tailieunhanh - Tunable lasers handbook phần 6

độ phóng đại quang học phải được tối ưu hóa tương đối so với kích thước chùm tia của dao động tổng thể để hoàn toàn điền vào các khối lượng hoạt động của các dao động bắt buộc. Cũng có. chùm tiêm nên được liên kết chính xác cho đồng tâm tuyên truyền dọc theo trục quang học của dao động bắt buộc. | 6 Transition Metal Solid-State Lasers 235 y - r jr2I y2_1 0. j 21 2 5 z7 r K2 9 j - K_3 e ộ j 21 - . 6 Electron orbits described by these linear combinations of functions are graphed in Fig. 6. As can be seen the 3 7F orbits are maximized along the .V y. and -axes that is the orbits are directed toward the positions of the nearest neighbors. On the other hand the 3d orbits are maximized at angles directed between the nearest neighbors. Because the nearest neighbors usually have a net negative charge it is logical that the orbits directed toward the nearest neighbors would have a higher energy. In essence the electrons are being forced to go where they are being repulsed. A calculation of the energies of the molecular bonding orbits must include the effects of the mutual repulsion. Mutual repulsion energy contributions can be expressed in terms of the Racah parameters A B and c. Racah parameters in turn are expressed in terms of Slater integrals however it is beyond the scope of this chapter to delve into the details. Suffice it to say that the A term is an additive term on all of the diagonal elements. When only energy differences are to be calculated this term drops out. The B and c energy terms occur on many off-diagonal elements. However Tanabe and Sugano observed that the ratio of C B is nearly constant and in the range of 4 to 5. A slight increase of this ratio is noted as the nuclear charge increases while the number of electrons remains constant. A ratio of QB of was expected based on Slater integral formalism. Thus the mutual repulsion contribution to the energy levels can be approximated if only a single parameter is known. Usually this parameter is the Racah parameter B. Hence many of the Tanabe-Sugano calculations are normalized by this parameter. Crystal field contributions to the energy of the molecular orbits can be described by the parameter Dq. Remember that lODr is the energy difference between the 3dr and the 3d levels for a single 3d .