In a laser resonator with an intra-cavity spiral phase plate, a passive Q-switched pulsed vortex laser carrying a positive unit topological charge is formed by the coherent superposition of the supported off-axis multiple-pass transverse (MPT) resonant modes. Under different pumping conditions, the modal interaction induces spatiotemporal instability and results in periodic and aperiodic oscillations in the vortex laser pulses while the vortex structure remains stable. The constituting off-axis MPT modes that form the vortex strongly overlap in the time domain and can be simulated by a modified Tang–Statz–DeMars model including coherent modal interactions. Expected potential applications using this vortex laser include the manipulation of laser chaos and stochastic events.
We propose to generate optical vortices using a degenerate optical resonator with an intra-cavity spiral phase plate (SPP). The rays retracing skewed V-shaped paths in the resonator are phaselocked to form vortex laser with wavefront dislocation mirroring the topological charge of the SPP. Experimental demonstrations on diode-pumped solid state system using Nd:YAG crystal emitted randomly polarized optical vortices at a wavelength of 1064nm when the pump power went above 1.52W and the slope efficiency was 0.19. For long-term operations a power fluctuation of 2.2% and pointing stability of 2.6µrads was measured. This system also serves an useful platform to study the laser dynamics and to combine radiations coherently.
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