Conversion efficiency is boosted by using tandem crystal optical parametric amplifier
geometry. We have undertaken comprehensive numerical modeling of the optical
systems, where the output beam for the first stage are calculated and then propagated to
the second stage. As a concrete example periodically poled lithium niobate crystals are
experimentally examined. The phase and amplitude information about the pump and
signal beams were retrieved using the Fresnel phase retrieval method and used as input in
the theory. This enabled real laboratory conditions to be modeled. Subsequently, the
amplitude and phase of the complex pump and signal beam from the crystal was
calculated and the results were validated by experiments. Non-collinear interactions in
the second stage also yielded an efficient idler output over a broad range of temperatures.
ZnGeP<sub>2</sub> crystals were used in the numerical simulations with first and second stage
amplification. We predicted an idler energy increase by a more than a factor of 3.
Using Fresnel phase retrieval method for two intensity profiles, we first construct the phase-map of the HeNe laser beam in a specially built optical system. After validating this result with the analytical value we proceeded to the nonlinear three-wave interaction. The Fresnel technique is once again employed to obtain the phase map of the input pump and signal beam. The phase information of these input beams are then used in a two-dimensional numerical model we have developed for three-wave nonlinear interactions. The outcome from the numerical model is then compared to the phase map of the output pump and signal beam.
We present a numerical model of a multi-crystal approach that increases the quantum efficiency of a parametric
amplifier. Here is a two-crystal approach where the second stage crystal uses the signal energy from the first stage to
amplify the desired idler wavelength. The numerical model allows for arbitrary input beam profiles and it can
accommodate multiple crystals and optical elements. In this study a pair of PPLN crystals was modeled leading to more
than double the idler output energy. The maximum M<sup>2</sup> value for the output idler beam calculated was 5.2.