Dephasing and Field-Induced Modulations of Optical Coherent Transients of Ions in Crystals

The purpose of this study is to investigate the fundamental interactions between coherent light--the laser, and optically active ions in crystals. The methods employed in this work are the optical coherent transient techniques which have proven to be powerful tools for examining dynamical processes in solids. Coherent transients of particular interest to our study are the optical free induction decay (OFID) and the photon echoes. Besides being used as a high power, high spectral resolution light source, in these coherent transient experiments, the laser is also employed as a source of coherent excitation. A coherent state of the system under investigation (Er ^{3+} or Cr^{3+ }-doped crystals) is first prepared with the laser, and through various methods the decay of coherence due to dephasing (caused by dynamical perturbations) is then monitored as a function of time. The information about the homogeneous spectral line broadening, hence the dynamical processes occurring in the crystals, can be studied in detail through these investigations. We develop a new frequency switching technique for OFID using a pair of Helmholtz coils. The effects of the externally applied electric or magnetic field on the optical transition frequencies of the doped ions in crystals can also be studied with great accuracy through their modulation of the photon echo intensity. The collective behavior of these echo-producing ions under the influence of the external field can be understood quantitatively. We also show that ultrahigh resolution spectroscopy is possible through these echo modulation experiments with pulsed, uniform electric fields.