Engineering quadratic nonlinear photonic crystals for frequency conversion of lasers

Abstract

Nonlinear frequency conversion offers an effective way to extend the laser wavelength range. Quadratic nonlinear photonic crystals (NPCs) are artificial materials composed of domain-inversion structures whose sign of nonlinear coefficients are modulated with desire to implement quasi-phase matching (QPM) required for nonlinear frequency conversion. These structures can offer various reciprocal lattice vectors (RLVs) to compensate the phase-mismatching during the quadratic nonlinear optical processes, including second-harmonic generation (SHG), sum-frequency generation and the cascaded third-harmonic generation (THG). The modulation pattern of the nonlinear coefficients is flexible, which can be one-dimensional or two-dimensional (2D), be periodic, quasi-periodic, aperiodic, chirped, or super-periodic. As a result, these NPCs offer very flexible QPM scheme to satisfy various nonlinear optics and laser frequency conversion problems via design of the modulation patterns and RLV spectra. In particular, we introduce the electric poling technique for fabricating QPM structures, a simple effective nonlinear coefficient model for efficiently and precisely evaluating the performance of QPM structures, the concept of super-QPM and super-periodically poled lithium niobate for finely tuning nonlinear optical interactions, the design of 2D ellipse QPM NPC structures enabling continuous tunability of SHG in a broad bandwidth by simply changing the transport direction of pump light, and chirped QPM structures that exhibit broadband RLVs and allow for simultaneous radiation of broadband SHG, THG, HHG and thus coherent white laser from a single crystal. All these technical, theoretical, and physical studies on QPM NPCs can help to gain a deeper insight on the mechanisms, approaches, and routes for flexibly controlling the interaction of lasers with various QPM NPCs for high-efficiency frequency conversion and creation of novel lasers.

Intense ultraviolet–visible–infrared full-spectrum laser

“…The sample has a dimension in length, width, and thickness of 20 mm × 6 mm × 2 mm, respectively. Microscopic images of the etched CPPLN structure, fabricated using an electric poling technique 19 , 21 , 24 , are displayed in Fig. 1e, f .…”

Non-destructive quality evaluation of periodically poled MgO:PPLN and Rb:PPKTP crystals based on parametric light generation

“…As a result, stable periodically poled domains (gratings) are formed, creating a medium where effective nonlinearity periodically changes sign. [7][8][9] These QPM devices enable efficient processes such as parametric light generation, up-conversion, and THz generation by leveraging the largest nonlinear optical susceptibility tensor elements. [10][11][12][13] To ensure efficient operation of the QPM device, it is crucial to evaluate the accuracy of the PP structure.…”

Rigorous solution to second harmonic generation considering transmission and reflection of light at air–crystal interface

“…Different second-order nonlinear optical effects such as second harmonic generation (SHG), sum frequency generation (SFG), difference frequency generation (DFG), and optical parametric oscillation and amplification allow spectral range to expand to new wavelength band. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Two schemes called the birefringence phase matching (BPM) [2,17] scheme and quasi-phase-matching (QPM) [3,8] scheme have been proposed to achieve high conversion efficiency. By changing the sign of the second-order nonlinear susceptibility χ (2) to compensate for the phase mismatching, many periodic, [4,6,18,19] quasi-periodic, [20] chirped, [21] aperiodic [20,22] structures have been designed.…”