Toxic Pb-containing piezo-, pyro- and ferroelectrics continue to dominate the market even though they were banned from use in consumer products more than a decade ago. There is a strong need for sustainable alternatives, but the lack of facile synthesis routes for thin films exhibiting suitable functional properties have limited the transition from Pb workhorse materials like Pb(Zr,Ti)O3 and Pb(Mg,Nb)O3 - PbTiO3. Atomic layer deposition has proven capable of the deposition of possible successors, such as LiNbO3, (K,Na)NbO3 and K(Ta,Nb)O3, albeit with limited control due to water reservoir effects resulting from the hygroscopicity of intermediate products. In this article, we show that replacing H2O with O3 in the deposition of complex alkali oxides provides an alternative and much more controlled process. We exemplify this by deposition of crystalline K(Ta,Nb)O3 with high compositional control and over a larger composition range than previously reported. This opens new doors to a simplified synthesis of polar functional lead-free alternatives.

Spatially analyzing non-uniform distributions of electric phenomena such as electric field and permittivity in ferroelectric devices is very challenging. In this study, we apply an optical beam deflection method to map the non-uniform electric phenomena in relaxor ferroelectric potassium tantalate niobate (KTN) crystals. To adequately correlate the physical parameters and their spatial distributions in KTN crystals, a general model that describes the giant electro-optic response and associated beam deflection is derived. The proposed model is in good agreement with the experimental results and is envisioned to be useful for analyzing electric field-induced phenomena in non-linear dielectric materials and devices.

In this Letter, we reported anomalous electro-optic potassium tantalate niobate (KTN) devices, in which both electrons and holes were injected into the KTN crystal via ultraviolet (UV) illumination-assisted charge injection. This could not only significantly enhance the performance of electro-optic devices (e.g., a 270% increase in the deflection angle in terms of the KTN deflector) but also enable the new bi-directional scanning capability. The results in this work would be very useful for a variety of devices and applications, such as electro-optic based vari-focal lenses.

Electric field-induced phase transition in perovskite relaxor ferroelectric crystals has been studied using Raman spectroscopy. The findings revealed that by switching the applied electric field, the intensity ratio of the Raman spectra of the electric field-induced phase transition in relaxor ferroelectric potassium tantalate niobate KTa0.61Nb0.39O3 (KTN) crystals can be a function of temperature and thermal history, which is explained by the two-stage kinetic model of first-order phase transition in disordered ferroelectrics. Moreover, because of the charge injection by the applied voltage, the non-uniform electric field-induced phase transition in KTN was spatially resolved by Raman mapping. The results of this study will be of use for fundamental scientific studies on the physical mechanisms of the electric field-induced phase transition in perovskite relaxor ferroelectric materials and has practical applications for electromechanical and electro-optic devices and systems.

Most applications of a ferroelectric-based electro-optic (EO) beam deflector have been limited by the high applied voltage. In this Letter, we report a dramatically increased EO beam deflection in relaxor ferroelectric potassium tantalate niobate (KTN) crystals by using the electric-field-enhanced permittivity. Due to the existence of the electric-field-induced phase transition in relaxor ferroelectric materials, the dielectric permittivity can be substantially increased by the applied electric field at a certain temperature. Both the theoretical study and the experimental verifications on the enhanced beam deflection and EO effect in the case with the electric-field-induced high permittivity were conducted. The experimental results confirmed that there was a three-fold increase in the deflection angle, which represented a dramatic increase in the deflection angle. By offering a wider deflection range and a lower driving voltage, such a largely enhanced beam deflection is of great benefit to the KTN deflector. (C) 2019 Optical Society of America

Due to its appreciable electro-optical properties, potassium tantalate niobate (KTN) thin films of high quality are expected to enhance the functionality of integrated photonics optical modulators. Unfortunately, they are inherently hard to synthesize. Herein, the authors present atomic layer deposition (ALD) of oriented KTN for the first time. They study the variability in phase content with respect to potassium concentration across a variety of substrates. Films grown with a slight overstoichiometry in potassium show excellent crystal quality of a pure perovskite phase. Highly oriented films were obtained on substrates of a similar lattice constant to bulk potassium tantalate niobate. Nearly stoichiometric potassium contents yield films with similar quality, albeit with trace amounts of pyrochlore. Potassium deficient films consist of an overwhelming amount of pyrochlore. Phase control and orientation control are essential when considering device integration of optical modulators. The authors believe that ALD is an ideal technique to obtain KTN thin films with high growth control.

We report a new type of photoconductive semiconductor switch (PCSS), consisting of a semi-insulating gallium arsenic (GaAs) substrate and a front-bonded ruby crystal. The 532 nm laser pulses from an Nd-YAG laser incident on the front surface of the ruby crystal. A portion of the laser pulse passes through the crystal and reaches the GaAs substrate, and the remaining portion of the laser pulse is absorbed by the ruby crystal. This results in the emission of 694 nm fluorescent light. Furthermore, a portion of emitted fluorescent light also reaches the GaAs substrate. The high-fluence 532 nm short laser pulse with a pulse width around several nanoseconds is used to trigger the PCSS entering the high-gain nonlinear mode, whereas the low-fluence long-lifetime (on the order of a millisecond) 694 nm fluorescent light is used to maintain the lock-on time. Thus, an ultralong lock-on time on the order of millisecond is achieved, which is 3 orders of magnitude longer than a typical lock-on time of high-gain GaAs PCSS.

To overcome the depth limitation of the space-charge-controlled (SCC) potassium tantalate niobate (KTN) deflectors, we report in this paper a method of increasing the aperture of SCC-KTN deflectors by harnessing the physical mechanism of blue light photon excitation. The experimental results show that the deflection angle can be increased from 0.7 mrad without the blue light excitation to 2.5 mrad with the blue light excitation at a penetration depth of 5 mm under the same external applied voltage, which is consistent with the theoretical analysis. This represents a substantial increase in the deflection angle at a much deeper penetration depth, which can be very useful for applications such as high speed 3D printings and displays.

In this paper, we present a novel large capacity (a 1000+ channel) time division multiplexing (TDM) laser beam combining technique by harnessing a state-of-the-art nanosecond speed potassium tantalate niobate (KTN) electro-optic (EO) beam deflector as the time division multiplexer. The major advantages of TDM approach are: (1) large multiplexing capability (over 1000 channels), (2) high spatial beam quality (the combined beam has the same spatial profile as the individual beam), (3) high spectral beam quality (the combined beam has the same spectral width as the individual beam, and (4) insensitive to the phase fluctuation of individual laser because of the nature of the incoherent beam combining. The quantitative analyses show that it is possible to achieve over one hundred kW average power, single aperture, single transverse mode solid state and/or fiber laser by pursuing this innovative beam combining method, which represents a major technical advance in the field of high energy lasers. Such kind of 100+ kW average power diffraction limited beam quality lasers can play an important role in a variety of applications such as laser directed energy weapons (DEW) and large-capacity high-speed laser manufacturing, including cutting, welding, and printing.

In this paper, a high-speed non-mechanical two-dimensional KTN beam deflector is reported. The scanning mechanism is based on the combination of space charge controlled beam deflection and temperature gradient enabled beam deflection in a nanodisordered KTN crystal. Both theoretical analyses and experimental investigations are provided, which agree relatively well with each other. This work provides an effective way for realizing multi-dimensional high-speed non-mechanical beam deflection, which can be very useful for a variety of applications, including high-speed 3D laser printing, high resolution high speed scanning imaging, and free space reconfigurable laser communications.

In most beam steering applications such as 3D printing and in vivo imaging, one of the essential challenges has been high-resolution high-speed multi-dimensional optical beam scanning. Although the pre-injected space charge controlled potassium tantalate niobate (KTN) deflectors can achieve speeds in the nanosecond regime, they deflect in only one dimension. In order to develop a high-resolution high-speed multi-dimensional KTN deflector, we studied the deflection behavior of KTN deflectors in the case of coexisting pre-injected space charge and composition gradient. We find that such coexistence can enable new functionalities of KTN crystal based electro-optic deflectors. When the direction of the composition gradient is parallel to the direction of the external electric field, the zero-deflection position can be shifted, which can reduce the internal electric field induced beam distortion, and thus enhance the resolution. When the direction of the composition gradient is perpendicular to the direction of the external electric field, two-dimensional beam scanning can be achieved by harnessing only one single piece of KTN crystal, which can result in a compact, high-speed two-dimensional deflector. Both theoretical analyses and experiments are conducted, which are consistent with each other. These new functionalities can expedite the usage of KTN deflection in many applications such as high-speed 3D printing, high-speed, high-resolution imaging, and free space broadband optical communication.

Experimental nonlinear absorption data obtained using the open-aperture Z-scan technique are presented for 2, 3, 7, 8, 12, 17, 18-octaethyl-21H, 23H-porphine ruthenium (II) carbonyl in tetrahydrofuran. These data show saturation of nonlinear absorption dominating at low fluence but being overcome by induced absorption (reverse saturable absorption) at high fluence. Large-angle scattering measurements demonstrate that the induced absorption is real and not merely the result of scattering of light outside of the collection aperture of the detector by scattering centers induced at high fluence. A possible mechanism based on a four-band effective rate equation model is proposed. The model is used to accurately predict the results of Z scans taken at different pulse energies and to extract values for excited-state lifetimes and absorption cross sections from the experimental data.

This paper presents a nanosecond speed KTN varifocal lens. The tuning principle of varifocal lens is based on the high-speed refractive index modulation from the nanosecond speed tunable electric field. A response time on the order of nanoseconds was experimentally demonstrated, which is the fastest varifocal lens reported so far. The results confirmed that the tuning speed of the KTN varifocal lens could be significantly increased by avoiding the electric field induced phase transition. Such a nanosecond speed varifocal lens can be greatly beneficial for a variety of applications that demand high speed axial scanning, such as high-resolution 3D imaging and high-speed 3D printing.

In this paper, a multi-dimensional KTN beam deflector is presented. The multi-scanning mechanisms, including space-charge- controlled beam deflection, composition gradient-induced beam deflection, and temperature gradient-induced beam deflection are harnessed. Since multi-dimensional scanning can be realized in a single KTN crystal, it represents a compact and cost-effective approach to realize multi-dimensional scanning, which can be very useful for many applications, including high speed, high resolution imaging, and rapid 3D printing.

A non-uniform space charge-controlled KTN beam deflector is presented and analyzed. We found that a non-uniform space charge can result in a non-uniform beam deflection angles. This effect can be useful for some applications such as electric field controlled beam separation. However, a non-uniform space charge needs to be avoided if one wants uniform beam deflection throughout the entire crystal.

In this paper, we report a three orders-of-magnitude increase in the speed of a space-charge-controlled KTN beam deflector achieved by eliminating the electric field-induced phase transition (EFIPT) in a nanodisordered KTN crystal. Previously, to maximize the electro-optic effect, a KTN beam deflector was operated at a temperature slightly above the Curie temperature. The electric field could cause the KTN to undergo a phase transition from the paraelectric phase to the ferroelectric phase at this temperature, which causes the deflector to operate in the linear electro-optic regime. Since the deflection angle of the deflector is proportional to the space charge distribution but not the magnitude of the applied electric field, the scanning speed of the beam deflector is limited by the electron mobility within the KTN crystal. To overcome this speed limitation caused by the EFIPT, we propose to operate the deflector at a temperature above the critical end point. This results in a significant increase in the scanning speed from the microsecond to nanosecond regime, which represents a major technological advance in the field of fast speed beam scanners. This can be highly beneficial for many applications including high-speed imaging, broadband optical communications, and ultrafast laser display and printing.

Organic molecular materials are a class of materials in which the organic molecules retain their geometry and physical properties when crystallization takes place. Changes occur in the physical properties of individual molecules during crystallization, but they are small compared with those that occur in ionic or metallic solids. The energies binding the individual molecules together in organic solids are also relatively small, making organic molecular solids mere aggregations of molecules held together by weak intermolecular (van der Waals) forces . The crystalline structure of most organic molecular solids is more complex than that of most metals or inorganic solids; 1 the asymmetry of most organic molecules makes the intermolecular forces highly anisotropic. Owing to the electronic structure of organic molecular solids, their optical properties are often much more nonlinear than those of inorganic solids. Organic molecular materials exhibit many types of nonlinear optical properties, but three types are of interest in our investigations: optical bistability, excited-state absorption, and secondharmonic generation. There are many more nonlinear optical properties, such as sum-difference frequency generation, third-harmonic generation, and intensity-dependent index of refraction, but these are not included in our present investigation. Current materials research is centered in three areas: (1) molecular crystals, including compounds such as urea, 2-methyl-4-nitroaniline (MNA), organic dyes, and organic charge-transfer complexes (including organometallics); (2) natural products such as proteins, lipids, and alkaloids; and (3) organic polymers, including substituted polydiacetylenes, polypyrroles, and liquid crystals. Since structural modifications in the individual molecules lead to changes in the bulk properties of the solid, techniques known as "molecular engineering" have been developed. By molecular engineering deliberate chemical modifications are made on the individual molecules to effect changes in the bulk solid so that a desired optical property is enhanced. Such modifications simplify devict: processing technology by locking the optical properties of the device into the molecular structure itself, thus reducing the number of fabrication steps. Only recently have optical devices been based on organic single crystals and polymers exhibiting a variety

In this paper, a nanosecond speed KTN beam deflector is presented. The beam deflector is based on the combination of pre-injected space charge field and high speed (nanosecond) switching field. A beam deflection speed on the order of nanosecond was demonstrated, which was fastest beam deflection speed reported so far. The experimentally results confirmed that the speed limitation of KTN beam deflector was not limited by the electro-optic (EO) effect itself but the driving electric source and circuit. With a faster speed driving source and circuit, it is possible to develop GHz frequency beam deflector.

In this paper, a new type of waveguide switch-field induced dynamic optical waveguide switch is presented. The switching mechanism is based on electric-field induced dynamic waveguiding effect in nanodisordered potassium tantalate niobate (KTN) crystals. By applying an electric field at different locations, different waveguide paths are created, which result in different output locations. The major advantages of this unique optical switch are broad bandwidth, covering the entire 1300 nm - 1600 nm fiber optic communication window, and ultrafast switching speed (on the order of nanosecond), which can be very useful for next generation optical networks such as the one used in data center networks.