Study of low-coherence laser source and its application

This thesis is organized into three parts : (a) the theory of quasi-phase matching, quasi-phase matched optical parametric oscillator (QPM OPO), and speckle (b) the design of transversely-displaced three-QPM structures in periodically poled LiTaO3 (PPLT) for constructing 1064nm broadband OPO laser and a multi-chirped PPLT device for generation of broadband green laser (c) implementation of a QPM-OPO system, second harmonic generation (SHG) experiment, spatial distribution of laser beam intensify and speckle reduction with broadband green lasers. First, the theory of QPM, OPO and speckle is introduced in chapter 2, chapter 3 and chapter 4. In the second part, the designed periods of PPLT is introduced. A 532 nm nano-second laser pumped 1064 nm broadband OPO is achieved by simultaneously the exciting tri-QPM structures in parallel with each periodicity of 7.63, 7.64, and 7.65 um, respectively, and 200 um width and 10 um spacing. The chirped periods for constructing broadband green lasers is from 5.495 to 9.845 um. Finally, based on the Fabry Perot effect, a thin flat is used as the output mirror for the OPO to construct a broadband infrared frequency comb. The output OPO spectrum for the period 7.65_7.63_7.64 um design has the largest spectral bandwidth of 70 nm at 132°C. The IR combs are then used as fundamental source to pass through the multi-period chirped PPLT for generate of broadband green lasers. For comparison, pumping from two different directions and two different chirp rate are studied. The output spectrum for PPLT-SHG 1010 mm Long Short Long Short sample gets the broadest bandwidth of 47 nm. Moreover, using this broadband green laser to implement the analysis of spatial distribution and speckle. The resulting of speckle contrast ratio below 5% by engineering the low temporal-and-spatial coherence of the laser source.