Mode hopping in single-mode microchip Nd:YAG lasers induced by optical feedback

The mode hopping phenomenon induced by optical feedback in single-mode microchip Nd:YAG lasers is presented. With optical feedback, mode hopping strongly depends on two factors: the ratio of external cavity length to intra-cavity length, and initial gains of the two hopping modes. When external cavity length equals an integral multiple of intra-cavity length, there is almost no mode hopping. However, if the external cavity length does not equal an integral multiple of intra-cavity length, mode hopping occurs. The ratio of external cavity length to intra-cavity length determines the position of two-mode hopping. The initial gains of the two hopping modes determine the corresponding peak values and oscillating periods of them in the intensity modulation curves.