Pockels cell

Figure 9.4 Use of Pockels cell (PC) in a laser cavity to produce 0-switchmg...

Drummond, D. R., Carter, N. and Cross, R. A. (2002). Multiphoton versus confocal high resolution z-sectioning of enhanced green fluorescent microtubules Increased multiphoton photobleaching within the focal plane can be compensated using a Pockels cell and dual widefield detectors. J. Microsc. 206, 161-9. 

Intense nanosecond pulses (Ins = 10 9s) can be produced by Q-switching. A shutter is placed between the laser rod and one of the mirrors, thus inhibiting lasing. If the shutter is suddenly opened, the excitation is dumped in one huge burst. One type of shutter is the electro-optic Pockels cell (KH2P04 crystal with a high applied potential). 

The use of fluorescence from alexandrite for temperature sensing was first reported by Augousti etal.(57,5S) using a low-power LED or a HeNe laser with a rather inefficient modulation accessory made of a bulky, high-voltage controlled Pockels cell,... 

Pockel cells use the linear electro optic effect in crystals to turn the plane of polarization when an external electric field is applied. A detailed description with references is given in... 

Fig. 6. Experimental arrangement for lifetime measurements by the phase-shift method, using laser excitation. The laser beam is amplitude-modulated by a Pockel cell with analysing Nicol prism and a small part of the beam is reflected by a beam splitter B into a water cell, causing Rayleigh scattering. This Rayleigh-scattered light and the fluorescence light from the absorption cell are both focused onto the multiplier cathode PMl, where the difference in their modulation phases is detected. (From Baumgartner, G., Demtroder, W., Stock, M., ref. 122)).

Until recently a general drawback of this passive Q-switching scheme was the difficulty of obtaining an exact synchronization of the giant pulse with other events in more complex experiments. This difficulty does not exist with active Q-switching in which an electro-optic device, e.g. a Kerr-cell or Pockels-cell, is used instead of a dye cell, and one is able to determine exactly the time at which... 

There is another way to obtain giant laser pulses of a few ns duration, known as active Q-switching. The shutter is an electro-optical cell which is triggered at some preset time after the pump flash. These electro-optical shutters are Kerr cells or Pockels cells. 

The shortest integration time of the counter is currently set to 1 jls, corresponding to a maximum sampling rate of 1 MHz. The actual time resolution is limited by the high voltage driver of the Pockels cell with approximately 20 jis switching time. 

Fig.4. Timing diagram for piezo mirror and Pockels cell with phase tracking and exposure. Details can be found in Ref. [34]. From Ref. [34]...

Fig. 23. Setup for periodic amplitude modulation, x and y are the two axes of the Pockels cell. They are rotated by 45" with respect to the polarization of the laser beam. S = U/UK, and U is the voltage for 180" phase shift.

In Ref. [75], it is discussed in more detail why it is advantageous to convolute the response of the temperature grating into the excitation and how to treat systematic errors arising from this approximation and from imperfections of the components in the setup. Especially the switching properties of the Pockels cell require careful analysis, since the switching number increases from 2 in case of pulsed excitation to approximately N in case of pseudostochastic binary sequences. 

The reason for these localized perturbations stems from a slight delay and asymmetry in the switching characteristics of the Pockels cell [75]. As a consequence, x (t) in Fig. 25 must be replaced by... 

Fig. 28. Imperfections of the Pockels cell lead to echoes in g(t) when measured with MLBSs...

Figure 4.12 Longitudinal Pockels cell. The kdp electro-optic crystal between two crossed polarizers makes an intensity modulator.

The application of an external field onto many materials will induce optical anisotropy. If the applied field oscillates, a time-dependent modulation of the polarization of the light transmitted by the device will result. Modulators of this sort include photoelastic modulators (PEM) [30,31], Faraday cells [32], Kerr cells [32], and Pockel cells. 

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