Lasers, Holography and Photonics Primer: Here is a great PDF student study guide that you can read and / or download to help with your understanding of lasers, optics, and holography. It also contains history and bios of some of the early researchers in the field. You may use it for homework assignments. Please give credit to holoworld.
Holo Kids: Understanding Lasers and HologramsPublishing Notes:
Updated 11 APR 2018
by Frank DeFreitas
Hello elementary, middle, and home school students from all around the world. My name is Frank DeFreitas (bio), and I am a retired holographer, which means I worked in the fields of lasers and holography, and I made (and taught about) laser holograms. For over 35 years, I worked with literally tens of thousands of students just like you.
By arriving here, you have found the original "HoloKids" page. It has been on the Internet since 1997. The following information has been updated on a regular basis. Parts are also taken from my classroom booklet "Introduction to Holography", which was used by my students at The Franklin Institute in Philadelphia, Pennsylvania. You have my permission to print and use this page for reports. Please give credit to holoworld.com.
Do you think that holograms are only for big kids and adults? I say "no way"! I have visited many elementary and middle schools bringing lasers and holograms to students just like you. Holograms are going to be a big part of your future someday. And I hope that with this page, I can help you learn a little bit about them.
What is Holography?HOLOGRAPHY is the science and technology of making a three-dimensional image of an object using the special light from a LASER. Unlike photography, which only records the brightness and contrast of an object, a HOLOGRAM records brightness, contrast and DIMENSION. This allows holography to display the final image in true 3D. It is the most accurate 3D image in the world today. You do not need any special glasses to view a hologram. Although the hologram is most famous for 3D images, holograms can also be of a 2D image as well. What both share in common is that they were created through the use of a LASER.
Unlike other 3-D "pictures", holograms provide what is called "parallax". Parallax allows the viewer to move back and forth, up and down, and see different perspectives -- as if the object were actually there.
In addition, holography is much more than just 3D. It has many uses in science and technology. Holograms can be used to store information (holographic data storage), and test various manufactured parts under stress (holography interferometry) with non-destructive testing.
The science of holography begins with physics: notably light and optics. The first hologram was conceived of, and produced in 1948 by Dr. Dennis Gabor, a researcher at the Imperial College of London. It was in 1971 that Dr. Gabor received the Nobel prize (in physics) for his invention of holography. Originally, Dr. Gabor's hope was to improve the resolution of the scanning electron microscope.
In the early 60's, upon the invention of the LASER, University of Michigan researchers Leith and Upatnieks created the first three-dimensional holographic images. Around this time, Yuri Dennisyuk of the former Soviet Union also began creating holograms that were viewable using ordinary white light.
To this day, holography continues to provide the most accurate depiction of three-dimensional images in the world, along with many scientific and technological applications.
Holograms themselves are a type of optical element that are created with the use of special light from lasers (more on this later). When creating a hologram, one works with lenses, mirrors, beamsplitters, pinholes, and light-sensitive recording media. Chemistry is also involved through the development of silver gelatin film and glass plates. Other scientific disciplines include polarization, constructive and destructive interference, reflection, refraction, and coherence. Mathematics come into play when setting up the recording angles, taking beam path measurements, and calculating exposure times.
What is a HOLOGRAM?Well, a hologram is like a picture. Sort of. You see, when you look at a picture, like a photograph, it is flat. If you took a regular picture of a big marble, and it had a smaller marble behind it, you would not be able to look around the big marble to see the little one.
With a hologram, you are able to look around the big marble and see the little one behind it. Its true. That's because a hologram is in 3D. The letter "D" in "3D" stands for the word "dimension". The "3" in "3D" stands for how many "dimensions" something has.
A photo, a piece of paper, or even this computer screen, is 2D, or two dimensions: (1) up and down, and (2) left and right. When something has 3D, like the world in which we live, or a hologram, it has an added dimension: (1) up and down, (2) left and right, and (3) forwards and backwards, or DEPTH. So . . . when we say that a hologram has 3 dimensions, it means we can see up and down, and left and right, just like a picture or photo . . . but we can also look "into" the hologram because the hologram, and the objects that it contains, has depth.
Looking at a certain types of holograms is just like looking at something that is really in front of your eyes. In fact, some holograms are so real that you want to take your hand and touch the object in it, but your hand goes right through thin air. Imagine getting up to get a soda while you're watching a holographic television show. When you walk across your living room, you'd walk right through the actors!
When you shine a light on the hologram, the information that is stored as an interference pattern takes the incoming light and re-creates the original optical wavefront that was reflected off the object. Your eyes and brain now perceive the object as being in front of you once again.
Are all Holograms the Same?
There are many different types and styles of holograms -- each requiring it's own individual technique for production. Some holograms require a laser to view them, others rely only on regular light. There are holograms that show motion, and also holograms that change images as you move by them. Holograms can be in full-color, change color and even project their image out in space toward you when you view them.
As stated above, each hologram has its own individual technique when made. Some holographers know all of the techniques, others specialize in only one. The easiest hologram to make is the "single-beam" hologram. Many holograms that you see in stores and museums are "split-beam" holograms -- many of them copied from holographic masters.
There is a lot to learn and experience when it comes to holography. This is why it is so popular as a hobby for many people.
BUT DID YOU KNOW THIS??? . . .
Get ready for news that might surprise you: holograms do not have to be 3D. That's right! In fact many of the holograms produced do not have anything to do with 3D at all. You see, there are many technical and scientific uses of holograms that are not related to 3D images. One type of use is for what are called "holographic optical elements" or "HOE's". These types of holograms usually do not contain any type of object image at all. They are used to alter and direct light in some special way. If you make a hologram of a lens, the holographic image of the lens acts just like the real lens! Some day soon, and in some cases already today, when you store your photos and documents in "the cloud", your information is actually being written to hologram storage drives. In other words, your data (or bits and bytes of information) is written to a hologram. So please remember this: holograms do not have to contain 3D images. You won't find many web sites mentioning this fact, but it is a very important fact for any young scientist and technician!
These early holograms required a laser to both record and view the image. It wasn't long however, before new techniques allowed the hologram, although still requiring a laser to record, to be viewed with ordinary light (such as a light bulb). Also, many different types of holograms were developed, each with their own technique used to produce them.
The excitement of viewing a hologram is only exceeded by the thrill of actually making one. Today, it is fairly easy to make small holograms using inexpensive and easy-to-find equipment. Students from elementary school to high school are making holograms. The expensive lasers of the past have been replaced by the inexpensive laser pointers of today.
A LASER illuminates a 3D Hologram of chess pieces in my laboratory.
How do holograms impact our lives?
1. With holography, we can test all kinds of things . . . from automobile engines, to aircraft tires, to artificial bones and joints. This type of holography is called "interferometry", and the resulting hologram is called an "interferogram" (inter-fero-gram).
2. Holography is also used in medical imaging where doctors can look at a 3-dimensional cat scan and actually go in and take measurements within the holographic image (because the 3D image is made entirely out of light).
3. Very simple (and colorful) holograms are used on consumer packaging materials such as cereal and toothpaste boxes, and a host of other items. This increases their attraction on the supermarket and store shelves.
4. Holograms are used for security for credit cards and for identifying manufactured objects such as clothing to help cut down on counterfeiting.
5. Holographic Optical Elements (HOE's) are used by airplane pilots for navigation. It allows them to keep their eyes on the sky or runway, while still being able to read their instrumentation . . . which appears to float in front of their cockpit window. This feature is already available as an option on several automobiles.
6. Holographic lenses and contacts can make one lens provide several different functions, such as correcting regular vision and also act as magnifiers for reading -- all in the same lens, and throughout the entire lens at the same time.
7. Holograms can be made into portraits of people, pets, etc.
8. Artists use holography to express their creativity and are shown in art galleries around the world.
9. Holograms are used in printing for magazine and book covers. National Geographic (American Eagle) as well as Sports Illustrated (Michael Jordon) have been famous examples.
10. They can be used for point-of-purchase advertising, taking the place of a photograph of a product or service in a store or supermarket. It appears as if the product is right in front of you.
11. Holograms can be used for data storage such as holographic memory. The entire contents of the Library of Congress can be stored in the area the size of a sugar cube.
12. As the technology grows and develops we will see holographic television and motion pictures as mentioned earlier.
13. I am now using holograms to take the place of actual physical objects under the 3D stereo microscope! Yes, you've read that right! I make holograms of 3D objects, then those holograms can be placed under 3D stereo microscopes. When you look through the microscope, you can see the object -- in 3D -- as if it were really there. Many copies can be made, and then sent around the world to various research laboratories.
Holograms in Graphic Arts and Communication Technology
As a tool for visual communication, holograms provide the ultimate in realism, and also in the abstract. With a hologram, two solid three dimensional objects can both occupy the same three dimensional space, at the same time. So situations that are not physically possible in the "real" world, are possible with holograms. This certainly leads to some fanciful work by artists! Products can be depicted as if they were physically present, except that your hand passes right through the images. Full-color, computer-generated holograms are becoming better all the time, as computer processing capabilities increase. And true holographic television has been demonstrated on a small experimental scale. With the advent of diode lasers, more amateur and hobbyist holographers are now setting up their own hologram studios, very similar to the amateur and hobbyist photography boom of the 1950's, '60's, and '70's. While holograms on product packaging has declined in recent years, the use of holograms for product security and authentication continues to grow.
What about TV and Movies?
One of the biggest promises of holography is the dream of holographic television and motion pictures. Unfortunately, we are not quite there yet. A hologram contains a tremendous amount of information . . . and just like the information that you watch on your television, it has to get there somehow. We do not currently have the technology that would allow us to transmit holographic television -- although holographic movies have been experimented with for many years now worldwide.
One day, you will be able to sit down and watch your favorite entertainment holographically projected into your living rooms. Perhaps you will be one of the people that will help make this happen!
The Technology of Holography
Holography is the most advanced imaging science and technology in the world. Especially computer-generated holograms that are written by calculating the three dimensional optical wavefronts that would come off of imaginary objects and scenes. Remember, 3D wavefronts must be calculated from every possible position of the viewer. Unlike the simulated 3D of computer screens, televisions and motion pictures, holographic images must be reproduced in TRUE three dimensional fidelity. If it were possible to zoom in on a holographic object from afar, one would be able to resolve surface bacteria on that object. THAT is the resolving power of holography, and gives some indication of just how much information a hologram stores. From the precise manufacturing tolerances for diode lasers, to the surface coating of the most precise mirrors, at its upper end holography is truly the ultimate in futuristic media production.
If you want to study holography, you will find an entire universe of learning possibilities. You do not need to know everything about the science of holography in order to make a hologram. Just as you do not need to know the light-path mathematics behind your digital cameras optical system to take great pictures. Holography does, however, contain the potential to provide a little bit of everything, from the technical to the artistic. It is a great team activity, especially when combining science students with visual arts students. It allows for dialog between these two groups that normally does not take place in the workplace. But the best holographer of all is the person who excels in both the scientific and the artistic. This is the requirement of the future: to be the best you can be in both. Holography provides the opportunity to do just that!
Questions and Answers:
What is LIGHT? And why is it important with HOLOGRAMS?
In order to understand a hologram (and how to make one), it is also important to understand light. Why? Because the holographic image is made up entirely of light.
What is light? The truth is, no one really knows for certain. Much of light still remains a mystery. One of the problems in trying to find out is that we cannot actually see it. What we see is the *effect* that light produces by hitting an object and bouncing back to our eyes. This is called "reflection". But where is the light? Part of the difficulty in detecting and measuring light lies in its speed. At 186,000 miles per second, and never ever at rest, it is hard to get a hold on it! But what we do know about light gives us enough information to make holography possible.
One of the more common instruments we use to produce light is the lightbulb. An ordinary household lightbulb produces light that we perceive as primarily white light. This is because, in actuality, the bulb is producing many different colors (or wavelengths) at the same time which, when combined, produce white. The light is also traveling away from the lightbulb in many different, random directions. There is very little structure or uniformity in each of the colors or waves. We call this type of light "incoherent" light. Incoherent light is incapable of producing any holographic image (a hologram).
To produce a hologram, we need a light source that produces what is known as a "coherent" type of light. The requirements needed for a source of light to be considered coherent is that the light is of a single frequency and wavelength. Prior to 1960, there were no known sources of true coherent light that could provide great depth in a hologram. The introduction of the LASER changed all this.
How do LASERs make light?
This computer drawing of a working laser is from 1994.
Back then, the Internet was just starting to show images!
(we didn't have images on the early Internet -- just text!).
The term LASER is actually an acronym, which means that each letter in the word represents a word itself. For instance, the term LASER stands for Light Amplification by Stimulated Emmission of Radiation.
The LASER was invented in 1960. There are many different types of lasers, ranging in size from several football fields to the size of a single grain of salt. There are gas lasers, such as the Helium-Neon and Argon lasers; solid-state lasers, such as the ruby laser; and Semi-conductor lasers such as the laser diodes that are found in CD and DVD players and your CD-ROM drives. Each has it own method of producing laser light.
LASERs produce light that has very special characteristics: First, the light is monochromatic, or a single wavelength/color. There are LASERs that produce several wavelengths/colors at the same time, but usually the wavelengths are separated and used individually. Second, the light from a LASER is coherent. Coherent light has all of it's waves traveling in sync with one another -- like a "wave train". Third, the light is highly collimated into a beam, which means that it takes a lot of distance to notice any divergence or convergence of the light.
What are LASERs Used For?
The uses of lasers are too numerous to mention. Lasers perform many different tasks, from removing a cancerous tumor to laying bricks in a straight line to sending your voice across the country when you talk on the phone. Every day there are more and more jobs that require lasers -- and people to fill those jobs.
If you have a highway near you that is under construction, chances are the engineers are using LASER's to layout the new highway. Police will use LASER's to see how fast you are traveling on the new highway. LASER's can be used to restore paintings that are centuries old -- removing oxidation and grime without touching the actual paint. They are used at your supermarket check-out, scanning your purchase. You can have skin blemishes removed.
LASER's have been fired to the moon and bounced back using equipment left there by the Apollo astronauts. They entertain us with LASER light shows. We enjoy music on our CD's, movies on our DVD players and store and retrieve information from our computer's CD-ROM, all though the use of lasers. We then print out our information with LASER printers.
Did you ever have one of the frozen "BBQ" hamburgers for lunch? Did you notice the BBQ grill marks on the hamburger? They are not put there from a BBQ, they are put there by passing the hamburger over laser beams before packaging!
With automobiles, many of the parts were welded together using LASERs attached to robotic arms at the factory.
And the list goes on and on. As you can see, LASER's have become a very important part of all of our lives. And its use will continue to grow well into the next century and beyond.
Are LASERs Dangerous?
LASER light is a very "concentrated" type of light and therefore you should NEVER look directly into the beam no matter how low power the laser is. This includes the popular laser pointers currently on the market.
Military LASERs are so powerful that they can knock missles out of the sky. LASERs can provide enough heat to weld metal parts together -- or actually vaporize others.
The LASERs that you will probably come in contact with in your classroom or as an amateur or hobbyist holographer will commonly fall under the category of low-power LASER. Most of the LASERs used for creating holograms fall in the power range of milliwatts, or thousandths of a watt. Classroom power LASERs are very safe LASERs to work with, however, as with all LASERs, you still should never look directly into the beam.
Help keep LASERs and holography safe -- practice good experimental procedures at all times.
You are the generation that will see holograms become an everyday experience. They will be present from entertainment, to saving someone's life through holographic medical imaging. Perhaps one day you will become involved with holograms yourself. If you do, I hope that you remember your short time here at the HoloKids web page! However, regardless of what it is that you choose to do, I want to wish you the very best of luck in your journey through life. I always like to remember a quote by President Abraham Lincoln. It goes like this: "Whatever you are, be a good one."
One last VERY important message . . .It is very important that you realize that the Internet is filled with misinformation about holograms and what they are. Not just a little bit of misinformation, but a LOT of misinformation. Just because something is 3D, does not mean that it is a hologram. The ONLY time that something can be called a TRUE hologram, is when it is created using the science and technology of HOLOGRAPHY, a Nobel Prize-winning field of study. Then, and only then, can it be a hologram. So . . . beware, okay?
Allentown, Pennsylvania 2018