Abstract
Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting an incident light beam into the beam (or beams) of different frequency with spatially modulated amplitude and phase. The realization of such frequency conversion and shaping processes critically depends on the matching of phase velocities of interacting waves, for which nonlinear photonic crystals (NPCs) with spatially modulated quadratic nonlinearity have shown great potential. Here, we present the first experimental demonstration of nonlinear wavefront shaping with three-dimensional (3D) NPCs formed by ultrafast-light-induced ferroelectric domain inversion approach. Compared with those previously used low-dimensional structures, 3D NPCs provide all spatial degrees of freedom for the compensation of phase mismatch in nonlinear interactions and thereby constitute an unprecedented system for the generation and control of coherent light at new frequencies.
Highlights
Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies
The second harmonic generation (SHG) process fulfills a general conservation law for the orbital angular momentum (OAM)[19], i.e. lSH = 2lFB + mlc, where lSH and lFB represent the OAM of the second harmonic (SH) and fundamental beams, respectively, lc is the topological charge of the fork structure, and m is the nonlinear diffraction order of the SH wave
Using a three-layer nonlinear photonic structure comprising fork grating, regular 1D grating, as well as circular grating embedded inside the crystal, we demonstrated a simultaneous conversion of a fundamental Gaussian beam into second harmonic vortex, Gaussian, and conical beams
Summary
Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting an incident light beam into the beam (or beams) of different frequency with spatially modulated amplitude and phase The realization of such frequency conversion and shaping processes critically depends on the matching of phase velocities of interacting waves, for which nonlinear photonic crystals (NPCs) with spatially modulated quadratic nonlinearity have shown great potential. Depending on the geometry of interaction, the QPM can be implemented through the schemes of nonlinear Bragg diffraction[15], Čerenkovtype[16] emission and nonlinear Raman-Nath diffractions[17] In these NPCs the wavefront shaping often relies on transversely patterned nonlinearity, i.e., χ(2) varies spatially (typically between +| χ(2) | and −| χ(2) |) in a plane perpendicular to the propagation direction of the incident beam[18,19,20]. This process introduces significant scattering losses[30] for interacting beams and has limited practical applicability
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