Tunable high-efficiency femtosecond pulse second harmonic generation in a slab periodically poled lithium niobate crystal

A typical 1D slab periodically poled lithium niobate (PPLN) crystal with a fixed auxiliary reciprocal lattice vector (RLV) normally achieves only a single-wavelength second harmonic generation (SHG) under the quasi-phase-matching (QPM) technique. Here, we propose a 1D slab PPLN crystal as a research sample to vary incident angles of a high peak power ultrashort femtosecond pump laser to drive the crystal, and theoretically predict and experimentally demonstrate efficient SHG over a substantial spectral tuning range. The fundamental wave (FW) tuning is accomplished from 800 to 814 nm within a tunable incident range of 0°–50° in a 4 mm long crystal with a tuning range of peak wavelength as wide as 14 nm and a tuning rate of 0.28 nm/°, producing SHG pulses with an average conversion efficiency of 14.36%. Compared with conventional temperature, period, and electric field tuning methods, our scheme is simple, rapid, stable, ensures maximum QPM gain, and has relatively considerable spectral range tuning performance. This scheme broadens the avenue for tunable frequency conversion of 1D slab PPLN crystals via the QPM mechanism, is also expected to be applied to higher integration of lithium niobate on insulators and brings better techniques and tools for tunable nanosecond, picosecond, and femtosecond laser devices.