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Study on the Laser Performance of Nd3+(Yb3+) Doped CaF2Crystal

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Tutor: LiuJie
School: Shandong Normal University
Course: Optics
Keywords: Nd,Y:CaF2,Yb,Y:CaF2,continuous wave,passively Q-switched,passivelymode-locking
CLC: TN248.1
Type: Master's thesis
Year:  2014
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Abstract:
With the emergence of high power laser diode (LD), LD pumped solid state laser hasachieved rapid development. LD pumped solid-state pulse lasers have many merits such ashigh peak power, short pulse width, high beam quality, small size, light weight, firm structure,long life duration, high stability and high conversion efficiency. With the output laser pulsewidth on picosecond level obtained by LD pumped solid-state pulse lasers, the pulses havebeen widely used in the scope of military, industry, medical treatment and scientificresearches.Because the laser medium is an important part of solid-state lasers-an important way toachieve a breakthrough laser is the innovation and development of laser materials. As atraditional crystal material, CaF2is also an excellent optical material, which has a veryimportant position in industrial applications and scientific research. Doped trivalent rare-earthions, CaF2shows a more superior laser characteristics. In this article, we study the allsolid-state lasers on doped Nd3+(Yb3+) in CaF2crystals systematically. First, based onNd,Y:CaF2crystal, we experimentally investigate the output performance of continuous waveand passively Q-switched laser with the Cr4+:YAG saturable absorbers. Then, based onYb,Y:CaF2crystal, the output performance of continuous wave and passively mode-lockedlaser by graphene saturable absorbers are also experimentally investigated. The contents canbe outlined as follows:1. The characterizations and the developments of CaF2are summarized simply.Particularly, the characterizations and the advantages of the novel Nd,Y:CaF2and Yb,Y:CaF2crystals are also introduced. The historical and recent research progress on these crystals arereviewed.2. Based on several different Nd3+(Yb3+) doped concentration of the Nd,Y:CaF2andYb,Y:CaF2crystals successfully grown by the temperature gradient technique (TGT), by using five different concentration doping Nd,Y:CaF2crystals as the gain medium, adiode-pumped continuous-wave laser is realized, with different resonators. After comparingthe spectral properties of Nd,Y:CaF2laser crystal, the largest continuous wave output powerof488mW at1057nm are measured on the doping concentration1%Nd,10%Y:CaF2. TheLD pumped continuous wave laser characteristic of Yb,Y:CaF2crystals with different dopingconcentrations is investigated severally for the first time. By comparison, with concentrationof5at.%Yb,5at.%Y:CaF2crystal laser performance is the best, then we obtain the maximumcw output power of746mW on it.3. We introduce the passively Q-switched theory and technology in detail. Owing to therelatively mature technology and excellent optical properties of Cr4+:YAG, a diode-pumpedpassively Q-switched laser operation is demonstrated on the Nd,Y:CaF2crystal around1¦Ìmfor the first time to our knowledge. According to the cavity design theory, we design a simplev-folded cavity with Cr4+:YAG as the saturable absorbers. At the absorbed pump power of1.63W, the maximum average output pump power of120mW is observed, corresponding tothe shortest pulse width of132ns with the highest pulse repetition rate of6.2kHz.4. We comprehensively describes the principle and technology of passivelymode-locking. By using a cavity design software, we calculate the best resonator. Based onthe5at.%Yb,5at.%Y:CaF2crystal, a passive mode-locking laser is achieved with thegraphene saturable absorber for the first time. The short pulses at a repetition rate of98MHzwere obtained at the central wavelength of1.05¦Ìm. The maximum average output power was204mW, corresponding to the pulse energy of2.08nJ.
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