Detection interferometric

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

Circular dichroism employs standard dispersive or interferometric instmmentation, but uses a thermal source that is rapidly modulated between circular polari2ation states using a photoelastic or electro-optic modulator. Using phase-sensitive detection, a difference signal proportional to the absorption difference between left- and right-polari2ed light, AA is recorded as a function of wavenumber. Relative differential absorptions... 

X 0.75 cm) Ve i = 28 ml = 50 ml eluent 0.05 M NaCI flow rate 0.80 ml/min detection Optilab 903 interferometric differential refractometer applied sample mass/volume 200 /tl of 2-mg/ml aqueous solutions sum of individual chromatograms (theory —) and (theory/experimental) ratio (—) plotted for quantification of deviations in separation performance between narrow distributed samples and broad distributed samples. 

At 10Hz in a typical Nd-YAG laser 1000Hz/- /Hz, and the typical finesse asymmetry is of the order of one percent. In order to detect a gw signal the laser frequency noise has to be lowered by six orders of magnitudes (compared to the noise of a free running laser), and the two arms made as identical as possible. In order to achieve this complex frequency stabilization methods are employed in all interferometric detectors, and in order to insure the perfect symmetry of the interferometer, all pairs of Virgo optical components are coated during the same run (both Fabry-Perot input mirrors then both end mirrors are coated simultaneously). 

Both methods obtain the necessary sensitivity by modulating the electrode potential between two values which define two distinct states of the electrode surface thus the chemistry to be observed is directly modulated and may be detected with great sensitivity by an appropriate form of synchronous detection. In the case of EMIRS, the modulation frequency is made sufficiently high compared to the wavelength scanning rate to enable a phase sensitive detection system to be used whereas, for SNIFTIRS, the electrode potential is held for a sufficient period at each potential to accumulate data from several interferometric scans and, after an adequate number, the two sets of data are ratioed. 

The NIR femtosecond laser microscope realized higher order multi photon excitation for aromatic compounds interferometric autocorrelation detection of the fluorescence from the microcrystals of the aromatic molecules confirmed that their excited states were produced not via stepwise multiphoton absorption but by simultaneous absorption of several photons. The microscope enabled us to obtain three-dimensional multiphoton fluorescence images with higher spatial resolution than that limited by the diffraction theory for one-photon excitation. 

Interferometric sensors frequently have also been applied to biosensor measurements. Thereby, the evanescent field technique (Mach-Zehnder interferometer) has been compared with other optical detection principles regarding information on layer structure and in case of biosensing30. The... 

The interferometric measurements with RIfS can be parallelized as demonstrated in Figure 18. In this case, instead of white light interferometry, only a few wavelengths are used to allow parallel detection of all measurement dots. A filter wheel selects one wavelength at a time from the white light source, while the CCD camera monitors the intensity distribution at the transducer for all spots, in this case in a microtiter plate35. 

Brandenburg A., Krauter R., Kunzel C., Stefan M., Schulte H., Interferometric sensor for detection of surface-bound bioreactions, Appl. Opt. 2000 39 6396-6405. 

Liu, N. Hui, J. Sun, C. Dong, J. Zhang, L. Xiao, H., Nanoporous zeolite thin film based fiber intrinsic Fabry Perot interferometric sensor for detection of dissolved organics in water, Sensors 2006, 6, 835 847... 

Xu, J. Suarez, D. Gottfried, D. S., Detection of avian influenza virus using an interferometric biosensor, Anal. Bioanal. Chem. 2007, 389, 1193 1199... 

The universal interferometric response of a balanced two-port interferometer is shown in Fig. 11.2 as a function of the fixed phase offset between the two waves. The maximum slope of the intensity curve occurs when the fixed phase offset between the waves is an odd integer of = re/2. These conditions of maximum slope are called the conditions of phase quadrature. There are two quadrature conditions per cycle, with opposite slopes and hence opposite signed responses to modulated phase. These are the positions of maximum phase-to-intensity transduction and are the operating points for interferometric detection of protein or DNA on spinning discs. 

Phase quadrature is an over-arching concept for all interferometric detection. However, achieving a common-path configuration that locks in a stable quadrature condition puts constraints on possible system designs. This section reviews the several configurations of common-path quadrature that have been demonstrated so far in spinning-disc systems. These are the micro-diffraction class, the adaptive optical class, the phase contrast and the in-line class. At the end of this section, we show that the phase-contrast and in-line classes are conjugate quadratures of each other. 

Wang, X. Zhao, M. Nolte, D. D., Common path interferometric detection of protein on the... 

Zhao, M. Nolte, D. Cho, W. Regnier, F. Varma, M. Lawrence, G. Pasqua, J., High speed interferometric detection of label free immunoassays on the biological compact disc, Clin. Chem. 2006, 52, 2135 2140... 

The interferometric sensor platform is highly sensitive and is the only one that provides an internal reference for compensation of refractive-index fluctuations and unspecific adsorption. Interferometric sensors have a broader dynamic range than most other types of sensors and show higher sensitivity as compared to other integrated optical biosensors . Due to the high sensitivity of the interferometer sensor the direct detection of small... 

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