A What is the difference between 1/2 wavelength and 2 overlapped wavelength? (pulsed laser autocorrelation)

Summary
So, I was working on autocorrelation for my pulse laser system and I started to wonder what is the difference between single wave with 400nm of wavelength and two 800nm waves overlapped.
In the knowledge, I know of, is that wavelength is the length between two picks.
So, I was working on autocorrelation for my pulse laser system and I started to wonder what is the difference between single wave with 400nm of wavelength and two 800nm waves overlapped.
In the knowledge, I know of, is that wavelength is the length between two picks.

And when it is pulse laser, often we use co-linear autocorrelation to obtain time width of our pulse. When I do this, how accurately I overlap two beams it shows 800nm not 400nm but in my dumb head I can't help but think this should be 400nm.

I know it is not 400nm cuz I saw it, but I just wanna know what is the main difference.
 

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mjc123

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If you overlap two 800 nm waves, exactly half a wavelength apart, you will get destructive interference and no intensity. You will not get a wave of wavelength 400 nm.
 

Andy Resnick

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Summary: So, I was working on autocorrelation for my pulse laser system and I started to wonder what is the difference between single wave with 400nm of wavelength and two 800nm waves overlapped.
In the knowledge, I know of, is that wavelength is the length between two picks.
I'm confused- why do you associate a single wavelength with a laser pulse?
 

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