Nonlinear Absorption

Yandong Peng, Aihong Yang, Yan Xu +4 more

We investigate tunneling induced nonlinear absorption phenomena in a coupled quantum-dot system. Resonant tunneling causes constructive interference in the nonlinear absorption that leads to an increase of more than an order of magnitude over the maximum absorption in a coupled quantum dot system without tunneling. Resonant tunneling also leads to a narrowing of the linewidth of the absorption peak to a sublinewidth level. Analytical expressions show that the enhanced nonlinear absorption is largely due to the fifth-order nonlinear term. Competition between third- and fifth-order nonlinearities leads to an anomalous dispersion of the total susceptibility.

Avijit Lahiri

Wolfgang Demtröder

Yoshinobu Maeda, Toshikazu Yamada, Shiho Imai +1 more

The temperature dependence of the negative nonlinear absorption (NNA) effect was investigated in an erbium-doped yttrium aluminum garnet (YAG) crystal using a 787.3 nm laser diode. The NNA effect was obtained in a temperature range of 15 to 400 K. An absorption peak corresponding to both the 4 I 15/2-4 I 9/2 and 4 I 13/2-2 H 11/2 transitions of Er3+ in the YAG at 400 K was displaced from that at 300 K. It is considered that the NNA effect weakened at high temperature because the absorption cross section decreased due to the shift of the absorption peak. In addition, the dependence of the NNA effect on the modulation degree was investigated. The characteristic of the increase in the incident laser intensity was almost the same as that for the decrease. It was confirmed that the mechanism of the NNA effect can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. It is suggested that the NNA effect weakened at the low temperature because the number of phonons decreased due to the low temperature.

Li Wang, Lu Cheng

In the n-type four-level atomic system, we have studied the nonlinear theory of electromagnetically induced absorption. The results show that the probe light Rabi frequency and the attenuation distribution coefficient A affect the nonlinear absorption and then the absorption of a medium. When the probe light intensity is weak, the absorption of the medium and the linear absorption are the same, showing the characteristics of electromagnetic induction absorption. When the probe light intensity is increased, the absorption of the medium and the linear absorption are no longer the same, and now the medium absorption curve will show hole burning phenomenon, and then it will show the gain phenomenon. At the same time, the nonlinear absorption is affected by the value of A. Even if the probe light is weak, the medium absorption will change the electromagnetic induction absorption into the gain phenomenon with the A value decreasing.

O. V. Lukashina, А. Н. Ораевский, Игорь Евгеньевич Проценко