Fig. 1. Schematic diagram of probe light interference.

Fig. 2. (a) Transient absorption spectra in GaN:C sample with different delay times. (b) Transient absorption spectra in GaN:C sample with different pump fluences at td=2  ps. (c) Transient absorption curves under different delay times in GaN:C sample. (d) The pure oscillation curve extracted by the TAS and the pure absorption spectral oscillation curve at td=2  ps in the GaN:C sample. The pump wavelength is 365 nm. In (a), (c), and (d), the pump fluence is 1.16  mJ/cm2.

Fig. 3. Semi-logarithmic plot of the transient absorption dynamics in GaN:C sample under (a) various excitation fluences and (b) different pump wavelengths. The probe wavelength is ∼600  nm; the solid lines are the theoretical fitting.

Fig. 4. (a) Transient absorption spectra at 2, 100, and 1000 ps delay time in GaN:C. (b) Δλ under different delay times. The absorption response of Δn under (c) different signs and (d) different magnitudes is simulated by using the refraction-related interference model. The arrow direction corresponds to the peak offset during the time delays. In both (a) and (b), the pump wavelength is ∼365  nm with the pump fluence of ∼1.16  mJ/cm2.

Fig. 5. (a) Transient absorption spectra restored by interference model and Δn (td=2  ps) dispersion relation in GaN:C sample (GaN:Mg sample; see inset) with the excitation wavelength of 365 nm. The solid lines are the theoretical fitting. (b) Dispersion curves of the Δn (td=2  ps) in GaN:C sample with the excitation wavelengths of 350, 360, and 375 nm. The inset shows a dispersion of Δn (td=2  ps) in GaN:Mg at 365 nm. The solid line is the Drude model fitting.

Fig. 6. Maximum Δn dynamics at (a) 365 nm and (b) 350 nm in GaN:C sample with the probe wavelength of ∼580  nm. The pump fluence is 1.16  mJ/cm2. The solid lines are the theoretical fitting, and the inset shows the semi-logarithmic plot under logarithmic coordinates after 10 ps.

Fig. 7. (a) Excitation and capture processes for the transition of different charge states of CN and tri-carbon defects. (b) Transiens CN concentration simulated by the rate equation.

Fig. 8. Absorption response (a) without pump excitation and (b) with pump excitation simulated by interference model. (c) ΔmOD obtained by subtracting (a) from (b). The dashed lines represent the absorption responses without light interference.

Fig. 9. Maximum Δn dynamics at (a) 360 nm and (b) 375 nm in GaN:C sample. (c) Maximum Δn dynamics at 365 nm in GaN:Mg sample. Probe wavelength is ∼580  nm, and the pump fluence is 1.16  mJ/cm2. The solid lines are the theoretical fitting, and the inset shows the semi-logarithmic plot under logarithmic coordinates after 10 ps.