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Name: Ilian T.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: Saturday, April 20, 2002

What will happen when one splits a laser beam in two parts of equal(not NECESSARILY) amplitude and then collect them again in the a same direction with a lambda/2 path shift? The beams should extinguish each other - negative interference? Now: What about Energy conservation law? If light returns back in the laser what is the path where it goes and why? If it has a positive interference direction where is it and is the balance for the energy OK.

Good question! It turns out that it is always impossible to make the two light beams overlap completely in a region where they are lambda/2 out of phase. There are other regions where they are in phase and this, of course, always works in such a way that energy is conserved.

Consider, for example, two slit diffraction patters. On the screen There are dark and light bands corresponding to negative and positive interference.

Light reflected back into a laser will interfere with the light in the laser producing positive and negative interference patters. Once again, you can rest assured that energy is conserved.

Best, Dick Plano

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