 So the first layer (L0) is 10nm thick, L1 is 7.5nm thick, L2 is 6nm thick, and so on.The silver alloy reflective layers that are behind each recording layer also become progressively thinner, so the L0 silver layer is 100nm thick, the L1 layer is 9nm thick, the L2 layer is 7nm thick, and so on.The separation layers that separate the recording layers from one another also progressively become thinner.