Beam radius waist

Open-aperture z-scan experiments with 7 and 20 p,m beam radii are given in Fig. 25. The sample 2 in Fig. 24a with 68% transmittance with 7 p,m beam waist radius shows very low NL absorption. The sample has no NL absorption, while the transmittance is 82%. On the other hand, open-aperture z-scan experiments with 20 Jim beam waist radius have high NL absorption for both transmittances, Fig. 25. 

Any thermal effect due to heat accumulation was not observed in these experiments. The NL absorption coefficients obtained from 7 xm beam waist radius were... 

It is common to call tvp the beam-waist radius. In the literature one often finds the phrase at the beam waist, which refers to that value of z for which the function u has its minimum radial extent. For u defined by (8), this occurs at z = 0. The distance Zp is called the confocal distance. When z < Zp we say that the Gaussian beam is in the near field. When z > Zp, the Gaussian beam is in the far field. The majority of this chapter is concerned with the behavior of u in the range 0 < z < Zp, the near-field region. The phase and amplitude of m is a complicated function of position in the near field. When z Zp and p z or when we are in the far field and the paraxial approximation is valid, it is straightforward to show that the asymptotic behavior of u approaches a diverging spherical wave from a point source at z = 0. 

Fig. 5. FIR-ESR semiconfocal resonator showing horn coupling. The beam-waist radius in the resonator is 2.2 mm. [From Lynch et al. (1988), by permission of the AIP.]...

A given mesh reflectivity imposes a lower bound for the beam-waist radius, below which appreciable coupling losses can occur. The basic problem is that a Gaussian beam will continue to diverge upon repeated reflection within a planar interferometer as shown in Fig. 12b. If the spherical mirror of the cavity is designed to match the original (input) beam waist, beam divergence will cause a mismatch at the output, which... 

From (5.150) we obtain the beam waist radius W2 in the collimated region... 

Fig. 3.10. Variation of the normalized differential scattering cross-sections with the beam waist radius...

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