THE VERTEX :


The «VERTEX» is a commercial spectrometer from the Bruker company dedicated to far infrared to visible studies. Three energy ranges can be explored : the FIR, the MIR and the VIS. An helium flux cryostat  allows to vary the samples temperature from  300 K to 4 K.


The FIR i.e the Far Infra-Red from 20-600 cm-1 that is 5-74meV for our equipment

    - source : mercury lamp

    - beamsplitter : Si

    - detector : DTGS FIR (hot) and a bolometer

    - optical windows : polyethylene


The MIR i.e theMid Infra-Red from 600-8000cm-1 that is 74-992meV for our equipment

    - source : globar lamp

    - beamsplitter : KBr

    - detector : MCT (cool down with liquid nitrogen)

    - optical windows : ZnSe


The VIS i.e visible from 8000-21000cm-1 that is 992meV-2,6eV for our equipment  

    - source : tungsten lamp

    - beamsplitter : quartz

    - detector : DTGS (hot)

    - optical windows quartz


The figure bellow presents the ratio of two successive one minute measurements. The ratio indicates the noise level. The noise level is quite inferior to 1% for the MIR and the VIS but not within the FIR range where the detector is less efficient (despite a wider optical aperture).






FIR, MIR and  VIS spectra.



An helium flux cryostat  allows to vary the samples temperature from  300 K to 4 K. The cryostat rotates while been cold  in order to measure regularly a reference mirror to correct from any time derivations. An in situ gold evaporation is possible. The gold evaporation on the sample allows to measure the reflexion of a gold mirror which surface is perfectly identical to the sample one. The stake is to  accurately quantify the number of photons reflected by the sample for each photon energy w. This quantification gives access to the peculiar dynamic of the sample.



                                   

The cryostat cold finger is a Janis ST30 one. The outside of the cryostat has been completely changed.

The plans have been realized by David Jegouso of the Néel  Institute. The pieces have been machined by François Greiner of the Néel  Institute. Many thanks to Riccardo Lobo who inspires the design of this cryostat.



 

OPTICAL SPECTROSCOPY

  1.     STAKES

  2.     PRINCIPLE

  3.     THE VERTEX

  4.     THE MARTIN-PUPLETT