Irit Juwiler

Two-dimensional nonlinear beam shaping

We develop a technique for two-dimensional arbitrary wavefront shaping in quadratic nonlinear crystals by using binary nonlinear computer generated holograms. The method is based on transverse illumination of a binary modulated nonlinear photonic crystal, where the phase matching is partially satisfied through the nonlinear Raman-Nath process. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into three Hermite-Gaussian and three Laguerre-Gaussian beams in the second harmonic. Two-dimensional binary nonlinear computer generated holograms open wide possibilities in the field of nonlinear beam shaping and mode conversion.

EFFICIENT QUASI-PHASE-MATCHED FREQUENCY DOUBLING WITH PHASE COMPENSATION BY A WEDGED CRYSTAL IN A STANDING-WAVE EXTERNAL CAVITY

In standing-wave enhancement cavities for frequency doubling, second-harmonic fields are generated in both directions of propagation. To add the fields coherently, one should compensate for the phase shifts introduced by dispersive elements in the cavity. We experimentally demonstrate phase compensation in a compact standing-wave frequency-doubling cavity by use of a wedged periodically poled KTP crystal. The highest conversion efficiency and second-harmonic power obtained by pumping with a 1064-nm cw Nd:YAG laser were 69.4% and 268 mW, respectively.

All-optical polarization switch in a quadratic nonlinear photonic quasicrystal

We present an all-optical intensity-dependent polarization switch based on cascaded three-wave-mixing interactions in a quasiperiodic quadratic nonlinear photonic crystal. The polarization switching is realized by simultaneous quasiphase matching of upconversion and downconversion processes in LiNbO3 and achieves three orders of magnitude better efficiency than previous devices based on cascaded cubic nonlinearities. The switch allows extending mode-cleaning and mode-locking techniques to considerably lower input power. We demonstrate experimentally that a single linearly polarized 1550 nm fundamental wave generates a new fundamental wave of orthogonal polarization.

Nonlinear computer-generated holograms

We propose a novel technique for arbitrary wavefront shaping in quadratic nonlinear crystals by introducing the concept of computer-generated holograms (CGHs) into the nonlinear optical regime. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into the first three Hermite-Gaussian beams at the second harmonic in a stoichiometric lithium tantalate nonlinear crystal, and we characterize its efficiency dependence on the fundamental power and the crystal temperature. Nonlinear CGHs open new possibilities in the fields of nonlinear beam shaping, mode conversion, and beam steering.

Efficient frequency doubling by a phase-compensated crystal in a semimonolithic cavity

In multiple-pass nonlinear frequency conversion devices, interacting waves may accumulate different phases, owing to dispersive elements in the system. Phase compensation is therefore necessary for efficient frequency conversion. We experimentally demonstrate phase compensation in a compact semimonolithic frequency-doubling cavity by using a periodically poled KTP crystal. The conversion efficiency of the crystal was found to decrease at high pump powers, owing to power-dependent thermal lensing. This experimental observation was supported by a theoretical calculation of the conversion efficiency in a cavity, considering the mismatch between the modes thermally loaded and unloaded cavities. A design procedure was also presented to compensate for the thermal lensing effect. The highest conversion efficiency of 56.5%, corresponding to a second-harmonic power of 117.5 mW at 532 nm, was achieved with a cw Nd:YAG pump power of 208 mW.

Generation of second-harmonic beams with switchable curved trajectories

Beams which follow curved trajectories are useful in a variety of applications, but up to now have been realized mainly in linear media. We demonstrate theoretically and experimentally the generation of second-harmonic (SH) beams which follow arbitrary convex caustic trajectories. These beams are created in a nonlinear photonic crystal with a second-order susceptibility having a tailored pattern; hence, the SH beam follows the desired trajectory after exiting the crystal. The same crystal can incorporate more than one trajectory, enabling the nonlinear creation of bottle beams as well as beams with switchable caustic trajectories that can be controlled by the phase-matching conditions.

Nonlinear beam shaping by non-collinear interactions

Nonlinear diffraction occurs when light encounters a periodicity in a nonlinear coefficient, for example, a periodically altered second order nonlinear coefficient impinged by a pump beam will result in a diffraction pattern in the second harmonic (SH). An interesting case of nonlinear diffraction is when the pump beam enters the crystal with an angle. This results with an asymmetrical diffraction pattern and enlarges the operational bandwidth [1]. In a perfectly periodic structure the result of diffraction for a Gaussian pump beam is a Gaussian beam in the SH. However, if the structure is modified using a computer generated hologram (CGH) encoding technique, the obtained SH beam can have any arbitrary shape. This method enables 1D nonlinear beam shaping by a simple 1D modulation of the nonlinear coefficient. Moreover, it enables fully phase matched, and hence efficient scheme for 2D nonlinear beam shaping.

Two-dimensional nonlinear beam shaping: erratum

In an earlier Letter [Opt. Lett. 37, 2136 (2012)], a conversion efficiency was improperly given. That error is corrected here.

Generation of ultrafast visible and mid-IR pulses via adiabatic frequency conversion

A method for efficient, broadband sum and difference frequency generation of ultrafast pulses is demonstrated. Using aperiodically poled nonlinear crystals and a single step nonlinear mixing process, conversion efficiencies up to 50% are reported.