Measurement of the free spectral range of the laser cavity based on multi-longitudinal mode laser self-mixing vibrator

A method by tracing the multi-longitudinal mode laser self-mixing vibrator waveform with adjusting of the external cavity length based on the laser self-mixing effect is proposed to measure the free spectral range of the laser cavity. According to the variation period of the external cavity, the free spectral range of the He-Ne laser cavity is calculated to be 0.633 GHz with the resolution of 2.67 MHz. Simultaneously, we further investigate the relationship between the waveform separation degree and the phase delay of two adjacent peaks caused by the superimposed self-mixing vibration signal waveforms of different modes. The experimental results have been demonstrated that this strategy is appropriate for the measurement of the free spectral range of the laser cavity duo to the significant merits of general complexity and cost, and non-contact measurement. (C) 2018 Elsevier Ltd. All rights reserved.