Matt Lehmann Holography - Technique and Practice

A discussion of what a hologram is and how it is made is followed by a detailed procedure describing how to determine whether a proposed holographic system will be successful. Particular attention is given to the formation of the fringe pattern as it is the delineation of the fringes which determine the requirements and quality in holography. Several holographic systems are discussed giving the advantages and disadvantages of each as well as a description of the optical elements required. Introduction During its short life, the laser has probably had more misinformation published about it than any other scientific discovery. A few years ago a San Francisco newspaper published a full page advertisement, depicting. a laser cannon shooting down missiles, entitled ‘The Incredible Laser’. Dr Arthur Schawlow, one of the inventors of the laser, has this advertisement posted on the door of his laboratory with the sub-caption, ‘For CREDIBLE Lasers, See Inside!’ The laser is, however, truly an ‘incredible’ tool in the field of optics. It has made possible the technique of wave-front reconstruction, more popularly known as holography. The dramatic realism achieved by holographic reconstruction has captured the imagination of scientist, engineer and layman alike. As with any new dramatic discovery, reports frequently have scant regard for verisimilitude. However, an understanding of what holography is, how it can be accomplished, and its limitations and advantages are essential to its utilization as a valuable tool for engineers and scientists in all fields of endeavour. Although holographic recordings are not limited to photographic techniques alone, what applies to photographic methods are readily adapted to any other recording systems. 1. What is a hologram? What precisely is a hologram and how does it differ from a conventional photograph? Since we are all familiar with conventional photography the difference between holography and photography will be a good place to start. MATT LEHMANN HOLOGRAPHY-TECHNIQUE AND PRACTICE The light reflected from each point on an object is scattered in all photographic, film can record only intensity (the square of the amplitude). directions. If a photographic plate is illuminated by this scattered light, it would be uniformly exposed and no image would be recorded. This We can trick the film into recording phase and amplitude by removing the lens or pinhole and provide a reference source of unmodulated light can be readily seen as a ray of light from any point on the object and can energy (fig. Ic). The light intensity recorded by the photographic film be traced to every point on the plate (fig. Ia). If we insert a pinhole is now a function of the amplitude of the wave from the object and of