4.3 Axicon systems

Some systems use CO2 laser beams focused by a conical lens. This configuration, called “axicon”, generates a ring-shaped intensity profile on the mirror. We do not attempt to compute an analytical model of the compensation power flow. We use numerical intensity measurements carried out by the Virgo/Rome team [15]. The FB coefficients of the optical power flow are computed numerically. The profile of the corresponding thermal lens can be seen in Figure 31View Image.
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Figure 31: Thermal lens profile created by an axicon system
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Figure 32: Thermal compensation with an axicon: minimization of coupling losses. Solid line, short dashed, long dashed: resp. 10 mW, 20 mW, 30 mW, dissipated by the readout beam.

Table 12: Thermal compensation with an axicon system
dissipated power initial losses compensation power minimal losses wavefront curvature
10 mW 350 ppm 1.2 W 5 ppm ∞
20 mW 1,400 ppm 2.4 W 19 ppm ∞
30 mW 3,100 ppm 3.6 W 43 ppm ∞
100 mW 34,300 ppm 12 W 481 ppm ∞

We can see (Table 12) that the performance of the axicon system is better than that of the heating ring (lower compensating powers, lower optimal losses), but not by orders of magnitude.

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