Ewesly / Making a test strip
Preamble
This section of the Web Site is the Benchmark Project for the TIE 594 Web Process in Education class that I have taken at National-Louis University, and as such is written with an educator's overview. Big shout out for NLU to host this site (at least until I get my degree!) and to Dr. Craig Cunningham who has been so very patient with me!
There is a decided lack of how exactly to run these simple holographic recording materials calibration tests in textbooks and on the web, so I decided it’s high time to demonstrate this all-important aspect of the holographic recording process.
Introduction
- This lesson’s subject matter is the methodology of peaking getting the best (brightest or most easily viewed) hologram on commercially available films and plates.
- Students will learn the importance of exposure by making a test strip and the importance of development time, plus the role and interesting results obtainable by two different types of processing chemistries.
This curriculum is centered on controlling the variables of the holographic recording film’s processing procedure, and how to troubleshoot processing errors. This entails varying the following parameters and analyzing the results.
Exposure as a function of intensity and time * exposure test series * role of the developer * developing time variations * different types of developers * the role of the bleach * different types of bleach.
At the end of this unit, the student holographer will be able to:
- Make a test strip of a sensible order of exposures
- Choose the developer and bleach combination that will give the final desired color
- Follow the timing of the processing steps
- Troubleshoot exposure and processing errors
Once you are committed to becoming a holographer, you admit that you are a laser nerd and want to soak up all the possible information about the process, so there would be a very positive mental attitude carried into this lesson. The information might be totally brand new to some, and would be even better appreciated by those who have had some success and failures, as they may have not approached the problem in a systematic way.
Since the whole process is extremely technical and there was some capital outlay for the equipment and film, there would perforce be a very positive mental attitude, especially if the holographer has a certain goal in mind for the finished piece.
The point of this exercise is to show how to tune in the exposure and processing aspects of recording a hologram. The directions included with the film (when they are included) are oftentimes erroneous, behind the times, irrelevant, etc.By playing with the parameters, the students should learn the methodology and apply it to the holographic films currently available or those that may appear in the future.
The holographer needs to know the dynamic range of the material if it is foreseen to do multiple exposures for color blending or double exposed interferometry.
Once a system is tuned in with exposure parameters constant any object can be placed in position and the same exposure and development can be used to give optimal results. The brightness of the final holograms would be affected by the relative reflectivity of the objects, stronger reflectors giving brighter holograms, and weaker objects could be compensated for by bumping up the exposure time.
The Single Beam Reflection Hologram recording scheme was chosen for this tutorial as it \is very popular in introductory holography classes with its immediate gratification of a hologram that doesn’t need a laser to be viewed. It is also quick to set up as there is no need for beamsplitting, only beamspreading. With a split beam set up there is more versatility as far as objects, beam balance ratio, etc., goes, however there are more parameters to keep under strict control and more optics to keep still during exposure. With a solid object that has kinematic positioning, like the Standard Holographic Object waffle iron, object movement is not an issue.
This SBR set up (often known as the Denisyuk scheme, after the Russian Holographic Deity, Yuri Denisyuk), puts high resolution demands on the recording material, with its fringe spacing on the scale of a half a wavelength of the recording laser color, so it is a good test to see how good the material really is. Not all holographic films and plates are capable of recording this type of hologram well or even at all!
For the sake of this lesson, it is assumed that the student has the necessary prerequisites.
Prerequisites
For this lesson, it is assumed that the student probably has heard the basic raps on the theory of holography and how it’s different from photography has followed directions either from this site or some other source and has the necessary equipment (laser, beamspreader, isolation table, object, holographic film and chemistry) to set up the necessary optical configuration to record a hologram, (preferably the type known as Single Beam Reflection) (the Googling is left up to the reader, start with Single Beam Reflection Hologram or Denisyuk hologram) and is ready to load the holographic film into the set up.
By the time the student holographer is ready to make an exposure, they will have built the optical configuration. It is probably unlikely that they have worked in a photographic darkroom, which is the void that this unit will try to fill. Unless the students have no interest in the process and have been coerced into the lab, they will have a positive mental attitude toward the whole thing, and the only danger is that they might be so over-enthusiastic that they might not want to go through the discipline of a systematic shakedown of the exposure and development process. But even if their exuberance overpowers common sense, they will come back to this lesson when they want to make the best possible result.
