Joerg Imbrock

Cascaded Čerenkov third-harmonic generation in random quadratic media

We investigate experimentally and theoretically the conical emission of Cerenkov-type third-harmonic generation in strontium barium niobate of random 2D-χ(2) distribution. The azimuthal intensity distribution is explained by the polarization properties of the fundamental and Cerenkov second-harmonic waves, depending on the cascaded origin of the generation process. Moreover, we show the role of the individual domain shape in an additional modulation on the conical emission, controlled by the electrical switching of the spontaneous polarization of the ferroelectric medium.

Three-dimensional visualizing of ferroelectric domain growth and switching using Čerenkov second-harmonic generation

In this contribution we demonstrate for the first time to our knowledge a three-dimensional monitoring of the evolution of the spontaneous polarization (Ps) during electrical poling and temperature annealing in multi-domain strontium barium niobate using Cerenkov-type second-harmonic generation.

Tailoring the effective second-order nonlinear coefficients in random media

We study experimentally and theoretically the relative relationship between the non-zero components of the χ(2)-tensor in dependence of different degrees of ferroelectric domain disorder in quadratic media for frequency doubling and cascaded third harmonic generation.

Direct Inscription of Quasi Phase-Matching Waveguide Structures in Lithium Niobate

We report monolithic fabrication of quasi phase-matching waveguides in lithium niobate by direct femtosecond laser writing. The circular type-II waveguide with an embedded multiscan grating enables efficient second harmonic generation of 1064 nm radiation.

Nonlinear beam splitter based on second-harmonic generation by femtosecond laser-induced phase gratings in lithium niobate

Parametric processes such as second-harmonic generation (SHG) and sum-frequency generation (SFG) are often realized in nonlinear optical crystals by collinear phase matching. However, it is known that noncollinear phase matching (NCPM) offers an additional degree of freedom by intersecting the fundamental waves under an angle to compensate for not only the phase mismatch but also the group velocity mismatch. The latter one is especially important for parametric processes using ultrashort laser pulses. NCPM can be typically achieved in the same wavelength range where birefringent phase matching is possible. However, the angular tuning range is strongly limited by the specific cut of the crystal. One can omit an external beam splitter if a diffraction grating is integrated in the crystal which allows for NCPM over a large wavelength range in a single crystal. The diffraction grating splits the fundamental beam into two or more beams which are intersecting inside the crystal at the appropriate NCPM angle. This process has been demonstrated in KH2PO4 and β-BaB2O4 by directly writing of relief gratings at the crystal surface with femtosecond laser pulses.

Effect of domain shape on noncollinear second-harmonic emission in disordered quadratic media

In this contribution, we study the role of the individual ferroelectric domain shape in planar second-harmonic (SH) emission in strontium barium niobate as an example of nonlinear photonic crystal. The noncollinearly emitted SH signal is scanned at different incident angles for different domain size distributions.

Light in disordered nonlinear photonic structures

We present selected wave propagation phenomena in disordered nonlinear photonic structures ranging from high harmonic generation in disordered quadratic media to Anderson localization in optically induced refractive index distributions.