Professor Robert Taylor

Abstract:

Femtosecond transient transmission spectroscopy has been used to study the generation and thermalisation of hot photoexcited electrons and holes in semiconductors. Work on bulk AlxGa1-xAs has been extended to include a detailed numerical model of carrier thermalisation and cooling, which allows for dynamic screening of carrier-phonon interactions. This model shows excellent agreement with experimentally observed effects such as hole burning, single LO-phonon emission by electrons and two-temperature behaviour of electrons and holes at early times (<10 ps). Hole burning measurements have also been made on type-I GaAs/AlAs superlattices, where the density dependence of the transient transmission spectra has been investigated. © 1992.

Abstract:

Femtosecond time-resolved measurements of the optical Kerr effect in molten caesium chloride have been made. Amplified laser pulses of 115 fs duration and 1 mu J energy were used to induce a birefringence. The transmission of a weak probe pulse of the same duration gives a value of 180 fs for the relaxation time of the induced birefringence; this value is consistent with that expected for binary ionic collisions. The magnitude of the Kerr coefficient is estimated to be approximately=3*10-22 m3 V-2 (3*10-13 esu).

Abstract:

Femtosecond optical absorption spectra of AlxGa1-xAs reveal rapid thermalisation of the electron-hole plasma to a two-temperature carrier distribution after ∼ 500fs. The carriers thermalise to a single-temperature distribution at ∼ 10ps. Single phonon emission by electrons is observed at early times when the carrier density is low. Theoretical calculations which model analytically the principal carrier-carrier and carrier-phonon interactions responsible for thermalisation give good agreement with the data. © 1989.

Abstract:

Photoluminescence intensity correlation measurements of GaAs quantum wells using 120 fs laser pulses show relatively slow relaxation times ≤ 10 ps at high energy close to the L valley conduction band minimum. This value is consistent with recent measurements of the L → Γ scattering time. However, theoretical estimates show that nonequilibrium phonon effects can also give rise to slow relaxation on this timescale.