Patent ID: 7460569

Claim:
A frequency conversion apparatus comprising: a first crystal set having at least one non-linear optical crystal, a second crystal set having at least one non-linear optical crystal, said first crystal set is arranged to receive a beam of coherent radiation that passes through said first crystal set, said second crystal set is arranged to receive said beam after passage through said first crystal set, and said beam passes through said second crystal set, wherein one of said first and second crystal sets is aligned for efficient harmonic generation by frequency conversion of said beam in a cold state of that crystal set wherein said cold state is a state prior to heating of a crystal set by absorbed laser energy and the other of said first and second crystal sets is aligned for efficient harmonic generation by frequency conversion of said beam in a warm steady state of said other crystal set, wherein said warm steady state is a state when a crystal set has been heated by absorbed laser energy and the heating has reached a steady state.