Resolution, axial

Secondly, a short pulse duration is required in order to achieve a good axial resolution, i.e. two signals close together should be detected without interference. The task can be, for example, to detect a small reflector close to the surface or back wall of the test object, as the inspection has to cover the total volume as complete as possible, including the near-surface regions. 

Composite transducers will replace conventional transducers in applications where the improvement of test sensitivity, signal to noise ratio and axial resolution are mandatory. It must nevertheless also be noted in connection with the broadband feature that though composite probes have a specified nominal frequency, the echo signals allow no echo amplitude... 

Although the processing time unit basically could be further improved table 1 gives some idears what the achieved results and axial resolution mean in several interesting applications and low center frequencies. With low frequencies a lot of attenuation problems available in new engineered materials could be solved. 

The VMOS-pulser with a rise time lower than 6 ns provides high axial resolution and high-frequency inspections above 10 MHz with an excellent signal-to-noise ratio. The output voltage amounts to about 228 V without load, and 194 V with a load of 75 H, A damping control from 75 Q to 360 Q matches the impedance to the transducer. 

B1.18.5.2 OPTICAL SECTIONING, SMALLEST SLICE THICKNESS AND AXIAL RESOLUTION... 

Gordienko D V, Bolton TB, Cannell MB 1998 Variability in spontaneous subcellular Ca2+ release in guinea-pig ileum smooth muscle cells. J Physiol 507 707-720 Ho R, Shao Z 1991 Axial resolution of confocal microscopes revisited. Optiik 88 147—154 Holz GG, Leech CA, Heller RS, Castonguay N, Habener JF 1999 cAMP-dependent mobilization of intracellular Ca2+ stores by activation of ryanodine receptors in pancreatic [j cells. A Ca2+ signaling system stimulated by the insulinotropic hormone glucagon-like peptide-1-(7-37). J Biol Chem 274 14147-14156 Lipsius SL, Hiiser J, Blatter LA 2001 Intracellular Ca2+ release sparks atrial pacemaker activity. News Physiol Sci 16 101-106... 

FIGURE 3.4 Performance of the fluorescence up-conversion microscope, (a) Evaluation of the time-resolution with the 100 x objective lens , up-converted fluorescence -F-, the first derivative. By the fitting analysis, the time-resolution of the microscope was evaluated as 520 fs. (b) Evaluation of the transverse (XY) spatial resolution with the 100 x objective lens. A CCD image of the excitation pulses (inset) and the beam profile along the lateral (X) direction. By the fitting analysis, the transverse resolution was evaluated as 0.34 pm. (c d) Evaluation of the axial (Z) spatial resolution with the 100 x objective lens , up-converted fluorescence -I-, the first derivative. By fitting analysis on the first derivative coefficient, the axial resolution was evaluated as 1.1 pm with the 50 pm pinhole (c) and 5.3 pm without pinhole (d). (Rhodamine B, 2 x 10" mol dm in methanol, 600 nm.) (Erom Eujino, T. and Tahara, T., Appl Phys. B 79 145-151, 2004. Used with permission.)... 

Two-photon excitation can be used for the fluorescence up-conversion microscope, and high axial resolution was achieved without a pinhole in this case. Figure 3.5 shows the up-converted fluorescence from a coumarin 522B solution at a fluorescence wavelength of 520 nm observed in the same manner of Figure 3.4d without pinhole. In this measurement, a fundamental laser pulse at 800 nm was used for excitation. The axial resolution with two-photon excitation was evaluated to be 0.97 pm (FWHM) by fitting for the first derivative of the obtained data. This result indicates... 

FIGURE 3.5 Evaluation of the axial (Z) spatial resolution with two-photon excitation (objective lens, lOOx). By fitting analysis, the axial resolution was evaluated as 0.97 pm. 

Dyba, M., and Hell, S. W. 2002. Focal spots of size lambda/23 open up far-field florescence microscopy at 33 nm axial resolution. Phys. Rev. Lett. 88(16) 163901. 

Typical OCT systems provide a axial resolution of around 10 pm, ultra-high resolution is of the order of 1 pm. OCT systems typically use near infrared light with penetration depths in soft tissue of the order of a few millimetres. The mode of contrast in OCT is based on boundaries between zone of differences in refractive index within a specimen specifically, layers of different types of tissue can show up prominently on OCT images. Since the mid-1990s OCT has been suggested to be promising for real-time optical biopsy [42, 43], State-of-the-art probe systems have dimensions of a few millimetres and can be readily used at endoscopy. 

Technically, the heterogeneity of skin and the presence of refractive index gradients likely impose some constraints to the accurate determination of imaging parameters. However, uncertainties in the determination of spatial resolution and axial location in transparent samples from which spectra are extracted, such as those described by Everall [21-23] and others [24, 25], are probably not important for highly opaque skin samples. We estimate the axial resolution to be 2-3 pm with the 785 nm excitation wavelength used in the current measurements. A study from this lab has suggested that errors in depth measurements are less than 15% which is probably adequate for most current purposes. 

The reflection confocal microscope (RCM) is an attractive configuration as a readout system of multilayered optical memories because it has extremely high axial resolution and its configuration is substantially easier than that of transmission confocal microscopes, A typical RCM system is shown in Figure... 

An alternative readout system is a scanning differential phase-contrast microscope with a split detector as shown in Figure 16.5. The optical configuration is compact and easy to align. The memory medium, in which the data bits have been recorded, is located at the focus of an objective lens. The band limit of the optical transfer function (OTF) is the same as that of a conventional microscope with incoherent illumination. The resolution, especially the axial resolution of the phase-contrast microscope, is similar to that obtained by Zemike s phase-contrast microscope. The contrast of the image is much improved compared to that of Zernike s phase-contrast microscope, however, because the nondiffracted components are completely eliminated by the subtraction of signals between two detectors. The readout system is therefore sensitive to small phase changes. 

Improving the Axial Resolution by Combining the Aperture of Two Lenses... 

The 2 -resolution of any standard far-held light microscope is at least three times poorer than that in the focal plane which is particularly limited in 3D-imaging transparent objects such as cells. Therefore, in the quest for nanoscale resolution in far-held optical microscopy, it was most natural to start out with the axial resolution problem. 

The reason for the poorer axial resolution is that the focal dihraction spot is elongated along the optic axis Az > Ar). This elongation stems from... 

All diffraction-unlimited nanoscopy methods can provide improved axial resolution even when implemented with a single lens [77,83,120,131,132[. However, because it starts out from less favorable values, the -resolution usually remains worse than its focal plane counterpart. The coherent use of opposing lenses pioneered in 4Pi microscopy and FM, however, facilitates an independent resolution improvement factor by 3-7-fold along the optic axis as has already been demonstrated with STED [83,84,87]. In the stochastic single molecule switching modalities, a similar gain in resolution will take place by the coherent use of opposing lenses [133]. Thus, while 4Pi microscopy and FM did not break the diffraction barrier, they remain cornerstones of far-field fluorescence nanoscopy in the future. 

M.G.L. Gustafsson, D.A. Agard, J.W. Sedat, Sevenfold improvement of axial resolution in 3D widefield microscopy using two objective lenses. Proc. SPIE 2412, 147-156 (1995)... 

RE. Hanninen et al., Two-photon excitation 4Pi confocal microscope Enhanced axial resolution microscope for biological research. Appl. Phys. Lett. 66, 1698-1700 (1995)... 

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