一种测量薄膜磁性的表面磁光克尔效应装置

介绍表面磁光克尔效应谱（ＳＭＯＫＥ）的一种新方案。通过适当分光并测量信号束和参考束的光强比，可以明显改善由于激光的光强不稳造成的误差，还使得随机偏振激光器也能用于ＳＭＯＫＥ装置。同时该方案中没有采用信号调制，因此对探测器等硬件要求很低。实验结果表明，采用光强稳定度为５％的普通国产Ｈｅ－Ｎｅ随机偏振激光器，其测量灵敏度能够达到目前国际上通常用于超薄膜磁性测量的ＳＭＯＫＥ的同类水平。     

一种全偏振参数的显微测量系统

本文设计了一种用于Mueller矩阵测量的全偏振参数显微镜测量系统.该测量系统以液晶调制器键合于偏振分束棱镜表面的模块为核心器件,实现了以10次光强获取为周期的Mueller矩阵参数测量功能,能够方便地实现Mueller矩阵中全部参数图像的实时测量,比前人设计系统的测量效率有很大提高.基于该系统,本文进行了Mueiler矩阵快速调制测量方案的具体设计,并给出了测量结果.论文还对该系统进行了测量误差的分析,实验结果及误差分析表明,系统的相对测量误差能够控制在2%以内.     

激光器光束质量测量技术研究

由于半导体激光器结构的特点,在其应用中需对其波束进行整形,为了有利于大功率半导体激光器的推广应用,需准确识别大功率半导体激光器的输出分布特性。该文从M2因子、远端发散角,近端及远端的光强分布等方面对大功率半导体激光器的光束质量进行了测量技术研究,给出了相应的测量方案和误差分析。     

单频激光干涉仪条纹的偏振移相细分技术

提出了一种用于单频激光干涉仪条纹细分的偏振移相技术.通过偏振分光镜、波片等光学元器件产生四路依次相差90°相位的激光干涉信号,经过硬件电路的整形、放大和比较后,可以解决常见的光强"零漂"问题.共光路设计有效地消除了由于环境因素给测量带来的误差,提高了干涉系统的稳定性和重复性.移相技术不仅充分地利用光能量,而且四路信号更便于干涉条纹的计数和判向,同时为电子细分技术奠定了基础.     

用于非连续曲面轮廓测量的激光差动像散传感器

针对目前工程领域中亟待解决的三维曲面轮廓的精密测量问题,研制了具有纳米级轴向分辨力的光瞳滤波式激光偏振光差动像散传感器(PLDAP).该传感器基于像散检测原理,利用位于两柱面镜焦前、焦后等距放置的两探测器上的光斑形状信号差动相减和光强归一化处理得到聚焦误差信号,对被测表面进行高精度双极性绝对测量,可用于大倾角表面的测量.PLDAP中,偏振差动光路布置光强归一化技术的采用,有效抑制了环境光波动、光源波动、物体表面光学特性以及光学器件问多次反射对测量结果的影响,显著提高了像散检测技术的抗干扰能力.实验表明:当测量物镜采用数值孔径NA =0.65时,PLDAP测量范围达±10μm,分辨力优于5 nm,可测倾角20°,稳定性优于2%.该传感器为非连续表面轮廓的跟踪、瞄准测量提供一种新的技术途径.     

纳米级二维激光外差干涉仪的设计

提出了一种５０μｍ测量范围内，２ｎｍ不确定度，、０．５ｎｍ分辨率的二维激光外差偏振干涉仪的设计。其中用声制器和稳频Ｈｅ－Ｎｅ激光器获取频差小于２００ｋＨｚ的正交偏振双频激光束，Ｘ和Ｙ二臂偏振干仪将采用差分干涉仪，采用相位解调技术进行外差干涉信号的处理。     

光纤传感器中偏振开关法消偏振衰落技术

针对低双折射光纤双光束干涉型传感器两臂偏振态随机变化引起的信号衰落,提出的一种新型消偏振方式可以在可见度略有下降的情况下,较好地消除偏振态变化引起的干涉信号可见度的随机变化。该方案是通过相互正交的两个偏振态,补偿由于其中一个偏振态变化导致的干涉信号衰落。通过自动增益控制电路（AGC）可以使传感信号稳定,能够在信噪比有所下降的情况下消除偏振衰落的影响,实现干涉型光纤传感器的消偏振衰落。     

基于干涉解调技术的光纤激光器水声传感系统

分析了基于Michelson干涉解调技术的光纤激光器水声传感的原理,在一段掺铒光纤中写入具有π相移的光纤光栅构成光纤激光器,水声压力作用在激光器上引起激光工作波长的变化;采用基于3×3耦合器的偏振无关的非平衡光纤Michelson干涉仪将激光波长变化转化为干涉仪的相位变化;干涉仪的输出由光电探测器转换后使用DSP进行信号解调.针对3×3耦合器分光比不对称的问题,本文提出利用实时调整幅度的2路干涉信号进行解调的方案,该方案不需要3×3耦合器有严格的分光比,消除了外界环境对解调输出的非线性影响.水声探测实验表明,光纤激光器水声传感系统的声压灵敏度为-166.5 dB(参考值1 rad/μPa),解调结果与水声信号具有良好的线性关系.     

新型偏振特性因子及其传递关系的研究

偏振遥感图像通常可以采用强度、偏振度、偏振角或HIS柱形彩色空间表征目标偏振特性.本文通过建立光束在多层介质中传递的简单模型,找到一种新型偏振特性因子.此偏振特性因子所成图像是偏振度图像和偏振角图像信息复合的结果,其实质反映了偏振光束中的线偏振光的光强相对含量及它的偏振角方向.对伪装过的车牌进行偏振成像,实验表明此偏振特性因子可以用于特定环境下的伪装辨别.     

一种新型单频激光干涉系统的研究

这种单频激光干涉系统采用共光路设计布局,通过偏振分束器以及1/4波长片等光学器件对干涉条纹进行空间移相,提取相位依次相差90°的三路干涉输出信号,进行比较放大,解决了常规单频激光干涉仪中的光强“零漂”问题。利用共模抑制技术,提高了干涉系统的测量稳定性和重复性。采用光程差放大技术,提高了干涉系统的分辨力。     

Investigation of magnetic properties and microstructure of ultrathin Co films grown on Si(111)- 7 x 7 surface

Magnetic properties and growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface have been studied by using both surface magneto-optic Kerr effect (SMOKE) and scanning tunneling microscopy (STM), respectively. STM results show that the growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface at room temperature belongs to Stranski-Krastanov (SK) growth mode. Due to formation of CoSi2 layer, no magnetic signal could be detected by SMOKE for 1-4 ML Co deposited on Si(111) surface. Because of rougher surface, both longitudinal and perpendicular magnetic anisotropy configuration appear for 4.2-10 ML Co/Si(111) films. When the Co thickness is increased to 10 ML, only longitudinal anisotropy configuration is found, resulting from the contribution to the volume anisotropy. Furthermore, in-plane coercivity increases with Co coverage because of enhancement of ferromagnetic coupling with Co thickness, out-of-plane coercivity increases with Co coverage due to the increment of demagnetized field, induced by the rougher Co surface and pinhole structures.     

Magnetic phase composition of strontium titanate implanted with iron ions

Thin magnetic films were synthesized by means of implantation of iron ions into single-crystalline (1 0 0) substrates of strontium titanate. Depth-selective conversion electron Mössbauer spectroscopy (DCEMS) indicates that origin of the samples magnetism is α-Fe nanoparticles. Iron-substituted strontium titanate was also identified but with paramagnetic behaviour at room temperature. Surface magneto-optical Kerr effect (SMOKE) confirms that the films reveal superparamagnetism (the low-fluence sample) or ferromagnetism (the high-fluence sample), and demonstrate absence of magnetic in-plane anisotropy. These findings highlight iron implanted strontium titanate as a promising candidate for composite multiferroic material and also for gas sensing applications.     

Study of FePt films prepared by reactive sputtering

In the present study, ⁵⁷FePt films are prepared with reactive ion beam sputtering using mixture of argon and nitrogen gases. Energy-dispersive X-ray reflectivity is used to estimate the thickness of the as-deposited films. Structural and magnetic properties of the as-deposited and annealed films are studied using grazing incidence X-ray diffraction (GIXRD), magneto-optical Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). Significant difference in structural and magnetic properties i.e., formation of ordered L1₀ phase and perpendicular magnetic anisotropy are observed for the films prepared with mixture of nitrogen and argon as compared to the film prepared with argon only. From the GIXRD, peaks corresponding to the ordered face-centred tetragonal FePt phase are observed for the films prepared with mixture gas. The results of CEMS clearly show the perpendicular magnetic anisotropy (PMA) for the films prepared with mixture of nitrogen and argon. The observed enhanced chemical ordering and the development of PMA in the films prepared with mixture gas is due to the role played by the defects created as a consequence of nitrogen escape in the films with high temperature annealing.     

Intermodulation measurements in YBaCuO films

A technique for measuring the intermodulation signal arising in a nonlinear high-temperature superconductor film is suggested. Using a one-port resonator, the technique significantly increases sensitivity of the measuring system as compared to that of a two-port-resonator design. Specifically, it lowers the minimum measurable power at a given magnetic field strength on the film surface. Measurements of the intermodulation signal power as a function of the input power for YBaCuO films differing in surface resistance and thickness are reported. Based on the measured data, the intermodulation characteristic magnetic field is computed. The quantity characterizes nonlinear film properties of the regardless of the measuring system employed.     

Dynamic magneto-optic detector for analog readout

The addition of a polarization azimuth vibrator, such as a Faraday cell, to a conventional Kerr apparatus yields a dynamic detector with a high SNR capability. The method described here has been utilized in the past as a null detector to observe Kerr rotation. It can be used equally well for analog readout of the magnetic state of the film element. The improved Kerr apparatus is well-suited to a common-mode noise rejection configuration. The common-mode configuration is usable both as a measuring instrument and as a high-speed analog readout system. Dynamic single- and double-ended Kerr apparatus are discussed and typical photodetector output waveforms are shown.     

Structure and magnetic properties of hcp and fcc nanocrystalline thin Ni films and nanoparticles produced by radio frequency magnetron sputtering

We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.     

Proposal for a magnetic-film memory accessed by combined photon and electron beams

A magnetic-film memory accessed by combined photon and electron beams is proposed. The electron beam is used to heat a selected bit, which results in lowering the switching threshold so that information can be written selectively into that bit by means of an external magnetic field. Reading is accomplished by simultaneously illuminating a bit with an electron and a photon beam. Then a thermally modulated magnetic-optical signal is generated by intensity modulation of the electron beam. This arrangement is advantageous since a high-resolution photon beam and photon deflector are not required. The frequency response for thermally modulating a 1-μm bit is calculated to be ∼500 MHz; the necessary temperature dependence of the magneto-optical coefficient and the coercive force can be obtained by using composite films made from layers having different Curie points. Various magneto-optical configurations are readily devised which yield the value of a bit (one or zero) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. The shot noise limited signal-to-noise ratio (SNR) is determined by heating of a bit from the photon beam. It is calculated that for a low-loss magnetooptical material such as EuO a 1-μm bit can be read in 1 μs when illuminated with a 1000-μm photon beam. The base-line temperature rise due to heating from the photon beam can be kept small by using narrow pulses of light (widthsim10^{-11}second), as, for example, from a mode-locked laser.     

Kerr effect enhancement in ferromagnetic films

The enhancement of the Kerr magneto-optic effect by overcoating a ferromagnetic film with a dielectric film is studied. It is treated as an impedance-matching problem for the light wave. Closed form solutions are obtained for the polar Kerr effect. The same analysis, with modifications, can be applied to the longitudinal Kerr effect. The effect of the dielectric thickness on the enhancement is continuously monitored with a laser beam (λ = 6328Å) during the dielectric film deposition. The amplification of the longitudinal Kerr signal with SiO films on iron film is of the order of five, and the enhancement varies periodically as a function of dielectric thickness. The experimentally observed period, 1600Å, agrees well with the calculated value. The sense ofB-Hloops, which also varies periodically as a function of the dielectric thickness, is explainable in terms of the phase factor which appears in the difference between the reflection coefficients.     

Selective sensitivity of ellipsometry to magnetic nanostructures

Magneto-optic (MO) ellipsometry of ferromagnetic materials is extremely sensitive to ultra-thin films, multilayers, and nanostructures. It gives a possibility to measure all components of the magnetization vector in the frame of the magneto-optic vector magnetometry and enables us to separate magnetic contributions from different depths and materials in nanostructures, which is reviewed in this article. The method is based on ellipsometric separation using the selective MO Kerr effect. The figure of merit used to quantify the ellipsometric selectivity to magnetic nanostructures is defined on the basis of linear matrix algebra. We show that the method can be also used to separate MO contributions from areas of the same ferromagnetic materials deposited on different buffer layers. The method is demonstrated using both: (i) modeling of the MO ellipsometry response and (ii) MO measurement of ultra-thin Co islands epitaxially grown on self-organized gold islands on Mo/Al₂O₃ buffer layer prepared using the molecular beam epitaxy at elevated temperatures. The system is studied using longitudinal (in-plane) and polar (perpendicular) MO Kerr effects.     

真空退火Co/Pt多层膜的结构、磁及磁光特性分析

本文用直流磁控溅射方法制备了Co／Pt多层膜,并对其进行了较为细致的真空退火处理,结果表明,适度的低温退火可增加Co／Pt多层膜的矫顽力,而并不削弱其磁滞克尔回线的矩形特征．当退火温度达到300℃以后,Co／Pt多层膜的矫顽力、垂直各向异性和克尔角将强烈下降,晶体结构的改善及应力的释放、晶粒的增长、层间原子扩散引起的Co层有效厚度减薄,进而居里温度的下降,分别是Co／Pt多层膜在低温、中温、高温退火过程中,磁及磁光性能变化的主要机制．