MEASUREMENT OF THE SPONTANEOUS EMISSION FACTOR OF A 3.39-MU-M HENE LASER

The spontaneous emission factor N(sp) = N2/(N2 - N1) of a 3.39 mum HeNe laser is determined from spontaneous emission light radiated from the side of the gain tube. N(sp) is shown to depend linearly on the intra-cavity optical intensity. This linear power dependence of N(sp) will give rise to a power-independent contribution to the quantum-limited spectral linewidth of the laser. We predict that at an output power of 190 muW this contribution will already make up half of the fundamental laser linewidth.