Investigation Of 880nmLD Pumped High Power CW Single-Frequency Nd: YVO₄ Laser

Laser technology has been widely used in science, industry, national defense and other aspects of the national economy and LD end-pumped solid state lasers with a compact configuration, long life and good beam quality have been widespread concerned. In the field of coherent information processing, quantum optics, atomic trapping, gravitational wave measurement the lasers must have the good characteristic of frequency and the stability of output power so the single-frequency lasers play an important role in these scientific researches. With the progress of scientific research the single-frequency laser with a higher output power has been required and the high power single-frequency of 1064 nm laser is the most demanded. The thermal effect of laser crystal directly affects the stability of laser performance and the beam quality which is particularly serious in high-power laser so reducing the thermal effect of laser crystal is the most important technical problem in the development of high power single-frequency solid-state lasers.Our laboratory has used a variety of measures to reduce the laser's thermal effects, including the use of refrigeration system, the use of composite crystal, double-end pump and other methods. Based on the work of the past the purpose of this work is to diminish the heat generation by reducing the quantum defect in four-level lasers under pumping into the emitting level and to develop a 1064nm continuous single-frequency high power laser with good operation characteristics to provide a pump source of superior performance for quantum optics experiments.In this paper, first, the history of LD end-pumped solid state lasers and LD directly end-pumped technology is introduced briefly. Secondly, physical properties, optical properties and laser properties under the directly pumped of the Nd:YVO4 crystal is summarized and then analysis the thermal effect of laser crystals and how to reduce it. Then, based on the four-level laser system of space rate equation, the relation of the threshold power and the input-output power are obtained theoretically and the mode-matching affected by the thermal effect is explained.In our experiment in order to improve the absorption efficiency of the crystal, we use the polarization double-end-pumped and a long laser crystal, by adjusting the temperature of LD pump source so that the output wavelength of the pump source falls exactly on the peak absorption of laser crystal; and using the double-end-pumped and a long laser crystal make pump energy absorb uniform, which can reduce the thermal effect of the laser crystal. According to the theory of mode matching between laser beam and pump beam and the laser stability condition, considering the thermal lens effect, an appropriate cavity length is designed through theoretical and experimental research. The single-frequency laser is achieved by placing the optical isolator in a ring cavity and the optical isolator is formed by theλ/2 wave plate, TGG crystal and magnet. A 1064nm high power CW single-frequency laser is gotten when the pump power injected into the crystal is 50W and the laser output power is more than 20W with an optical-optical conversion efficiency of 40% and the long-time power fluctuation with four hours is less than±1.1%.At the same time the observed laser frequency drift is 43.3MHZ within 30s and the beam quality M2<1.1. The last part is the summary and prospects.