Beam Alignment and Positioning Techniques

In four sections, this chapter guides the reader through variety of mechanisms for controlling the beam. Manual stages for angular alignment are considered in the first section: three-contact gimbals, flexible hinges, rotating wedges. Displacement curves and deflection nomogram with analytical formula are presented for the reference purposes. Lateral alignment with the pairs of flats and mirrors is explained in the next section, also supported by the nomogram and formula The third section summarizes most common beam steering elements: the widely used galvano-mirrors and much more rare Risley prism. The rules of coupling galvano-mirrors to light sources through relay optics ( Chap. 1) are explained and graphically illustrated. The reader will find design details, performance, and practical realization of two-dimensional scanners with the example of a simple laser marking arrangement. Angular precision of this type of scanners is determined by optical feedback, using quadrant photodiodes ( Chap. 3). Experimental results presented in the form of oscilloscope traces give good impression of the capabilities of these devices. The Risley prism is a very efficient but much more expensive solution for beam steering. Beam steering devices often require F-theta lens for focusing. This special type of lenses, which was not mentioned in Chap. 1, is explained in detail in this section: the principle, design considerations, and mathematical explanation of its rather peculiar shape. The forth section is a source of concentrated information about manual and motorized translation stages that may be found in the laboratory. Some simple recommendations and practical know-how may significantly improve performance of translational stages. High-precision differential stages and micrometer screws are explained. Detailed discussion of stepping motors—connection diagrams, drivers, microstepping modes, electromagnetic noise, vibrations—illustrated with experimental oscillograms is supposed to clarify many practical questions. Scrutinized analysis of geared motorized stages unveils some rarely known facts about their precision. The section and the chapter end with detailed explanation of design and characteristics of piezo-stages. Although the basic principle of piezo-electric deformation is widely known, particular design and technology of contemporary multilayer piezo-actuators with 0.1 % excursion are not in the public domain. The effects of hysteresis, poling, and repolarization are explained in order to avoid possible mistakes in applications. Finally, the chapter presents impressive experimental comparison of a geared motorized stage with the piezo-stage.