Effect of pressure on the refractive index of Ge and GaAs

We have measured the dispersion of the refractive index n({ω}) of Ge and GaAs between 0.6 and 1.4 eV for hydrostatic pressures up to 8 GPa. The frequency dependence of n({ω}) is extrapolated to zero energy by using an oscillator model of the dielectric function. In this way, we obtain the variation with pressure of the electronic static dielectric constant ε_∞. We find that for the volume change of {Δ}V/V₀{}8% covered in this experiment the volume dependence of ε_∞ is well described by a single scaling coefficient r=d lnε_∞/d lnV with r=1.58(3) for Ge and 0.73(4) for GaAs. Results are discussed in relation to semiempirical theoretical models.