TEMm „ modes

From the definition of the Hermitian polynomials [321], one can see that the indices m and n give the number of nodes for the amplitude A(x,y) in the x- (or the y-) direction. Figures 5.9 and 5.11 illustrate some of these transverse electromagnetic standing waves, which are called TEMm, modes. The diffraction effects do not essentially influence the transverse character of the waves. While Fig. 5.9a shows the one-dimensional amplitude distribution A(x) for some modes. Fig. 5.9b depicts the two-dimensional field amplitude A(x,y) in Cartesian coordinates and A (r, )) in polar coordinates. Modes with m = n = 0 are called fundamental modes or axial modes (often zero-order transverse modes as well), while configurations with m > 0 or n > 0 are transverse modes of higher order. The intensity distribution of the fundamental mode /qo oc /loo oo can be derived from... 

In the previous seetions we have seen that without specific manipulation a laser generally oscillates in many modes, for which the gain exceeds the total losses. In order to select a single wanted mode, one has to suppress all others by increasing their losses to such an amount that they do not reach the oscillation threshold. The suppression of higher-order transverse TEMm modes demands actions other than the selection of a single longitudinal mode out of many other TEMoo modes. 

The suppression of higher-order TEMm,n modes can be achieved by a proper choice of the resonator geometry, which has to be adapted to the cross section and the length L of the active medium (Sect. 5.4.2). 

---

See also in sourсe #XX -- [ ]

---