Q-switched Pulse Laser Technology With Carbon Nanotubes Saturable Absorber

With the rapid development of science and technology, scientific research andindustrial productions require laser have higher pulse energy, and more narrow pulsewidth, which improved the laser Q-switched technique. Q-switched laser has beenwidely used in remote sensing, medical, laser radar, laser precision measurement etc.As a saturable absorber, the absorption intensity can be controlled by the membranethickness. The absorption peak position and absorption bandwidth can be controlledby the diameter and the diameter distribution of the carbon nanotubes. In addition,compared with the semiconductor saturable absorber, carbon nanotube saturableabsorber is more easy manufacture and low cost. As it has such excellent properties,scientists have carried out extensive research on its. In this paper, the main contentsare as follows:(1) Made a detailed analysis on the Q-switched laser theory，and discussed theinfluence of the quality factor Q on a Q-switched laser. Achieved the parameters ofthe pump rate, Q value and gain material for Q-switched lasers. By solving the rateequations, the peak power(Pm)，cavity photon number(Ф),output energy(E) and pulsewidth of the Q-switched laser have been obtained.(2) The properties of Nd:YCOB crystal is discussed, and a passively Q-switchedNd:YCOB laser with a single-walled carbon nanotube saturable absorber is beendemonstrated. The transmission-type SWCNT–SA is used in a V-type cavity. Wemeasured the spectrum diagram at different pump powers to test the system stability.The effects of the output power, the pulse width and pulse repetition frequency on thepump power were obtained.(3) The properties of Yb3+doped fiber is discussed, and a Yb3+doped fiber laserwith a single-walled carbon nanotube saturable absorber is been reached. In theexperiment, we achieve the output wavelength at both1033.44nm and1040.39nm inthe Q-switched laser. The effects of the output power, the pulse width and pulserepetition frequency on the pump power were obtained.(4) The characteristics of the wavelength selection of a photonic crystal fiber isdiscussed. By using it, we could get a single wavelength laser in the Yb3+doped fiberQ-switched laser. According to the Maxell’s equations of electromagnetic wave，theband gap is simulated which based on the plane waves expansion method(PWM).The capability of light guiding is simulated by beam propagation method(BPM). Theeffects of the air hole diameter, air hole filling ratio, the air hole distance andrefractive index of the medium on the band gap photonic crystal fiber is simulated.Two kinds of bandgap photonic crystal fibers were designed, which could be used tomake the Yb3+doped fiber laser to get a single wavelength output laser.