Single Beam Splitting for enhanced Denisyuk reflections

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jeff-blyth
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Single Beam Splitting for enhanced Denisyuk reflections

Post by jeff-blyth » Wed Dec 20, 2017 9:24 pm

Beam splitting and “single beam” holography
“Single beam” holography commonly known as Denisyuk or reflection holography is really a misnomer because of course all holography involves the interaction of never less than 2 beams from a single source. This means that we always have to split the beam up into two (or more) parts. In the case of “single beam” holography, the object itself is the “beam splitter” component. We strive to produce interference or standing waves which we can capture in our recording material. During the capture phase, i.e. the exposure time, the standing wave pattern is supersensitive to the tiniest change in distance between the object and the recording plate because any such change or movement will blur the pattern and weaken or entirely destroy the later hoped-for holographic image. However a great feature of the single beam method is that you can rest your object on top of a horizontal recording plate and after checking that it is wobble-free , you can rely on gravity to hold it in place during your exposure without needing to set up on a special vibration-isolation table which would have been essential if you had been using a conventional beam splitter such as a semi-silvered mirror . In the conventional beam splitter system the set-up is vertical and the beam is split into a reference beam and object beam . The object beam is arranged to take most of the light energy and the exposure time to make a reflection hologram is usually more than ten times longer than in the case of the “single-beam” set up. The demand for stability is extreme over the much longer exposure time and much longer path lengths from the beam splitter to the object and vertical recording plate. I advise beginners not to try it or it may put them off DIY holography for life! Back in the late 1970’s I started using an adjustable frame that enabled me to use an enhanced Denisyuk system to get a larger proportion of the light onto the object. It was at the time quite novel and probably a world first. A lot of glue gunning was needed to get pieces of mirror to reflect parts of a widely spread laser beam focused by various magnifying glasses onto parts of a complicated object such as a stuffed baby crocodile . There did need to be stability within the frame so that the subsidiary beams could interfere with the reference beam. The path length differences were well within the coherence length of the 20 mw HeNe red laser being used. The system was published in the Photographic Journal of October 1986, (edited by Graham Saxby) .

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admin_jsfisher
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Re: Single Beam Splitting for enhanced Denisyuk reflections

Post by admin_jsfisher » Wed Dec 20, 2017 10:55 pm

Is there a reprint you can share?

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