Central Peak Intensity Research Articles

Optimization of measurement in self-aligned liquid crystal optical control devices with two-slit Young’s experiment

We have investigated an interference experiment of the two-slit Young experiment using an improved self-alignment (SA) liquid crystal optical control device structure. The newly developed SA process and optimization of slit structure and slit width were redesigned to micron size in order to make the interference pattern clear. As a result, we observed a clear NOT logic operation where the center peak intensity of the incident light is inverted.

Propagation of synchrotron radiation through double microchannel plate device: Comparison of experimental data and wave-approach simulation

Since third-generation synchrotron radiation facilities are highly brilliant sources, the scattering of a partially coherent beam gives rise to strong interference effects. We present and discuss in this contribution the comparison of simulated and experimental diffraction patterns collected with an optical device made by two identical flat Micro Channel Plates (MCPs) illuminated by synchrotron radiation at different energies. The experimental patterns clearly show the increase of the density of the main peak with respect to those collected with a single flat MCP. Data demonstrate that the use of a device based on two MCPs is an ideal optical system to condense the primary radiation in a narrow intense central peak.

Brillouin Scattering Study of Electro-Optic KTa1-xNbxO3 Crystals.

The functionality enhancement of ferroelectrics by local polar clusters called polar nanoregions (PNRs) is one of the current interests in materials science. KTa1-xNbxO3 (KTN) with perovskite structure is a well-known electro-optic crystal with a large Kerr effect. The existence of PNRs in relaxor-like ferroelectric Nb-rich KTN with homovalent B-site cations is controversial. This paper reviews recent progress in understanding precursor dynamics in Nb-rich KTN crystals studied using Brillouin scattering. The intense central peak (CP) and significant softening of sound velocity are observed above the Curie temperature (TC) due to the polarization fluctuations in PNRs. The effects of Li-doping, defects, and electric fields on the growth and/or creation of PNRs are found using changes in acoustic properties. The electric-field-induced TC, which is shifted to higher values with increases in applied voltage, including critical endpoint (CEP) and field gradient by trapped electrons, are discussed as well. This new knowledge may give new insight into advanced functionality in perovskite ferroelectrics.

Engineering of Aberrated PSF by Asymmetric Apodization with the Complex Shaded Aperture

The point spread function (PSF) produced by a coherent optical system under the influence of defocus, coma, and primary spherical aberration (PSA) is examined in this work. This paper deals with asymmetric apodization and pupil engineering to control monochromatic aberrations. To reduce the influence of monochromatic aberrations on the diffracted PSF, this approach uses amplitude and phase apodization. Analytical investigations on intensity PSF are carried out with varying amounts of aberrations and degrees of amplitude and phase apodization. Computed central peak intensity and full width at half maxima (FWHM) and analyzed. The resolution of a diffraction-limited optical imaging system is improved by using an asymmetric optical filter that minimizes the effect of defocus.

Broadband Brillouin scattering study of ferroelectric instability of barium sodium niobate

The barium sodium niobate (BNN) with tungsten-bronze structure is one of well-known optical crystals for electro-optic and nonlinear optic applications. This paper reviews the ferroelectric instability of BNN crystals. BNN is a uniaxial ferroelectric with a spontaneous polarization along the tetragonal c-axis. There is no report on the observation of an optical soft mode responsible for a ferroelectric phase transition. In the vicinity of the Curie temperature, TC = 560°C, an intense central peak (CP) related to the polarization fluctuations along the c-axis was observed by the broadband Brillouin scattering experiment. The relaxation time determined by the CP width shows the critical slowing down towards TC. This fact indicates that the ferroelectric instability of BNN is an order-disorder type.

Effects of turbulent atmosphere on the propagation properties of vortex Hermite-cosine-hyperbolic-Gaussian beams

The propagation properties of a vortex Hermite-cosh-Gaussian beam (vHChGB) in atmospheric turbulence are investigated based on the extended Huygens–Fresnel diffraction integral and Rytov method. The analytical formula for the average intensity of a vHChGB propagating in turbulent atmosphere is derived in detail. The influence of the turbulence strength on the intensity distribution under the change of beam parameters conditions is illustrated numerically and discussed. Results show that the profile of the initial vHChGB remains unchanged within small propagation distance range, and at certain propagation distance a central peak intensity appears, and finally the beam evolves into Gaussian profile–like in far-field. The rising speed of the central peak intensity is faster when the turbulence strength is larger or the beam parameters such as the beam order, the vortex charge and the Gaussian waist width are smaller. With a small decentered parameter b, the beam profile changes faster as the wavelength is larger, whereas the reverse behavior occurs when b is large. The obtained results may be useful for the practical applications of vHChGB in optical communications and remote sensing.

Thermal effect induced dynamically lasing mode tuning in GaN whispering gallery microcavities

Thermal modulated real-time wavelength tuning of semiconductors has shown great potential for GaN-based sensors or photo-electricity modulators. Herein, we study the temperature mediated photoluminescence (PL) properties in GaN materials via PL and time-resolved PL measurement in situ and synchronously. We then broaden the phenomenon to lasing mode tuning of whispering gallery cavities. To understand the underling mechanism, time, and frequency domain properties of spontaneous emission from GaN film, amplified spontaneous emission and stimulated emission from floating GaN microdisks in a temperature region from 0 °C to 50 °C are compared. According to analysis of temperature-related changes in the central wavelength, peak intensity, full width at half maximum (FWHM), and carrier dynamics, the thermal controlled PL properties of various structures are well understood. Material structure-related changes in exciton combination channels and temperature-related changes in central wavelength, peak intensity, FWHM, and exciton combination times are observed. Finally, real-time lasing mode modulation in floating GaN microdisks is realized. Our work reveals the lasing tuning method in situ, implying a promising strategy for fabricating high performance thermal-optic modulation devices.

Tunable low-coherence light source with high spectral brightness

Operation of a tunable tandem-type low-coherence light source with high spectral brightness based on commercially available optical elements (superluminescent diode, semiconductor optical amplifier, and bulk dwiffraction grating) is studied experimentally. A unique combination of the output source characteristics, namely, a spectral power density of 36 mW nm−1, a wavelength tuning range of 35 nm (834 – 869 nm), and a more than 20-dB excess of the central peak intensity over the superluminescent pedestal, is experimentally obtained. It is shown that the output radiation spectrum with a width of 1.4 nm has a smooth bell-shaped profile with side lobes lying below the superluminescent pedestal. It is proved that such a light source is of practical interest for various applications.

Fundamental mode intensity evolution in tapered optical fibres

The mode field intensity, spot size, central peak intensity evolution and adiabaticity are calculated for different points along the transition of an optical fibre taper that adiabatically tapers from the standard 125 nm down to 1 µm and then to 440 nm diameter for low loss operation at 1550 nm wavelength. The first section of the taper is evaluated using a weak guidance approximation. The second section is treated as a three-index layer structure (double-clad) and evaluated with eigenvalue equations for three refractive indices. The third and thinnest section of the taper is studied using an exact mode eigenvalue equation. The results show that the fundamental mode for the third section has a discontinuity at the fibre edge with a peak intensity larger than the intensity at the centre of the fibre. Since the guiding by the core disappears in the first section of the taper, the mode field does not simply reduce monotonously along the taper with the outer diameter of the fibre. By this novel approach, and for the first time, to the best of our knowledge, the taper shape that complies with the adiabaticity criterion, the mode intensity profile and the spot size (first Petermann definition) of the fundamental mode evolution, along their position on the taper are determined.

Transformation of double-half inverse Gaussian hollow beams into superposition of finite Airy beams using an optical Airy transform

In the present work, we investigate theoretically the transformation of a double-half inverse Gaussian hollow (DHIGH) beam into a superposition of finite Airy beams by using an optical Airy transform system. The analytical expression of the generated finite Airy beam is derived by means of the generalized Huygens–Fresnel integral diffraction. Numerical calculations show that the optical Airy transform system converts the central dark spot of the hollow incident beam into peak intensity. It is demonstrated that the characteristics of the transverse intensity distribution of the output finite Airy beam are determined by the phase pattern’s constants of the Airy transform system and the radius size of the incident DHIGH beam. Moreover, it is shown that the profile of the central peak intensity of the generated beam can be controlled by means of the radius size of the incident hollow DHIGH beam.

Vibrational Dynamics of Ferroelectric K(Ta1-xNbx)O3 Studied by Inelastic Light Scattering

The Fano resonance of non-doped KTa1-xNbxO3 (x = 0.32) single crystals was investigated by the Raman spectroscopy. The intensity of central peak (CP) and parameters of the Fano resonance revealed a significant anomaly in the vicinity of the Curie temperature, TC = 259 K. The vibrational dynamics and the symmetry breaking in the cubic phase are discussed in the framework of weak random fields. It is concluded that the coupling between continuum states induced by polar nanoregions (PNRs) and a transverse optic (TO2) phonon at about 194 cm−1 is the origin of a Fano resonance in non-doped KTN crystals.

Successive phase transition of lead-free ferroelectric sodium potassium niobate crystals studied by Raman scattering

ABSTRACTThe lattice instability of lead-free potassium sodium niobate, (K0.5Na0.5) NbO3 (KNN50) piezoelectric crystals were studied by Raman scattering in the temperature range between 20 and 550 °C. The KNN50 undergoes the cubic to tetragonal ferroelectric phase transition at TC = 430 °C, and the tetragonal to monoclinic structural phase transition at Ttr = 190 °C. In the monoclinic phase, the lowest frequency mode at 68 cm−1, which is related to the soft mode of KNbO3, is clearly observed at room temperature. On heating from room temperature it shows noticeable softening towards Ttr and becomes overdamped. For further heating, the intense central peak (CP) appears in the tetragonal phase just above Ttr, and the CP intensity shows a peak at TC. The relaxation time determined from the CP width shows the critical slowing down towards TC.

Polarization rotation associated with phonon dynamics in monoclinic C phase near morphotropic phase boundary studied by diffuse and inelastic X-ray scattering from a Ti-composition-gradient Pb[(Mg1/3Nb2/3)1–xTix]O3 single crystal

ABSTRACTWe have investigated polarization rotation associated with phonon dynamics in the relaxor ferroelectrics Pb[(Mg1/3Nb2/3)1–xTix]O3. The intensity distributions of the diffuse scattering patterns show intensity- crossover behavior in the monoclinic-C(MC) phase over a wide Ti composition range (29 < x < 32 mol%). The transverse acoustic (TA) mode of the crossover region along the [001] direction softens and is damped, strongly correlating with the central peak intensity, which originates in the polar regions. These results indicate that the lattice can easily deform in the MC phase, and the polarization can rotate easily by associating with the TA mode.

Generating a three-dimensional hollow spot with sub-diffraction transverse size by a focused cylindrical vector wave

A three-dimensional (3D) hollow spot is of great interest for a wide variety of applications such as microscopy, lithography, data storage, optical manipulation, and optical manufacturing. Based on conventional high-numerical-aperture objective lenses, various methods have been proposed for the generation of 3D hollow spots for different polarizations. However, conventional optics are bulky, costly, and difficult to integrate. More importantly, they are diffraction-limited in nature. Owing to their unique properties of small size, light weight, and ease of integration, planar lenses have become attractive as components in the development of novel optical devices. Utilizing the concept of super-oscillation, planar lenses have already shown great potential in the generation of sub-diffraction, or even of super-oscillatory features, in propagating optical waves. In this paper, we propose a binary-phase planar lens with an ultra-long focal length (300λ) for the generation of a 3D hollow spot with a cylindrical vector wave. In addition, we experimentally demonstrate the formation of such a hollow spot with a sub-diffraction transverse size of 0.546λ (smaller than the diffraction limit of 0.5λ/NA, where NA denotes the lens numerical aperture) and a longitudinal size of 1.585λ. The ratio of central minimum intensity to the central ring peak intensity is less than 3.7%. Such a planar lens provides a promising way to achieve tight 3D optical confinement for different uses that might find applications in super-resolution microscopy, nano-lithography, high-density data storage, nano-particle optical manipulation, and nano-optical manufacturing.

Electric field induced critical points and field gradient by trapped electrons in Li-doped KTa1-xNbxO3 single crystals

The effects of electric field and trapped electrons on a ferroelectric phase transition of the 5%Li-doped KTa0.74Nb0.26O3 crystals were investigated by micro-Brillouin scattering and dielectric measurements. In micro-Brillouin scattering, the remarkable changes of the central peak (CP) intensity were observed at the paraelectric cubic to ferroelectric tetragonal phase transition. The critical electric fields to induce the paraelectric to ferroelectric phase transition were found to shift to higher values with increasing temperature. From these CP results, we estimated lines of critical points for phase transitions including critical end point (CEP), (E, T) = (1.6 kV/cm, TC-T+3.4 °C) in the composition-temperature-electric field (x-T-E) phase diagram. The clear difference of the CEP was observed between Brillouin result at a fixed small area and dielectric result averaged over all area of a sample. It can be caused by the field gradient, which is induced by the trapped electrons. The existence of gradient of electric field was also discussed using the observed result of position dependence of the CP intensity.

Non-diffractive beam in random media

Beam propagation has been given important attention in a variety of applications in medicine, remote sensing and information science. Especially, the beam propagation in highly scattering media, which is called random media, is important. In general, the multiple scattering gets rid of beam characteristics, e.g., intensity distribution, phase front, and polarization. In this study, self-converging effect of annular beam was applied in random media. Diluted milk was used as random media, and the transmitted light was detected with a narrow view angle of 5.5mrad. The collimated annular beam of a few tens millimeters takes a few hundred meters to transform its beam shape into the non-diffractive beam in free space, while this transformation was shorten only to 20cm in random media, that is, the collimated annular beam caused its transformation at only 20cm in random media. The transformed beam kept its optical characteristics of “non-diffractive beam”. Such transformation of the annular beam needs the appropriate condition of random media. Media concentration and propagation distance control the generation of the center peak intensity of the transformed beam. This study indicates the generation of the non-diffractive beam in random media and reveals its appropriate condition.

Asymmetric apodization for the comma aberrated point spread function

This paper deals with the study of light flux distributions in the point spread function formed by an optical system with a one-dimensional aperture under the influence of the coma aberration. The traditional design of an asymmetric optical filter improves the resolution of a diffraction-limited optical imaging system. In this approach we explore the control of monochromatic aberrations through pupil engineering with asymmetric apodization. This technique employs the amplitude and phase apodization for the mitigation of the effects of third-order aberrations on the diffracted image. On introducing the coma wave aberration effect, the central peak intensity in the field of diffraction is a function of the edge strips width and the amplitude apodization parameter of a one-dimensional pupil filter, whereas the magnitude of the reduction of optical side-lobes is a function of the degree of phase apodization at the periphery of the aperture. The analytically computed results are illustrated graphically in terms of point spread function curves under various considerations of the coma aberrations and a different degree of amplitude and phase apodization. Hence, for the optimum values of apodization, the axial resolution has been analyzed using well-defined quality criteria.

Spherical Aberration of Point Spread Function with Asymmetric Pupil Mask

Point spread function underneath spherical wave aberration with antiphase apodization has been obtained by one-dimensional pupil mask functions. In the presence of spherical aberration, suppression of optical side-lobes has increased on one side of the point spread function with the width of the periphery strips within the pupil mask. On introducing wave aberration effect, there exists dependence of the lateral resolution of central peak of the asymmetric point spread function on the amount of amplitude masking. However, the magnitude of intensity of central peak is originated be to amplified by the highest degree of amplitude and phase masking. Additionally, for aberrated asymmetric PSF, FWHM increases and it further decreases with the control parameters of amplitude and phase mask. The magnitude of this corollary can quantify the super resolution of diffracted structures under spherical aberration.

The role of polar-nanoregions in KTa1-xNbxO3 single crystals studied by Raman scattering

ABSTRACTThe dynamical properties of KTa1-xNbxO3 (x = 0.40) crystals were investigated by Raman scattering. The remarkable change of the central peak (CP) intensity was observed in the vicinity of TC. The physical origin of the CP in the cubic phase caused by the fluctuating polar nanoregions (PNRs) with A1(z) symmetry was discussed using the results of the angular dependence of Raman scattering. The phase difference between different Raman tensor components related to PNRs with the A1(z) symmetry was observed. The local symmetry breaking in the cubic phase was discussed on the basis of the evolution of the PNRs.

Fano resonance of Li-doped KTa(1-x)NbxO3 single crystals studied by Raman scattering.

The enhancement of functionality of perovskite ferroelectrics by local structure is one of current interests. By the Li-doping to KTa1−xNbxO3 (KTN), the large piezoelectric and electro-optic effects were reported. In order to give new insights into the mechanism of doping, the microscopic origin of the Fano resonance induced by the local structure was investigated in 5%Li-doped KTN single crystals by Raman scattering. The coupling between the continuum states and the transverse optical phonon near 196 cm−1 (Slater mode) caused a Fano resonance. In the vicinity of the cubic-tetragonal phase transition temperature, TC-T = 31 °C, the almost disappearance of the Fano resonance and the remarkable change of the central peak (CP) intensity were observed upon heating. The local symmetry of the polar nanoregions (PNRs), which was responsible for the symmetry breaking in the cubic phase, was determined to E(x, y) symmetry by the angular dependence of Raman scattering. The electric field induced the significant change in the intensity of both CP and Fano resonance. From these experimental results, it is concluded that the origin of the Fano resonance in Li-doped KTN crystals is the coupling between polarization fluctuations of PNRs and the Slater mode, both belong to the E(x, y) symmetry.