Photon-echo attenuation in rare-earth-ion-doped crystals

We study the optical properties of rare-earth-ion-doped inorganic crystals with an emphasis on the dependence of two-pulse photon echoes on the excitation density in the system. The experimental investigations concentrate on Pr{sup 3+}:Nd{sup 3+}:Eu{sup 3+} codoped Y{sub 2}SiO{sub 5} and YAlO{sub 3} crystals at low temperatures. With two pulses of one laser the echo is induced in one ion species and with a third, {open_quote}{open_quote}scrambler{close_quote}{close_quote} pulse of a second laser another species is excited. These scrambler excitations lead to a dephasing and thus to an echo attenuation which depends on the strength, frequency, and time of the scrambler pulse. The spectral sensitivity of the echo attenuation is used for a spectroscopic technique: {open_quote}{open_quote}photon-echo attenuation spectroscopy.{close_quote}{close_quote} As a function of the delay time {ital t}{sub {ital s}} between the scrambler pulse and the onset of the two-pulse echo sequence the attenuation shows a very specific behavior dictated by the excitation-induced frequency shifts (EFS{close_quote}s). For {ital t}{sub {ital s}} between the two echo-inducing pulses the echo intensity is partially regained by the {open_quote}{open_quote}dephasing-rephasing balancing{close_quote}{close_quote} of the reversible EFS{close_quote}s. For the theoretical description a stochastic model is introduced and the dephasing by excitation-induced lattice vibrations and by EFS{close_quote}s are analyzed in detail. The present results are discussed in the light of previous experimental and theoretical investigations. {copyright} {ital 1996 The American Physical Society.}