Role of intraband transitions in photocarrier generation

We theoretically investigate the role of intraband transitions in laser-induced carrier generation for different photon energy regimes: (i) strongly off resonant, (ii) multiphoton resonant, and (iii) resonant conditions. Based on the analysis for the strongly off resonant and multiphoton resonant cases, we find that intraband transitions strongly enhance photocarrier generation in both multiphoton absorption and tunneling excitation regimes, and thus, they are indispensable for describing the nonlinear photocarrier generation processes. Furthermore, we find that intraband transitions enhance photocarrier generation even in the resonant condition, opening additional multiphoton excitation channels once the laser irradiation becomes sufficiently strong. The above findings suggest a potential for efficient control of photocarrier generation via multicolor laser pulses through optimization of the contributions from intraband transitions.

Figure 1

Laser-induced electronic excitation energy in $\alpha$-quartz after the laser irradiation. The dots represent the results of the TDDFT calculation (red dots and solid line), the parabolic two-band model (green dots and solid line), and the nonparabolic two-band model (blue dots and dashed line).

Figure 2

Schematic picture of intraband transitions (red) and interband transitions (blue) in the parabolic two-band model.

Figure 3

Number of excited electron-hole pairs after the laser irradiation in the strongly off resonant regime, computed using Eq. (16). The dots represent the result of the full model (red dots and solid line), and the pure interband model (blue dots and dashed line). A polynomial fitting by $a{E}_0^2+b{E}_0^{14}$ is also shown as a green short-dashed line.

Figure 4

Distribution of photoinduced electron-hole pairs in the strongly off resonant condition $\left(\hslash \omega =1.55\mathrm{eV}\right)$ with the field strength of $2.74\times {10}^{10}$ V/m. The results of the full model (red solid line) and the pure interband model (blue dashed line) are shown.

Figure 5

Number of excited electron-hole pairs after the laser irradiation in the three-photon resonant regime. The dots represent the result of the full model (red dots and solid line) and the pure interband model (blue dots and dashed line). A polynomial fitting by $a{E}_0^6$ is also shown as a green short-dashed line.

Figure 6

Distribution of photoinduced electron-hole pairs in the three-photon resonant condition with a field strength of $0.274\times {10}^{10}$ V/m. The results of the full model (red solid line) and the pure interband model (blue dashed line) are shown.

Figure 7

Number of excited electron-hole pairs after the laser irradiation in the resonant regime. The dots represent the result of the full model (red dots and solid line), and the pure interband model (blue dots and dashed line). The square of the field strength, $E_0^2$, is also shown as the green short-dashed line.

Figure 8

Distribution of photoinduced electron-hole pairs in the resonant condition. (a) The result of the full model and (b) that of the pure interband model.