Dual-wavelength Nd:YAG Microchip Laser

The compact dual-wavelength solid-state lasers with high-power output,have been widely used in the fields of light radar,terahertz wave,laser surgery and so on.And development of compact dual-wavelength solid-sate lasers is a hot spot in laser fields.Although various methods have been used for developing dual-wavelength solid-state lasers,dual-wavelength microchip laser has been demonstrated based on the energy level splitting of activated ions in laser gain medium in the thesis.The Nd:YAG crystal with long fluorescence lifetime,large emission cross section and excellent thermal properties has been used as a gain medium.In this thesis,simultaneous dual-wavelength laser oscillation at 1061 and 1064 nn has been demonstrated in a fiber-coupled 885 nm laser diode directly pumped Nd:YAG microchip laser.The 1061 and 1064 nm dual-wavelength laser with frequency difference of 0.7 THz is a suitable laser source for generating THz with frequency differential method,which expands the applications Nd:YAG lasers.In this paper,the coupled rate equations have used to theoretically analyzing the threshold pump powers for 1061 and 1064 nm dual-wavelength NdrYAG microchip laser.The effects of the transmission of output coupler(Toc)and the length of NdrYAG crystal on the performance of dual-wavelength Nd:YAG microchip laser have investigated theoretically.The theoretical results show that when Toc<16%,the threshold pump power for 1064 um laser oscillation is higher than that for 1061 nm laser oscillation,which makes Nd:YAG microchip laser possible to achieve dual wavelength operation at 1064 and 1061 nm.When the length of Nd:YAG crystal is in the range of 0.25-2.5 mm,the threshold pump power at 1061 nm is lower than that at 1064 nm.And the difference between threshold pump power for 1061 and 1064 nm is large when the length of the Nd:YAG crystal is within the range from 0.5 to 1.25 mm,which makes the dual-wavelength laser oscillation easily achievable.Dual-wavelength laser at 1061 and 1064 nm has been demonstrated experimentally in a Nd:YAG microchip laser directly pumped with a fiber-coupled 885 laser diode.And comparable laser output has been obtained at different incident pLump powers.The effects of the transmission of the output coupler and the length of Nd:YAG crystal on the dual-wavelength laser performance of Nd:YAG microchip laser have been investigated systematically.Dual-wavelength laser oscillation is cdemonstrated when the Toe is 2 and 10%,while only 1064 nm laser is obtained when Toe is 20%.which is in good agreement with theoretica:l prediction.The ideal laser with comparable laser output power at 1061 and 1064 nm has been achieved with 1-rmm thick Nd:YAG crystal as gain medium,and optical efficiency is 9%.Two distinct methods are used to optimize the performance of dual-wavelength Nd:YAG microchip laser.One is to change the angle between the gain medium and the output coupler by tilting the output coupler.The performance of dual-wavelength Nd:YAG microchip laser is improved by increasing the tilting angle between Nd:YAG crystal and output coupler.The best performance of Nd:YAG microchip laser has been achieved at an inclination angle of 0.15 mracd,and the laser intensity at 1061 nm is significantly improved.And the overall optical-to-optical efficiency is improved to 10%.The laser intensity of the dual-wavelength laser at 1061 and 1064 nm is comparable with a ratio of 1:1.The second method is to change the cavity length of Nd:YAG microchip laser.Single microchip laser cavity with different cavity lengths and coupled laser cavity are formed for investigating laser performance of dual-wavelength Nd:YAG microchip laser.-The coupled microchip laser by controlling the gain and loss.The performance of the dual-wavelength Nd:YAG microchip laser is enhanced by adjusting the reflectivity of the output coupler and the cavity length to balance the gain between 1061 and 1064 nm.This work provides a simple and effective method to develop highly efficiency dual-wavelength microchip solid-state lasers.