Shutters electro-optical modulator

A half-wave plate (HWP) and a polarizer (GLP) are positioned after the oscillator and are used to variably attenuate the laser output power to the desired input power required by specific experiments. Using a beam sampler (M ), a small portion of the laser beam is directed into a beam diagnostic unit (AC). In it, the laser pulse is characterized both in the time and frequency domains by employing an autocorrelator and a spectrometer. The laser beam is then expanded to match or overfill the back aperture of the objective lens. This is accomphshed using two positive lenses with the appropriate focal lengths. At the focal point of the first lens, a pinhole (SF) is carefully positioned to spatially filter the laser beam. An electro-mechanical shutter (S), used to control laser exposure times in the sample, is placed before this assembly. If exposure times shorter that a few milliseconds are required, faster response shutters such as acousto- or electro-optic modulators can be used. 

Application optical modulator, polarizing device, electro-optical shutter... 

Electro-optic effects describe a change in optical properties arising from an applied electric field. This can include changes in colour or optical absorption, characteristic of electrochromic materials (Section 9.6), or a change in refractive index. In perovskites, it is this latter effect that is important. These crystals have been used in electro-optic devices to modulate the phase, the amplitude or the polarisation of a light beam traversing the medium and so function as shutters and other components in optical/electronic circuits. 

Fig. 10.11 Basic setup for evaluating electro-optic shutter/modulator characteristics (open condition shown). Reproduced with permission from [131]. Cop5uight 1999, John Wiley Sons...

The linear electro-optic effect in a cholesteric, i.e. a hard-twisted chiral nematic (the helical pitch must be less than the wavelength of visible light) was a very original proposal for using the flexoelectric effect in a new display, shutter or modulator device. The patent application by R.B. Meyer and J.S. Patel dates from 1987 and was granted in 1990. The physics was developed in a series of papers by these authors and later elaborated by others.It is now commonly called the flexoelectro-optic effect. 

Ferroelectric liquid crystal displays have potential as very fast displays and also do not require active matrix addressing technology. Due to their fast response times, they also have potential applications as high-speed electro-optical shutters or spatial light modulators. However, due to fabrication... 

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