Absolute nonradiative energy-conversion-efficiency spectra in ${\mathrm{Ti}}^{3+}$:${\mathrm{Al}}_2$${\mathrm{O}}_3$ crystals measured by noncontact quadrature photopyroelectric spectroscopy

Photopyroelectric spectroscopy (PPES) was used in a noncontact experimental configuration to obtain high-resolution absolute spectra of the optical-to-thermal energy-conversion efficiency (nonradiative coefficient), ${\mathrm{\eta }}_{\mathrm{NR}}$(λ), of Ti:sapphire laser crystals with widely different figures of merit. Optical-absorption-coefficient β(λ) spectra were obtained from the PPES signal in the purely optical transmission mode. These were subsequently used self-consistently in a theoretical model along with PPES-signal quadrature spectra (purely thermal transmission mode) to extract ${\mathrm{\eta }}_{\mathrm{NR}}$(λ) spectra. These spectra were found to depend on the optical quality of the bulk and of the polished surfaces of the Ti:sapphire material. Therefore, they can be used for fundamental energy-conversion studies of the excited-state deexcitation manifold, as well as for establishing a practical monitoring criterion of crystal growth and processing quality in ${\mathrm{Ti}}^{3+}$:${\mathrm{Al}}_2$ ${\mathrm{O}}_3$.