The FB coefficients of can easily be numerically computed. The resulting profile of the thermal
lens is shown for a particular case in Figure 28
.
The power in the compensation lens must be adjusted in order to get zero curvature when added to the
heat source coming from the readout beam. For small readout-beam dissipation (less than a few mW), this
minimizes the matching losses. An example is given in Figure 29 in which one tries to compensate for the
thermal lens caused by an
mode of width w = 2 cm dissipating either 10, 20 or 30 mW on the
coating. One sees that, by increasing the compensation power, it is possible to reduce the coupling losses
from their initial (uncompensated) values by a factor of about 15 (see Table 10). However, it can be seen
that the residual loss is proportional to the dissipated power, which means that, in the case of cavities
storing about 1 MW, even with thermalization rates on the order of 1 ppm, the system is useless. For
100 mW dissipated, one can see that the TCS is able to reduce the initial losses of almost
3.5% to about 0.24 %, which is still much too high, and at the price of 26.5 W TCS power
dissipated.
dissipated power | initial losses | compensation power | minimal losses | wavefront curvature |
10 mW | 350 ppm | 2.7 W | 24 ppm | ![]() |
20 mW | 1,400 ppm | 5.3 W | 96 ppm | ![]() |
30 mW | 3,100 ppm | 8.0 W | 220 ppm | ![]() |
100 mW | 34,300 ppm | 26.5 W | 2392 ppm | ![]() |
In the latter case, we see in Figure 30 that even if the mean curvature radius is infinite, it does
not mean that the lens is exactly flat, so that, even if the focusing effect is suppressed, some
losses are to be expected due to departure of the lens from a plane (or from a sphere having
a large radius). Only six Zernike polynomials are required to retrieve this special TCS lens:
It is probably possible to enhance these results up to a certain extent by tuning the parameters and
, but not to seriously change the orders of magnitude. However, results are better with higher-order
modes (see Table 11).
dissipated power | initial losses | compensation power | minimal losses | wavefront curvature |
10 mW | 56 ppm | 50 mW | 6 ppm | ![]() |
20 mW | 213 ppm | 100 mW | 11 ppm | ![]() |
30 mW | 474 ppm | 130 mW | 15 ppm | ![]() |
100 mW | 5,218 ppm | 450 mW | 122 ppm | ![]() |
http://www.livingreviews.org/lrr-2009-5 | ![]() This work is licensed under a Creative Commons License. Problems/comments to |