Patent ID: 7035298

Claim:
Apparatus for the nonlinear frequency conversion of optical radiation, the apparatus comprising: a) an optically nonlinear medium that receives at least one input beam wherein each of said at least one beam makes N passes through the nonlinear medium, wherein each pass is spatially separate from all preceding passes, where N is an integer≧2, to thereby generate at least one additional beam wherein the sum of the input and additional beams is M, wherein ∑ i = 1 M ⁢ S mi ⁢ ω i = 0 for each nonlinear frequency conversion process m, wherein i denotes a particular beam of the M beams, ω i denotes the frequency of a beam i, wherein S mi is +1, 0 or −1; and b) a telescope subassembly having an ABCD matrix with matrix coefficients substantially A=−1, B has any real value, substantially C=0 and substantially D=−1, for receiving and coupling the input and additional beams emitted from the nonlinear medium after a pass number J, back into the medium for a pass number J+1, where 1≦J<N, and wherein the additional beam issues from the nonlinear medium after pass number J+1.