Lai Tian-Shu

Optical Switch Formation in Antimony Super-Resolution Mask Layers Induced by Picosecond Laser Pulses

Sb is a classic material of a super-resolution near field structure (super-RENS) mask layer in which the optical switch formation is often realized by nanosecond laser pulse stimulation. We achieve fast and repeatable optical switching driven by picosecond laser pulses in a proper fluence range on Sb thin films. The optical properties of Sb thin films before and after switching are studied by surface-sensitive micro-area ellipsometry. The change of optical constants after switching is less than 2% in the whole visible range. The Sb mask layer is shown to be very promising for ultrafast super-resolution optical storage applications.

Ultrafast Relaxation of Coherent Control Photocurrent in AlGaAs/GaAs Multi Quantum Wells

We theoretically and experimentally study the ultrafast dynamics of coherent control photocurrent in AsGaAs/GaAs multi quantum wells at room temperature. A ballistic photocurrent relaxation time of ~200 fs is deduced based on the theory of density matrix and is evidenced with the three-colour femtosecond pump–probe measurements.

Spin Dynamics of B2 and L2 1 −Ordered Co 2 FeAl 0.5 Si 0.5 Heusler Alloy Films

Measurements of magnetization precession are performed for L21 and B2-ordered Co2FeAl0.5Si0.5 full Heusler alloy films using the time-resolved magneto-optical Kerr effect technique in the out-of-plan configuration. Dependence of the precession frequency on the external magnetic field can be fitted by the Landau-Lifshitz-Gilbert equation. The chirp parameters are close to each other for the L21 and B2 structures, and decrease with the external magnetic field increasing. The relaxation rate of the B2-ordered film is smaller than that of the L21 one.

Spin-Wave Modes in Exchange-Coupled FePt/FeNi Bilayer Films

A simple magnetic modulation structure of the exchange-coupling FePt/FeNi bilayer film is fabricated and studied for its magnetization dynamics using time-resolved magneto-optical polar Kerr spectroscopy. It is found that two spin-wave modes can be excited. One is fixed at ~3.2 GHz in frequency for any external field and may serve as a frequency-stabilized spin-wave filter, while the other is external field dependent. In contrast, only the external field-dependent mode is excited in single-layer FeNi, supporting the localized origin of the mode at ~3.2 GHz, which is confined to a thin exchange-coupling region. The other external field-dependent mode in frequency is attributed to the Kittel mode.

Effects of bandgap shrinkage in femtosecond absorption saturation measurements of GaAs film

Using CPM dye laser and self-mode-locked Ti sapphire laser as pump-probe optical sources, the effects of bandfilling and bandgap shrinkage on the femtosecond absorption saturation spectra of GaAs film have been studied. For exciting photon energy of 1.97 eV and carrier density of 1 × 1018 cm-3, an optical-induced absorption increase is observed and is attributed to bandgap shrinkage. The dependence of the absorption coefficient change on the carrier temperature and the carrier densities is discussed.

Femtosecond Studies on Third-Order Optical Nonlinearities of Polyanilines

The ultrafast dynamics of third order nonlinearities of polyaniline (PAn) and polyaniline doped in polymethyl mathacrylate (PAn-PMMA) films are investigated using femtosecond absorption spectroscopy. An ultrafast initial exciton deformation time of about 100 fs is observed in PAn film. In PAn-PMMA film, the third-order nonlinearity results in an efficient two-photon absorption at about 2 eV.