Optical angular mapping for pattern recognition using self-pumped phase conjugation

An optical angular feature mapping of an object for pattern recognition is presented that uses self-pumped phase conjugation followed by a vertical projection. In this method the vertical contour features of an object are most enhanced and vertically projected at each angle as the object is rotated. The vertical enhancement of the contour and the projection are performed optically with self-pumped phase conjugation and a cylindrical lens, respectively. The peaks in the resulting projection at the angle are located and integrated to produce an angular signature function. The signature function is then energy normalized for scale invariance, and pattern recognition is performed by calculation of a cross correlation between two signature functions. The method exhibits invariance to shift, rotation, and variations in scale. Effects of a spatial filter and incident-beam conditions used for phase conjugation are also discussed along with experimental results.     

Reflection-grating self-pumped phase conjugation with optical feedback free of input conditions

A reflection-grating self-pumped phase-conjugate mirror is demonstrated with a photorefractive KNbO(3) crystal in a novel ring configuration. The feedback beam in the ring configuration is made to track the input probe beam automatically so that the phase conjugation is sustained without readjustment of the optical feedback loop when the angle or the position of the input probe beam is changed. The tracking feedback is realized by means of a simple three-lens erect imaging system. The angular and the positional acceptances for a tightly focused input beam of 50-μm diameter are Δθ(x). = 55 mrad, Δθ(y), = 67 mrad, and Δ(x) = 2.1 mm, Δ(y) = 4.2 mm, respectively.     

Generation of self-pumped phase conjugation from the -c face of BaTiO3 with femtosecond pulses

We demonstrate a new configuration of self-pumped phase conjugation in BaTiO(3) with 450-nm femtosecond pulses. The pump beam enters the -c face of the crystal at an acute angle with respect to the +c axis. This geometry is different from all known geometries of self-pumped phase conjugations in BaTiO(3). Phase-conjugate reflectivity of 1.7% and a rise time of ~24 s are obtained at an average pump power of 10 mW. The ability of the phase conjugator to serve phase distortions correctly is demonstrated. We propose that the femtosecond phase conjugator operate with the hologram mechanism sharing as the double phase conjugator. The self-pumped phase-conjugate pulses are analyzed by femtosecond electric-field cross correlation.     

Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

Abstract

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO₃:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi₁₂SiO₂₀ (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.     

Self-pumped phase conjugation in microspheres

When a microscopic sphere is illuminated by a laser beam, interference fringes inside the sphere lead through the Kerr effect to a holographic grating. This grating is capable of phase conjugation, which is particularly strong when optical resonance takes place. According to numerical simulation, based on the Green function method, phase-conjugation reflectivity R = 0.5 can be achieved in a single silica sphere of approximately 9-microm diameter with realistic laser power. Such spheres can be aligned together to become a phase-conjugation mirror of large area and high reflectivity.     

相位共轭方法的声源定位分辨率研究

相位共轭方法可实现声波的反向传播和自适应聚焦,可用于声源定位。基于有限阵元平面阵列和球面阵列使用数值方法对相位共轭方法的定位分辨率进行了研究,研究了相位共轭阵列的形式及阵列与声源间距和声源定位分辨率的关系,还研究了在声源处设置声汇对噪声源定位分辨率的影响。数值结果表明:只有在近场测量声压梯度并使用偶极子源的相位共轭才能突破声波衍射极限分辨率;平面阵列距离点声源的距离越远分辨率越低,闭合球面阵列的分辨率不随阵列距离点声源距离的改变而改变;使用声汇后基于非近场测量也能突破声波衍射极限分辨率。     

Pentagon-shaped 0 degrees -cut BaTiO3 as an efficient self-pumped phase conjugator

A pentagon-shaped 0(o)-cut undoped BaTiO(3) crystal was used to construct a high-quality self-pumped phase conjugator. The conjugator shows a steady phase-conjugate output with a high reflectivity (as high as ~68%), a fast rising time, and a large angular range of acceptance. It also shows a good fidelity in the phase-conjugate reconstructed image; the resolution reaches 17 mum.     

Enhanced stimulated photorefractive scattering self-pumped phase conjugator in Ce-doped BaTiO 3 with external mirrors

The characteristics of stimulated photorefractive scattering self-pumped phase conjugator (SPS-SPPC) in BaTiO3 :Ce crystal without and with an external mirror have been studied and compared. The experimental results show that the SPS-SPPC becomes unstable at a larger incident angle. An additional external mirror can create a stable optical path in the crystal and improve the stability of the SPS-SPPC effectively, and, at the same time, it can enhance the response rate and the phase conjugate reflectivity as well. We offer a reasonable explanation of the experimental results by using a semilinear cavity model.     

The influence of phosphorous pentoxide on the phase composition and formation of Portland clinker

The influence of phosphorous pentoxide (P₂O₅) on the phase composition and formation of Portland clinker was studied in laboratory conditions. Phosphorous pentoxide in the form of calcium phosphate was added to common cement-making raw meal in graded quantities up to 5 wt.%. The raw meal properties were studied by thermal analysis. The development of clinker formation by burning for periods ranging from 20 s to 30 min in a special semi-automatic oven with a manipulator was followed using light optical microscopy. The phase composition of clinkers burnt to equilibrium was quantified by the optical point counting method. The entry of P₂O₅ into clinker minerals was determined by electron microprobe analyses. The laboratory tests show that at 0.7 wt.% of P₂O₅ in the clinker the alite (Ca₃SiO₅) content decreases and belite (Ca₂SiO₄) content increases. At a P₂O₅ content of 4.5 wt.% alite formation was totally blocked and the resulting clinker contained free lime in equilibrium with belite.     

ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

This paper reports the synthesis and characterization of Cu₂ZnSnS₄ (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 °C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

     

Influence of the internal photoinduced electric field on the formation of self-pumped phase conjugation in doped (K(0.5)Na(0.5))(0.2)(Sr(0.75)Ba(0.25))(0.9)Nb(2)O(6) crystals

The obvious influence of the internal photoinduced electric field on the formation of self-pumped phase conjugation in doped (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals has been investigated with intermittent and continuous laser beams. An analysis is given that involves the migration of charge carriers driven by the photovoltaic (PV) and the pyroelectric (PY) electric field. Deviation from the optimal state of energy transfer owing to the PV effect and the self-adjusting of holograms owing to the PY field are the two important dominant processes in the self-pumped phase conjugator. The influence of the photoinduced electric field on the conjugation fidelity and the stability of the phase-conjugate output is also observed and analyzed. The bump feature of the two-wave mixing and the oscillating situation of the self-pumped phase conjugator are observed and are explained in view of the photoinduced internal field.     

阵列形式和界面条件对相位共轭阵列聚焦特性的影响

相位共轭阵列可以基于声压测量或质点速度测量使用单极子源或偶极子源在近场或非近场来进行时间反转,海面和海底等反射界面对相位共轭阵列的聚焦特性有影响。采用有限阵元平面阵列使用数值方法研究了5种不同相位共轭阵列的聚焦特性。结果表明：只有在测量距离小于1/5波长,基于声压梯度测量并使用偶极子源的相位共轭阵列才能突破声波衍射极限分辨率。还研究了界面条件对相位共轭阵列聚焦特性的影响,结果表明：界面反射条件对聚焦分辨率影响不大,只是增大了聚焦的强度,界面反射系数的绝对值越大,相位共轭声场的声压幅值越大;当阵列测量距离在声源的近场时,界面对阵列聚焦特性的影响非常小;当阵列测量距离较近时,刚性界面对声压幅值的影响大于自由界面的影响,但自由界面的影响随着阵列与声源距离的增大而增大,当测量距离较远时,自由界面的影响已远大于刚性界面的影响;随着界面与阵列和声源的距离的增大,界面对聚焦特性的影响越来越小。     

Approximate phase conjugation with a retroreflecting array in microscopy

Some experiments on image recovery in microscopy are described. The aperture stop of a microscope objective is partially obscured, and a retroreflecting array is used as an approximate phase conjugator to return the beam through the unobstructed part of the aperture. An application is made to the measurement of the absolute reflectance of small samples by use of a variant of Strong's method.     

Multi-frequency parametric phase conjugation of ultrasound beams in magnetic ceramics

A new operation mode of a parametric phase conjugation of ultrasound waves above the threshold of absolute parametric instability of phonons is reported. A deviation of the carrier frequency in a sequence of incident ultrasound bursts and in a proper sequence of electromagnetic pumping is applied. The deviation avoids amplification of the reverberation noise in the active medium when the repetition time of the conjugation is short enough to be comparable with the relaxation time of acoustic reverberations. As a result, a decrease of repetition time and a correspondent increase of the average output power of a phase conjugator becomes available. The advantage of the new operation mode is demonstrated on an example of supercritical phase conjugation in magnetoacoustic ceramics.     

The influence of processing pressure on the formation of the high-T c 2223 phase in Bi-Pb-Sr-Ca-Cu-O superconductors

The effects of processing pressure on the superconducting critical transition temperature, T _c, of Bi_1.6Pb_0.4Sr_1.9Ca_2.05Cu_3.05 O_x were investigated. Uniaxial cold- and hot-pressed samples prepared from mixed oxide and chemically coprecipitated powders were studied. The uniaxial cold-pressed specimens were pressed at a low pressure of 34.5 M Pa (5000 p.s.i.) and a high pressure of 138.7 M Pa (20 120 p.s.i.) and sintered at 845 °C for times ranging from 24–200 h. The mixed oxide samples showed a 0.5 K increase in T _cas the pressure was increased, while the chemically coprecipitated samples showed a 3.6 K increase in T _cwith the same increase in pressure. The uniaxial hot-pressed specimens were hot pressed at 845 °C for 6 h in oxygen at a pressure of 34.5 MPa (5000 p.s.i.) and post-annealed for 24–30 h in air at 845 °C. These samples, both mixed oxide and chemically coprecipitated, showed an increase in T _cof approximately 25 K from the hot-pressed state to the post-annealed state. The highest T _cachieved by either of these processing methods was 108.4 K.     

Possibilities for correcting aberrations of imaging laser systems by phase conjugation

The reported method of using phase conjugation to correct distortions induced by projection optics was realized experimentally. In particular, the method was used on a low-quality 50-cm-diameter objective mirror to form laser radiation with a near diffraction-limited beam divergence of 2.4 × 10(-6) rad. The method could be applied to high-resolution imaging of objects in coherent light.     

Optical encryption system that uses phase conjugation in a photorefractive crystal

We implement an optical encryption system based on double-random phase encoding of the data at the input and the Fourier planes. In our method we decrypt the image by generating a conjugate of the encrypted image through phase conjugation in a photorefractive crystal. The use of phase conjugation results in near-diffraction-limited imaging. Also, the key that is used during encryption can also be used for decrypting the data, thereby alleviating the need for using a conjugate of the key. The effect of a finite space-bandwidth product of the random phase mask on the encryption system's performance is discussed. A theoretical analysis is given of the sensitivity of the system to misalignment errors of a Fourier plane random phase mask.     

Double phase conjugation in copper-doped potassium sodium strontium barium niobate crystals

We show a double phase conjugator with novel crystals of copper-doped potassium sodium strontium barium niobate. The phase conjugation reflectivity can reach 278% and depends on relative input positions of both incident beams. The response time with the input beam power ratio is measured and modeled as a function of input beam power ratio. The formation of the arch coupling loop is analyzed with theoretical simulation results and a positive feedback process is proposed. The influence of a self-pumped phase conjugation process on double phase conjugation fidelity is also discussed. It is necessary to avoid generating self-pumped phase conjugation to prevent the reduction of double phase conjugation fidelity.     

The influence of plastic properties on chip formation

A two-dimensional finite-element model of the chip formation process is used to study the influence of the material law determining plastic flow on chip formation of titanium alloys at high cutting speeds. For simplicity, friction and thermo-mechanical properties of the tool are neglected in the simulations. Titanium chips are strongly segmented and therefore especially suitable to study the role of segmentation for the cutting force and other cutting parameters. Of special interest is the influence of the thermal softening parameter in the material law. Increasing thermal softening leads to a drastic decrease in the cutting force and a corresponding increase in chip segmentation. A variation of the hardening exponent is also performed. It is shown that the simulation results can be understood by using adiabatic flow stress curves. The variation of the hardening exponent leads to strongly differing chip shapes, although the cutting force stays nearly constant. This shows that mean cutting forces should not be used as simulation verification parameters.