Confocal domains

Hexagonal mesophases can be recognized by their typical fan-shape texture (Fig. 7a). Lamellar mesophases typically show oily streaks with inserted maltese crosses (Fig. 7b). The latter are due to defects, called confocal domains, that arise from a concentric rearrangement of plane layers. In some lamellar mesophases these defects prevail. Hence no oily streaks occur but maltese crosses are the dominant texture (Fig. 7c). 

Figures 9a-c represent transmission electron micrographs of different lyotropic liquid crystals after freeze fracture without etching. The layer structure of the lamellar mesophase including confocal domains, hexagonal arrangement of rodlike micelles within the hexagonal mesophase, as well as close-packed spherical micelles within the cubic liquid crystal can be clearly seen.

The textures in homeotropic lamellar phases of lecithin are studied in lecithin-water phases by polarizing microscopy and in dried phases by electron microscopy. In the former, we observe the La phase (the chains are liquid, the polar heads disordered)—the texture displays classical FriedeVs oily streaks, which we interpret as clusters of parallel dislocations whose core is split in two disclinations of opposite sign, with a transversal instability of the confocal domain type. In the latter case, the nature of the lamellar phase is less understood. However, the elementary defects (negative staining) are quenched from the La phase they are dislocations or Grandjean terraces, where the same transversal instability can occur. We also observed dislocations with an extended core these defects seem typical of the phase in the electron microscope. 

Figure 6. Some visible confocal domains. The transversal striations are clearly visible.

Figure 7. Scheme of a confocal domain in an homeotropic sample. Lamellar details are not featured. Broken line axis of revolution. 

Friedel (2) interpreted the transversal striations on oily streaks as small adjacent confocal domains that have a tendency to gather in lines. We already noted that such a situation exists in DADB (12) (but the lines are attached to the surface), and that c domains pin up on l lines moreover, oily streaks in cholesterics have clear confocal domains. However, the transversal striations on l or L lines are not compatible with c domains since we do not see there the typical Maltese cross on the contrary, the hyperbolic directions would be at a small angle to the sample plane if they exist. We do not reject FriedeFs explanation, but we must make it compatible with observations, particularly with the longitudinal striations. 

Figure 10.31 Smectic A layers forming Dupin cyclides. In (a), the disclination lines are an ellipse and a hyperbola the ellipse passes through the focus of the hyperbola and the hyperbola passes through the focus of the ellipse. In the degenerate case (b), the ellipse becomes a circle and the hyperbola becomes a line. The cone is an isolated confocal domain. (From Lavrentovich, reprinted with permission from Sov. Phys. JETP 64 984, Copyright 1986, American Institute of Physics.)...

With the aim of elucidating molecular dynamics in a small domain, we have constmcted several microspectroscopic systems, that is, (i) the confocal microscope with the excitation light source being a femtosecond NIR laser emitting a 35 fs pulse, and (ii) the fluorescence correlation spectroscopic system with optical tweezers. 

Lifetime imaging can be implemented both in wide field and in scanning microscopes such as confocal microscopes and two-photon excitation microscopes. The most common implementations in time-domain fluorescence lifetime imaging microscopy (FLIM) are based on TCSPC [8, 9] and time-gating (TG) [2, 10],... 

Historically, this has been the most constrained parameter, particularly for confocal laser scanning microscopes that require spatially coherent sources and so have been typically limited to a few discrete excitation wavelengths, traditionally obtained from gas lasers. Convenient tunable continuous wave (c.w.) excitation for wide-held microscopy was widely available from filtered lamp sources but, for time domain FLIM, the only ultrafast light sources covering the visible spectrum were c.w. mode-locked dye lasers before the advent of ultrafast Ti Sapphire lasers. 

Confocal fluorescence microscopy can be combined with time-domain and frequency-domain techniques to produce lifetime imaging (see Section 11.2.2.3). 

As shown in Section 11.2.1.1, more details can be obtained by confocal fluorescence microscopy than by conventional fluorescence microscopy. In principle, the extension of conventional FLIM to confocal FLIM using either time- or frequency-domain methods is possible. However, the time-domain method based on singlephoton timing requires expensive lasers with high repetition rates to acquire an image in a reasonable time, because each pixel requires many photon events to generate a decay curve. In contrast, the frequency-domain method using an inexpensive CW laser coupled with an acoustooptic modulator is well suited to confocal FLIM. 

Domain formed by deformed smectic layers that fold around two confocal line defects preserving equidistance of structural layers everywhere except in the vicinity of the defect lines. 

Note 5 A focal-conic domain built around two confocal parabolae is called a parabolic focal-conic domain. 

Buranachai C, Kamiyama D, Chiba A et al (2008) Rapid frequency-domain FLIM spinning disk confocal microscope lifetime resolution, image improvement and wavelet analysis. JFluoresc 18 929-942... 

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