Hi Everyone This is a question which, in various forms has been asked in various places on the Internet but I have never seen a satisfactory answer. I have therefore decided to try and ask it in a unique way which will start off conventionally to begin with. If I have two side-by-side lasers of identical wavelength and amplitude completely overlapping at a far-away target with a half-wavelength phase difference, thus causing the target to be dark, where does the energy go? The following are intensity diagrams which show Lasers A and B, initially in phase and not overlapping and then being moved so that they overlap. These are ASCII diagrams using the Courier (fixed-width) font which hopefully will display correctly on your computer. Please ignore the underscores. I am using them because spaces at the beginning of a line are ignored. The height of the blocks represents intensity. In phase: 1. No overlap: AAA BBB AAA BBB 2. 1/3 overlap: __B __B AAABB AAABB 3. 2/3 overlap: _BB _BB AAAB AAAB 4. Total overlap: BBB BBB AAA AAA Now 1/2 a wavelength out of phase: 1. No overlap: AAA BBB AAA BBB 2. 1/3 overlap: AA BB AA BB AA BB 3. 2/3 overlap: A B A B A B A B A B A B 4. Total overlap: ? Can anyone complete the sequence? Is it the same as when the lasers are in phase? Is 1 to 3 correct? Thank you very much.