Single mode range of operation

In Section 14-10, we introduced the concept of profile volume. We showed in the case of clad power-law profiles of equal volume that some properties, such as the range of single-mode operation and the fundamental-mode intensity distribution are insensitive to profile shape, whereas other properties, such as waveguide dispersion, depend critically on profile shape. Within the Gaussian approximation, we can demonstrate directly the insensitivity of the intensity distribution to profile shape. 

The higher-order mode approximation of Section 15-6 is inadequate for determining the range of single-mode operation of arbitrary clad-profile fibers. At cutoff of the 1 = ffi = 1 modes, the clad fiber fields satisfy Eq. (11-54) when n(R) = n, and thus have an R radial dependence in cyhndrical polar coordinates. The corresponding dependence of Eq. (15-17) is always exponential and is thus a poor approximation. To overcome this deficiency, we use the estimate for in Table 15-2 based on equal profile volumes. However, a much... 

If we use Eq. (15-27) to determine the range of single-mode operation for the Gaussian profile of Eq. (15-6), we find that 2.62. This differs from the exact value in Table 15-2 by only 1.2% [4,7]. 

The light source is a home made CM ring LD 700 dyo laser, pumped by a Kr+ laser. In the range 730-780 nm (wavelength of the two-photon 2S-nD transitions for n 8 it provides a power of about 1W on single mode operation. The frequency stabilization is made by locking the laser to an external auxiliary Fabry-Perot cavity indicated FPA in Fig.2 the resulting... 

In the argon-ion laser the width of the gain profile is about 8 GHz. With a free spectral range of Av = c/(2nr) = 10 GHz of the intracavity etalon, single-mode operation can be achieved. This implies with n = 1.5 a thickness t = 1 cm. 

For high-resolution spectroscopy the bandwidth of the dye laser should be as small as possible. With two etalons having different free spectral ranges, single-mode operation of the Hansch-type laser (Fig. 5.83) can be achieved. For continuous tuning both etalons and the optical length of the laser resonator must be tuned synchronously. This can be realized with computer control (Sect. 5.4.5)... 

With such a system single-mode operation without etalons has been achieved. The wave number could be tuned over a range of 100 cm without mode hops. 

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