Second optical harmonic generation in nonlinear crystals with a disordered domain structure

Čerenkov-type second-harmonic spectroscopy in random nonlinear photonic structures

“…In far-field, the second-harmonic intensity is proportional to the square of the Fourier coefficients, which result from the Fourier transform of the spatial distribution of the χ (2) nonlinearity [26,28,29]. For a two-dimensional (2D) χ (2) structure modulated in the xy-plane the SH The Fourier coefficients involved inČerenkov SH emission at normal incidence at 600 nm are marked with solid circles. The scan range Δk x at one side is indicated by dashed lines.…”

“…In recent years, much attention has been devoted to investigate second-harmonic generation via quasi-phase matching in crystals with a random distribution of their ferroelectric domains, i.e. with a random distribution of the χ (2) nonlinearity [1][2][3][4][5][6]. This new class of random nonlinear photonic crystals offers a versatile way to realize frequency conversion processes over a wide spectral range [7][8][9].…”

“…This new class of random nonlinear photonic crystals offers a versatile way to realize frequency conversion processes over a wide spectral range [7][8][9]. Among the most interesting phase-matching schemes to achieve secondharmonic emission is the so-calledČerenkov-type phase matching which has been demonstrated in different bulk nonlinear media [10][11][12][13], waveguides [14] as well as in crystals with a periodic, quasi-periodic, and random modulation of the χ (2) nonlinearity [4,13,15,16]. It is a result of light-matter interaction satisfying only the longitudinal phase-matching condition [7].…”

“…If this velocity is higher than the phase velocity of light v s , the conical emission due to constructive interference at a certain angle γ given by cos γ = v s /v p can be detected. The physical origin of the existence of this phenomenon in random nonlinear photonic crystals is still ambiguous, being attributed either to reciprocal grating vectors of the χ (2) structure [10,12] or to the enhancement of χ (2) at domain walls as suggested in [18]. However,Čerenkov-type second-harmonic generation can also be observed in an extreme case where a single boundary between two inversely oriented ferroelectric domains is illuminated [19,20].…”

Non-stoichiometric grain-growth in ZnSe ceramics for χ(2) interaction

“…Despite the lack of long range order, these materials can serve as efficient nonlinear frequency converters by way of the random quasi-phase-matching (rQPM) process [14][15][16]. These process has been extensively studied both theoretically [17,18] and experimentally [19,20]. In these ceramics, the randomly-oriented crystallites all contribute to the nonlinear conversion process but with random phases and yet, the total contribution to the generated field is nonzero.…”