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Two-photon absorption spectrum of aniline is recorded using thermal lens effect with optical parametric oscillator as the pump source. Studies show that the two-photon absorption spectrum observed corresponds to ¹A₁ → ¹B₂ transition of aniline.

We present a numerical study for the design of efficient MgO:PPLN based pulsed nanosecond optical parametric oscillator (OPO), with input pump pulses of top-hat transverse intensity profile, and a double-pass pump cavity configuration. In particular, we investigate the effect of domain shape on the conversion efficiency. We considered two types of domain structures: "perfect vertical-wall" and "wedge-shaped" domains and our numerical results show that at higher pump pulse energies, the conversion efficiency saturates, and the saturated efficiency is almost independent of the domain shapes. Based on our study, we also propose a new scheme for development of compact high-power OPO sources using MgO:PPLN chips of relatively short lengths and large cross-sectional area.