Ady Arie

Generation of electron Airy beams

We report the first experimental generation and observation of Airy beams of free electrons. The electron Airy beams are generated by diffraction of electrons through a nanoscale hologram, that imprints a cubic phase modulation on the beams’ transverse plane. We observed the spatial evolution dynamics of an arc-shaped, self accelerating and shape preserving electron Airy beams. We directly observed the ability of electrons to self-heal, restoring their original shape after passing an obstacle. This electromagnetic method opens up new avenues for steering electrons, like their photonic counterparts, since their wave packets can be imprinted with arbitrary shapes or trajectories. Furthermore, these beams can be easily manipulated using magnetic or electric potentials. It is also possible to efficiently self mix narrow beams having opposite signs of acceleration, hence obtaining a new type of electron interferometer.Within the framework of quantum mechanics, a unique particle wave packet exists in the form of the Airy function. Its counterintuitive properties are revealed as it propagates in time or space: the quantum probability wave packet preserves its shape despite dispersion or diffraction and propagates along a parabolic caustic trajectory, even though no force is applied. This does not contradict Newton’s laws of motion, because the wave packet centroid propagates along a straight line. Nearly 30 years later, this wave packet, known as an accelerating Airy beam, was realized in the optical domain; later it was generalized to an orthogonal and complete family of beams that propagate along parabolic trajectories, as well as to beams that propagate along arbitrary convex trajectories. Here we report the experimental generation and observation of the Airy beams of free electrons. These electron Airy beams were generated by diffraction of electrons through a nanoscale hologram, which imprinted on the electrons’ wavefunction a cubic phase modulation in the transverse plane. The highest-intensity lobes of the generated beams indeed followed parabolic trajectories. We directly observed a non-spreading electron wavefunction that self-heals, restoring its original shape after passing an obstacle. This holographic generation of electron Airy beams opens up new avenues for steering electronic wave packets like their photonic counterparts, because the wave packets can be imprinted with arbitrary shapes or trajectories.

Photonic quasicrystals for nonlinear optical frequency conversion.

We present a general method for the design of 2-dimensional nonlinear photonic quasicrystals that can be utilized for the simultaneous phase matching of arbitrary optical frequency-conversion processes. The proposed scheme--based on the generalized dual-grid method that is used for constructing tiling models of quasicrystals--gives complete design flexibility, removing any constraints imposed by previous approaches. As an example we demonstrate the design of a color fan--a nonlinear photonic quasicrystal whose input is a single wave at frequency omega and whose output consists of the second, third, and fourth harmonics of omega, each in a different spatial direction.

Tunable midinfrared source by difference frequency generation in bulk periodically poled KTiOPO4

We demonstrate quasi-phase-matched difference frequency generation in periodically poled KTiOPO4. A midinfrared (3.2–3.4 μm) idler with a power level of 0.17 μW is generated by mixing a Nd:YAG laser and tunable external cavity laser near 1550 nm which is amplified by an erbium-doped fiber amplifier. The wavelength, temperature, and angle tuning characteristics of this device are determined. The experimental results are used to derive a Sellmeier equation with improved accuracy in the midinfrared range for the extraordinary refractive index of flux-grown KTiOPO4.

Absolute frequency stabilization of diode-laser-pumped Nd:YAG lasers to hyperfine transitions in molecular iodine.

Diode-laser-pumped Nd:YAG lasers were frequency stabilized by locking their frequency-doubled output to Doppler-free absorption lines of the (127)I(2) molecule. The successive two-sample deviation of the beat frequency between two independent iodine-stabilized lasers is less than 650 Hz, or 2.3 x 10(-12) of the laser frequency, for averaging times between 24 and 80 s.

Highly sensitive dynamic strain measurements by locking lasers to fiber Bragg gratings

A novel, sensitive, simple, and robust strain interrogation technique is analyzed and experimentally tested. By locking a laser wavelength to the midreflection wavelength of a standard fiber Bragg grating and measuring the error signal, we achieve high dynamic strain sensitivity of 45 picostrain/ radicalHz rms at 3 kHz, where the dominant noise in the experiment is the laser frequency noise.

Three-dimensional ferroelectric domain visualization by Cerenkov-type second harmonic generation.

We show that focusing a laser light onto the boundary between antiparallel ferroelectric domains leads to the non-collinear generation of two second harmonic (SH) beams. The beams are emitted in a plane normal to the domain boundaries at the angles that satisfy the Cerenkov-type phase matching condition. Moreover, these beam disappear when the laser light is focused on a homogenous part of a single domain. We utilize this effect for 3-dimensional visualization of fine details of the ferroelectric domain pattern with a submicron accuracy.

Cerenkov-Type Second-Harmonic Generation in Two-Dimensional Nonlinear Photonic Structures

We study the Cerenkov-type second-harmonic generation in several different two-dimensional nonlinear photonic structures formed in birefringent crystals with the 3 m symmetry. Depending on the degree of birefringence, we observe either single or double Cerenkov-like second-harmonic rings. We discuss the properties of these parametrically generated rings and show that their sixfold azimuthal modulation is associated with the hexagonal symmetry of the individual ferroelectric domains.

Temperature-dependent dispersion equations for KTiOPO4 and KTiOASO4

We have measured the thermal expansion and the temperature dependence of z and y components of the refractive index for KTiOPO4 and KTiOAsO4, in the wavelength range 532-1585 nm and temperature range 25-200 degrees C, using an interferometric technique. The measurements were used to derive temperature-dependent Sellmeier equations for the two materials. These equations predict with good agreement the temperature dependence of quasi-phase-matched nonlinear frequency converters.

Geometrical representation of sum frequency generation and adiabatic frequency conversion

We present a geometrical representation of the process of sum frequency generation in the undepleted pump approximation, in analogy with the known optical Bloch equations. We use this analogy to propose a technique for achieving both high efficiency and large bandwidth in sum frequency conversion using the adiabatic inversion scheme. The process is analogous with rapid adiabatic passage in NMR, and adiabatic constraints are derived in this context. This adiabatic frequency conversion scheme is realized experimentally using an aperiodically poled potassium titanyl phosphate KTP device, where we achieved high efficiency signal-to-idler conversion over a bandwidth of 140 nm.

Green and ultraviolet quasi-phase-matched second harmonic generation in bulk periodically-poled KTiOPO4

Abstract A periodically-poled flux-grown KTP crystal was used for first order quasi-phase-matched (QPM) second harmonic generation of a Nd:YAG laser. The normalized conversion efficiency of the 1 cm long, 0.5 mm thick sample was 1.28% W −1 . A lower limit on the nonlinear coefficient of KTP, d 33 ≥ 14.9 ± 1.5 pm/V was derived from these measurements. The temperature and wavelength tuning coefficients near 1064 nm were determined. The same device was also used for third order QPM frequency doubling of 784 nm light, and the normalized conversion efficiency in this case was 0.12% W −1 .