Ultrafast Dynamics of Optical Nonlinearities in β-Ga2O3

We report the different nonlinear optical mechanisms and defect-related carrier dynamics in Sn-doped β-Ga2O3 crystal by utilizing time-resolved pump-probe technique based on phase object under UV excitation. The obtained nonlinear optical parameters arise from bound electron can be well explained by the theoretical calculation of two-band model and Kramers-Kronig transformation. By tuning the probe wavelength, the carrier nonlinearity can be modulated greatly due to additional absorption of defects within the bandgap. The results reveal that by choosing a proper probe wavelength that matches the defect state to the valence band, the nonlinear absorption and refraction of the carriers can be greatly enhanced, which provides an important reference for the design of gallium oxide-based waveguide materials and all-optical switching materials in the future.

Influence of the Probe Laser Wavelength in Transient Reflectance Measurement of Gold

Transient reflectance of gold is measured with ultrafast spectroscopy by tunable probe wavelength. The influence of the probe wavelength on the signal is analyzed. It is found that when probed around 490 nm the signal is most sensitive to electron excitation and there is a simple linear relation between the reflectance change and the electron temperature change after sufficiently weak excitation. The two-temperature model is applied to calculate the electron-phonon coupling factor by fitting the transient reflectance signal.

Pump- And Probe-Wavelength Dependencies of Picosecond Anti-Stokes Raman Spectrum of Trans-Stilbene in the S1 State

Vibrational relaxation dynamics of trans-stilbene in the S1 state immediately after photoexcitation is studied by picosecond time-resolved anti-Stokes Raman spectroscopy with several pump and probe wavelengths. Pump-wavelength dependence of the anti- Stokes spectrum indicates that, when pump photons with high excess energy (≈5200cm-1) are used, the anti-Stokes Raman bands at 0 ps delay time arise from vibrationally excited transients with excess vibrational energy not thermally distributed in the molecule. Probe-wavelength dependence suggests that the vibrationally excited transients at 0 ps are mostly on the lowest excited vibrational levels, as far as the olefinic C═C stretching and the C–Ph stretching modes are concerned. The vibrational relaxation process of S1trans-stilbene is discussed on the basis of the observed results.