I have seen expansions of many English words such as POLICE, MUSIC, GOD, LASER, where each letter supposedly stands for another word, as in an acronym. Are these expansions in any way real, that is, written in a standard dictionary, or are they just made up?
Police is not an acronym or abbreviation, normally. You could make a backronym for it if you wanted.
People Ostensibly Licensed In Crime Eradication
In general, any word older than the 1950s is pretty much guaranteed not to be derived from an acronym. There are exceptions, but if someone tells you a word is really an acronym, just disbelieve until you've checked a reputable reference.
The word laser was originally an acronym, which stood for:
Light Amplification by Stimulated Emission of Radiation - LASER
According to the Oxford on-line dictionary entry for laser, this originated in the 1960s.
However, through common usage, the word laser has been adopted in its own right and is defined as:
a device that generates an intense beam of coherent monochromatic light (or other electromagnetic radiation) by stimulated emission of photons from excited atoms or molecules. Lasers are used in drilling and cutting , alignment and guidance, and in surgery; the optical properties are exploited in holography, reading barcodes, and in recording and playing compact discs.
There are other examples of acronyms that have been adopted into the English language as words in their own right:
RADAR - RAdio Detection And Ranging - defined as:
a system for detecting the presence, direction, distance, and speed of aircraft, ships, and other objects, by sending out pulses of radio waves which are reflected off the object back to the source.
SCUBA - Self-Contained Underwater Breathing Apparatus - defined as:
Some other examples:
Maser: "Microwave Amplification..."
Jeep: "general purpose"