I have a problem with which I would appreciate any help that is offered: I have a 266nm laser (frequency quadrupled 1064nm Nd:YAG), and the energy losses along the route are a little strange. The beam is reflected by two UV mirrors; however, the first mirror loses ~7% of the in-going energy, but the second loses ~12% of the in-going energy. I have swapped the mirrors, and the effect remains. The beam that is emmitted by the laser contains some 1064nm and 532nm fractions, and I feel that the losses of these frequencies (they should be minimally reflected by the UV mirrors) at the first mirror must relate to the problem, but I cannot figure out why. Can anybody understand this effect?