Picosecond time resolved studies of nonradiative relaxation in ruby and alexandrite

Dynamics of the nonradiative transitions between the ⁴T₂ pump band and the ²E storage level of the trivalent chromium ion in ruby and alexandrite crystals is studied using the picosecond excite‐and‐probe absorption technique. A 527‐nm picosecond pulse excites the ⁴T₂ state of the Cr³⁺ ion, and an infrared picosecond probe pulse monitors the subsequent growth and decay of population in the excited states as a function of pump‐probe delay. An upper limit of 7 ps is determined for the nonradiative lifetime of the ⁴T₂ state in ruby. A vibrational relaxation time of 25 ps for the ⁴T₂ band in alexandrite is estimated. The time to attain thermal equilibrium population between the ²E and ⁴T₂ levels of alexandrite following excitation of the ⁴T₂ band is estimated to be ∼100 ps.