When a laser beam passes through a gas, it generates ultraviolet light. But this light is very weak: out of a thousand laser photons, only one becomes ultraviolet. Scientists long wondered why so few, until they took a closer look at the edges of the gas cloud. It turned out that at the boundary, where the gas density smoothly changes from zero to maximum, many photons are lost. The smoother this transition, the greater the losses.
Now it is clear what to do: make the gas boundary as sharp as possible. To do this, the holes in the cell can be drilled with a laser in a thin foil, so that the transition zone shrinks from 1.5 mm to 0.1 mm, and the efficiency increases almost 10 times. This can already be applied in existing setups to make ultraviolet sources brighter and more useful for microscopy and chip manufacturing.
The transition length of the gradient was determined by analogy with the rise time of a signal in electronics: between the 10% and 90% levels.