I'm watching a documentary about WW2. In it fighter planes are using laser guns to shoot at each other. Why aren't they used today still?

Fighter planes are shooting what looks like pulses of high energy light at each other, and warships are equipped with the technology too. If laser weapons existed in the 1940s, why are they no longer in common use today? Is it because of the Geneva Convention?
Update: Thank you to the three people who spotted I was talking about tracer rounds. To the other eight respondents - I slightly despair for you.
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