Optical bounce

This transient effect manifests itself in a direct way in the behaviour of a twisted nematic cell (see 3.4.2). When the external field (assumed to be sufficiently strong) is switched off, the light transmission shows an optical bounce effect , i.e., it does not decrease monotonically but rises again to a peak before decaying to its off value. Calculations have confirmed that the peak in transmission corresponds approximately to a perpendicular alignment of the director in the central portion of the cell. This is caused by fluid motion, which also gives rise to a reverse-twist. ... 

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

Size cut enhances resolution, optically important aerosol analysis, low artifact potential, particle bounce amenable to automated compositional analysis automated versions available large networks under development... 

For SFM, maintaining a constant separation between the tip and the sample means that the deflection of the cantilever must be measured accurately. The first SFM used an STM tip to tunnel to the back of the cantilever to measure its vertical deflection. However, this technique was sensitive to contaminants on the cantilever." Optical methods proved more reliable. The most common method for monitoring the defection is with an optical-lever or beam-bounce detection system. In this scheme, light from a laser diode is reflected from the back of the cantilever into a position-sensitive photodiode. A given cantilever deflection will then correspond to a specific position of the laser beam on the position-sensitive photodiode. Because the position-sensitive photodiode is very sensitive (about 0.1 A), the vertical resolution of SFM is sub-A. 

As the emitted radiation bounces back and forth between the two mirrors, it becomes coherent. Some of the energy traveling back and forth through the optical cavity is transmitted though the less reflective mirror and becomes a laser beam. 

The unique field penetration into the liquid of a nonevanescent resonant mode like Tlij(7)0 is very promising for the sensing applications. To understand the origin of this behavior and further optimize the devices, a ray optical picture71 is presented. This type of resonant modes exist as if rays are bounced at the liquid/silica interface and confined in the liquid region as plotted in Fig. 8.32. From the viewpoint of ray optics, light is partially reflected (termed ray 1) and partially transmitted when it is... 

There are two types of optical communication systems passive reflective systems and active-steered laser systems [War 01, War 05], A passive reflective system, such as a comer-cube retroreflector (CCR), consists of three mutually orthogonal mirrors that form the comer of a cube. Light entering the cube bounces off the mirrors and is reflected back to the sender. By electrostatically actuating the bottom mirror, the orthogonalty can be disturbed and the reflection is no longer returned to the sender. 

Most of the current optics using Synchrotron Radiation diffracts in the vertical plane and thus is sensitive to vertical bouncing of the beam. The horizontal optical plane of the dispersive scheme combines this extra advantage which helps to keep superior energy resolution since the orbit seems to show a better stability in the horizontal direction. Owing to the horizontal polarization of S.R., one must consider the cos (20) attenuation factor which reduces the Darwin width of the crystal. This results in a lower reflectivity and an improved energy resolution as well. 

A diode laser operates in essentially the same fashion as an LED. Two additional requirements must be met for a direct gap semiconductor to be an efficient laser. The first is that larger forward bias currents are needed for a laser than for an LED, because lasers require a higher degree of population inversion—a large number of electrons in the conduction band above empty levels in the valence band. Lasers also require an optical cavity light bounces back and forth within the cavity, building up intensity. In a diode... 

The inclusion of the extra optical elements (e.g., the four extra bounces from the two detuned channel-cut postmonochromator crystals) in the optical path while producing the desired effect of increasing the XSW phase (or atomic positional) resolution, come at the cost of reducing the X-ray intensity incident on the sample. Using Figure 12a one can visually estimate this effect by comparing the emittance from the second Si(004)... 

A similar laser, with diode end-pumping, could produce pulses of 128 ns at a repetition rate of 230 kHz, with a slope efficiency of 9 % [151, 152]. One of the examples was a LD-end-pumped passively g-switched Nd YAG ceramic laser, operated at 1319 nm with a V YAG saturable absorber [151]. An average output power of 1.8 W was achieved at the pump power of 23.7 W, which corresponded to an optical conversion efficiency of 7.8 % and a slope efficiency of 9 %. The minimum pulse width of 128 ns at a pulse repetition rate of 230 kHz was obtained with a T = 2.8 % OC at the pump power of 23.7 W. Another example was a side-pumped Nd-doped Gd(0.6)Y(0.4)VO(4) bounce laser, which was combined with a V YAG saturable absorber crystal [152]. It offered a passively g-switched output of 6.5 W at 1.3 pm. Output powers of 6.5 and 6 W were observed at a maximum pump level for the multi- and TEM(00)-mode operations, demonstrating optical-to-optical efficiencies of 17.5 and 16.2 %, respectively. 

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