Holograms are three-dimensional (3D) images made with lasers. Holograms are found on bank cards, bank notes, driver’s licenses, labels and in displays for art and entertainment; you can even get holographic portraits. Holograms are also used in medicine and research. In this workshop, you learn how to make a hologram.
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Step 1: What Is a Hologram?
What is Photonics?
Photonics is the science and technology of light: making light, controlling it and sensing it. Photonics (like electronics) technologies are found in all of the technologies we use in our daily lives; smartphones, laptops, the internet, medical instruments and lighting. Learning about holograms will teach you the basics of how light works, and how we can use it to help us.
Careers with Photonics:
There are thousands of different careers, or jobs, which rely on people knowing about Photonics: people who work with engineering and physics and the internet, people who work in medicine diagnosing illness and treating it with light (scans, laser surgery, treating cancer with radiation), or researching how to prevent illness need to work with light. Photonics is helpful to thousands of jobs, but there is a shortage of people with the skills to fill them.
Read more about careers with Photonics here: https://www.optics4kids.org/careers
There are two slightly dangerous parts to making holograms;
1. the laser you will be using to make your holograms,
2. the chemicals that you will use to develop your holograms.
The laser is called a laser diode, similar to the type of red lasers you see in barcode scanners in shops, in DVD players or laser pointers. Since laser beams tend not to spread out, they can travel directly into our eyes and be focused to a very bright spot on the retina (the back of the eye) which can damage your eye.
IT IS VERY IMPORTANT TO REMEMBER:
NEVER LOOK DOWN A LASER BEAM! and NEVER POINT A LASER BEAM AT ANYONE ELSE!
If you do get to work with the chemicals, make sure you wear safety glasses, gloves and lab coats. Also, wash your hands after you use the chemicals. The chemicals will hurt if they get in your eyes, are poisonous to drink and may ruin your clothes with dark spots.
What is a hologram?
Holograms are three-dimensional (3D) images made with
lasers. Holograms are found on bank cards (Figure.2), bank notes, driver’s licenses, labels and in displays for art and entertainment; you can even get holographic portraits. Holograms are also used in medicine and research.
Photo 1 shows a security hologram on a bank card. The hologram is stuck on the card to stop people from trying to copy it. Photo 2 shows a hologram made from a ‘CT’ Scan made from hundreds of X-Ray images of a skeleton inside a mummy. The mummy was covered in bandages and you couldn’t see the skull - archaeologists were able to explore the mummy without destroying it. Holograms from scans of live people can be used when planning difficult surgeries. Photo 3 shows a hologram of a Fabergé Egg designed to be displayed in a Museum, because the egg is too fragile and expensive to transport easily.
The science behind holograms
In this section we will learn the following about light and lasers;
what a spectrum of light is; why laser light is special, how light travels, what happens when light hits and object and how the hologram is made.
What is a spectrum of light?
White light is made up of all the colours of the rainbow. These colours are known as a spectrum and they become visible when white light hits a prism or a rain drop. While light always travels in straight lines, the light from a laser beam travels in tiny waves within those lines and all the different colours in white light are made up of different sized waves. These waves are so small that they are billionths of a metre in length and are measured in nanometers (nm). To get an idea of how small this is; your hair and nails grow at about 1 nm a second. An illustration of different light waves is shown below in photo 4. (You will though never be able to see the waves as they are too small).
The EM Spectrum consists of different wavelengths; radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All these wavelengths of light play an important part in our lives; we use radio, microwaves and infrared for example in telecommunications so we can talk, snapchat, email and see one another from all over the globe; our internet systems relying on infrared lasers to send signals down fibre optics from one computer to another across the web. Astronomers, use ultraviolet light, x-rays and gamma rays and visible light to watch the stars and the planets, and some of the technology they use ends up working in hospitals, enabling medical imaging and cancer treatments. Scientists working with all areas of the EM Spectrum rely on understanding photonics, the science of light. People who use photonics in their careers need to know how to control light waves for different purposes.
Why is laser light special?
Laser light is different to white light in that it is only made up of one colour (i.e. one wavelength). We will use a red laser diode – similar to the type of laser found in scanners in shops, DVD players and laser pointers – to make our holograms. Usually laser light emerges from a laser in a thin red line. However we have removed a lens from our diode laser and the beam will spread out as shown in photo 5.
We measure light in nanometers, or billionths of a meter. To understand what sort of distances we are using; 1nm is the amount that your hair or nails grow in 1 second.
How does light travel?
While we know that light travels in straight lines and in waves, when we are learning about holograms we need to understand what happens when light hits objects, so we need to know about reflection and refraction. This is explained on the next page.
Reflection: When light hits a shiny object, such as glass or mirror, some of the light will be absorbed and some reflected. Reflection involves a change in direction of the light wave. The light will reflect off at the same angle that it hit the object. This is known as the law of reflection, shown in photo 6. The light in is known as the incident light ray, and the light out is known as the reflected ray.
Refraction: Light bends as it travels from one medium to another. In a hologram light bends as it travels from air through glass, and the holographic emulsion as shown in photo 7 (the emulsion is a layer of transparent gelatine containing tiny particles of silver halide crystals which are light sensitive). These particles of silver direct light around and help form the holographic image.
How does laser light interact?
Interference is the phenomenon that occurs when two waves meet while traveling along the same medium. When the crests (upward displacement) or troughs (downward displacement) of the laser light meet we see constructive interference (bright areas of light) and when we have a crest and a trough meeting we see destructive interference (dark areas). An Interference pattern is the overall pattern resulting after two or more sources of light have interfered, this basically shows us how much light we have at a particular point on a surface. Photo 8.
You also notice a speckle pattern while the beam is spread out (in the dark) onto an object. Tiny dots of light and dark that are nanometers (or billionths of a meter) apart. (A nanometer is how long your hair grows in 1 second!) Photo9. It’s this pattern of light and dark, known as interference, which is used to make a holo- gram. We can only see this pattern with laser light.
How the hologram is made
Both reflection and refraction are important in making a hologram. Light from a laser travels to the holographic plate (shown in red), refracts through the glass and emulsion side and then hits an object. The objects we use to make holograms of are shiny so the light is reflected back onto the holographic plate (shown in blue). The beam reflected from the object copies the shape of the object. When light from the laser meets the reflected light from the object these two beams interact with each other and impact the millions of tiny particles of silver in the holographic plate, causing the particles of silver to blacken when they are developed. The particles will blacken based on how much light they interacted with shown in photo 10.
Light from the laser travels through the transparent holographic plate and reflects off an object back onto the holographic plate. Where the laser beams cross over at the plate, constructive or destructive interfer- ence occurs. Constructive interference causes bright areas of light, and destructive interference results in a dark area. The tiny dots of constructive interference cause tiny particles of silver in the holographic plate to blacken when developed. When you light the finished hologram with a torch, light reflects off those clumps of silver in the holographic plate in different directions, forming the final image you made your hologram of.
Light reflects off the object back onto the plate causing constructive and destructive interference: Bright points of light are recorded on the emulsion.
The silver halide in the emulsion responds to the light waves just like it responds to light waves in an ordinary photograph. When you develop the emulsion, parts of the emulsion that receive more intense light get darker, while those that receive less intense light stay a little lighter. These darker and lighter areas become the interference fringes.
Turning these fringes back into images requires light. The tiny, overlapping interference fringes can make the hologram so dark that it absorbs most of the light, letting very little pass through for image reconstruction. For this reason, processing holographic emulsion often requires bleaching.
Once a hologram is bleached, it is clear instead of dark. Its interference fringes still exist, but they have a different index of refraction - rather than a darker color. In a bleached hologram, variations in the index of refraction change how the light waves travel through and reflect off of the interference fringes.
Step 2: Part List
These photonics parts can be bought with Integraf: http://www.integraf.com/shop/hologram-kits
*Clear safety glasses
For pepper ghost:
For the scratch hologram:
*Protractor with a hole in the centre
*2x Push pins
*Acetate or a Perspex square (approximately 5cm x 5cm)
Step 3: Holography Set-up
The wavelength of light we are using is very small (635nm) which means that any tiny movement in the room while the holograms are being made can change the pattern being produced by the laser beam during the exposure and ruin the final image.
THE HOLOGRAMS ARE SO SENSITIVE THAT THE FOLLOWING CAN RUIN THEM:
· Air Conditioning – moving the air
· A machine running in another room – vibrating the floor
· A car passing by the building – moving the air and floor
· A noisy airplane flying past – vibrating the walls and air
· A student leaning on a table that the set-up is on – vibrating the table
· Students talking in another room – vibrating the air
To prevent as much vibration as possible, we use sand as a dampening agent in our set up. See drawing below in figure 10. Try to make sure that the environment you are setting up in is as quiet as possible. For example, make sure your workshop leader has turned off machinery when making holograms, make sure you and your fellow students are quiet during the exposure – and not touching tables, talking or moving their feet/chairs.
Step-by-Step guide to setting up the equipment:
1. Make a firm base for the laser: fill the mug with sand.
2. Unscrew the lens from the laser and clip a wooden clothes-peg carefully around the diode holding it at the edges. N.B. Don’t put your fingers over the front of the laser as you may damage it. Push the peg and laser firmly into the sand.
3. Make sure that the laser is placed facing away from you so you, or other students cannot accidentally look into the beam. (It won’t hurt you, but may dazzle your eyes temporarily!)
4. Place the mug on the table. At approximately 15-20 cm place the tray filled with sand (fill it fully so you will not get any shadow from the edge of the tray).
5. Place the object on the sand. Put the batteries in the laser and turn it on, fully illuminating the object. Reposition the mug with the laser until the object is well lit. (Example shown in Figure 14) Use an old/exposed plate to design your set up.
Please note that the top of the object must be positioned closest to the on-coming beam, because the final hologram is lit from the same angle at which it was exposed.
Once the object is fully illuminated, place a piece of cardboard in the path of the beam between the laser and object.
Photo 1&2: Holography set-up. Your laser is fixed in a clothes peg. The laser should always face away from you towards the wall. Put your object on the sand with the laser shining on your object.
Photo 3: Use an old/exposed plate to design your set up. Please note that the top of the object must be positioned closest to the on-coming beam, because the final hologram is lit from the same angle at which it was exposed.
Photo 4: Suitable objects to make a hologram of are small, shiny flat objects with the set-up we are using. Examples are shown in photo 4.
A good result could look like the image in photo 5.
During the process of making the hologram – light has to be shone on the object for a set amount of time. You may need to experiment to find out for how long, but probably 20 seconds. This is known as an ‘exposure’. The silver in the emulsion on your holographic plate reacts to light during that time. Once the hologram has been exposed, then it needs to be developed in trays of chemicals.
Step 4: How to Make You Hologram?
How to handle a hologram: Always hold your holographic plate at the edges as shown in the illustration in photo 1, so you don’t damage it.
A holographic plate is made of two sides: a glass side and an emulsion one.
The emulsion side contains silver particles that interact with light, trapped in a layer of gelatin (like jelly) and should NOT be touched. This side will be facing the object when we shoot the hologram and facing upward when we develop it (so it doesn’t get scratched).
Holographic plates are similar to photographic film: if they were not developed and we open them in a lit room we destroy them and they can’t be used anymore.
Only open the box of holograms in the dark!!!!
To find the emulsion side we can blow on the plate and see which side fogs up – that is the glass side, as shown in photo 2. NOTE: when you blow on the hologram keep it close to your mouth and observe if it fogs WHILE you blow on it. You will need to do this in the dark. Turn and face a dim light source, such as the light coming from under a door.
WITH THE LIGHTS OFF (90% darkness is OK)
Put the batteries in the laser and turn it on, fully illuminating the object. Reposition the mug with the laser until the object is well lit. Use an old/exposed plate to design your set up. (Real plate must only be used in the dark). Please note that the top of the object must be positioned closest to the on-coming beam, because the final hologram is lit from the same angle at which it was exposed.
Once the object is fully illuminated, place a piece of cardboard in the path of the beam between the laser and object.
Shooting the Hologram
Take the holographic plates out of its wrappers, remove any plastic edge strips which might be protecting the plate, remember to only hold the plate by the edges! Then CLOSE THE BOX.
Breathe on the plate to figure out which is the emulsion side (the side that does not fog). Place the holographic plate with the emulsion side on the object .
Allow about one minute for the object to settle, holding still and quiet.
Lift the cardboard 1-2 cm above the table while still blocking the laser light, and wait 10 seconds for the vibrations to subside. (Don’t touch the table it will ruin the hologram!)
Lift the cardboard all the way up, allowing the laser light to escape from under the card and fully light up the holographic plate and object. Hold for approximately 25 seconds then replace the book in front of the laser blocking out the light again. This is known as ‘shooting’ or ‘exposing’ the holographic plate.
Give your plate back to your workshop leader. Make sure they put the hologram back into a box and CLOSE THE BOX of holograms so your hologram doesn’t get ruined. TURN THE LIGHTS BACK ON!
Step 5: How to Develop Your Hologram?
SAFETY!!! Put on a lab coat to protect your clothes, along with safety glasses and rubber gloves. (Please note the chemicals can drip and ruin your shoes – so if you’re worried about your clothes get someone else to develop the hologram).
The holographic 3D Image is now recorded on your plate – tiny clumps of silver have been produced in the plate where the laser light hit the plate, but we need to ‘develop’ the plate in chemicals to be able to see the image. This is the developing process; put your hologram in developer, wash, bleach and then wash it.
Plug in a green safe light. Make sure that when you start shooting the holograms there are no trip hazards in the room (no boxes or bags on the floor) as the room will be very dark.
TURN THE LIGHTS OFF!
Four different trays of chemicals and water are set up for your hologram. Photo 1
Mix developer A&B together in a tray.
Remove the holographic plate from the box. Close the box.
Place the hologram emulsion-side-up in the developer for 10 seconds (4 students at a time can place holograms in the corners of the developing tray – count down 3-2-1- and place all the plates in the developer together). Agitate the tray for the 10 seconds (a student should time the developing). Remove them immediately after 10 seconds is up (or they will turn opaque).
Distilled/deionised water wash 1:
Place the holograms in the wash tray with de-ionised/distilled water. (Always place holograms emulsion side-up to prevent scratching the emulsion). Agitate the tray for 20 seconds to wash the holograms.
Remove your hologram from the water and drop it in the bleach. Count 3-2-1 drop! Leave them in the bleach for approximately 1 minute until the plates become entirely transparent, count for another 10 seconds, the remove the plate.
Distilled/deionised water wash 2:
Rinse the holograms for 20 seconds in the last tray. You can take the hologram out of the water yourself.
N.B. Replace the distilled water after every 4 holograms are developed. Wash your hands when you have finished developing!
TURN THE LIGHTS BACK ON!
Step 6: How to Dry Your Hologram?
Once the hologram has been taken out of the water, wipe the glass side (blow on the hologram to check which side mists up – that’s the glass side) as shown in photo 1.
CAREFUL! If you get the wrong side you’ll ruin your hologram. Next dry your hologram off, with a hair dryer (hold the hair dryer at arm’s length from the hologram and dry both sides as shown in photo 2). Alternatively, the plates can be left to dry off overnight. Make sure that the plate is thoroughly dry before placing it in paper. Never touch the emulsion or you will get finger prints on the hologram which cannot be removed.
Step 7: How to Light Your Hologram?
If the plate is not yet dry - light the hologram from the back (emulsion side with the light shining towards you through the plate). See photo 1&2. The angle you light the hologram will depend on how much you tilted your hologram when you shot it.
If the plate is dry aim a torch light at the glass side of the hologram. Rotate the hologram and tilt the hologram until you see a reddish coloured object appear as shown in photo 3. You should see a hologram if the plate is dry. The best lighting for the hologram is bright sunlight!
How to look after your hologram?
Once the hologram is completely dry it can be wrapped either in the black paper it came in, in its original box, or in white paper.
Keep the hologram away from moisture or water. The hologram can be painted black with spray paint to protect the emulsion. Spray the side that doesn’t fog up (the emulsion side) to seal the hologram.
Step 8: Troubleshooting
When the hologram is lit if there are any areas of darkness on the plates, this means there has been movement. If there are dark lines on the object, the object has moved. If there are dark lines or dark areas on the plate, then the plate moved. The following can cause movement problems:
· air-conditioning, or the heat of the room, machinery on in other rooms in the building
· people moving about during exposure or touching the tables during the exposure
· trucks passing by the venue
· doors slamming
In the developer - If the plates don’t turn black quickly, this means they needed more laser light exposure. In the bleach – if the plates take a long time to clear – the exposure was too long. Any chemical marks are often due to problems with leaving the holograms in the bleach for too long, or washing the holograms in dirty water. Keep replacing the water in the wash trays.
The object you chose might be unsuitable. The best objects for holograms are small, reflective objects as shown above. Unsuitable objects would include: anything made out of material, anything flimsy, glass, dark in colour, green objects (will appear black in the red light), anything with a lot of depth.
Step 9: Extension: Making a Mobile Ghost (a Smartphone 3D Projection)
In this activity a smartphone is used, along with an inverted pyramid made out of acetate on top of the phone.
What is a Mobile Ghost?
More commonly known as Pepper’s Ghost, the ‘mobile ghost’ is an optical illusion often used in haunted houses and concerts to make an image appear 3D and float in mid-air as shown in photo 1.
The light theory which makes this illusion is as follows:
The ghostly image is formed when rays of light from an object are reflected off one surface onto another reflective surface into our eyes.
If the second reflective surface is transparent, part of the image is reflected and part is transmitted. The object appears slightly translucent and seems to float behind the transparent reflective surface. The ‘Ghosts’ look 3D because we see a slightly different image with both of our eyes. Our brain combines both views and interprets the object as being three dimensional. Photo 2.
Making your Mobile Ghost screen
*Cut out your template (photo 3) by cutting along the dashed lines on the acetate sheet. (photo 4)
*Fold the template along the solid lines.
*Tape the folded cut-out into a flat-topped pyramid shape as shown in photo 5.
Viewing your Mobile Ghost
*Download a ready-made Pepper’s Ghost app such as “Hologram Pyramid Videos” from the Google Play store for Android, or the iTunes store for iOS.
*Go to the link:
*Place your inverted pyramid onto the smartphone screen and see the image appear to be floating in the center of your Mobile Ghost Screen.
If the floating animated image is difficult to see – turn the lights off in the room, or make sure that the image has a dark background.
Step 10: Extension: Making a Scratch Hologram
Create an image scratched out of acetate, or Perspex, that appears three-dimensional and animates as you move the hologram under a light. Photo 1
Photo 2 & 3: Draw an object at the bottom of a piece of paper. Line up the protractor over the drawing. Place hole in the centre of the bottom of the protractor on one point of your drawing. Place a piece of acetate over black paper just above the drawing and tape down both the black paper, and the acetate to keep them in place.
Once the acetate has been placed over the black card on top of your drawing, tape down the edges of the black paper and acetate and your drawing so that nothing moves.
Photo 4, 5, 6: Place a pin in the hole in the centre of the protractor into your drawing, at the end of one of the lines that you have drawn. Then very lightly scratch an arc into the acetate with another pin, drawing the pin from right to left, from approximately 130 to 30 degrees, making sure that only the finest line is barely visible. If you scrape the acetate and remove material you are pressing too hard.
Photo 7,8, 9: Next, move the pin in the protractor hole approximately 1 mm along the line you have drawn on your object and make another scratch very lightly, following the curve of the top of the protractor as shown in the images above. Make approximately 20 pinholes and arcs for each line of your drawing. An example is shown below. Note how fine the lines are.
The scratches need to be very light - if you are scratching tiny pieces of acetate, or perspex out of the surface then you are pressing too hard.
When you finish tracing the lines of your object with pinholes and tiny scratches, shine a light on the scratch hologram. Either use a bright torch, or the data projector in your FAB LAB. (Or bright sunlight). You will see your object appear in the scratches and the object will move along the arc of the scratches as if you are seeing the object from different sides.
You could reproduce your initials, which will probably only be about 40 lines/scratches, or any other shape you wish.
Photo 10 & 11: The result.
Step 11: End Result and Conclusions
What we learned?
As a result of taking part in these two activities we hope that you have worked with the science of light relevant to your studies at school, and may have learned something new.
You will have revised how light travels; in straight lines, reflecting, refracting (or bending) as it travels through glass. You should also have been reminded what happens when light is absorbed, and what the terms opaque and transparent mean.
You have learnt that when light from a laser is transmitted through a holographic plate, reflects off an object and back onto the plate, the combination of the two beams form an image in the light sensitive holographic emulsion. The emulsion darkens on contact with light, capturing the reflected light from the object as a result. Holograms have to be developed, and lit with a torch, or sunlight, to be seen.
You have learned new skills; making a Mobile Ghost projection, making a scratch holography and working safely with a laser to make a hologram.
There is an international shortage of people who know about Photonics, the science of light, and who know how to make holograms. There are so many different ways holography can be used, such as in security, advertising, medicine, art and education, but we need more people to experiment with it. Working with the laser technology you have used today has given you a lot of information that people who work in holography need to know in order to make successful holograms; they need to be able to control and manipulate light with reflection and refraction, and understand how to prevent vibration. Hopefully you will have enjoyed your experience today, and will want to learn more about light in the future.
The laser technology you have used today has given you a lot of information that people who work in holography need to know. They need to be able to control and manipulate light, with a knowledge of interference and vibration issues in order to make holograms. Viewholographics made a hologram of CT medical scans of a mummy. The actual mummy was covered in bandages and you couldn’t see the skull. The CT Scans provided 3D images from a complex x-ray image. Capturing the medical imaging techniques surgeons use to help them with complex surgery, archaeologists were able to explore the mummy without destroying it. This is one of the many interesting things we can do with holography.
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