Two-photon lasers

Daniel J. Gauthier, Hope M. Concannon

William J. Brown

This thesis describes the development of a novel quantum oscillator known as a two-photon Raman laser. It is based on two-photon stimulated emission in strongly driven potassium atoms. Two-photon lasers were Þrst proposed in the 1960s, but only recently have such devices been experimentally realized. The two-photon Raman laser is an important step forward as it provides the Þrst oppurtunity to study the turn-on behavior, instabilities, and noise properties of a pure two-photon optical device. The necessary ingredients for a two-photon laser are a medium displaying two-photon laser beam ampliÞcation and an optical resonator. In my two-photon Raman laser the ampliÞcation arises from a multi-photon process in which state-prepared potassium atoms undergo two-photon Raman transitions. This ampliÞcation process was studied using a high-density, small-Doppler-width potassium atomic beam that was driven by a strong pump laser and probed by a weak probe laser. I observed two-photon Raman ampliÞcation for a range of pump laser frequencies, atomic beam

S. Swain

We consider the theory of the two-photon laser using the Scully–Lamb theory developed for ordinary single-photon lasers, concentrating on the calculation of the linewidths and the cross-correlation coefficient. In a previous publication we have shown that the quantum-mechanical noise in the modes of a two-mode laser may be highly correlated. Here we show that the same situation appertains to the two-photon laser, that is the two modes are strongly positively cross-correlated when the laser is operating well above threshold. The two-photon laser has the advantage of tunability over the two-mode or quantum-beat laser. The point of using modes whose noise properties are strongly correlated is that in an appropriate two-photon experiment the noises may effectively ‘cancel out’ leaving a very low noise signal. We present a brief development of the two-photon laser theory and show the connection between our work and that of other approaches.

B. Nikolaus, D. Z. Zhang, P. E. Toschek

Shi-Yao Zhu, Xiao-shen Li

A quantum theory of a two-photon laser in a three-level atomic system of the cascade type is presented starting from an original microscopic Hamiltonian. The master equation of the laser operation is derived by using the method of Scully and Lamb [Phys. Rev. A 159, 208 (1967)] for a single-mode laser containing a two-level medium. The photon-number distribution of the laser is studied in detail. The curve of the distribution may have a two-peak structure. One of the peaks located at the origin comes from the single-photon process and reflects the thermal property of the laser, while another comes from the two-photon process and reflects the coherent property of the laser. We cannot find an exact criterion for the threshold of the two-photon laser. The two-photon laser can approximately be considered as a coherent state for certain values of A/C, which can even be much smaller than the threshold for the nonresonant single-mode laser in a two-level system, but it is much larger than the threshold for the resonant one.

G. Grynberg, E. Giacobino, F. Biraben