Illumination collimated beam

In the last five sections we have shown how a lens, on the one hand can increase source efficiency for collimated beam illumination of a fiber, while, on the other hand, it is ineffective at increasing the efficiency of the diffuse source. If we couple these facts with the description of the diffuse source as a superposition of collimated beams, it is evident that the efficiency of a partially diffuse source can be increased by a lens. The situation is illustrated in Fig. 4—8. We assume the step-profile fiber is weakly guiding so that 9 1, and the focal length satisfies... 

Once a diffraction-limited excitation spot is achieved, the same microscope objective that is used for illumination can also be used to collect light from the sample similar to the case of SNOM. If the incoming beam of light is collimated, the beam of collected light is also collimated for a chromatically corrected microscope objective. The use of collimated beams... 

The technique used to (effectively) overcome the VBE is to reduce the effective spatial coherence of the light source used for the development exposure by rotating the sample. Alternatively, the sample could be illuminated simultaneously from many different directions, but it is more convenient to use a moderately collimated beam striking the sample surface at a shallow angle while rotating the sample about an axis perpendicular to that surface. The time constants involved in the polymerization process are typically of the order of minutes, so that rotation rates of the order of 1 rps are usually more than sufficient. 

Start with the laser in the position for epifluorescence illumination. A collimated beam exits the objective. 

Collimation of the beam hardly works beyond a reduction of 50% in illuminated area, The collimator must be placed some distance in front of the sample to avoid that forward or backward detectors pick up positrons stemming from muons stopped in the collimator, The divergence of the muon beam and especially scattering of muons by the collimator and also in the start counter, the cryostat windows etc. break up the collimated beam again in the case of surface muons. 

It is worth noting at this stage that a refractive index ratio of near unity (e.g., when using an oil-immersion objective), this effect is greatly reduced. Also, the analysis assumes that diffraction effects are negligible and that the (laser) illumination is emanating from a point source or collimated beam. 

Figure 16.13 Setup for holographic writing of a micro Fresnel lens. A linearly polarized collimated beam from an Ar + -Laser (wavelength 351 nm) is divided by a beam splitter into two beams the object beam illuminates the test object through a lens L2. The reference beam recombines with the object...

In PM the textures are mostly observed in transmission under collimated (parallel) illuminated light beams, where the light enters the film normal to its surfaces (orthoconic observations). The microscope in orthoconic observations gives a magnified, inverted 2D image of the texture. 

The sensor concept with a collimated illumination beam in the measurement volume (Fig. 12.12) differs from the SE-F-Sensor only by a different collimator which collimates an illumination beam with an approximately constant e diameter in the measurement volume. The divergence of the light beam along its propagation direction is significantly lower than with the focused light beam. For... 

For the investigations presented in this paper, two collimators are used for the SE-C-PH-Sensor concept a collimator which collimates an illumination beam with... 

Cheng and Kohl (29) demonstrated that fiducial patterns on one side of an n-lnP wafer, defined in photoresist, could be photoelectrochemically etched through to the other side of a wafer about 90 pm thick. The metallized mask served the dual purpose of the electrical contact, which was at the front surface in this case. The process was carried out by illumination with a collimated beam from a HeNe laser and an electrode polarization of 0.2 - 0.4 volt (SCE) in 2 - 4 N HCI. Best results were obtained at light intensities <260 mW/cm due to reduced effects of diffraction and light scattering within the growing hole. 

The parameters for the linear taper of Fig. 5-6(a) are identical with those of the previous example and the taper angle is SI We can determine very simply the minimum taper length for total power transmission when a meridional ray enters the taper at z = —L and makes angle 0q with the axis. This result apphes to both direct on-axis illumination by a collimated beam, i.e. 0q = 0, and the inclusion of a lens, as discussed in Section 4-11, which transforms the on-axis beam into acone of meridional rays at angle d(, > 0. 

In the present and previous sections we have demonstrated the considerable simplification which results from using generalized parameters to describe the spatial transient when a fiber is illuminated by a diffuse source. A similar simplification occurs when the generalized parameters are used to describe the spatial transient due to collimated-beam excitation [11]. 

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