WO2023025727A1 - Système laser raman - Google Patents

Système laser raman Download PDF

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Publication number
WO2023025727A1
WO2023025727A1 PCT/EP2022/073341 EP2022073341W WO2023025727A1 WO 2023025727 A1 WO2023025727 A1 WO 2023025727A1 EP 2022073341 W EP2022073341 W EP 2022073341W WO 2023025727 A1 WO2023025727 A1 WO 2023025727A1
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diamond
laser system
single crystal
raman laser
raman
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Ian Friel
Timothy Peter Mollart
Daniel James Twitchen
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Element Six Technologies Ltd
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Element Six Technologies Ltd
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
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    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/28—After-treatment, e.g. purification, irradiation, separation or recovery
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
    • C23C16/27—Diamond only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
    • C23C16/27—Diamond only
    • C23C16/274—Diamond only using microwave discharges
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/04—Diamond
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/1086—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering using scattering effects, e.g. Raman or Brillouin effect
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
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    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/3027—IV compounds
    • H01S5/3045—IV compounds diamond
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0619—Coatings, e.g. AR, HR, passivation layer
    • H01S3/0621—Coatings on the end-faces, e.g. input/output surfaces of the laser light
    • H01S3/0623—Antireflective [AR]
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094038—End pumping
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094049—Guiding of the pump light
    • H01S3/094053—Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping

Definitions

  • This invention relates to Raman laser systems, and particular Raman laser systems that use diamond.
  • Chemical vapour deposition is an established technique for depositing material onto a substrate.
  • the technique has been extensively described in patent and other literature.
  • the CVD process typically involves providing a gas mixture that, on dissociation, can provide carbon and hydrogen.
  • the dissociation of the source gas mixture is brought about by an energy source, such as microwaves, radio frequency energy, a flame, a hot filament or jet-based technique.
  • the reactive species are allowed to deposit onto a suitable substrate, typically held at between 700°C and 1200°C, to form diamond.
  • the increasing presence of these defects is detrimental to several properties of the CVD diamond material.
  • An increasing presence of all types of defects affects certain properties, for example, decreasing the thermal conductivity (as phonons are scattered).
  • the point defects also affect absorption of photons and are therefore deleterious to optical transparency. Dislocations result in local birefringence due to their anisotropic disruption of the cubic symmetry of the lattice and so are also detrimental to the optical properties of the diamond material.
  • dislocations in homoepitaxial CVD diamond layers tend to nucleate at or near the interface with their substrate. It has also been found that dislocations generally have line directions that are close to perpendicular to the local growth surface and that, as a result, the strain-related birefringence shows a characteristic anisotropy, being much more obvious for a viewing direction parallel to the growth direction.
  • W02004/046427 describes the production of diamond material via the CVD process by utilising a controlled, low level of nitrogen to control the development of the crystal defects. It is described how nitrogen present in the CVD diamond material must be sufficient to prevent or reduce local strain generating defects whilst being low enough to prevent or reduce deleterious absorptions and crystal quality degradation.
  • Single crystal diamond finds a potential application within Raman lasers, as described in US2005/0163169. Such an application places severe requirements on the diamond material that can be utilised.
  • Raman lasers rely on the process of Raman scattering.
  • Spontaneous Raman scattering occurs when a photon incident on a material results in the excitation of a vibrational mode from its initial energy level to an excited, virtual state. This virtual state can then return to an energy level different to the original level, producing a photon of different energy (and frequency) to that of the incident photon.
  • the final energy level is higher than the initial level, the scattered photon therefore has a lower energy than the incident photon, this is termed Stokes scattering.
  • the energy difference between the incident and scattered photons results in the production of a phonon (a quantised lattice vibration).
  • the scattered photon is utilised to stimulate further Raman scattered photons of the same wavelength: stimulated Raman scattering (SRS).
  • SRS stimulated Raman scattering
  • the Raman laser is therefore capable of changing the frequency of the input light, advantageously producing an output beam with a frequency in a part of the electromagnetic spectrum that was previously unattainable with conventional laser technology.
  • Single crystal diamond is a promising material for use as the Raman scattering medium within the Raman laser. It has a high Raman gain coefficient, possesses low absorbance in a wide range of the electromagnetic spectrum (allowing versatility in the choice of input, intermediate and output frequencies), it is a good dissipater of thermal energy which is generated in the form of phonons as an integral part of the process, and possesses a low thermal expansion coefficient (minimising temperature related distortions).
  • the Raman gain coefficient, gp is defined as (Equation 1) where 7' is the optical phonon decoherence time, s is the Stokes-shifted output wavelength and const is a material dependent constant of proportionality.
  • the polarisation of the pump beam with respect to the symmetry axes of the crystal is a parameter which affects the Raman gain coefficient.
  • the Stokes beam is polarised parallel to the pump beam.
  • the Stokes beam is polarised perpendicular to the pump beam.
  • Diamond Raman lasers can operate in a number of configurations. The most simple is as a Raman generator, as illustrated in Figure 1 , in which a high intensity pulsed pump laser 2 is focused onto the diamond Raman gain crystal 4, resulting in conversion of the pump wavelength to multiple Stokes orders which constitute the output beam 6 of the laser. Although this is a relatively simple design which does not require an optical cavity, in practice such a configuration is of little use due to the limited control of the output spectrum
  • a second type of configuration is as an external Raman resonator, as illustrated in Figure 2.
  • the Raman crystal 4 is placed within an optical resonator comprising an input mirror 8 and an output mirror 10 in order to reduce the SRS threshold, increase the conversion efficiency and tailor the output wavelength 14.
  • the cavity is pumped externally with either a continuous wave (cw) or pulsed laser source 12. Due to diamond’s high Raman gain coefficient the Raman crystal can be kept short compared to other Raman gain materials.
  • Such an external diamond Raman resonator can therefore be viewed as a simple, compact add-on enabling frequency conversion for a wide variety of laser sources.
  • a third configuration is an intracavity Raman resonator, as illustrated in Figure 3, in which both the pump laser medium 16 and the Raman crystal 4 are placed within a cavity, comprising input mirror 8 and output mirror 10, resonant at both pump and Stokes wavelengths.
  • This configuration takes advantage of the high intracavity pump field which leads to enhanced conversion to the output beam 20.
  • the cavity may also include other optical elements such as a Q-switch 18 for pulsed mode operation.
  • the birefringence can be minimised, which minimises depolarisation losses in diamond Raman laser systems in which the polarisation is a controlled design parameter.
  • a diamond Raman laser system comprising a laser for providing laser light having a wavelength less than 750 nm, the laser comprising at least one pump laser and further comprising a Raman oscillator, the at least one pump laser and the Raman oscillator being configured to provide an n-order Raman oscillation, where n is an integer.
  • the Raman oscillator comprises single crystal diamond, the single crystal diamond having an optical absorption coefficient measured by optical spectroscopy at 450 nm of less than 0.5 cm -1
  • the single crystal diamond has an average optical birefringence, measured at 20°C along the direction of pump or Stokes beam propagation, such that the birefringence over at least 80% of the cross-sectional area does not exceed 2 x 10' 5 .
  • the single crystal diamond optionally has an optical absorption measured by optical spectroscopy at 450 nm selected from any of less than 0.3 cm -1 , less than 0.2 cm -1 and less than 0.1 cm -1 .
  • the single crystal diamond comprises a single substitutional nitrogen, N s °, concentration as measured by electron paramagnetic resonance, EPR, selected from any of less than 100 ppb, and less than 50 ppb.
  • the single crystal diamond optionally comprises a single substitutional nitrogen, N s °, concentration as measured by electron paramagnetic resonance, EPR, selected from any of greater than 5 ppm and greater than 10 ppb.
  • the diamond Raman laser system has an operating power selected from any of at least 200 W, at least 500 W, at least 1000 W, and at least 1500 W.
  • the diamond Raman laser system has a beam parameter product selected from any of less than 60 mm mrad, less than 40 mm mrad, less than 20 mm mrad, less than 10 mm mrad, and less than 5 mm mrad.
  • the laser optionally has a Stokes wavelength in a range selected from any of 240 to 700 nm, 300 to 600 nm and 400 to 500 nm.
  • the pump laser comprises at least one laser diode.
  • the pump laser comprises a plurality of laser diodes.
  • the plurality of laser diodes are coupled together by optical fibre.
  • the single crystal diamond is selected from any one of chemical vapour deposition, CVD, diamond, high pressure high temperature, HPHT, diamond, and natural diamond.
  • the single crystal diamond has an anti-reflective surface coating.
  • the single crystal diamond has been annealed at a temperature of at least 1400°C to reduce the absorption coefficient.
  • the diamond Raman laser system optionally comprises a heat sink in thermal contact with the single crystal diamond.
  • the single crystal diamond optionally forms a first layer in a composite single crystal diamond, the composite single crystal diamond further comprising a second layer of single crystal diamond, the second layer having a higher single substitutional nitrogen concentration than the first layer.
  • the second layer may therefore form an integral heat sink.
  • the composite single crystal diamond may comprise a third layer of single crystal diamond embedded in the heat sink.
  • the diamond has a linear dimension in the path of the laser of at least 2 mm.
  • the diamond Raman laser system is used for processing materials having a low infra-red absorption.
  • materials having a low infra-red absorption include copper and platinum.
  • examples of a use include machining or welding.
  • Figure 1 illustrates schematically in a block diagram a Raman laser in a known Raman generator configuration
  • Figure 2 illustrates schematically in a block diagram a Raman laser in a known external Raman resonator configuration
  • Figure 3 illustrates schematically in a block diagram a Raman laser in a known intracavity Raman resonator configuration
  • Figure 4 shows the optical absorption spectra of examples diamonds made using recipes A and B;
  • Figure 5 shows the optical absorption spectra of examples diamonds made using recipes A using different heat treatments
  • Figure 6 shows the optical absorption spectra of examples diamonds made using recipes B and C.
  • Figure 7 shows birefringence for an exemplary CVD single crystal diamond.
  • the absorption of the diamond is as low as possible at the operating wavelength, but it has been found that at wavelengths of, for example, 450 nm, certain defects in diamond that are not detrimental at higher wavelengths give rise to higher absorption at shorter wavelengths. Examples of such defects include vacancy clusters which do not significantly impact the absorption at 1064 nm, but have a significant effect on the absorption at 450 nm.
  • the inventors have found that diamond can be optimised for use in Raman laser systems operating at wavelengths below 750 nm, for example at 450 nm, by careful control of defects that would otherwise introduce significant absorption at 450 nm. In practice this can be done through control of the synthesis conditions, control of post-synthesis treatment such as annealing, or a combination of both.
  • the following examples show how the absorption coefficient of single crystal diamond at 450 nm can be controlled by synthesis conditions and by post-growth annealing. Absorption spectra are shown to illustrate how significant these changes are at 450 nm compared to at ⁇ 1 pm where the absorption coefficient for the same diamond changes by much smaller amounts.
  • single crystal CVD diamond was grown in a microwave plasma reactor comprising a temperature monitoring system and substrate temperature control system.
  • the microwave plasma reactor comprises the following basic components: a plasma chamber; a substrate holder; a microwave generator for forming a plasma within the plasma chamber; a microwave coupling configuration for feeding microwaves from the microwave generator into the plasma chamber via dielectric windows; and a gas flow system comprising source gases, one or more gas inlets, and one or more gas outlets for feeding process gases into the plasma chamber and removing them therefrom.
  • a gas flow system comprising source gases, one or more gas inlets, and one or more gas outlets for feeding process gases into the plasma chamber and removing them therefrom.
  • the plasma chamber is configured to form a resonance cavity supporting a standing microwave in use.
  • the plasma chamber is configured to support a TMom standing microwave in use, e.g. a TMon mode.
  • the operational frequency may be in a range 400 to 500 MHz, 800 to 1000 MHz, or 2300 to 2600 MHz.
  • Source gases including a carbon source and molecular hydrogen are fed into the plasma reactor vessel and can be activated by the standing microwave field to form a plasma in high electric field regions.
  • a substrate configuration is provided in close proximity to the plasma such that reactive carbon containing radicals can diffuse from the plasma to the substrate and be deposited thereon. Atomic hydrogen can also diffuse from the plasma to the substrate and selectively etch off non-diamond carbon from the substrate such that diamond growth can occur.
  • the microwave plasma reactor further comprises one or more temperature measurement devices configured to take at least two temperature measurements, including one or more measurements in a central region of the support substrate and one or more measurements in a peripheral region of the support substrate.
  • the temperature measurements may be taken simultaneously or within a short time interval of each other and the substrate temperature control system may be used to correct any temperature variations.
  • the temperature measurement device may comprise a pyrometer. Two pyrometers may be provided, one to take the central temperature measurements and one to take the peripheral temperature measurements. Alternatively, a plurality of thermocouples can be embedded into the substrate. Pyrometric measurements may focus on the temperature of the growing CVD synthetic diamond material.
  • the temperature of the diamond material will be approximately the same as the temperature of the underlying support substrate.
  • the temperature measurements may thus be taken between the growing CVD single crystals.
  • Table 1 shows three exemplary recipes for CVD diamond growth using the system described above.
  • Recipe A contained significantly more gas-phase nitrogen than recipes B and C and was prepared at a higher temperature. It can therefore be expected that the concentration of nitrogen and other absorbing optical defect centres in the diamond of recipe A would be significantly higher than that of recipes B and C.
  • the estimated concentrations of NsO are 150 ppb for recipe A, and 20 ppb for recipes B and C, within ⁇ 30%.
  • the samples were prepared, they were cleaned to remove any polycrystalline diamond, and cut and polished to form plates with a largest linear dimension of around 4 mm and a thickness of around 1 mm. Cutting and polishing to form parallel plates was required in order to produce samples that gave reproducible optical absorption spectra.
  • Optical absorption was measured by UV-vis spectroscopy, as is well known in the art. Simply, a beam of radiation at the desired wavelengths is directed through a sample, and the intensity of the radiation that is transmitted through the sample is measured. The intensity of the transmitted radiation can be used to calculate the absorption coefficient. Note that optical absorption may also be measured using calorimetry, which is a more sensitive technique than UV-vis spectroscopy.
  • Recipe C was prepared in the same way as Recipe B, but with a synthesis temperature 60°C lower than that of Recipe B.
  • Figure 6 shows the optical absorption spectra of examples diamonds made using recipes B and C.
  • the UV-vis optical absorption spectrum of Recipe C is significantly higher than that of Recipe B at wavelengths below around 600 nm. Indeed at 450 nm, the optical absorption of Recipe C is around 0.2 cm -1 compared to less than around 0.05 cm -1 for Recipe B. Again, this makes the diamond of Recipe B more suitable for use in diamond Raman laser systems operating at 450 nm. However, note that the diamond of Recipe C still has an improved optical absorption at 450 nm compared to the un-annealed diamond made according to Recipe A. For certain optical applications it is desirable to provide a material which has low optical absorbance and low optical birefringence.
  • Embodiments of W02004/046427 are described as producing a layer of single crystal CVD diamond having substantially no regions of high birefringence and containing single substitutional nitrogen in a concentration range 3 x 10 15 atoms/cm 3 to 5 x 10 17 atoms/cm 3 as measured by electron paramagnetic resonance spectroscopy (EPR).
  • EPR electron paramagnetic resonance spectroscopy
  • Such materials having low and controlled levels of nitrogen and low strain are described as being manufactured using a chemical vapour deposition technique in which low and controlled levels of gas phase nitrogen are introduced into the synthesis atmosphere within a concentration range 300 ppb to 5 ppm.
  • Diamond synthesized according to Recipe A has been found to have an optical birefringence such that in a sample of the single crystal CVD diamond material having an area of at least 1 .3 mm x 1 .3 mm, and measured using a pixel size of area in a range 1 x 1 pm 2 to 20 x 20 pm 2 , a maximum value of An[ a vera ge ] does not exceed 2 x 10’ 5 , where Anfaverage] is an average value of a difference between refractive index for light polarised parallel to slow and fast axes averaged over the sample thickness. Nominally a lower limit for the maximum value of Anfaverage] may be 1 x 10’ 7 .
  • Figure 7 shows birefringence measured for a CVD single crystal diamond made according to Recipe B.
  • Figure 7a shows the birefringence measured in a direction parallel to the growth direction, and has a An ma x of 1.7x1 O’ 4 .
  • the sample size in each case was approximately 2 x 2 x 2 mm.

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  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Nonlinear Science (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Lasers (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)

Abstract

Un système laser Raman à diamant comprend un laser destiné à fournir une lumière laser présentant une longueur d'onde inférieure à 750 nm, le laser comprenant au moins un laser de pompe et comprenant en outre un oscillateur Raman, ledit laser de pompe et l'oscillateur Raman étant configurés pour fournir une oscillation Raman d'ordre n, n étant un nombre entier. L'oscillateur Raman comprend un diamant monocristallin, le diamant monocristallin présentant un coefficient d'absorption optique mesuré par spectroscopie optique à 450 nm inférieur à 0,5 cm-1.
PCT/EP2022/073341 2021-08-24 2022-08-22 Système laser raman Ceased WO2023025727A1 (fr)

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