BeamLine Description
IUVS is composed by two separate branch-line, one devoted to the UV Brillouin scattering, one to the Raman one. The common part includes the undulator and the “heat-load” chamber. Two so called “Figure-8” undulator provide photons in the tunable range of 5-11 eV, by a proper selection of the undulators gap. Two grazing-incidence mirrors compose the heat-load chamber. They allow to disperse the heat generated by high-order energetic harmonics. After the heat-load chamber a removable 5 degree grazing incidence silicon mirror acts to deviate the beam from the Brillouin set-up to the Raman one.
UV Resonant Raman set-up
In the following is schematically shown the overall Raman set-up
Overview of the Raman set-up
After the switching mirror chamber, the beam is bring out the UHV chamber by means of a fused silica viewport. From this point the UV-beam in the 200-280 nm range can be optically treated and transported as occurs form the common lasers beams.
At this point the incoming beam is characterized by a bandwidth or ≈ 20 nm and needs to be monochromatized before being used to employ Raman spectroscopy.
A combination between two plane and one spherical metallic parabolic mirror, with focal length of 750 mm, lead the beam inside a 750 mm Czerny-Turner spectrometer (Princeton Instruments), equipped with three holographic UV optimized gratings of 1800 g/mm, 2400 g/mm and 3600 g/mm. By this way it is possible to allow a final band-width ranging from 50 to 10 cm-1.
After the monochromator the beam is collimated by a spherical lens and bring to the sample in order to get Raman scattering. A proper combination of kinematic mirrors allows to choose which kind of radiation send to the sample. Alternatively to the synchrotron Radiation beam coming from monochromator, ancillary laser beams of 266 nm and 213 nm can be provided.
Independently from the beam source, a 45 degree small mirror deviates the beam to the sample. A Sperical lens with 2 inches of diameters and a focal length of 100 mm acts as focusing and collecting lens, thus providing a backscattering configuration.
The analyser system is composed by three interconnected Czerny-Turner spectrometer (Trivista system, Princeton Instruments) with focal length of 500 mm, 500 mm and 750 mm respectively. The three spectrometer have been coupled to work both in additive and subtractive configurations. The first one allow to get Raman measurements with very high resolution (up to 0.3 cm-1 at 633 nm), the second one allows to strongly reduce the elastic component witouth using notch or longpass filter. By this way it is possible to measure Raman peaks up to ≈ 50 cm-1.
In the set-up has been included a micro-Raman system with the aim of get micro-Raman measurements in the UV regime exploiting the 266 nm laser
The micro-Raman set-up
Sample environment for Raman measurements
The backscattering configuration and the geometrical characteristics of the Raman set-up allow the use of a large variety of sample environments.
For measurements of liquids and/or aqueous solution, we have employed a specific sample holder, able to thermalize the sample in a temperature range of 5-120 °C.
UV Brillouin set-up
Overview of the Brillouin set-up
The inelastic light scattering spectrometer uses an undulator source, and is conceptually composed of three stages: the NIM monochromator, the scattering sample and the NIM analyser. The incident photon energy is tuned in the 5-11 eV range by the monochromator, with a relative energy resolution in the 10-5 to 10-6 range. The analyzer allows to analyze the energy of the photons diffused of the sample, with an energy loss or an energy gain in the energy region typical of phonon like excitations in the considered momentum region. The momentum transfer, Q, will be in the 0.02 to 0.25 nm-1 range, as determined by the incident photon energy, by the choice of the scattering angle, and by the refraction index of the sample. The typical momentum resolution will be ΔQ/Q = 0.05, with some degree of tunability by varying the analyzer collection angle
The monochromator and analyzer chamberulticols}
The sample holder
The Brillouin branchline is also equipped to make temperature-scans on solid and liquid samples. These kind of measurements can be obtained by means of a thermal bath, with cooling capabilities down to le T= -20 oC, coupled with a resistive heating system. In this way it is possible to control the sample temperature with an accuracy of less than 0.5 oC in the range of -20-120 oC. A liquid nitrogen cryostat is also available to cool the sample up to 77 K.
A pressure cell is also available at IUVS (see figure on the right). It allows to cover a pressure range up to 4 Kbar
The pressure cell
