A laser beam carries energy from a source to a destination.

Let's take a nice smooth clean collimated laser beam (i.e., TEM00 mode Gaussian profile).   With a beam splitter, produce two beams.  Delay one beam by an odd-multiple of a half wavelength.  Recombine the two beams in a second beam splitter.  Due to the delayed path of one of the beams, they will destructively interfere, yielding no output beam.

Where did the energy go?  Or, asking another way, what part gets hot?

In my office we fill out a time sheet each week, which has a yellow background and must be printed out on a laser printer.  I print mine in colour, but many colleagues print the sheet in black and white so the background colour comes out light grey.  They claim this is more environmentally friendly.  But I say there's no evidence that black ink has a higher environmental cost than yellow ink, so it makes no difference.  Who is right?

I have a Laser Detector for my Rotating Building Site Level. In a room with an Energy Saving bulb, if I only turn the detector on , it ‘Beeps’, advising it has received a signal. This doesn’t happen in a room fitted with an old fashioned tungsten bulb. Does an Energy Saving bulb give off Laser Light?