Pseudo-Stark effect and FM/Stark double-modulation spectroscopy for the detection of statistical fine structure in alexandrite

Using laser FM spectroscopy and transient spectral hole burning, the R1m transition of Cr3+ ions in alexandrite is shown to exhibit a linear pseudo-Stark effect with coefficients of 0.141 and 0.0538 MHz cm V-1 at 1.6 K for electric fields along the crystal a and c axes, respectively. This result was used to develop a sensitive FM/Stark double-modulation method for the detection of statistical fine structure (SFS) on the inhomogeneously broadened R1m line. While the final signal-to-noise ratio is not much greater than unity, autocorrelation of the measured spectra provides the first strong evidence for the presence of SFS in an inorganic material. © 1988.