Effect of the spatial coherence of a laser field on the efficiency of two-photon absorption

Tatiana N. Smirnova, Eugene A. Tikhonov

An investigation was made of the dependence of the two-photon absorption of ruby laser radiation in alcohol solutions of rhodamine 6 G on the intensity of the exciting field in the case of single-frequency emission and emission of a large number of transverse modes. The efficiency of the two-photon absorption in the case of multimode excitation was 1.8 times (determined with a relative error of 25 % ) greater than the efficiency of the absorption as a result of single-frequency excitation. The measured absorption coefficient was close to that calculated on the assumption that the single-frequency field was spatially coherent and the spatial fluctuations of the multimode field were described by a Gaussian distribution.

Е. С. Воропай, A. M. Sarzhevskii, P. A. Torpachev

Давид Николаевич Клышко, B. V. Polkovnikov

Gordon N. Sinclair, Xiaoyi Bao, Daniel S. Elliott +1 more

Measurements of two-photon absorption spectra have been made for the case where the exciting laser has a random-telegraph phase. The resulting spectral shapes are compared to theoretical predictions and to previous data taken with a phase-diffusing laser field [Elliott et al., Phys. Rev. A 32, 887 (1985)]. A striking dependence of the absorption spectrum on the second-order coherence of the field was observed. Using the theory for the propagation of second-order spatial coherence, we draw an analogy between diffraction and two-photon absorption which we use to interpret the two-photon absorption spectra.

Fuminori Shiga, Shunji Imamura

Wenjing Cheng, Pei Liu, Guo Liang +4 more

It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light–matter interaction. Previous studies mainly focused on the multi-photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi-photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second-order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect (e.g., four-photon absorption) can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four-photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.