Abstract
We propose a novel type of quasi-phasematching for the second harmonic generation in periodically-poled nonlinear crystals. In contrast to the conventional quasiphasematching where one (or few) quasi-wavevector(s) of periodical poling compensate for the momentum mismatch between a pair of the fundamental photons and the SHG one, with the proposed mechanism the momentum mismatch between several pairs of fundamental and SHG photons is compensated with one quasi-wavevector of periodical poling.
Highlights
Generation of the second harmonic (SHG) of infrared (IR) light offers one of the most preferred ways for realization of compact visible laser sources with a number of cutting-edge applications in microscopy, spectroscopy, biophotonics and photomedicine
The last requirement of the photon momentum conservation is difficult to achieve due to dispersion of the refractive index in the nonlinear crystal
We propose a fractional order of poling period of nonlinear crystal
Summary
Generation of the second harmonic (SHG) of infrared (IR) light offers one of the most preferred ways for realization of compact visible laser sources with a number of cutting-edge applications in microscopy, spectroscopy, biophotonics and photomedicine. Since its first introduction in 1960s [2,3], the preferred approach for the phase-matching between interacting harmonic and fundamental waves is the periodical poling (or “quasiphase-matching” - QPM) of the ferroelectric nonlinear crystals. This is normally achieved by periodically reversing the crystals polarization under large electric field. With the mth order poling, in contrast to the first-order poling, it is necessary to ‘utilize’ not one, but m quasi-wave-vectors of the periodical poling for compensation of the momentum mismatch m.kΛ= k=kλ–2k2λ as shown schematically in figures 1(c) and (d) Speaking, this process is very similar to the high-order diffraction with the conventional diffraction grating
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