced diffusion coefficient in mm "1 .
• R (p, t) is a function of the time of flight and the wavelength.
• T a ( ⁇ ) ⁇ a , T F ( ⁇ ), both functions of the wavelength ⁇ (which are the two functions sought).
• This analytical solution is an approximation of the probability distribution of the spectro-temporal image. With the counting mode, an addition of fish-type adjustment to this analytical solution is possible.
• One of the axes of the innovative characteristics of the present invention is the use of partial derivatives in wavelength and in time of this picture.
• This equation always has 4 solutions, two of which are real and positive. These last two realistic solutions correspond to 2 inflection points for a single given wavelength.
• the spectro-temporal image is only considered as a zero-order moment where all the authors manipulate it (for example passage to the Log (image)) only in itself without operators of partial derivation. It is the partial derivatives which best reveal the nature of this imagery. So we have just seen an example of a method using the relationships between the partial derivatives and the image itself.
• the extraction of the data sought, the function ⁇ a [ ⁇ ], or some exceptional points (maximum, minimum, maximum slope area, inflection points ...) from a non-clear medium takes place via the methods proposed in the present invention. If the study of the environment is more physical (search for ⁇ s ' [ ⁇ ] and exceptional points) then the approaches are also of the same order.
• one or more can be used. several monochromatic light implusions, to illuminate the non-limpid medium, and acquire at least one spectro-temporal image of transmission from this medium, by performing a spectral scan.
• one or more broad spectrum light pulses to illuminate the non-limpid medium, and to acquire at least one spectro-temporal transmission image from this medium, without spectral scanning.
• broad spectrum light pulse is meant a light pulse whose spectrum is greater than or equal to the spectral window of the acquisition means, namely the polychromator and the streak camera in a given example above.

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