Quasi-phasematched (QPM) Theory And Its Frequency Conversion

Utilizing Quasi-phasematched(QPM) technique to achieve a given useful laser frequency conversion is a practical and challenging topic. On account of QPM can take advantage of thelargest element of x tensor , and any interaction with transparency range of the material can be noncritically phase matched without walk-off angle. Therefore, the conversion efficiency in longer crystal may be improved. At same time. OSL (optical supperlattice) doesn't change the optic property of crytal. and only modulate the direction of the tensor d33 periodically. So QPM enlarge the application range of the crystal in existence. Presently diode pumped all-solid-state lasers have been developing quickly, which provides an ideal pump source for QPM. So lower power all-solid-state laser frequency conversion by QPM has been becoming a research focus.Due to QPM takes on many virtues, and its material is easy to fabricate, QPM technique have been becoming the focus of the frequency conversion. Along with the development of QPM theory and the perfection of fabrication method, QPM will show quite exciting application foreground. At home, the national laboratory7 of solid microstructures. Nanjing University keeps ahead in the design and fabrication of PPLT. The author have chance to cooperate with them, for the first time, achieve the multi-wavelength second generation of ps pulse. Experimental results are accurately consistent with theoretical results.In this paper, various frequency conversion by QPM technique will be studied in theoretically and experimentally and the fabrication methods of OSLs will be presented:1. Look back the history of laser frequency conversion and present the present situation and the trend of quasi-phasematched(QPM).2. From wave equation, under small signal approximation, a theoretical calculation ofSHG efficiency and acceptances is presented. According to this, the acceptances of wavelength, period, temperature and incidence angle are calculated. These will guide the experiment and the fabrication of optical supperlattice(OSL).3. Introducing several OSL fabrication methods, mainly electric field poling method is investigated, and discussing the limit relation among poling electric field E, poling current I and natural poling intensity Ps, and analyze the various factor affecting the OSLs quality.4. The experiment of aperiodical LiTaOs multi-wavelength SHG is demonstrated. For the first time, high frequency conversion efficiency is achieved at home, and output wavelength range is form visible to infrared.5. Introducing the present situation of QPM-OPO laser, from the three waves couplingequation, we analyze the theory of PPLN-OPO, and explain the cascade phenomena successfully.6 .By comparing the relative intensity between 914nm radiation and 1064nm radiation in Nd:YVO4 with different Nd concentration. We design a 457nm all-solid-state blue laser as pumping source for QPM-OPO.