Reference Number: 0-1

Project Holography (phase I):

Design and Structure for an Off-axis System

(Jeremy) Yu Gong

7 September 2014

The Purpose for the design and structure of creating an off-axis holographic system is to

construct our very first holographic image by the simplest experiential settings, with fewest

possible experiential equipments, in a most successful-ensured method. The reason for the

participation for an off-axis based optical system rather than the in-line system, is to ensure the

coherence of the illumination and reference beams. This report serves as a pre-section analysis

for our further work, it will briefly cover the theory of off-axis holographic optics, the physical

structure of the experiment, and an introduction of our test run process.

1. Theory

As we have mentioned before, an off-axis optical system has the most advantage of

ensuring the coherence of the illumination and reference beam, however, may not be the

easiest one to physically construct. The creation of an holographic image requires its

photographic film (holographic plate) to record the interference patterns rather than the

traditional real image created by camera lens, therefore, the coherent accuracy dose play

an important role in this experiment.

The following figure shows a basic structure for creating an holographic image:

The laser will provide a stable source for the incident beam within a considerable

diameter, while a transparent mirror separates certain amount of the incident beams into

two directions: one continues to illuminate the object, the other one curves towards the

holographic plate, and intersects with scattered rays from the illuminated object, thus its

inference pattern will be recorded by the holographic film consequently. The separation

for the incident beams ensures the same nature of both illumination and reference beams,

in turn, a better quantified holographic image would be yielded by the interference

pattern, reflectively to the in-line holographic system.

2. Physical Structure and Experiential Settings

Based on the principle in the previous section, our off-axis holographic system thus is

designed and will be arranged as following figure shows:

The laser generator is located at a fixed position, which provides the incidental beam to

the transparent mirror. The incidental beam is then separated into transmitted and

reflected beams: where, the transmitted beam will soon be gone though the telescope,

therefore has its diameter enlarged and illuminates the objective area; meanwhile, the

reflecting mirror will re-direct the reflected beam through the other telescope, after its

diameter is to be enlarged, it will illuminate the holographic plate (film). One should

notice that, the transmitted beam serves as the illumination beam, and the reflected one is

treated as the reference beam to our optical system.

After the object were to be illuminated, the light (transmitted laser rays) will scatter

through the space, indeed, some of them will interfere with the reference beam on the

holographic plate, thus to created their patterns of interference, which are to be recorded.

According to our design, the list of the equipment is as follows:

two telescopes, with at least 10x enlarge rate;

one laser source;

one transparent mirror, with low intensity consuming rate;

one reflecting mirror;

several holographic films.

3. Further Analysis and Test Run Process

There remains still several minor issues for the setting up of our experiment:

First of all, as there are two mirrors in our system, we have to somehow conclude the

images of the object that are constructed by those two mirrors, however, as the setting up

for the transparent mirror, its image will not affect the system at all, meanwhile, we have

to very carefully adjust the front-direction for the reflected mirror, as its image appears at

the same side as our object. Further calculation may not be quite necessary for such issue,

since a manual justification is to be more practical a choice, one should set the mirror

relatively far from the object (as the scattering intensity is considerably low), so that its

image would gain twice distance from the holographic plate, therefore, to vanish its

affection. Considering such effect, the reflection from the illuminated area may have

illuminate the telescope as well, due to the length of exposure duration, a slight secondary

scattering may create a holographic image for the telescope itself as well; to have this

issue resolved, we might set the telescope relatively far from the objective area, base on

the same principle as we solve the previous one.

Secondly, as there are two inter-medias throughout the overall laser path, it will have

serious effect on the reduction of the laser intensity on the holographic plate, which in

turn, requires us have a thoughtful calculation of the exposure length. More importantly,

we have to solve for the intensity for each transmitted and reflected rays; hopefully, we

could set up an intensity "meter" made by three polarization plates to solve the problem,

indeed, it was the topic of my first project in PHYS 320.

Nonetheless, as the required length of the exposure, a constantly slight building vibration

will cause serious negative effects on the overall qualities of the image, however, as we

are in the first phase of this project, qualities of the image barely matters if we still get a

relatively clear-looking holographic image, yet for our future experiments and further

accuracy, a "noise-free" experiential condition will be required.

Reference Number: 0-3

Project Holography (phase I):

Closure Report:

Experimental Operations and Conclusion

(Jeremy) Yu Gong

30 September 2014

The purpose of our experiment for the phase one of the Project is to successfully

construct a hologram with proper resolution and quality; study the procedure of recording and

developing of a hologram, further to structuralize any potential improvements for our future

work. Our experiential developing has taken place around a month, and the optical system is

designed based on off-axis structure for transmission holograms, thus far, we have created our

very first hologram "the Bishop", a chess piece stood on a sandbox, with a solid good resolution,

a firm quality, and image depth.

1. Structure and Designs for the Experiment

As our optical system for recording the hologram is constructed based on an off

axis transmission structure; it requires both of the illumination and reference beams being

capable of reaching at the same spot of the holographic plate surface with exactly the

same time phase. Accordingly, we have designed two structures for executing the

recording process.

The following picture indicates the structure of a simple optical system for the

recording process.

As the scattered beam is required from the source, we thus choose a 5mW (solid)

diode laser as its generator. One may easily noticed from the above figure that the

illumination beams and the reference beams would travel towards roughly the same

direction, while the scattered beam from the object area is capable of sharing the same

range with the reference beams that on the surface of the holographic plate. The

following figure shows the physical arrangements during the recording process, one may

also noticed that, the whole optical system is build on surface of a sand box, as to

stabilize the whole system from possible vibrations cause by the environment.

A more complicated yet precise structure could be formed by split the incidental

beam before it reaches the object surface, however, more optical components will be

added to the system, which in turn, causes more difficulties to stabilize the system. The

following figure shows how the precise system is designed and arranged:

Certain advantage of the above set up would be obtained as one may easily maneuver

around the direction of the reference and illumination beams, in order to achieve a more evenly

scattered beams and much closer front position for the holographic plate. In practice, the

following figure shows the arrangements of the experiment based on the precise design, however,

the vibration of the system is possibly created by each one of the following optical components,

which had us a hard time on stabilize the system.

The source is provided on the above figure by a hellion neon (gas) laser tube, with

5mW power, while it is certain that the power output is much more stable than a (solid)

diode laser, thus a better holographic quality, a more evenly illumination, and a higher

regulation for the hologram could be achieved for a relatively long exposure duration.

Additionally, as the illumination beam is separated on the object area with a much wider

angle, more individual objects could be captured at one time.

( For details, see "Reference", 8 October 2014, Page 2-3)

2. Experimental Procedure

Our experimental procedure contains two individual process with equal

importance: the recording process and the developing process.

Before the holographic recording process is started, it regularly requires a firmly

long warm up duration for the laser tube, for instance, it takes five minutes for a (solid)

diode laser to stabilize itself, and almost fifteen minutes for a hellion neon laser to do the

same.

Right at the very beginnings of the warm up of the power sources, one should set

the holographic plate in place, cover the laser source with a black shield of paper as a

shutter, wait for the laser source to be stabilized, and begin the recording process. Simply

keep still while the laser shutter is removed from the system, for as long as the exposure

duration lasts. The last step should be turning off the laser tube, leaving the holographic

plate to the developing process.

The next step is to set the recorded holographic plate into the developer,

meanwhile most of the instructions would have considered that a 20-second submerging

as a proper duration, however, over submerging the holographic plate in the developer

would cause the plate to be either too dark or to blue after the bleaching. An appreciated

duration, in practice, would start from submerging the plate into the developer until its

surface turns purely dark, whose duration actually varies with different holographic plates;

whenever the plate's surface turns dark, counts in three, and quick put it up from the

developer and sock it in water.

The rinsing process usually takes quite long, practically, the long the plate is

submerged under water after was set out from the developer, the better and much cleaner

the plate will look after the bleaching. The above process should be taken much longer

than the developer process, and usually is longer than three or four minutes. After the

first rinsing process, put the plate into the bleach container, one could slightly rock the

surface of the bleach liquid to accelerate the process, or simply wait still until the surface

of the plate turns transparent, however, most of the instruction considers a safe duration

of such process should be no less than one minutes and a half, in fact, the longer the plate

is soaked under the water the more risk one takes to have a over bleached (the surface

turns out to be too blue) result. A proper method is that, wait as soon as the surface turns

transparent, count until 20 seconds to put the plate out from the bleach container, quickly

submerge it in the water container, wait roughly five minutes, then set the plate up

vertically, for its drying.

Usually, without any wetting solutions, the plate should be dried in dark room for

around two hours, so that its coding from the developer could be fully applied to its

surface; in theory, however, the plate could be viewed as soon as after the bleaching

process, meanwhile, as the developer hasn't have enough time to complete the coding to

its chemical surface, one may take a great rick of double exposure the holographic plate.

Finally, to reproduce the image from a completed hologram, one needs but to

provide a laser which shines at roughly the same angle where the reference beams

intersects the plate's surface. A brief construction is provided on the following figure:

As one may easily noticed that, the laser tube is set in front of a wide plane mirror, which

will redirect the beam towards the telescope, the telescope will then enlarge the beam.

Since the scattered beam is directed towards the hologram holder, one may rotate the

holder at its fixed position on the optical axis until it reaches a certain angle where a

clean looking holographic image is visible.

( For details, see "Reference", 8 October 2014, Page 1; 17 October 2014, Page 1-2

Mixture of Solutions, see "Reference", 2 October 2014)

3. Brief Theory and Results

Our theory is mainly focus on the exposure duration of the recording process. Let

us assume for a free interference from one source to another, each of the source have

undetermined complex periodic functions for their electric fields:

Where r and o are electric fields on the surface of the holographic plate from the

reference beam and the scattering beams, respectively. The overall local interference

intensity on the surface of the plate that is generated by the above two electric fields is:

Also consider that the chemical on the surface of the plate has a linear exposure

rate with respect to the scattering beams, such that:

Therefore, we may substitute the above expression into the interference intensity,

and to have the following:

As we have assumed the linear exposure rate already, it is fine to convert the

complex conjugate back into scale forms, so that the above expression could be denoted

as:

Further reduce the form into:

As we aim to approach the overall intensity for the exposure on a large scale, it is

quite fine for us to take the expectation value of the above form, thus to convert the

vector operation into scalar productions, we therefore, should have that:

Where k is a linear constant that determines the increasing of the intensity with

respect to time of the exposure, while r, and is the overall (expectation) value of the

reference and scattering intensities.

We now assume that the incidental beam splits in two, one has the intensity factor

of f is the reference beam, such that:

We shall thus derive our previous expression as:

Where k, and C are constants, determined by the chemicals and linear exposure

rate of the holographic plates. During our experiments, we worked with the PG-01

holographic plates, which has a proper exposure duration for 10 seconds with 5mW laser

power input, and 40 seconds if the input power is cut by half, therefore, we could easily

obtain its linear exposure equation as:

Based on the above assumption and calculations, we have successfully

constructed our very first hologram, with a 5mW (solid) diode laser input, 70% reference

intensity, and 21 seconds exposure. The following pictures should provide general

information of the qualities and resolutions of our hologram ("the Bishop"):

The above two pictures were taken at the front side of the hologram, the left one has a

slight top view; the right one was taken when we reduced the reconstruction intensity by

a certain factor.

The left picture was taken by the rare side of the hologram, with roughly full

intensity from the reconstruction beam, while the right picture was taken at the front side

of the hologram, with half of the intensity from the reconstruction beam. Our reference

beam was, however, generated by a (solid) diode laser, yet the reconstruction beam was

from a hellion neon laser tube, which , in fact, provides as well, clean looking holograms.

( For details, see "Reference", 17 October 2014, Page 3-4)

4. Conclusions

Our experiment has taken places in nearly six weeks, yet the first clean looking

hologram is generated. We have gathered certain information of successfully created a

proper looking hologram, from both recording process and developing process.

From the recording process, for instance:

1. A simple structure with solid laser would better ensure the odds of success by

taking less risks of instabilities during the exposure duration; a gas laser, however,

provides relatively better power stability.

2. A warm up duration for any type of laser source is required before the

recording process, where, it takes a (solid) diode laser 5 minutes, and 15 minutes for a

(gas) hellion neon laser.

3. The shutter should never physically touch the laser tube either when it was set

in place, or it was being removed from the laser tube.

4. Any hologram taken by a solid laser could be viewed by a gas laser

reconstruction beam; the overall uncertainty for the wave lengths between the power

source is roughly with 20 nm.

Meanwhile, for the developing process, one might notice that:

1. The bleach is required, and is the most important part of the developing process,

the bleach could not be replaced by any other solutions, for instance, a fixer.

2. Remove the holographic plate as soon as its surface turns dark in developer

solutions, too long of a duration of submerging would result rough surface coating; more

importantly, the developer for holographic plates could not be replaced by any

photographic developer solutions.

3. rinsing process should be taken much longer than merely 2 minutes, the longer

the holographic plate is submerged in water, the less risk one might suffer from roughing

the surface coating.

4. It doesn't depend on the amount time one may spend on the bleaching process

to ensure the quality of plate's transparency, one should, however, submerge the plate

longer time before it is put to dry.

Reference Number: 1-4

Project Holography (phase II):

Closure Report

(Jeremy) Yu Gong

24 November 2014

The purpose of phase II of our project majorly focus on construction of mini-holograms

that are a quarter size of their predecessor, have fairly the same resolutions with much further

image depths. To test the practicability of the smaller-sized holograms, we have recorded those

mini-holograms with the same simple optical structure of phase I; however, to increase the image

depth, we have lately recorded our mini-holograms with a more advanced optical structure, the

new optical structure enabled us of ensuring the intensity ratio between the reference and

illumination beams. In addition, we have managed to create a vibration-free condition for the

holographic recording process, by means of minimizing the number of optical components in

total, and leaving a pure separation from the gas laser tube and the remaining optical system with

a laser shutter in between; the laser shutter, which, was isolated and was contact-free from either

of the systems. More importantly, we have measured the transmission (exceptional) intensity of

successfully recorded holograms, with respect to varies of exposure durations. Furthermore, in

the advanced optical structure, we have as well designed a shadow-free area, where the front-side

(to the holographic plate) of the object was fully illuminated, while leaving a proper contrast for

levels of surface intensities. In general, the phase II of our project aims to measure varies of

holographic proprieties in quantity, and (by the advanced optical structure) create windows of

opportunities for a better maneuverability for the holographic recording.

1. Introduction

As of the end of the phase I of our project, we were able to construct off-axis

transmission holograms in a fair resolution and image depth, with 63x63 PG-01

holographic plates. Our prototype was constructed with a simple optical structure

under relatively stable conditions, while certain flaws are obvious as we analyze the

quality of the image.

Since the holographic plate was exposed under a diode laser source in a firmly

long duration, the illumination beam on the plate surface was not evenly separated, in

turn, the uneven separation prevented us from viewing the image with one fixed angle;

our prototypical hologram was apparently, consist with angles for the reconstruction

beam in varies ranges, where the resultant brightness being not as expected. In the

meantime, visible background noises were caused by the unstable power input from

the diode laser; those tiny red "dots" are scatted on the holographic plates while the

image was reconstructed. Absence of a beam-spiller and a poor maneuverability

respectively, for the reference-illumination intensity separations and the ray directions

caused directly the loss of recorded intensity ranges and a short image depth.

As in phase II of our project, we have made certain improvements and redesigns

of the optical structure for each resultant flaws, accordingly. Thus to introduce our

advanced optical structure for recording a smaller-sized hologram. The unevenly

scatted reference beam could be simply avoid by the replacement of a 5mW He-Ne gas

laser, and to further minimize the angular separation, the former 63x63

holographic plate has been reduced into a quarter size of the predecessor. More

importantly, the more stabilized He-Ne gas laser did effectively prevent most

background noises from being generated by the instability of a diode laser power input.

A beam-spiller is also introduced to the new optical structure, fixing the intensity

separation between illumination and reference beams. The vibration caused by each

optical components remains, however, quite an issue for our new design: simply as one

additional optical component were to be added to the system, its probability of

vibration during the recording process would have been dramatically increased. This

fact reminds us to carefully maintain the purpose of the design, while minimizing the

numbers of necessary optical components in general. Nonetheless, we have designed

and crafted an independent laser shutter in-between the laser tube and remaining

optical system, which is capable of fully covering input area of the laser tube, and is

free of contact with either of the optical systems.

We have realized and constructed the advanced optical system based on our

designs, with the fewest possible optical components fixed on the a sand box surface,

and more stabilized gas laser input, a vibration-free condition during the exposure and

better image qualities are further ensured. The contact-free laser shutter worked

effectively, and its independent structure did not cause any vibrations during its

activation, while the shadow-free illumination also guaranteed a proper brightness in a

decent range. Several mini-holograms with were successfully constructed, which lately

allowed us of further analysis of their transmission intensities with varies of exposure

durations.

( For outline details, see "Reference and Measurements", 17 October 2014, Page 1-3)

2. Theory and Designs

The most practical theory for our experiment divides into two fields, the theory

for determining the intensity separations of reference and illumination beams would

bring out a proper value for the furthest image depth; meanwhile the theory for

measuring the transmission intensity on the reconstructed hologram would tell how

well the object was recorded. Although they all are well known for decades, it is

necessary to bring out the alternated forms of them, to support our adjustments and

analysis lately.

The complex form of the electric field expression has decent efforts on

simplifying the tedious calculations from terms to terms of cosine summations, an

alternative proof for it, could be derived starting with the most general formula for

coherent wave interferences, while we assume certain field density distributions

respect to the relative angles and position:

Where is the field density function that we have assumed before,

meanwhile, the surface polar radius r is as well a function of the angle , we may

further reduce the integral into a one variable operation:

Further reduce the form into:

Now to introduce the complex notion of the vector forms:

As we are only evaluating the intensity of the resultant field, thus it requires only:

Therefore, it is quite fine to assume that the overall electric field expression was

yielded following the form as:

Where the above values for each terms describe the expectation values evaluated

from the overall integral, which eventually allows us of calculating for the interference

intensity with respect to each single point:

Where, describes the complex form of electric field on the holographic plate,

consequently, we shall have its intensity expression as follows:

While further simplify the above as:

One shall as well consider the conservation of energy, where the overall intensity

from the reference and scattering beams are the resultants from one incidental provided

from the laser tube, thus:

Meanwhile, the holographic plate could only obtain intensity as much as was

provided by the scattering beams from the object, further exposure would only reduce

the intensity from the reference beam, we therefore, must ensure the best ratio between

the reference and illumination (scattering) beams. One way to think about it, is to

ensure the positive value under all angular conditions for the remaining intensity on the

plate, assuming a perfect exposure:

Combining the conservation expressions, we shall have the following intensity

restrain:

Meantime, as is a decreasing function in nature, so that the maximum

remaining intensity we can have is at:

Which alternatively yields the best illumination to reference ratio, that R:I=4:1.

Based on the intensity separation theory, our structure design is mainly focus on

the splitting the incidental beam, while securing the lowest possibility of vibrations by

caused by optical components. The eventual design is shown as follows:

One may notice from the above figure, the total number of micro/telescopes has

been reduced to one, which is directly set in front of the laser tube. The incidental

beam will be separated in the first place, while the beam splitter (R/T ratio 4:1). The

beam splitter is located right at the lens focal point, in order to reduce any unnecessary

surface observations. while minimizing the distance between the plane mirror. the

focused beam(s) are then redirected onto the holographic plate, as the reference beam

of the structure, while part of the beam is transmitted through the beam splitter, and

later on is reflected to the object. The third wide plane mirror at the bottom figure

would redirect the beam that has passed through the object, consequently creating an

overall shadow-free area in front of the holographic plate. As we have evaluated in

theory, the better, and more evenly the object is illuminated, the further the image

depth would be. One thing to be mentioned before we move on to the next section,

there is a contact-free laser shutter we had design and constructed to minimized the

scatted laser rays from the tube, also to have a better maneuverability for the

holographic exposure.

( For complete theory proof, see "Theory and Analysis", 5 October 2014, Page 1-6)

The another theory we must look into is to determine the exposure duration

relation respect to the illumination intensity provided. To begin with, we can assume

certain point to point intensity to the holographic plate, the increasing intensity during

the exposure is approximated as a linear function to time; we could thus measure the

transmission intensity by a intensity-to-voltage meter, the constant resistance will

provide a linear increasing for the voltage square with respect to the intensity on the

sensor, therefore, we shall obtain:

Where determines the background noises from the set up, by simply

measuring the intensity from the transmissions, we shall have a clear sense of how well

the holograms were exposed. The physical structure is shown on the following figure:

From the above figure, the incidental beam is directly aimed towards the

hologram, and its transmission beam goes directly into the intensity detector, the

intensity will then be converted into voltage, shown on the voltmeter. A regular light

source is set vertically above the hologram and an angular fixer, which the shadow on

the fixer-surface serves well as a reference to its angular position. One shall first turn

off the laser tube, while leaving the sensor to be turned on, measuring the voltage

shown on the voltmeter, which, this value should be the reference for the background

intensity; the next and the final step is to turn on the laser, leaving the hologram under

its exposure, adjust the transmission angle by referring to the shadows on the angular

fixer, the voltmeter should have a maximum value while the angle of the hologram is

fixed at exactly the same angle with its reference beam, record the angle and voltage

for further analysis.

(More information, see "Reference and Measurements", 17 October 2014, Page 6-12)

3. Experimental Procedures and Results

In practice, there are several issues to be resolved before we process through the

actual experiment. As we have mentioned before, the vibration remains constantly the

harshest problem. Practically, three sources of vibration from the physical structure are

to be concerned: the laser tube, the remaining optical components, and the shutter

placed in-between; while to have them resolved, we later on redesigned all parts

accordingly, having them isolated as individuals, therefore any possible vibration from

one system to another will not be affective at all.

The easiest burden comes to redesign a stable structure to the laser tube. We have

added up three extra components to the laser tube set, as the following pictures indicate:

The above picture set contains the front, side, and top views of the new laser

holder set. One shall notice that, the additional (red) holder will wipe out the effective

rotational center to the laser tube, while an extra weight to the opposite site very well

balances the remaining torque, the (heavy) disk weight is placed on the base pad,

lowering the vertical rotational center, while further balancing the structure. As the

recording process usually started after a twenty minutes long warm-up, during that

time period, the laser tube system is set to be isolated, where any vertical vibrations

shall be minimized.

Several concepts are concluded for the design of the laser shutter: as has

mentioned before, the laser shutter must be free of contact of all remaining components;

more importantly, one shall prevent as much incidental intensity from being scattered

when the shutter window is closed. Based on the above two requirements, we have

thus designed the laser shutter as the following figure indicates:

From the above figure, a shutter box in relatively large size is added in front of

the shutter window, covering the front laser tube area with a proper separation. the

shutter box and the shutter window area is designed to be covered with black sheet, so

to further minimize the reflection when is off. One may turn the window on and off by

operating the laser shutter in position that relatively is far from the shutter window;

meanwhile, a switch window is added to tell the position of the shutter window.

The physical laser shutter is made by thin wood, micro slices, and hard papers, the

overall weight of the laser shutter is lighter than 30 grams, which could be easily fixed

and held by two clips from its holder set.

The following pictures show for the front and rare surface of the completed laser

shutter, along with its isolated holder set:

The laser shutter will be placed normal to the front surface of the laser tube, while

maintaining 5 mm separation to it. the laser shutter is isolated from the system by a

stable holder structure, as the overall weight of the shutter is quite light, it could be

held and stabilized by two clips.

The above picture shows for the isolated structure for the laser shutter, one may

notice that the whole shutter holders are fixed by two heavy base rails, and the rails are

placed away from the laser tube set, and the sand box for the optical components. The

proper separation from the laser shutter to the front surface of the laser tube is around 5

mm, and more than 5 cm to the nearest optical component in the sand box. When

operating the laser shutter, any vibrations that were to be caused by the operation, are

not able to affect any of the remaining systems, as it is intended.

One extra concept we added to the new design is a shadow-free illumination

structure, simply introducing a plane mirror to the opposite side of the illumination

rays ensures the entire front area of the object is illuminated. As we have introduced

the designs of our new system, its physical is as the following pictures indicate:

The above picture set indicates the top and front view of the new system in

practice, one should have general ideas of the principle of its process: the laser shutter

is isolated from the optical system, while the incidental beams should go through the

shutter window when the shutter is turned on, as the incidental beam goes through the

microscope, it is enlarged by a certain factor when intersects the surface of the beam

splitter. The beam splitter will reflect 1/5 of the incidental intensity to the object, while

the remaining enlarged beams are mostly got reflected by the wide plane mirror, thus

to create a fully illuminated front area to the holographic plate. As another 4/5 of the

incidental intensity is transmitted through the beam splitter, the plane mirror behind the

splitter will redirected the enlarged beam to the holographic plate, thus to create a

reference beam to the system.

As the whole optical components are fixed and stabilized on a sand box surface,

any minor vibrations should be minimized during the recording process, the following

pictures should provide a general view of the shadow-free illumination during the

process:

The above two pictures were the front and top views of the shadow-free

illuminations, captured during a warm up duration before the recording process.

( Additional information, see "Design and Structure", 29 October 2014, Page 6-10)

4. Conclusions and Future Topics

The Phase II of our project has taken part in four weeks, we have completely

redesigned and upgraded the optical system, while minimizing the size of the hologram,

and the possibilities of minor vibrations. We have captured many new mini-sized

holograms with much decent image depths thanks to the well-measured intensity

separation, and the evenly illuminated surface of the holographic plate.

By the end of the Phase II experimental period, many valuable experiences could

be concluded in practice.

1. It is possible to construct an optical system for holographic recording by only one

beam separator (microscope), which requires a minimized separation between the

beam splitter and the plane mirror.

2. The best R:I ratio obtained from the intensity expression that:

Thus to have the furthest image depth, one shall consider a 4:1 R:I ratio for the

intensity separation between reference and the illumination beams.

3. A better and more practical method of stabilizing the optical system is to separate

the operational parts from the recordings components.

4. A shadow-free illumination area could be easily constructed by simply adding a

wide plane mirror opposite to the direction of the illumination beams.

For the future stages of our project, there are two possible directions to aim for;

firstly, as was mentioned before: less possible optical components would generally

result a more stabilized condition; we will therefore, design and construct such optical

component that replaces the microscope, beam splitter, and the plane mirror, thus to

further reduce the numbers of possible optical components in the system. More

importantly, it is possible to have an enlarged projection area for our mini-sized

holograms. Referring to the film-making principles, series of fast moving images for

instance, would result a virtually continuous motion; accordingly, as holograms are

able to record large scopes of the field, a fast moving hologram is possible to result an

enlarged size of three dimensional image.

In Phase III of our project, we will ensure the design and construction for the

combining optical components, replacing the mentioned three previous optical

components, and further stabilize the system; might as well seek windows of

opportunities to realize the design of the projector.

Reference Number: 2-1

Project Holography (phase III):

Closure Report

(Jeremy) Yu Gong

19 December 2014

1. Introduction

The purpose of Phase III of our project focus on designing the structure of an

optical component, in order to simplify as much the set up for every hologram recording

process. The design is featuring on stability, precision, flexibility, and portability. As

many experiments during our previous phases of the project, the vibration has became the

major issue to be concerned with, and more optical components in the structure would

significantly increase the probability of additional vibrations during the hologram

recording; to stabilize the structure, however, introduces tediously an extra amount of

work. During our experiments in previous phases, we had partially resolved such issue

caused by vibrations by seeking for a balanced design with minimized numbers of optical

components, while compromising the convince of the experimental arrangement and the

quality of holograms. The we intended to design of the new optical components that

contains every major optical component, while stabilizing each individual ones before

was to be put in use, so as to reduce the numbers of optical components used in general,

without compromising the quality of the hologram. Since the optical components inside

the container could be individually aligned before it is put to use, one may save certain

amount of work for the preparation of the experiments. We also added removable feature

to most of the optical components attached to the container, while ensuring the

maneuverability of the incidental intensity and the intensity separations for reference and

illumination beams. Nevertheless, the container is in small size and is portable as we

designed, one could carry it around and easily set up the experiment for hologram

recording for different conditions, skipping most of the tedious adjustments and

rearrangements while in different places.

2. Design and Analysis

The actual design shows as follow:

As the incidental laser beam goes through the front polarizer sets, one may adjust

the overall intensity in the first place; half of the incidental intensity goes through the first

beam splitter, and would be directed towards the illumination scope set, lately becomes

the reference beam for the holographic recording. The second half of the incidental

intensity would hit the second beam splitter, after went through the first one, certain

partial of intensity remains, and would be directed towards the reference scope set.

the reason why we add the second beam splitter instead of having another pair of

polarizer set, is that, based on the experimental facts, and certain intensity

approximations, the overall inference intensity would become even smaller than the

intensity it should be. It is quite obvious that, the overall intensity of an interference

patter that is created by two different rays with the same polarized angles is always

greater than those created by the different polarized angles. As we have managed to

reduce the overall intensity in the first place, one should not risk of reducing too much

intensity later on.

The second beam splitter, therefore, provides the transmitted beam with exactly

the same polarized angles as the incidental ones, it reduces only the intensity of the

transmitted one, meanwhile, the inner surface of the whole optical component is designed

to be cover by black-sheets, which further reduces the uncertainty caused by extra

reflections.

Since all the scopes are fixed on the stabilizers of the same surface, additional

vibration should have been minimized by such structure. One may as well, replace the

beam scatters on the stabilizers with concave and convex lens set, to create parallel

beams, or any other scopes based for other purposes.

3. Conclusion

There are several issues and concerns to be concluded.

First of all, the absolute intensity of the reference beam should be taken care of

before any further process were to take places. As any "tiny" unevenly scattered reference

beam would cause much brighter inference patterns on the holographic plate in the first

place, which makes the hologram unreadable after the exposure.

Furthermore, as many references indicated that the intensity separation ratio

between the reference and illumination beams is better to be 1:4, however, such ratio

does not increase the brightness of the holograms. The only intension of having such ratio

in most cases is to prevent zero intensity spots of occurring on the hologram, in practice,

if the ratio separation were to be 1:1, one may then observe tiny "dark spots" on the

surface of the object; however, for the small holograms recordings (63 mmx63 mm, 31

mm x31 mm), the "dark spots" were not that noticeable due to the overall size of the

hologram, therefore, a close to 1:1 intensity separation might as well serve the purpose.

More importantly, the holographic exposure does not share the same principle as

any in photographic natures. The exposure duration does not increase the brightness of

the hologram. In practice, longer exposure may make the holograms look sharper, yet not

brighter. One may easily tell if a holographic plate was well exposed during the

developing process: after soaking the holographic plate in developer, the surface color of

a well exposed holographic plate would turn brown, yet transparent; an over exposed

surface should turn purely dark, and opaque.

During the developing process, a proper rinsing duration determines the surface

quality of a holographic plate, typically the rinsing process after the plate was soaking

under the developer, the long the plate stays under water, the better and more transparent

the plate would look, after the bleaching.

Most importantly, a spatial filter must be sued for the reference beam, without it,

one may risk of having but diffraction patterns on the hologram. Although, reducing the

overall intensity may as well reducing the brightness of the possible diffraction patterns

on the holographic plate, yet to completely prevent such issue, without compromising too

much quality of the hologram, adding a spatial filter remains still, as the best of options.