Performance Of The Dual-vortex Passively Q-switched Microchip Laser

Optical vortex array is a well-arranged network of optical vortices that has been widely used in many applications such as enlarging the capacity of optical communication,manipulating multi-particles,measuring small-angle rotations and so on.The dual-vortex beam is one kind of optical vortex array which possesses the simplest structure with only two vortices and can be easily obtained in a variety of ways due to its simple light field.With the adjustable orientation and separation between the two vortices,dual-vortex beam offers more flexibility for dramatically increasing the storage capacity of the optical information.And dual-vortex beam provides more flexibility for manipulating particles and information processing.The traditional methods for generating dual-vortex beam are superposition of some specific transverse modes or utilizing the spatial light modulator.However,it is difficult to control the orientation and separation of the two vortices in the dual-vortex beam,which restricts applications of dual-vortex beam.Therefore,it is urgent to develop compact highly efficient and high peak power passively Q-switched microchip laser for directly generating the dual-vortex lasers with controllable orientation and separation between the two vortices.In this paper,a hollow focus lens has been used to shape the pump beam into a annular beam,and a thermal-bonded Nd:YAG/Cr4+:YAG composite crystal was used to construct the microchip laser cavity.When the annular pump beam was normally incident on the composite crystal,a vector vortex laser was obtained in the Nd:YAG/Cr4+:YAG composite crystal passively Q-switched microchip laser(PQSML).Maximum average output power of over 1 W is obtained at the incident pump power of 6.14 W,and the corresponding optical efficiency is 16.3%.The optical efficiency of the Nd:YAG/Cr4+:YAG composite crystal PQSML is 50%higher than that achieved in continuous-wave Nd:YAG vortex microchip laser.The pulse width of 3.4 ns and the highest peak power of 5.4 kW was obtained when the incident power was 4.75 W.The obtained peak power is about 31 times of that obtained in the Cr,Nd:YAG self-Q-switched microchip vortex laser.The helicity and the topology charge of the vortex laser keep unchanged with the increase of the pump power.The tilted annular pump beam was formed by offsetting the collimating lens away from the optical axis of the laser diode.The dual-vortex laser with controllable orientation and separation between the two vortices has been demonstrated in the PQSML pumped with the tilted annular pump beam for the first time.The performance of the dual-vortex Nd:YAG/Cr4+:YAG composite crystal PQSML is comparable to LGo,1-doughnut vortex laser.The optical efficiency was 15.5%,and the peak power of over 5 kW was obtained for the dual-vortex laser.The orientation and separation of the two vortices in the dual-vortex laser can be easily controlled by adjusting the offset of collimating lens.This work paves a new road for developing dual-vortex laser for various potential applications such as micro-particle manipulation,quantum computation,and optical communication.