Search

Pulsed-biased higher speed (> 10 MHz @ 30 V, 100 ns pulse width) and DC-biased wider angle (105 mrads @ 410 V/mm) linear electro-optic (EO) deflection is reported in a thermally-controlled domain engineered (DE) ferroelectric (FE) potassium tantalate niobate [KTa1−xNb x O3, KTN] crystal. DE-FE KTN crystals can not only provide a higher transmittance and larger linear EO coefficient, but also enable higher speed (10X) and wider angle (2X) deflection than that of its paraelectric equivalent. The physical mechanism behind the optimization of injected space charge on high deflection angles at high speeds is also addressed. This significantly improves its use in megahertz EO applications.

UV-illuminated, paraelectric-phased potassium tantalate niobate (KTN) single crystals mitigate the beam deformation effects of femtosecond pulsed lasers in KTN deflectors. UV light illumination can control the amount of trapped charge present and minimize domain inversion in KTN deflectors, owing to its generated electron–hole pairs. This enables high beam quality deflection of fs pulsed lasers, with access to larger deflection angles, deflection speeds, and modulation switching ratios. These results enable the use of KTN deflectors in many fs pulsed laser applications and hasten the advancement of fs applications that require these deflection qualities.

In this letter we present the first study on the electrode surface topology enhanced KTN deflector, in which one of the electrodes contains sharp edges. In this case, the electric field can be enhanced near the sharp edge. This can increase the injected charges, which in turn results in the increased deflection angle for the space charge controlled KTN deflector. Both the conducted simulations and experimental investigations agreed well. In the experiments, the sharp edge structures were created by two methods: nanofabrication and roughing with a sandpaper. Both cases experimentally obtained increased deflection ranges. This study would be beneficial to many deflector applications because it can enlarge the deflection angle without the need to increase the driving voltage.

In this paper, we present 2-dimensional (2D) large capacity time-division multiplexing (TDM) laser beam combining technique by potassium tantalate niobate (KTN) electro-optic (EO) beam deflectors. The use of the 2D TDM approach in laser beam combining brings the following key advantages: (1) a large multiplexing capacity compared to 1-dimensional combining, (2) high spatial and spectral beam quality (the combined laser beam has the same spatial and spectral beam profile as the initial individual laser beams), and (3) independency of the phase fluctuation of individual laser beams due to the nature of incoherent laser beam combining. To demonstrate an implementation of 2D beam combining, we recorded the beam after passing KTN crystals with a CCD camera. Our result shows beam combining with a high beam quality, leading to the higher capacity of the TDM technique, which can play a crucial role in applications such as highenergy lasers, laser manufacturing, and large-capacity high-speed laser manufacturing (3D printing).

In this study, we report an experimental analysis on the triggering performance of a GaAs photoconductive semiconductor switch (PCSS) array. Resistors in parallel are known to outperform a single resistor in terms of heat management, current manipulation, wattage control, etcetera. Reconstructing the shape of resistors to obtain such a performance can impose limitations that inhibit it to compete with its parallel counterpart. The creation and synchronous triggering of a PCSS array may also result in an improved current and triggering performance which can be useful for high-speed nanosecond applications.

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.

We report an ultrahigh light extraction efficiency (LEE) light emitting diodes (LEDs) by incorporating innovative asymmetric obtuse angle microstructured surfaces. The quantitative simulations show that the LEE can be as high as 90% with realistic parameters. The physical mechanisms that enable such an ultrahigh LEE are also analyzed. It is believed that the main reasons are (1) the increased interaction surface area and (2) the better randomization effect by replacing the symmetric structure with the asymmetric obtuse angle structure. We also show that the proposed asymmetric obtuse angle microstructured surfaces are manufacturable. Experimental results also verify that a higher light extraction can be achieved by harnessing the asymmetric obtuse angle microstructured surfaces. Such an ultrahigh LEE can significantly increase the overall light efficacy of solid state lighting sources (SSL) and expedite the deployments of SSL sources.

Curie Temperature plays an important role in the applications of KTN crystals. However, every crystal is grown with a fixed Curie temperature. In this study, we present a method of manipulating the Curie temperature using strain. This could optimize the performance of our KTN deflectors and other applications.

We reported a new type of GaAs photoconductive semiconductor switch (PCSS) with nanostructured surface. Since the light could be entered not only from the top surface but also the side surface of the nanostructures, the effective penetration depth was significantly increased. This resulted in a longer lock-on time, which could be highly useful for a variety of applications that require longer lock-on time.

In this study, we quantitatively simulate the thermal effect in the application of high-speed KTN beam deflectors. Dielectric heating can contribute to a substantial temperature increase in high-speed continuous KTN electro-optic (EO) beam deflection. The influence of dielectric heating in KTN is analyzed for different parameters, such as the beam deflection angle, geometric dimension, and the scanning frequency. The optimal structure that can minimize the thermal effect is explored.

In this paper, we present a compact size polarization-independent reflection-type potassium tantalate niobate (KTN) beam deflector, including (1) a single KTN crystal, (2) a quarter-wave plate, and (3) a retroreflector. Unlike the previously reported two KTN crystal based transmission-type polarization-independent deflector, our proposed deflector offers the advantage of compact size because only a single KTN crystal is needed. Furthermore, the reflection architecture allows more surfaces of the deflector to be cooled, enhancing the laser power handling capability and the deflection speed of continuous scanning. The experimental results were consistent with the theoretical model. Our proposed beam deflector can be beneficial for a variety of applications such as high speed, high resolution 2D/3D scanning, printings, and displays.

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.

We report a new, to the best of our knowledge, type of SI-GaAs photoconductive semiconductor switch (PCSS) with nanostructures. Since light can enter from both the top and side surfaces of nanostructures, the effective penetration depth is significantly increased. Lower on-state resistance and a longer lock-on time have been achieved in the nonlinear mode with this design, as well as a lower triggering fluence in the linear mode. This could be highly useful for a variety of applications that require lower on-state resistance and/or longer lock-on time such as pulsed power systems and firing set switches.

In this paper, we propose an enhanced c-axis potassium tantalate niobate (KTN) based electro-optic (EO) deflector by compensating the performance degradation using a thermal gradient. The naturally existing composition gradient in KTN crystals prevents KTN deflectors from working at its maximum functionality at all locations along the propagation path. To overcome this fundamental limitation, we propose a KTN deflector with a temperature gradient to ensure all locations of KTN to work at the temperature having its highest permittivity. Our experimental data shows the KTN deflector with temperature gradient has near three times higher deflection angle than that of the case under uniform temperature.

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.

In this paper, we quantitatively simulate the thermal effect of charging and discharging process of high speed KTN beam deflector. The influence of thermal effect on beam quality is quantitatively analyzed. The method of reducing the thermal effect via a multi-layer design is also explored.

The electric field or stress applied to a solid material can change its polarization or dimensions, thereby altering its properties and causing a piezoelectric effect. This effect can positively or negatively impact your material depending on the sought after application. In this paper, we present a quantitative COMSOL simulation on the influence of the piezoelectric effect on the performance of high speed KTN deflectors. This includes examining the following aspects: piezoelectric induced mechanical stress and refractive index modulation. Furthermore, methods of minimizing the negative impact of piezoelectric effect, such as soft clamping, are explored in order to optimize the performance of electro-optical deflectors.

To minimize the influence of the refractive index mismatch between transparent conductive layer (e.g. Indium Tin Oxide (ITO)) and glass substrate on the light outcoupling efficiency (LOE) of organic light emitting diode (OLED), in this paper, we present a blue OLED with high LOE by incorporating a layer of tilted nanotube array as an internal light extraction structure in an optimal location. In comparison with conventional planar OLED, the LOE can be increased from 10.9 to 55.3%. The increase in LOE is mainly due to the strong disruption of waveguided mode. The tilted structure can be potentially used to develop high efficiency OLEDs.

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.

Accuracy of the Harman measurement largely depends on the heat transfer between the sample and its surroundings, so-called parasitic thermal effects (PTEs). Similar to the material evaluations, measuring thermoelectric modules (TEMs) is also affected by the PTEs especially when measuring under atmospheric condition. Here, we study the correction methods for the Harman measurements with systematically varied samples (both bulk materials and TEMs) at various conditions. Among several PTEs, the heat transfer via electric wires is critical. Thus, we estimate the thermal conductance of the electric wires, and correct the measured properties for a certain sample shape and measuring temperature. The PTEs are responsible for the underestimation of the TEM properties especially under atmospheric conditions (10–35%). This study will be useful to accurately characterize the thermoelectric properties of materials and modules.

Although the Harman method evaluates the thermoelectric figure-of-merit in a rapid and simple fashion, the accuracy of this method is affected by several electrical and thermal extrinsic factors that have not been thoroughly investigated. Here, we study the relevant extrinsic effects and a correction scheme for them. A finite element model simulates the electrical potential and temperature fields of a sample, and enables the detailed analysis of electrical and thermal transport. The model predicts that the measurement strongly depends on the materials, sample geometries, and contact resistance of the electrodes. To verify the model, we measure the thermoelectric properties of Bi2-Te3 based alloys with systematically varied sample geometries and either with a point or a surface current source. By comparing the model and experimental data, we understand how the measurement conditions determine the extrinsic effects, and, furthermore, able to extract the intrinsic thermoelectric properties. A correction scheme is proposed to eliminate the associated extrinsic effects for an accurate evaluation. This work will help the Harman method be more consistent and accurate and contribute to the development of thermoelectric materials.

Ferrocene(1-1′-ferrocene-N-dioctadecyl carboxamide), flavin(7,8-dimethly-10-dodecylisoalloxazine), viologen [N-allyl-N7′-[3-propylamidoN″,N″-di(n-octadecyl)]-4,4′bipyridiumdibromide), and cytochrome c were used as an electron donor (D), sensitize (S), the first electron acceptor (A1), and the second electron acceptor (A2), respectively in fabricating molecular device. Malonic acid or poly-L-aspartic acid were used as a bridging molecule for the adsorption of A2 molecules onto A1 layers. In order to confirm the electron transfer, Scanning tunneling microscopy(STM) investigation was performed.