Research On Several Key Technologies In Sodium Guide Star Fiber Laser System

Image distortion caused by atmosphere turbulence can be solved by laser guidestar technology, which has a variety of applications in military and astronomy.Fiber-based Sodium laser guide star is promising candidate technology due to itscompact volume and excellent beam quality. With the development of single frequencyRaman fiber amplifier, the output power of Sodium guide star laser has been improveddramatically. However, further improvement of the output power is restricted by thehigh power1120nm pump source.Except that, research on different single frequencyfiber laser at1178nm, such as Yb-doped photonic bandgap fiber, is necessary toSodium guide star laser. The thesis investigates these key technologies of fiber guidestar laser theoretically and experimentally, whose primary contents are present asfollows:1. By reviewing the history of Sodium guide star laser, we point out thatfiber-based Sodium laser is one improtant candidate to guide star laser system.Due tothe significance of Yb-doped fiber to Sodium guide star laser, this paper mainlyresearchs on Yb-doped fiber laser at1120nm and fiber amplifier at1178nm.2. With polarization maintaining (PM) Yb-doped fiber, a100W fiber laser at1120nm is achieved. Firstly, employing FBGs polarization selection technology, linearlypolarized fiber laser at1064nm and1120nm are abtained. Secondly, the output powerof linearly polarized1120nm fiber laser is developed to100W, the operation mode canbe modulated to micro second pulses, and the experimental phonomenons areexplaining theoretically. Lastly, the applications of1120nm fiber laser to single ramanaplifiber at1178nm and1070nm fiber laser pumped cladding Raman fiber laser.Singlefrequency1178nm fiber laser of44W is achieved experimentally, and claddingpumped Raman fiber laser at1120nm can be calculated to10kW thoeretically.3. Employing actively Q-switched technology,all-fiber single mode laser at1120nm is demonstrated. At repetition rate of1kHz, output power of111mW at1120nm isobtained with a pulse width of140ns and peak power of0.8kW. Correspondingly, atrepetition rate of10kHz, the output power is285mW with a pulse width of180ns andpeak power of120W. The threshold of parasitic oscillation tandem pumped by1018nmfiber laser is4times higher than that pumped by976nm diode laser.4. Single frequency Yb-doped photonic bandgap fiber amplifier at1178nm isdemonstrated. Rate equation model including ASE, stimulated Brillouin scattering (SBS)and bandgap loss was employed to research the effects of seed power and fiber lengthon fiber amplifier at1178nm. Output power of10.3W was obtained at pump power of80W with injected seed of3W and20m fiber. Correspondingly,13.6W output powerwas obtained with injected seed of8.5W and6m fiber.