Laser hole burning spectroscopy: A high resolution probe of molecular environments

Laser induced hole burning in optical absorption bands of low temperature solids was investigated mechanisms for population hole burning, the interactions with the environment which limit the hole widths and the use of hole burning for ultra high resolution spectroscopy were emphasized. Examples of hole burning in new classes of materials are presented. Hole recovery was used to determine nuclear spin lattice relaxation rates in praseodymium doped crystals. For allowed optical transitions (e.g., singlet states of zinc porphyrin, dibromoindigo and color centers in alkali halides). For longer lived optical levels in crystalline materials, e.g., those containing rare earth ions, the hole widths are narrower and are limited by dynamical interactions with surrounding nuclei. In amorphous materials such as europium doped silicate glass, hole widths are much broader, limited by low frequency tunneling motions. Hole burning measurements were complemented by time domain coherent transient (photon echo, and optical free decay) measurements of homogeneous linewidths.