有机染料溶液中简并的四波混频和位相复共轭研究(英文)

研究了近共振增强的四能级系统有机染料溶液中简并的四波混频后向反射波及前向波的位相复共轭特性。用有效长度为5mm,浓度为2.5×10~(-5)mol的叶录素A甲醇溶液作介质,当调QNd:YAG倍频泵浦光的能量为8mj时,非线性反射率为22％。 对于若丹明6G酒精溶液,在相同条件下的反射率为10％。用象差板检证了位相复共轭特性。用调QNd:YAG激光辐射作泵浦源,研究了若丹明6G酒精溶液双光子共振增强的简并的四波混频作用。当介质浓度为10~(-4)克分子,有效长度为5mm,泵浦光能量为70mj时,非线性反射率达14％。测量了非线性反射率与介质浓度及入射物波与后向反射波的强度的关系曲线。理论分析了四波混频前向波的位相复共轭特性,用调QNd:YAG倍频激光作泵浦源,若丹明6G酒精溶液作介质,实验上证实了理论的预言。另外,把四重简并的四波混频推广到二重简并的情况。用若丹明6G酒精溶液作介质,实现了由6300A到5320A的象转换。用9740有机染料二氯乙烷饱和吸收溶液作介质,实现了1.06μm到5320A的象转换。当介质长度为5mm,泵浦光束的能量为5mj时,后者的转换效率为25％。理论分析表明,用对红外近共振吸收,而对可见辐射是透明的介质可以实现高效率的红外象转换。这种红外象转换的方法还具有实时、快响应等优点。     

简并四波混频与位相复共轭(Ⅱ)

四、简并四波混频的理论研究工作 多年来,围绕简并四波混频的物理机制及影响位相复共轭反射波产生的效率的各种因素,开展了许多理论研究.这里只能作一概要的介绍.1.透明介质的简并四波混频理论 理论分析最初由Yariv等人完成.在图9中,与非线性介质相互作用的有四个波,即抽运光波Ef和Eb,探测光波Ep和共轭反射波Ec.假定它们均近似表示为平面波 一般在实验中探测光波及其共轭反射波相对抽运光波都弱得多,因此可以假定在混频相互作用中抽运光强度不变.现集中研究Ep和Ec的变化.由于四波耦合的结果,产生了波矢分别为Kc及Kp的三阶非线性极化利用…     

Fe:LiNbO_3晶体简并四波混频(DFWM)在光学图象处理中的应用

本文介绍Fe:LiNbO_3晶体在波长为6328A的低功率激光下的简并四波混频(DFWM)现象。给出了在不同泵浦功率下,共轭波强度随照射时间变化的实验曲线。验证了共轭波的位相补偿特性,并利用该特性校正了位相畸变的图象,得到了与理论相一致的实验结果。     

有机染料溶液中简并的四波混频和位相复共轭研究

本文研究了近共振增强的四能级系统有机染料溶液中简并的四波混频后向波和前向波的位相复共轭特性。用有效长度为5毫米、浓度为2.5×10^-5克分子的叶绿素A甲醇溶液作介质,当调QNd:YAG倍频抽运光能量为8毫焦耳时,非线性反射率为22％。研究了若丹明6G酒精溶液双光子共振增强的简并的四波混频作用。测量了非线性反射率与介质浓度及抽运波和物波强度的关系曲线。理论分析了四波混频前向波的位相复共轭特性,实验证实了理论的预言。另外,把四重简并的四波混频推广到二重简并。用9740有机染料二氯乙烷饱和吸收溶液作介质,实现了1.06微米到5320埃的象转换。介质长度为5毫米,抽运光能量为5毫焦耳时,转换效率达25％。理论分析表明,用对红外近共振吸收而对可见辐射是透明的介质可实现高效率红外象转换。 关键词：     

Fe:LiNbO3晶体简并四波混频(DFWM)在光学图象处理中的应用

本文介绍Fe:LiNbO₃晶体在波长为6328?的低功率激光下的简并四波混频(DFWM)现象。给出了在不同泵浦功率下,共轭波强度随照射时间变化的实验曲线。验证了共轭波的位相补偿特性,并利用该特性校正了位相畸变的图象,得到了与理论相一致的实验结果。 关键词：     

在有机染料溶液中简并的四波混频作用和位相复共轭

本文研究了近共振吸收增强的有机染料溶液中简并的四波混频作用和位相复共轭特性。由直接位相复共轭得到了高质量的再现象。再现象分辨率为6条线/毫米。对于浓度为2.5×10^-5克分子若丹明6G酒精溶液,得到非线性反射率达10％。 关键词：     

光折变晶体中四波混频中间段强度特性的研究

对Ce:KNSBN晶体四波混频相位共轭中间段的强度特性进行了实验研究。建立了在弱后向抽运小信号条件下的理论公式,并进行了分析。实验结果与理论曲线趋势相一致。     

砷化镓晶体中的四波混频

本文报道了以1.06μm调QNd:YAG激光脉冲,采用简并四波混频的方法,在未掺杂的GaAs单晶中产生红外位相共轭短脉冲。研究了该光脉冲的主要特性。用实验的方法探讨了影响共轭光强弱的主要因素。     

用单池布里渊增强四波混频改善SBS系统位相共轭度

本文报道用布里渊增强四波混频改善受激布里渊系统位相共轭度的实验研究，与一般配置ＳＢＳ相比，系统位相共轭度从０．５８提高到０．７８。     

BR-PVA固体膜在四波混频相干场中的光栅特性和位相共轭波的暂态行为

利用Ar离子激光简并四波混频(DFWM)技术,对细菌视紫质(BR)-聚乙烯醇(PVA)固体膜的位相共轭波特性进行了理论和实验研究。采用BR光循环的双态模型和粒子数速率方程,以及全息光栅理论描述了该体系的PC波的衍射效率、时间响应和饱和特性,给出了相应的表达式。讨论了该体系在DFWM场中的光栅机制和上述特性对于输入波的偏振态,强度和强度比,到达样品的时间和形成的初始浓度光栅等参数的依赖关系。实验结果与理论分析相符。     

KNSBN：Co晶体自泵浦位相共轭特性的研究

本文报道在两块不同尺寸的KNSBN:Co晶体中实现了自泵浦位相共轭输出,通过实验验证了位相共轭反射率与入射角、入射位置以及波长有关,并给出各自的实验曲线.保持激光器工作波长为514.5nm不变,在大块晶体中可得到高达73.0%的位相共轭反射率.文章还给出共轭光的形成时间随系统光强变化关系的实验曲线,并指出自泵浦形成时透射光强和晶体表面反射光强的时间变化特性,解释了自泵浦形成的阈值特性.     

Nonlinear imaging of isoechogenic phantoms using phase conjugation of the second acoustic harmonic

Experiments on nonlinear C-scan acoustic imaging were performed using phase conjugation of the second harmonic of a focused incident beam. This method made it possible to obtain images of objects with close linear properties but with different nonlinear parameters. Nonlinear backward propagation of the conjugate wave was also considered and improvement of the image contrast was demonstrated for this case. The results obtained were generally in agreement with the theoretical predictions.     

A quality of parametric wave phase conjugation of ultrasound

The criterion, known from optics, of wave phase conjugation quality is accommodated for acoustical experiment. An incident focused sound beam at 5 MHz is propagated towards a supercritical magnetoelastic conjugator through an introduced random phase layer, and the conjugate beam propagates backwards through the layer to the source. 1D and 2D distributions of wave field are measured for the conjugate beam of finite amplitude using a membrane hydrophone. The maximum sound intensity of 640 W/cm2 and acoustic power of 4 W are registered in the focal maximum of the conjugate wave. The quality of WPC is calculated from the ratio between the power in the central maximum and the total power of the conjugate beam. The method is applied to compare two operation modes of a supercritical parametric conjugator. It is shown that in the linear mode the conjugator provides higher quality than in the nonlinear (0.54 compared to 0.24).     

BaTiO3自泵浦相位共轭镜

首次报道用国产光折变晶体BaTiO_6制成的反射率大于30%的自泵浦相位共轭镜(SPPCM).并使用它成功地完成了畸变像复原实验.文中给出了自泵浦相位共轭信号的建立与入射光强度.入射光和晶体晶轴夹角的依赖关系及其擦洗速率的实验结果.文中还首次提出了一种使用单块BaTiO_3晶体,使多束入射光同时获得各自相位共轭波的方法.     

Local heating of a liquid-like medium by a phase-conjugate ultrasound beam with self-adaptive focusing

Local heating of a liquid-like medium by means of self-adaptive focusing of a high-power phase conjugate ultrasound wave has been experimentally implemented. A sample of organic silicon polymer with a reflecting inhomogeneity was placed in water and exposed to a plane ultrasound beam so as to make the reflected acoustic field partially to enter the phase conjugation device. A parametrically amplified and conjugate wave was self-adaptively focused back to the inhomogeneity. Thermocouple measurements revealed ultrasound heating, which was localized near the inhomogeneity and depended weakly on its position within the aperture of the incident ultrasound beam. Themaximum heating value was about 6.5°C in 120 s with a frequency of ultrasound of 4.75MHz and a mean power of phase conjugate wave of about 0.1W.     

Lateral displacement of a Gaussian beam reflected from absorbing media

Lateral displacements of well-focused beams reflected from absorbing media are demonstrated in this paper. The incident beam is modeled as a tapered wave with a Gaussian spectrum. The field solutions are obtained on both sides of the interface by solving analytically from Maxwell's equations and by matching the boundary conditions at the interface. Numerical simulations are presented and the field values as well as the time-averaged power densities are computed. The influences of the polarization, the angle of incidence and the beam width on the displacement are discussed. The origin of the displacement lies in the absorption of the media, for which there is a phase shift between the incident and reflected waves. Because of this phase shift, the center of the reflected beam does not coincide with that of the incident one, similar to the Goos-Hänchen shift.     

Parametric phase conjugation for the second harmonic of a nonlinear ultrasonic beam

The effect of phase conjugation for the second harmonic of a focused ultrasonic beam was investigated experimentally and by numerical simulation. An ultrasonic pulse with the carrier frequency f=3 MHz was emitted into water and focused at a point between the source and the phase conjugating system. The phase conjugation for the second harmonic of the incident wave (2f=6 MHz) was performed in a magnetostrictive ceramic as a result of the parametric interaction of the incident wave with the pumping magnetic field (the pumping frequency was f_p=4f=12 MHz). The axial and focal distributions of sound pressure in the incident and conjugated beams were measured using a broadband PVDF membrane hydrophone. The corresponding calculations were performed by solving numerically the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation allowing for the nonlinearity, diffraction, and thermoviscous absorption. The results of measurements agreed well with the calculations and showed that the field of a conjugate wave adequately reproduces the field of the second harmonic of the incident wave. A certain advantage of focusing with the phase conjugation for the second harmonic was demonstrated in comparison with the operation at the doubled frequency of the incident wave. The results of this study can serve as a basis for the utilization of the phase conjugation of harmonics in ultrasonic tomography and nondestructive testing.     

高效率受激喇曼散射源

本文报道在有机溶液(CH₃)₂SO中,用宽带5314埃激光泵浦,得到强6296埃斯托克斯相干受激喇曼辐射的实验。在中等泵浦功率密度下,受激喇曼斯托克斯辐射前向波能量转换效率达38％,观察到了后向斯托克斯受激辐射,后向波强度是前向散射波强度的80％,测量了前向散射的增益为2.5×10^-3厘米/兆瓦,测量了前向、后向散射光束的空间分布。论证了后向散射光束方向性的改善。 关键词：     

Pump induced normal mode splittings in phase conjugation in a Kerr nonlinear waveguide

Phase conjugation in a Kerr nonlinear waveguide is studied with counter-propagating normally incident pumps and a probe beam at an arbitrary angle of incidence. Detailed numerical results for the specular and phase conjugated reflectivities are obtained with full account of pump depletion. For sufficient strengths of the pump a normal mode splitting is demonstrated in both the specular and the phase conjugated reflectivities of the probe wave. The splitting is explained in terms of a simple model under undepleted pump approximation.     

Optical properties of polarization-dependent geometric phase elements with partially polarized light

The behavior of geometric phase elements illuminated with partially polarized monochromatic beams is investigated both theoretically and experimentally. The element discussed in this paper is composed of wave plates with π-retardation and a space-variant orientation angle. We found that a beam emerging from such an element comprises two polarization orders; right-and left-handed circularly polarized states with conjugate geometric phase modification. This phase equals twice the orientation angle of the space-variant wave plate comprising the element. Apart from the two polarization orders, the emerging beam coherence polarization matrix includes a “vectorial interference matrix” which contains information concerning the correlation between the two orthogonal, circularly polarized portions of the incident beam. In this paper we measure this correlation by a simple interference experiment. In addition, we found that the equivalent mutual intensity of the emerging beam is modulated according to the geometric phase induced by the element. Other interesting phenomena concerning propagation will be discussed theoretically and demonstrated experimentally. The experiment made use of a spherical geometric phase element that was realized by use of a space-variant subwavelength grating illuminated with CO₂ laser radiation of 10.6 μm wavelength.