Study On The Technology Of High Efficient SHG With Short Pulse Broadband Laser

Q swithed green laser has a huge application market in the field of industry, medical treatment and so on. But the price of green laser produced by frequency doubling with diode pumped solid state laser is expensive. At present, the near infrared Q switched fiber laser is reliable in quality and low in price. By directly frequency doubling with near infrared fiber laser to generate green light can greatly save the cost. However, the bandwidth of the fiber laser is relatively wide, and the frequency doubling efficiency is generally very low. In this work, a theoretical study of the medium power broadband frequency doubling scheme is carried out. The main contents can be outlined as follows:1. A brief introduction to medium power broadband SHG has been made. The main reason for low conversion efficiency was pointed out. General methods of broadband harmonic conversion technology are compared, such as angular spectrum dispersion(ASD) scheme, chirp matching scheme, crystal cascade scheme and reentry point matching scheme.2. The physical model of medium power broadband SHG is established. The influence of the incident light intensity, bandwidth, focused beam size, focus position, on the frequency spectrum and the conversion efficiency were analyzed through numerically solving the three wave coupling equations of Gauss beam, while the crystal dispersion is considered properly.3. Three kinds of crystal(BBO, LBO, KTP) were studied. The allowable parameters, the matching style and the frequency doubling efficiency of these three kinds of crystal were calculated. The results show that LBO is most suitable for SHG with medium power wide spectrum fiber laser.4. Two kinds of broadband frequency doubling technology were analyzed which were ASD scheme and crystal cascade scheme. The theoretical calculation shows that both the two scheme can effectively improve the efficiency of frequency doubling. Among them, the ASD scheme can make the whole spectral range achieve the phase matching, so that the SHG efficiency could be as large as narrow band laser SHG efficiency.