'Contact glass for use with high power lasers--geometrical and optical aspects', by P. Roussel and F. Fankhauser (1).

Roussel and Fankhauser have proposed contact glasses with a collecting front surface centred on the bundle focus for use with high power lasers. We demonstrate here that the main contribution to the gain in energy density within the focus spot must be attributed to the front surface of the glass. This is at variance with the explanation given by Roussel and Fankhauser, namely that the energy gain is due to the difference in refractive index between the glass and the aqueous humour.