Device and method for observing and for measuring raman scattering

A method for Raman spectrometry and for viewing a sample comprising the following steps:

• superimposing an excitation laser beam having a spectral band B0 centered about a wavelength λ0 and a viewing beam having a spectral band BV distinct from λ0 and distinct from the spectral band BR of the Raman beam to be measured, so as to direct on a sample a combined excitation and illumination beam, wherein the spectral band B0 of said excitation laser and the spectral band BV of said viewing beam are defined in wavelength in such a manner that:
• BV<B0
• and in that the spectral band BV is in the blue-green-yellow domain of the visible spectrum
• collecting an optical beam scattered by said sample;
• spatially and spectrally separating said collected beam into two secondary beams, the first secondary beam comprising a spectral band chosen among the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam, and the second secondary beam comprising the two other remaining spectral bands among the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam;
• spatially and spectrally separating said second secondary beam into two tertiary beams, each comprising one of the two remaining spectral bands among the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam;
• directing the viewing beam that goes from the sample to a viewing camera, said viewing camera having a maximum sensitivity about the spectral band BV,
• simultaneously transmitting a very small part of the Rayleigh scattering beam toward the viewing camera so as to allow to view simultaneously the sample and the position of the excitation laser beam on the sample, without saturating the viewing camera;
• detecting the secondary or tertiary collected beam comprising the spectral band BR of the Raman scattering beam;
• detecting the secondary or tertiary collected beam comprising the spectral band BV of the viewing beam.

An optical device for Raman spectrometry and for viewing a sample, the device comprising:

• a first filter that:
• is positioned in an optical path of an excitation laser beam having a spectral band B0 centered about a wavelength λ0 and in an optical path of a viewing beam having a spectral band BV distinct from the spectral band B0 of the laser and distinct from the spectral band BR of a Raman scattering beam to be measured with BV<B0;
• combines the excitation laser beam and the viewing beam to form a combined excitation and viewing incident beam illuminating the sample;
• and
• separates a collected beam coming from scattering of the combined excitation and viewing incident beam on the sample into a first and a second secondary beam, the first secondary beam comprising one spectral band chosen from the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam, and the second secondary beam comprising the two other remaining spectral bands among the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam;
• a second filter that:
• is positioned in an optical path of the second secondary beam;
• and
• spatially separates the second secondary beam into a first and a second tertiary beam, each respectively comprising one of the two remaining spectral bands among the spectral band B0 of the laser, the spectral band BV of the viewing beam and the spectral band BR of the Raman scattering beam;
• and
• a viewing camera having a maximum sensitivity about the spectral band BV in the blue-green-yellow domain of the visible spectrum, wherein an extinction rate of at least one of the first and second filters is chosen such that only a portion of a Rayleigh scattering beam is transmitted toward the viewing camera so as to allow to view simultaneously the sample and the position of the excitation laser beam on the sample, without saturation of the viewing camera.