Integrated Acousto-Optical Temperature Sensor

In this work, we investigate the performance of a novel integrated acousto-optical temperature sensor fabricated in LiNbO₃ and operating with ultrashort light pulses (2 ps). Five parameters (time duration, bandwidth, time intensity maximum, frequency intensity maximum, and output energy on the output pulse converted for the TM mode, as a function of temperature) were observed for the switched pulse at the output of the sensor (TM mode) with and without the presence of an increasing linear self-phase modulation (SPM) profile. Comparing all analyzed parameters, one can conclude that the pulse intensity is presenting the larger variation (100.09%) as a function of the temperature change (24.5 to 400°C) in a configuration without profile. Considering the increasing linear SPM profile, all the analyzed parameters are presenting a significant increase in the percentile variations in the studied range of temperature (24.5 to 400°C). Comparing all the five parameters, in two configurations (with and without the use of linear SPM profile), one can conclude that the time intensity maximum showed to be the most suitable parameter as measurement to be accomplished in a schematic detection for the temperature sensing in the range 24.5 to 400°C. We can conclude that the sensitivity of the AOTS is improving in the configuration with the increasing nonlinearity profile (β = 2) and for higher temperature.     

A performance study of a logical gate using PPM optical pulse modulation for TDM systems

In this paper we propose the operation of an all-optical logical gate based in an acousto optical tunable filter (AOTF) operating with a pulse position modulation (PPM). The performance of an AOTF realizing two-input AND/OR logical functions, which can be applied in transmission and processing of signals in all-optical form in TDM systems, was examined. This novel integrated acousto optical logical gate operates with two ultrashort soliton light pulses (2 ps), which are modulated in agreement with the technique of pulse position modulation (PPM). Initially, we evaluated the effect resulting of an increment in the acousto optical interaction length, for the temporal position of the output pulse, considering the anomalous group velocity dispersion (GVD), nonlinear self phase modulation (SPM) and without loss propagation regime of TE and TM input pulses not modulated. We have analyzed the four possible situations for the two-input logical gate, modulating the TE and TM input pulses through temporal displacement and allowing a variation in the coding parameter offset (ε). We can conclude that is possible to get AND/OR logical operations for the modes TM or TE, without to insert PPM error, since a phase control (Δ?) exists (applied on the TM input pulse) in agreement with each situation in the truth table. Finally we defined the truth table, considering the adequate phase difference and coding parameter offset for the operation of the AND/OR logical gate based in the AOTF.     

Analysis of an optical logic gate using a symmetric coupler operating with pulse position modulation (PPM)

In this paper we propose the operation of an all-optical logical gate based in a symmetric nonlinear directional coupler (NLDC) operating with a pulse position modulation (PPM). The performance of a symmetric NLDC realizing two-input AND/OR logical functions, which can be applied in transmission and processing of signals in all-optical form in TDM systems, is examined. This integrated symmetric NLDC logical gate operates with two ultrashort soliton light pulses (2 ps), which are modulated in agreement with the technique of pulse position modulation (PPM). Initially, we evaluate the effect resulting of an increment in the PPM coding parameter offset (ε), for the temporal position of the output pulse, considering the anomalous group-velocity dispersion (GVD), nonlinear self phase modulation (SPM) and without loss propagation regime of input pulses, in the cores 1 and 2 of the NLDC. In this situation, we analyze the four possible situations for the two-input logical gate, modulating the 1 and 2 input pulses through temporal displacement and allowing a variation in the coding parameter offset. We can conclude that is possible to get AND/OR logical operations for the cores 1 or 2, without to insert PPM error, since a phase control (Δ?) exists applied in agreement with the logical level of the input pulse in the core 1. Finally we define the truth table, considering the adequate phase difference and coding parameter offset for the stable operation of the AND/OR logical gate based in the symmetric NLDC.     

百皮秒脉冲放大中自相位调制效应实验研究

利用掺镱双包层光纤放大器对百皮秒单脉冲（重复频率1 Hz）进行了放大实验,分析了其放大过程中自相位调制对脉冲时域和频域特性的影响.采用小芯径（纤芯直径6.5 μm）掺镱双包层光纤作为增益介质,研究了放大器中从小信号增益到增益深度饱和整个变化过程中自相位调制引起的频谱展宽效应,并分析了SPM引起的脉冲波形和频谱光强分布的变化.采用布喇格光纤光栅扫描方法观察了其光谱的变化,解决了单脉冲光谱不易测量的问题.结果表明：区别于无源光纤中的自相位调制效应,随着抽运功率的增加,百皮秒脉冲放大过程中增益饱和效应和自相位调制效应的共同作用,使脉冲频谱分裂成不对称双峰结构,且光强分布先向短波后逐渐向长波集中.     

A microwave absorption study in the thermochromic SrMnO3

We report electron paramagnetic resonance (EPR) and magnetically modulated microwave absorption spectroscopy (MAMMAS) studies at X-band (8.8–9.6 GHz) on powdered SrMnO₃ in the 90–400 K temperature range. EPR spectrum shows one broad single-line at room temperature, which is observed only above 280.5 K, being compatible with an antiferromagnetic order. The onset of the para–antiferromagnetic transition has been determined from the temperature dependence of three main parameters extracted from the EPR spectra: resonant field (H_res), peak-to-peak linewidth (ΔH_pp) and integrated intensity (I_EPR). The MAMMAS response shows a change in the region 276–283 K, compatible with the para–antiferromagnetic transition, without presenting any significant change in the region of thermochromism.     

水体中溶解有机物的荧光光谱特性分析

以355 nm激光为激发光源,在实验室中利用激光诱导荧光(LIF)方法对不同水体中溶解有机物(DOM)的荧光光谱进行了测量,并以最小二乘法-高斯拟合对水体荧光光谱进行了拟合,解卷积得出了水喇曼散射谱及DOM的荧光光谱.在改变激发光脉冲强度的条件下,以一定浓度腐殖酸溶液为测量样品分析了DOM的荧光饱和特性.结果表明,随着激发光功率密度的增加,水喇曼散射强度线性增加,而DOM的荧光强度随着激发光功率密度的增加先是线性增加,此时归一化荧光强度为一恒定值.当激发光功率密度大于55 mW/cm2时, 荧光强度增加缓慢,归一化荧光强度则逐渐降低.研究发现,在有机物浓度较高时,出现了激发态分子间的单重态-单重态猝灭,并且在低浓度情况下,随着有机物浓度的增加,出现了有机物荧光峰值强度位置的红移并伴有波形的展宽.     

Theoretical model for electromagnetic wave propagation in negative index material induced by cubic-quintic nonlinearities and third-order dispersion effects

We analyze the problem of characterization of electromagnetic (EM) wave that propagates in a negative index material (NIM) and compare to the behavior that observes in a positive index material (PIM), from the conventional technique of characterization of the pulse intensity profile. Firstly, we establish the nonlinear Schrödinger equation (NLSE) and use the Drude model to obtained the NLSE terms. Secondly, we apply the collective variables technique at each frequency range and show that the stability and the light pulse intensity are significantly depending on specific normalized frequencies. We determine the specific frequency range allowing a fear characterization of the intensity profile of light pulse when the frequency increases. We illustrate the effectiveness of this EM wave stabilization by applying the indicated frequency range. This conventional technique in NIM and PIM systems where the second-order dispersion, third-order dispersion, self phase modulation (SPM) and quintic effects originated from SPM called quintic phase modulation act to provoke strong perturbations.     

光参量啁啾脉冲放大中时间同步抖动对增益稳定性的影响

 在考虑了光参量啁啾脉冲放大中的脉冲波形、相位失配和时间同步抖动情况下,给出了计算光参量啁啾脉冲放大增益特性更为完善的三波耦合理论模型。并在1 ns的时间同步抖动情况下,对比分析了光参量放大在小信号放大及饱和放大时的增益稳定性。光参量放大的时间同步抖动对增益影响非常大,使放大信号光脉冲的增益光谱发生了明显的偏移,波形不对称和整个增益降低;并且信号光光谱越宽,光参量放大间的时间同步抖动对其增益影响越严重;但随着参量放大增益饱和的出现和加深,信号光和抽运光之间的同步时间抖动对放大信号光的输出强度影响减弱,即在饱和放大处可以获得更稳定的放大信号光输出。     

压缩平稳重调脉冲的色散渐减光纤的设计

文章根据平稳重调脉冲(SRP)在梳状光纤(CPF)结构中的压缩原理,对色散渐减光纤(DDF)的色散特性进行设计,结果发现该色散渐减光纤的色散特性呈线性递减.对于平稳重调脉冲其压缩比与功率比等于光纤始末两端二阶色散系数的比值.当色散渐减光纤的斜率足够小时,无啁啾基阶孤子可以近似为平稳重调脉冲,当色散渐减光纤的色散斜率较大时,无啁啾基阶孤子不能近似为平稳重调脉冲.当基阶孤子带有与光纤色散斜率成正比的线性啁啾时,脉冲的压缩比与功率比更接近于光纤始末两端二阶色散系数的比值.说明带有线性啁啾的基阶孤子比不带啁啾的基阶孤子更接近于平稳重调脉冲. 关键词： 平稳重调脉冲(SRP) 梳状光纤(CPF) 色散渐减光纤(DDF) 色散递减表达式     

水溶性CdTe量子点的稳态和纳秒时间分辨光致发光光谱

报道了以飞秒脉冲激光为激发光源的水溶性CdTe量子点(QDs)的稳态荧光光谱和纳秒时间分辨荧光光谱.实验发现CdTe量子点的荧光光谱峰值位置随激发波长变化发生明显移动，激发脉冲波长越长，荧光峰位红移越大.荧光动力学实验数据显示，在400nm和800nm脉冲激光激发下，水溶性CdTe量子点的荧光光谱中均含有激子态和诱捕态两个衰减成分，两者的发射峰相距很近，诱捕态的发射峰波长较长.在800nm脉冲激光激发下的诱捕态成分占总荧光强度的比重比400nm激发下的约高3倍，其相对强度的这种变化导致了稳态荧光发射峰位的红移. 关键词： CdTe 量子点 时间分辨 荧光光谱 上转换荧光     

基于光纤光参量放大的光脉冲压窄技术的研究

在高重复频率的光窄脉冲源中,为了获得更窄的脉冲,需要增加泵浦功率;但泵浦功率的提高会使光放大器的增益趋于饱和,放大的自发辐射噪音增强,脉冲光信噪比下降.为此,提出了利用啁啾管理和光纤光参量放大相结合的脉冲压窄方案.将强度调制后的泵浦光通过相位调制引入线性负啁啾,由于经参量过程后在新的闲频光上啁啾会加倍,从而进一步增大了...     

Self-focusing, channel formation, and high-energy ion generation in interaction of an intense short laser pulse with a He jet

Using interferometry, we investigate the dynamics of interaction of a relativistically intense 4-TW, 400-fs laser pulse with a He gas jet. We observe a stable plasma channel 1 mm long and less than 30 microm in diameter, with a radial gradient of electron density approximately 5 x 10(22) cm(-4) and with an on-axis electron density approximately ten times less than its maximum value of 8 x 10(19) cm(-3). A high radial velocity of the surrounding gas ionization of approximately 3.8 x 10(8) cm/s has been observed after the channel formation, and it is attributed to the fast ions expelled from the laser channel and propagating radially outward. We developed a kinetic model which describes the plasma channel formation and the subsequent ambient gas excitation and ionization. Comparing the model predictions with the interferometric data, we reconstructed the axial profile of laser channel and on-axis laser intensity. The estimated maximum energy of accelerated ions is about 500 keV, and the total energy of the fast ions is 5% of the laser pulse energy.     

啁啾光脉冲的自相位调制效应对压缩光脉冲的影响

 在超强激光系统中,对比度和本底宽度是压缩光脉冲极为重要的指标。在啁啾脉冲放大系统的压缩阶段,在啁啾脉冲宽度为141ps,啁啾系数为1000,B积分值分别为0,1和2的情况下,模拟了自相位调制效应（SPM）对压缩脉冲的峰值光强、脉冲宽度和本底宽度的影响。结果表明：在B积分值为2的条件下,若不补偿非线性色散,压缩脉冲的峰值强度降为无自相位调制效应时的65%左右,脉冲宽度约为种子脉冲宽度的2倍,本底宽度则增加到原来的3倍左右;在B积分值大于0.5的情况下,本底宽度和B积分值近似成线性关系。     

Structure and optical properties of sol–gel derived Gd2O3 waveguide films

Pure and rare earth doped gadolinium oxide (Gd₂O₃) waveguide films were prepared by a simple sol–gel process and dip-coating method. Gd₂O₃ was successfully synthesized by hydrolysis of gadolinium acetate. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structure of Gd₂O₃ films annealed at different temperature ranging from 400 to 750 °C were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Gd₂O₃ starts crystallizing at about 400 °C and the crystallite size increases with annealing temperature. Oriented growth of (4 0 0) face of Gd₂O₃ has been observed when the films were deposited on (1 0 0) Si substrate and annealed at 750 °C. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and propagation loss of the film measured by scattering-detection method is about 2 dB/cm. Luminescence properties of europium ions doped films were measured and are discussed.     

Beam Delivery of the Vanderbilt Free Electron Laser with Hollow Wave Guides: Effect on Temporal and Spatial Pulse Propagation

Hollow Wave Guides were evaluated as a beam delivery system for the Free Electron Laser (FEL) at Vanderbilt in preparation of surgical applications. They can transmit the mid-infrared wavelength range (2µm - 9µm) and tolerate the high peak intensity (>10¹⁴ W/m²) in the micropulse of the FEL. Changes in the temporal and spatial beam characteristics induced by the transmission through 1.5 meter Hollow Wave Guides with bore radii of 250 µm and 530 µm were investigated. Temporal broadening of the micro pulses was studied using intensity autocorrelation measurements and beam profile measurements were performed with a pyroelectric camera. Results demonstrate significant pulse broadening and development of higher order modes induced by sub-optimal coupling of the beam into the Hollow Wave Guide. Bending of the Hollow Wave Guide induced additional losses and reduced propagation of higher modes responsible for broadening the pulse. Calculations with a geometrical ray model support the findings on pulse broadening. Optimal coupling conditions are extremely critical for maximal transmission performance of the Hollow Wave Guide. Design consequences for a FEL delivery system are discussed.     

Current-confined-path (CCP) giant magnetoresistive (GMR) sensors

Current-perpendicular-to the plane (CPP) giant magnetoresistive (GMR) sensors with a current-confined-path (CCP) layer inserted within the Cu spacer have been manufactured using ultrahigh vacuum PVD sputtering, photolithography, and ion milling processes. Compared with a pure metallic CPP system, the CCP insertion layer enables a substantial increase in sensor resistance with an equivalent or better GMR ratio, and thus a significant improvement in the ΔRA amplitude. Heads with such a sensor have been tested under various bias currents, both quasistatically and on a spinstand. It was found that the resistance of the sensors increases with increasing bias current and voltage, following typical metallic behavior. Also, the CCP insertion layer enables operation at higher bias currents compared with the pure metallic sensors (without the insertion layer) and thus a higher output signal. This effect is attributed to less magnetic instability due to the reduced Ampere fields around the narrow (∼6 nm) current-confined paths. Finally, the CPP-GMR heads with CCP layer were tested under high-density recording conditions using the perpendicular recording media. Bit error rate (BER) as a function of linear density is reported. Microtrack profiles were also recorded to determine track density capability.     

Thermal analysis of magneto-optical thin films under laser irradiation

A two-dimensional finite-difference method was applied to study the thermal behavior of thin films irradiated by a pulsed Gaussian laser beam. In particular, the method was applied to rare-earth/transition-metal alloyed films for magneto-optic recording. The effects of film parameters (thermal conductivity, specific heat, absorption coefficient, and film thickness) and laser parameters (output power and pulse duration) on healing and cooling behavior were investigated extensively. The temperature profile of a film was sensitively dependent on these parameters. The results might be used to predict the recorded bit size and to optimize the laser parameters. For a given energy density of the laser beam, a large output power with a short pulse width was desirable for effective heating of a film. Heating by radial thermal diffusion became important with increasing thermal conductivity of a film. Therefore, to achieve high storage density, a film must have low thermal conductivity.     

Regulation of the output energy of a backward-wave linear accelerator by the duration of the rf power pulse

The problems of regulating the output energy of the accelerated beam of a backward-wave linear proton accelerator over a wide range without altering the beam intensity are investigated. The proton energy is regulated by adjusting the duration of the rf power pulse delivered to the accelerator and by regulating the delay time between the instant of injection and the instant at which the leading edge of the rf pulse arrives at the output end of the accelerator. The method is tested on the interdigital-type accelerating section of length 1.25 m of a linear proton accelerator. It is shown experimentally that the electron beam energy at the accelerator output can be varied approximately threefold without any appreciable sacrifice of the beam intensity by varying the duration of the rf pulse in the given accelerator section. Zh. Tekh. Fiz. 68, 135–137 (May 1998)     

Intensity measurement based temperature-independent strain sensor using a highly birefringent photonic crystal fiber loop mirror

A fiber-optic strain sensor is demonstrated by using a short length of highly birefringent photonic crystal fiber (HiBi-PCF) as the sensing element inserted in a fiber loop mirror (FLM). Due to the ultralow thermal sensitivity of the HiBi-PCF, the proposed strain sensor is inherently insensitive to temperature. When a distributed-feedback (DFB) laser passes through the FLM, the output power is only affected by the transmission spectral change of the FLM caused by the strain applied on the HiBi-PCF. Based on intensity measurement, an optical power meter is adequate to deduce the strain information and an expensive optical spectrum analyzer (OSA) would not be needed.     

光诱导分布反馈激发染料掺杂向列相液晶的放大自发发射

随着OLEDs的发展,有机/聚合物材料体系的放大自发发射也得到了广泛深入的研究。利用Lloyd镜面体系构建了分布反馈体系,研究了DCJTB在向列相液晶中的放大自发发射过程,利用布拉格方程计算了发射光谱的峰值波长。实验结果表明,DCJTB向列相液晶体系的放大自发发射阈值为与平面波导结构相比,分布反馈体系提供了良好的模式,半峰全宽明显变窄;随着电场的变化,不同角度的输出信号强度也变化明显,利用电场可以有效的对TE、TM两种模式的强度进行调制。