  We present a new experimental protocol for the spectroscopic study of the
dynamics of glasses in the aging regime induced by sudden pressure jumps
(crunches) across the glass transition line. The sample, initially in the
liquid state, is suddenly brought in the glassy state, and therefore out of
equilibrium, in a four-window optical crunch cell which is able to perform
pressure jumps of 3 kbar in a time interval of ~10 ms. The main advantages of
this setup with respect to previous pressure-jump systems is that the pressure
jump is induced through a pressure transmitting fluid mechanically coupled to
the sample stage through a deformable membrane, thus avoiding any flow of the
sample itself in the pressure network and allowing to deal with highly viscous
materials. The dynamics of the sample during the aging regime is investigated
by Brillouin Light Scattering (BLS). For this purpose the crunch cell is used
in conjunction with a high resolution double monochromator equipped with a CCD
detector. This system is able to record a full spectrum of a typical glass
forming material in a single 1 s shot. As an example we present the study of
the evolution toward equilibrium of the infinite frequency longitudinal elastic
modulus (M_infinity) of a low molecular weight polymer (Poly(bisphenol
A-co-epichlorohydrin), glycidyl end capped). The observed time evolution of
M_infinity, well represented by a single stretched exponential, is interpreted
within the framework of the Tool-Narayanaswamy theory.
