Techniques

• Polarization-sensitive surface plasmon enhanced ellipsometry biosensor using the photoelastic modulation technique
  Authors: W. Yuan, H.P. Ho, S.Y. Wu, Y.K. Suen, S.K. Kong
  SENSORS AND ACTUATORS A-PHYSICAL 151 23-28 (2009)
  Abstract: A surface plasmon enhanced ellipsometry (SPEE) biosensor scheme based on the use of a photoelastic modulator (PEM) is reported. We show that the polarization parameters of a laser beam, tan psi, cos Delta and ellipse orientation angle phi, can be directly measured by detecting the modulation signals at the first and second harmonics of the modulated frequency under a certain birefringence geometry. This leads to accurate measurement of refractive index variations within the evanescent field region close to the gold sensor surface, thereby enabling biosensing applications. Our experimental results confirm that the new scheme offers a respectable detection limit of 6 x 10(-1) refractive index unit (RIU) or 15 ng/ml of biomolecule solute concentration without any compromise in dynamic range. In addition, PEM offers the possibility of single-beam phase-sensitive SPR detection that drastically reduces the complexity of the optical system, thus readily making it possible for SPR to be adopted in label-free micro-array biochips.
  Email: hpho@ee.cuhk.edu.hk
  
  
• Nonlinear Optical Stokes Ellipsometry. 1. Theoretical Framework
  Authors: N.J. Begue, A.J. Moad, G.J. Simpson
  JOURNAL OF PHYSICAL CHEMISTRY C 113 10158-10165 (2009)
  Abstract: The theoretical framework for nonlinear optical Stokes ellipsometry (NOSE) is developed as a faster alternative to previous nonlinear optical ellipsometry (NOE) techniques. NOE is the determination of the complex-valued elements within the Jones chi((n))) tensor, from which all experimental observables in a given configuration can be predicted. By replacing the moving optics with a photoelastic modulator (PEM) operating at 50 kHz and employing a high repetition rate laser, full ellipsometric detection of the chi((2))) tensor can in theory be performed in as little as 20 mu s. Two complementary models were developed to analyze the proposed instrumental setup for NOSE. The first more general approach is based on a regression analysis method, which was compared to a second explicit analytical model valid for a particular experimental configuration. Additionally, the rigor of the regression analysis method against noise was investigated.
  Email: gsimpson@purdue.edu
  
  
• Nonlinear Optical Stokes Ellipsometry. 2. Experimental Demonstration
  Authors: N.J. Begue, R.M. Everly, V.J. Hall, L. Haupert, G.J. Simpson
  JOURNAL OF PHYSICAL CHEMISTRY C 113 10166-10175 (2009)
  Abstract: Second harmonic generation (SHG) has developed into a powerful tool for characterizing oriented thin films, surfaces, and interfaces. Furthermore, the nonlinear optical nature of wave-mixing processes typically results in the generation of a coherent signal beam with a well-defined polarization state. This coherence offers unique opportunities for the extraction of detailed molecular and surface properties from polarization analysis. In previous studies, nonlinear optical ellipsometry (NOE) has been developed as a means to retain sign and phase information between the different nonzero chi((2)) tensor elements present in a given sample. However, those previous methods and related approaches for polarization analysis have all relied on the physical movement of optical elements to perform the analysis. The time required to physically move the appropriate optical elements ultimately dictates the fastest analysis time possible in a given technique. Such long acquisition times have limited NOE analyses to systems exhibiting excellent photostabiCtty and have precluded the feasibility of NOE imaging. Development of nonlinear optical Stokes ellipsometry (NOSE) was shown to address many of these problems. By increasing the repetition rate of the laser system and replacing previously slow rotating polarization optics with a rapid photoelastic modulator, the acquisition time with full polarization analysis was reduced froth several hours to less than a second. This technique was validated against established NOE techniques using z-cut quartz as a reference sample and then demonstrated on a dye thin film. Additionally, an orientation analysis of the thin film was performed. These studies resulted in an order of magnitude improvement in precision relative to previous NOE techniques, while simultaneously accompanied by a reduction in acquisition tithe of more than four orders of magnitude.
  Email: gsimpson@purdue.edu
  
  
• Study of the new ellipsometric measurement method using integrated analyzer in parallel mode
  Authors: P.H. Mao, Y.X. Zheng, Y.R. Chen, Q.Y. Cai, R.J. Zhang, L.Y. Chen,
  OPTICS EXPRESS 17 8641-8650(2009)
  Abstract: A new type of ellipsometer using an integrated analyzer composed of 12 sub-analyzers with different azimuth angles was constructed and studied. By using a two-dimensional CCD array camera to measure the light intensity emerging in parallel from each sub-analyzer with the azimuth angles uniformly distributed in the range of about 180 degrees, the ellipsometric parameters were extracted within the data acquisition time less than 1 second. The ellipsometric parameters for the polished bulk Si sample were measured to show good agreement with the results measured by using another two ellipsometric methods. The new method having the merits of high speed and reliability in the optical data measurement can be potentially used in the fields where the in situ data acquisition with high precision is the key issue as required.
  Email: yxzheng@fudan.ac.cn, lychen@fudan.ac.cn
  
  
• Determination of optical constants of sol-gel derived Zn0.9Mg0.1O films by spectroscopic ellipsometry with various models
  Authors: S. Yang, Y. Liu, Y. Zhang, D. Mo
  SURFACE AND INTERFACE ANALYSIS 41 502-507 (2009)
  Abstract: The Zn0.9Mg0.1O thin films were prepared on Si (1100) substrates by the sol-gel method. The structural and the optical properties of Zn0.9Mg0.1O thin films, submitted to an annealing treatment in the 400-700 degrees C ranges, are studied by X-ray diffraction (XRD) and ultraviolet (UV)-visible spectroscopic ellipsometry (SE). The thickness, refractive index, and extinction coefficient of these films have been determined by analyzing the SE spectra using parameterized dispersion model. Moreover, we made a detailed comparison among various dispersion models and found that the Sellmeier model was superior to others in fitting the ellipsometric spectra in the transparent region. In the interband transition region, point-by-point fit was used. The spectral dependence of the refractive index and extinction coefficient was obtained in the photon energy range of 1.5-4.71 eV. The influence of annealing temperature on the refractive index, the extinction coefficient, and the optical bandgap energy was also discussed. We found that the refractive index and the extinction coefficient increase with increasing the annealing temperature, meaning the optical quality of Zn0.9Mg0.1O films is improved by annealing.
  Email: shenghongyang@163.com