Liquids lenses

The specimen-beam interactions that form the image also produce damage to the specimen. Careful specimen preparation can help minimize damage. The deposition of hydrocarbons onto the sample (contamination) can be reduced gready by a good vacuum system and use of the objective lens liquid nitrogen anticontaminator. Mass loss due to electron beam radiation is the most serious problem (8, 9), and can be somewhat reduced, but not completely eliminated. 

Many mechanically tunable microlenses are designed as circular chambers covered by thin flexible membranes. The membrane deforms when pressure is applied to the lens liquid through external actuation. In addihon, some microlenses are formed through air-liquid or liquid-liquid interfaces (immiscible, with different refractive indices). These interfaces may also be varied by applying pressure that adjusts the radii of curvatures of the spherical membranes in air-liquid devices and the focal lengths of the microlenses formed via liquid-liquid interfaces. 

In section 4, we have shown an optical design study of a 3 cell compound lens. Liquids considered were ionic liquids. From the theoretical point of view (diffraction limited behavior) optical behavior of this three-cell lens is good. Flowever, the fabrication of such a three cell compound lens needs the development of more accurate fabrication methods. Probably with MEMS technology the three cell compound lens could be made. With our low-technology method, comprising acrylic cells, just a two-cell compound lens with diameters of some millimeters can be done. 

The equilibrium shape of a liquid lens floating on a liquid surface was considered by Langmuir [59], Miller [60], and Donahue and Bartell [61]. More general cases were treated by Princen and Mason [62] and the thermodynamics of a liquid lens has been treated by Rowlinson [63]. The profile of an oil lens floating on water is shown in Fig. IV-4. The three interfacial tensions may be represented by arrows forming a Newman triangle ... 

Referring to Fig. IV-4, the angles a and /3 for a lens of isobutyl alcohol on water are 42.5° and 3°, respectively. The surface tension of water saturated with the alcohol is 24.5 dyn/cm the interfacial tension between the two liquids is 2.0 dyn/cm, and the surface tension of n-heptyl alcohol is 23.0 dyn/cm. Calculate the value of the angle 7 in the figure. Which equation, IV-6 or IV-9, represents these data better Calculate the thickness of an infinite lens of isobutyl alcohol on water. 

With the microfocus instrument it is possible to combine the weak Raman scattering of liquid water with a water-immersion lens on the microscope and to determine spectra on precipitates in equilibrium with the mother liquor. Unique among characterization tools, Raman spectroscopy will give structural information on solids that are otherwise unstable when removed from their solutions. 

The particle size analyzer, based on laser light diffraction, consists of a laser source, beam expander, collector lens, and detector (Fig. ] 3.45). The detector contains light diodes arranged to form a radial diode-array detector. The particle sample to be measured can be blown across the laser beam (dry sample), or it can be circulated via a measurement cell in a liquid suspension. In the latter case, the beam is direaed through the transparent cell. 

This system consists of a symmetrical pair of lens elements connected by a small volume of liquid. Each lens consists of a single spherical interface between the liquid and a lens rod. The lens element is formed by polishing a small concave spherical surface in the end of a sapphire rod. At the opposite end of the rod, a thin film piezoelectric transducer is centered on the axis of the lens surface. 

The resolution of an acoustic lens is determined by diffraction limitations, and is 7 = 0.51 /N.A [95], where is the wavelength of sound in liquid, and N.A is the numerical aperture of the acoustic lens. For smaller (high-frequency) lenses, N.A can be about 1, and this would give a resolution of 0.5 Kyj. Thus a well designed lens can obtain a diameter of the focal spot approaching an acoustic wavelength (about 0.4 /Ltm at 2.0 GHz in water). In this case, the acoustic microscope can achieve a resolution comparable to that of the optical microscope. 

Skogerboe, K. J. and Yeung, E. S., Single laser thermal lens detector for microbore liquid chromatography based on high-frequency modulation, Anal. Chem., 58, 1014, 1986. 

Tran, C. D., Huang, G., and Grishko, V. I., Direct and indirect detection of liquid chromatography by infrared thermal lens spectrometry, Anal. Chim. Acta, 299, 361, 1995. 

Siezen, R. J., Kaplan, E. D., and Anello, R. D., Superior resolution of y-crystal-lins from microdissected eye lens by cation-exchange high-performance liquid chromatography, Biochem. Biophys. Res. Comm., 127, 153, 1985. 

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