Ultrashort Pulse Laser Research Pumped By Diode-pump Based On New Saturated Absorber

Ultrashort pulse laser has many applications, because of its advantages of short pulse width, high peak power and wide spectral range. With the development of semiconductor technology, the ultrashort pulse laser pumped by semiconductor laser has become more and more compelling. Currently, using the saturated absorber as passive mode-locking is becoming a main way to achieve ultrashort pulse laser. A new saturated absorber of topological insulating materials which appeared recent years, has a development potential,because it have unique properties and cheap costs. The emergence of the new absorber provides a new platform for ultra-short laser. It make getting the ultra-short laser more high-performance and lower cost.Ultra-short laser cavity commonly used the form of folded cavity. In the folded cavity,astigmatism is introduced inevitable when light beam have oblique incidence to curved mirror, which will cause beam quality deterioration in and out of resonator. In the internal of laser medium, the uneven distribution of heat and thermal strain photoelastic will cause refractive index changes uneven, thus, resulting in thermal lens effect. The effect will bring a great impact to the stability of cavity. Therefore, it is necessary to study the astigmatism and thermal lens effect problems when we design the cavity. In recent years, Yb:KGW laser crystal have gained much attention. The crystal has many advantages, such as: it has wide bandwidth of emission; It has a high quantum efficiency as it's pump wavelength and the laser output wavelength is very close; it can achieve high-concentration dopant; it may pumped by matured InGa As semiconductor laser. This can have high conversion efficiency,small size, low system cost. These advantages make it gained much attention.The main research of the article are as follow:1) We found a simple and intuitive resonator designing method using the theory of transmission circle and transform circle. The method can guarantee astigmatism compensated in the two end arm sides. We only need give a curved mirror's focal length and folding angle, then give an end mirror's light spot size. Using these conditions, we can find the equation about the second curved mirror's focal length and folding angle. All parameters of focal length and folding angle that satisfy the equation can guarantee the cavity's two end sides' astigmatism compensated completely.2) we first use ? propagation circle theory to find a new resonate designing method.The new method can make mode-lock arm's astigmatism compensation insensitive to the thermal lens change. This is a kind of high quality resonator designing method and insensitive to the thermal lens' disturbance. We also verified it through experiment.3) With the new saturated absorber of WS₂, we tested it's nonlinear absorption characteristic by experiment of Z-Scan, and obtain it's maximum depth of modulation is around 6%. Using the WS₂ solution as a saturated absorbent body and make use of the method of designing astigmatism compensation and thermal stability cavity, we make Q-switching and mode-locked experimental study.4) We did some exploratory research about Yb:KGW laser through the cavity resonator of concave, V-type and Z-type cavity, which pumped by semiconductor laser.