LAboratoire de Spectrochimie Infrarouge et Raman – UMR 8516
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Conventional Raman

Les spectromètres Raman monocanaux RT30 et T800

The RT30 (Fig. 1.) and T800 are both mono channel macro Raman spectrometers with the same characteristics. The only difference lies in their external design. These instruments are dedicated to record Raman spectra with high spectral resolution and they can be used to explore the the low frequency domain.

spectrometer

display

sample plate

photons counting

Fig. 1. The RT 30 spectrometer

The sample plate (Fig.2.) includes mainly the support of the sample, a laser beam focusing lens and a transfer objective. The laser beam is focused onto the sample and in the general case of the study of the transverse Raman effect, the light scattered by the sample is collected in the direction perpendicular to the exciting beam by the transfer objective. This objective sends the scattered light onto the entrance slit of the spectrometer. A display shows the sample image formed on the entrance slit of the spectrometer. The sample stage can also be used to study samples in backscattering configuration.

Fig. 2. Sample plate and display

Fig. 3. The spectrometer
G : grating
M : miror
S : slit

These 2 Raman spectrometers are triple monochromators(Fig. 3.) in additive configuration. As each monochromator has a focal length of 0.8 m, the triple monochromator has the equivalent dispersion of a single monochromator of 2.4 m focal length. The 1800 grooves/mm gratings assure a spectral resolution of 0.3 cm-1 (at 514.5 nm) and a stray light rejection rate less than 10-13 at 50 cm-1 from the Rayleigh line with a resolution of 1 cm-1.

The spectrometer is equipped with a system scanning to explore the different elements of the scattered light successively by rotation of the three gratings. The spectral range of the spectrometer extends from 350 to 875 nm. It is possible to record “low frequency” Raman spectra by starting very close to the Rayleigh line (a few cm-1 according to the nature of the sample).

The Raman signal detection is performed by a photomultiplier (Hamamatsu R943) with a GaAs photocathode which has a constant response from the UV to the near infrared. The temperature of the detector is kept at -20°C by a Peltier device and the anodic signal is processed by a photon counter in order to discriminate the interference signals.

In order to obtain excitation profiles and/or to excite the resonance Raman scattering, two laser sources are available: ionized Argon and ionized Krypton lasers.
The main exciting lines from the 2 lasers are:
Ar+ : 457.9, 488.0, 514.5 nm
Kr+ : 568.2, 647.1 nm