Micro-interferometer

Refractive index detection A microvolume refractive index detection method has been developed for CE consisting of a micro-interferometer back-setter system, illuminated by a He-Ne laser giving a characteristic interference pattern. The change of such a pattern is due to the change of the refractive index caused by the separated substance. This detection system was tested for the separation of mono- and oligosaccharides. 

In the mid-IR, routine infrared spectroscopy nowadays almost exclusively uses Fourier-transform (FT) spectrometers. This principle is a standard method in modem analytical chemistry45. Although some efforts have been made to design ultra-compact FT-IR spectrometers for use under real-world conditions, standard systems are still too bulky for many applications. A new approach is the use of micro-fabrication techniques. As an example for this technology, a miniature single-pass Fourier transform spectrometer integrated on a 10 x 5 cm optical bench has been demonstrated to be feasible. Based upon a classical Michelson interferometer design, all... 

A miniaturized Fourier transform spectrometer for near-infrared measurements (FTIR, 2500-8330 nm) was developed at the Forschungszentrum Karlsruhe [120], Near-infrared measurements give information, for example, about the oil, water and protein content of liquids or solids. The dimensions of the detector chip are 11.5 x 9.4 mm, the device is essentially a miniaturized Michelson interferometer and it consists of a micro optical bench with beamsplitter, ball lenses, mirrors and the detector chip. The light beam is coupled in via a glass-fiber and an electromagnetic actuator. The signal is derived from the signal response of the detector by Fourier transformation. 

Ymeti A, Ranger JS, Greve J, Besselink GAJ, Lambeck PV, Wijn R, Heideman RG (2005) Integration of micro fluidics with a four-channel integrated optical young interferometer immunosensor. Biosens Bioelectron 20 1417-1421... 

Interferometers can easily be adapted to the required resolution. One interferometer may either provide the very high resolution needed for a analysis of gas spectra, or a high optical conductance at a lower resolution, which is ideal for quick and reliable routine analysis. Their simple, rugged construction make interferometers suitable even for the industrial environment, where they serve in production and quality control. Due to the development of modern micro electronics, the necessary Fourier transformation can now be performed in real time by micro processors, together with the other procedures needed to evaluate the spectra for analytical purposes. 

The sample arrangement of an interferometer is usually placed between the interferometer and the detector. Cuvettes with windows made of IR-transmitting material (Table 3.4-1) contain either a pure liquid sample or a solution usually in a thickne.ss of 5. .. 200 pm - defined by means of a spacer - sometimes, without a spacer ( capillary ) it may be even less. If the available amount of sample is very small or the concentration of the substance to be analyzed is very low, then the sample arrangement has to be optimized for this purpose as micro or trace arrangement respectively. 

Configuration There are many kinds of FPI for biosensors. A typical FPI interferometer consists of an LED, a channel for bio reaction, a micro-FPI, and a detector. 

Novel developments using micro-opto-electro-mechanical systems as moving mirrors in the interferometers (Kenda et al., 2011) bridge the gap between classical FTIR setups and microsystems. They target the miniaturization of the spectrometers. 

The micro-interferometric arrangement of Tiselius and Clsesson is shown diagrammatically in Fig. 1, where R is the interferometer cell where the solution flows from the adsorption cell through a gold capillary... 

Both dispersive (D) and Fourier transform (FT) micro-Raman are commercially available [507-509]. The choice between D- and FT-Raman has been discussed cfr. Chp. 1.2.3). However, as the intrinsic superiority of interferometers in terms of high resolution and geometrical extent cannot be exploited in micro-Raman spectroscopy, dispersive spectral analysers are preferred in combination with the microscope. FT-Raman instruments equipped with a microscope have thus far been limited to a sensitivity far lower than that of modern Raman microspectrometers equipped with multichannel detectors, which employ visible excitation. Consequently, FT-Raman microscopes often yield deceiving results with poor sensitivity and spatial resolution (from 15... 

However, calculation of a practical micro-cantilever is more complicated than that of an ideal cantilever. A tested sample was fabricated as a cantilever, 15 /rm in width and 90 /rm in length. The bottom electrode was a Pt/Ti layer on the substrate (LTO) and an upper electrode was Pt, coated on a PLZT surface. When a DC voltage was applied across the PLZT layer of the cantilever sample, the PLZT layer was shrunk due to the counter-piezoelectric effect and the cantilever was bent up, as shown in Figure 22-14. The displacement of the cantilever tip can be measured by using a laser interferometer (e.g.. Pan Cross, 1989). The displacement, S, of a cantilever is approximately proportional to the applied voltage V, when V is not very high (V< 10 V). The relationship between S and V can be expressed by the following equation ... 

Femtosecond pulsed lasers have been used to manufacture photonic devices (splitters, interferometers, etc.) and gratings. An ultrafast-laser driven micro-explosion method using a tightly focused femtosecond laser was exploited to fabricate three-dimensional (3D) void-based diamond lattice photonic crystals in a low refractive index polymer material (solid resin) [62]. 

Purely diffractive micro Fresnel lenses can also be obtained holographically, by the interference of a convergent or divergent laser beam with a planar wave in a Mach-Zehnder interferometer, as shown in Figure 16.13. Figure 16.14 shows the structure of a lens produced by this technique from a photosensitive nanocomposite material. 

At least two Raman spectroscopic methods are applicable in membrane surface characterization Fourier transform Raman spectroscopy (FT-Raman), and micro-Raman spectroscopy (Boccaccio et al., 2002 Gmger et al., 2001 Khulbe and Matsuura, 2000). In FT-Raman the sample molecules are excited with a near-infi ared (NIR) laser and appropriately configured Michelson interferometers, and Fomier transform processes are used in the collecting of scattered light and the analysis of the collected light. Almost the only requirement is that the sample to be analyzed with FT-Raman must not be black (Hendra, 2005). FT-Raman is a valuable tool in determining the overall chemical stmcture of a membrane, but it cannot characterize the asymmetric stmcture of a porous membrane matrix (Boccaccio et al., 2002). 

Fig. 2 Laser written micro-optical components, a Optical microscopic image of a Y coupler drawn in pure fused silica, which guides 514.5-nm light from an argon-ion laser. The scattered radiation from the coupled argon-ion light is observed in the photograph. The vertical direction is magnified with respect to the horizontal direction for clarity, b Phase contrast microscopic image of one of the two X-couplers that make up a Mach-Zehnder interferometer, c Optical microscopic image of a Fresnel zone plate...

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