Supporting techniques

Abstract

Video cameras and data acquisition techniques always support optoelectronic research. However, these areas are far from typical specialties of those who work in optics. Therefore, well filtered information on these subjects, compressed into four sections of this chapter, may be useful. The first section presents physical principles of charge coupled devices (CCDs) and complementary metaloxide structures (CMOS)—the two types of video sensors that dominate contemporary market. They have absolutely the same principle of photon detection but many structural and operational differences, carefully explained in historical succession: first APS (active pixel structer) CMOS sensor, CCD transfer cycle and matrix, sequential and parallel nature of readout. Fill-factor, rolling and global shutter—the main principle differences between the CMOS and CCD. However, in practice, not these rarely known factors determine the choice of a sensor but simple geometrical considerations: the format. The table and a comparative figure with dimensions clarify the standard notations of the type «1/1.800». The influence that different format may have on the image is clearly explained, presenting two pictures obtained with sensors of different format. Using colour cameras, it is important to realize the difference between the colour sensor and the so-called 3CCD cameras: the typical mistake of using the same type of lenses for them and polarization differences are explained. The second section discusses video cameras and how to connect them in a variety of schemes: power voltages, digital and analog outputs, advantages and disadvantages of USB and Ethernet connections. Awareness of the simplest practical tricks like extension rings may sometimes solve the problem. The next section introduces beam profilers: a video camera equipped with neutral filters and special software for numerical measurement of beam parameters. Numerical data from the image is a very important option, but it is not necessary to pay extra money for it, purchasing rather expensive beam profiler, if the user has the program that converts standard graphic file into mathematical array. The transcript of such a program written in Fortran is presented together with the result of its application. Data acquisition is often considered as something that an optical engineer must not do himself, totally relying on the help of others. However, with the National Instruments LabVIEW technology this view may be overturned, and the last section of this chapter presents the concentrated guide of how to do it. Types of data acquisition boards (DAQs), connectors, installation into the computer, cables, terminal blocks—everything that may be needed to assemble the measurement system is explained succinctly in the beginning of this section. This is followed by practical instructions of how to create the simplest DAQ virtual instrument. The connectivity know-how—proper use of connection options—is very important to avoid mistakes, and this topic is explained next, including identification of grounded and isolated sources. The rest of the section guides the reader through testing of the first virtual instrument, explains the difference between the differential and pseudo-differential connection, and shows what may happen when connectivity rules are breached.