analyseur de spectre à cristal de Bragg

Traductions

• anglais

  Auteur : Taillefer, Yves, 1982

  Définition

  A Bragg cell consists of a piezoelectric transducer and a block of crystalline material in which sound and light waves interact.

  Note :

  The transducer, bonded to one end of the cell, is tuned to a band of interest. When the transducer is excited with an electrical signal, a traveling acoustic wave is set up within the cell. Between the peaks and valleys of the acoustic pressure wave, acoustic energy causes slight changes in the refractive index of the crystalline material. When laser light is introduced at the correct angle, the reflections from the index changes add in phase. Bragg diffraction takes place and part of the input light beam is deflected. The deflected beam can be imaged on a screen or on a photodetector array. A Bragg cell not only deflects light, but modulates its amplitude and shifts its frequency. Since it is the sound waves generated by the transducer that deflect the incoming light, the amplitude of the deflected output is proportional to the drive amplitude. The angle of the deflected light is proportional to the sound frequency generated by the acoustic transducer. The higher the incoming frequency, the greater the angle of deflection. Finally, the frequency of the deflected light is increased from its original value by the amount of the acoustic input frequency.

  Terme :

  1. Bragg-cell