Quantum noise properties of small gas lasers

If a laser is made sufficiently small, its (unavoidable) technical noise can be overwhelmed by the quantum noise, i.e. the spontaneous emission. We discuss the conditions which are required for this situation to occur, specializing to the case of a small gas laser. Experimental examples taken from recent work are used to illustrate the quantum regime of phase noise and polarization noise. Using scaling arguments we compare these quantum-noise effects in small gas lasers with those in semiconductor lasers.