Fabrication of periodically poled crystals from the KTP family and their applications in nonlinear optics

Sammanfattning: Quasi-phasematched (QPM) nonlinear optical frequencyconversion is a powerful tool in the development of new lasersources, by providing high conversion efficiency and largeflexibility in terms of output wavelengths.QPM structures are preferably implemented in bulk crystalsbe periodic electric field poling. Bulk crystal interactionsareneeded for high power generation. In this thesis, methodsfor achieving periodic poling in materials from the KTP familyare developed. A novel technique for optical monitoring of thepoling is also described. These materials combine highnonlinearity with wide transmission range, good power handlingcapability, and high damage thresholds. Their low coercivefield also allows thick crystals to be poled into largeaperture QPM devices. On the other hand, the high and varyingionic conductivity in these materials has been identified asimportant factor complicating the poling process.Periodically poled QPM structures have been fabricated influx grown KTP, RTA and RTP. Up to 3 mm thick crystals of RTAand KTP have been periodically poled, which are the thickestperiodically poled crystals ever reported.The periodically poled crystals have been used in varioustypes of type-I QPM frequency conversion experiments, includingboth SHG (Second Harmonic Generation) and OPO (OpticalParametric Oscillation). Continuous wave powers exceeding 700mW in the blue, over 65% conversion efficiency for pulsedgeneration of green light and up to 17 mJ pulses at 1.58µm have been obtained. The shortest wavelength generatedis 390 nm using a QPM period of 2.95 µm. The possibilityof obtaining type-II QPM frequency conversion has also beendemonstrated.Keywords:quasi-phasematching, KTP, nonlinear optics,frequency conversion, periodic electric field poling,ferroelectrics, lasers, optical parametric oscillators.