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Abstract A renewed concept of a display exhibition in holography is presented. Such expositions organized by the Hellenic Institute of Holography and Saint-Petersburg ITMO University have been selected as examples of the new concept. Statistical data on the numbers of visitors， their age and their feedback has been analyzed. STEAM （science， technology， engineering， art， mathematics） methods have shown their efficiency for motivating students and re-educating the general public in areas of focused interest.
Keywords Art and science， science communication， holography， interactive exhibition， cognitive visualization， STEAM education
0〓Introduction
Scientific thinking has been developing over time into structured knowledge constantly bringing in new properties， principles， laws and concepts. Classification has resulted in a complex structure which cannot be assimilated as it is but instead has to be gradually taught. In turn， this is becoming a challenge as knowledge is to be transferred to more and more people. Thus， multiple schools of thought appeared in various areas.
Optics is a science which existed as a separate branch as early as in ancient Greece and Rome， and has widely developed ever since. "The appearance of antique optics can be seen it the works of Archytas and it comes to its peak in the works of Euclid and Ptolemy. Archimedes， Hero， Diocles and Theophrastus also were significant thinkers."[1] Optics has always been related to something that humans can witness through their vision and therefore this is why it was born very early as a branch of science. It also allows the combination of both visual and theoretical aspects because concepts can be proved. Throughout the centuries new and more sophisticated ideas were included in optics. Nowadays it looks just as most other sciences. However， the visible element remains its great advantage.
Education has much evolved during the past decades. For instance， alongside regular classes and conventional lectures， we can now see innovative methods of education： the educational process may include online courses administered through web pages of your browser or mobile phone applications in STEM-based classes which allow to master sciences together with technologies， engineering and mathematics. Such methods are used for education of adults as well.
However， there is another way to propagate scientific knowledge to general public， namely， through scientific shows and exhibitions. There are various exhibition concepts that can be implemented by the organizers of such events. These can be broadly classified into two groups： interactive and not interactive. Interactive techniques can be further based on a method of edutainment which motivates people to explore science through some kind of amusing interaction. This can be specifically appropriate for optical shows as visualization can be implemented. The interactive shows "Light Mysteries" and "Magic of Light" were based on this interaction of the visitors with the state-of-the-art innovations in visualization and light. These shows have holography as their core element and most of the exhibits are in some way related to holography. The purpose of this article is to show the benefits and advantages of the methods used in these shows and it describes the basic underlying principles of the shows as well as an assessment of the results.
1 From STEM to STEAM via holography
Over the past 20 years， interest in STEM education has been growing all over the world. It has been widely recognized that science education， instead of being focused exclusively on future scientists or engineers， should equally be diffused to the majority of young people and adults resulting in science-aware citizens able to cope with the complex challenges of modern technological societies and economic growth. In addition to STEM， a new initiative， STEAM， that is STEM plus arts， has been adopted in many educational systems as arts can definitely assist to the critical process of creativity and innovation combining rational thinking with the intuitive and inspirational approach of art in a very effective method of science communication. In view of these new principles of education， we consider "holography" as a valuable STEM/STEAM tool， as its theory and practice encompass and transverse most major fields of the disciplines involved.
The series of interactive shows "Images of Light"， under various marketing names， aims to trigger the interest of young people and adults in STEAM by exploring the properties of light and human vision through their relation to holography and stereoscopy and vice versa. In their implementation， various tools of communication are used for the introduction of optical phenomena to non-scientific visitors of various age groups and， through the raise of public interest in science and general inquisitiveness， evolves a new type of educational process.
Conventional holographic shows normally consist of analog and digital holograms， artistic holographic installations， multi-channel holograms and other parts. This approach is useful for a first introduction or a broader exposure to holography but cannot provide a deeper understanding of its essence. Combining holography display with demonstrations of other optical phenomena in one show guarantees a more elaborate and educative interactive involvement of visitors. In this case， holography becomes the key core technique for the explanation of various phenomena of wave optics， such as interference， diffraction， and polarization. Moreover， in addition to direct artistic expression with the use of holography as a medium， display holography indirectly connects art and science， for instance， in the case of optical clones of original historical artworks or of holograms depicting a cognitive visualization of scientific principles and information.
2〓Role of guides for the show
When conceiving a show， it is very important to let a person go through and explore it. The visitor can either explore it on his own or in a tour with a specially trained guide. According to our experience， most visitors are interested in getting into rather complex things related to holography （that is， the process of producing a hologram）， therefore， a guide service becomes necessary. It is important for an exhibition to communicate the general concept to a visitor in a proper manner. A leaflet cannot contain information that would be appropriate for every person， an audio guide and QR codes that can be placed near exhibits have the same drawback. However， guide service allows to prepare a method of giving different exhibit descriptions to different age groups. A talk appears to be the most effective way of communication， and this has been proved by numerous feedback reports in the Optics Museum of ITMO University in St. Petersburg.
The designated guide can instantly observe the visitor’s reaction and change the style， speed and language of the tour. In this way， questions can also be addressed just as they arise during the tour. Another important advantage of providing guide service is that it makes the show "alive" and more interesting.
For all these reasons， our shows employ specially trained guides who will learn the basic principles first and then ask specialists about some specific cases. The selection process is very important because the guide has to have both theoretical knowledge of the subject and communicative skills as well as linguistic fluency in order to attract the visitors. For the Museum of Optics of ITMO University and within the "Images of Light" shows we have found young people of the same age as visiting students to be the best guides. This can be attributed to their motivation for learning， interest and openness in communication. This effect is measured by a system of "likes" which allows visitors to rate the guide by giving a "like" card.
3〓History of 3D and true holography
There are many misconceptions and biases around the things that we cannot touch or feel. This can be clearly seen from the public views on holography. Mass media and big companies often use the term "hologram" in order to refer to the various techniques which have no relation or even reference to holograms. This is why people tend to wrongly consider holograms as lenticulars[2]， Pepper’s ghost setup， mirror mirages， holho constructions and other various kinds of projections[3]. In order to eliminate those misconceptions， visitors are invited to see a retrospective and various types of 3D techniques. Thus， in our shows we set a sequence of the following objects： stereoscopes， anaglyphs， chromadepths， lenticulars， "scratch-holograms" and various pseudo-holographic projection systems. This is our adopted approach in practice and we consider it to be a very effective method for helping people realize what really is holography and what is not. These exhibits allow the guide to visually show the difference between holographic and non-holographic methods of 3D visualization. Besides static objects， the exhibitions include demonstrations of short 3D videos on anaglyph， lenticular and polarized 3D displays. When running a 3D movie， the guide can explain the basic principles of the technology. The same is with the animated 3D "holho" setup that is often called holographic. In terms of spatial allocation within an exhibition， this part of the exhibition with various 3D exhibits can come either before or after the strictly holographic part.
In order to further elaborate in the holographic origination technique， we demonstrate various optical setups illustrating hologram recording processes. In practice， this results in two holographic setups used in the Museum of Optics： Leith’s and Denisyuk’s. The differences and the similarities of these two setups are very important to demonstrate for explaining holography， lasers， interference， diffraction and other associated phenomena.
In parallel with demonstrating hardware holographic setups， the Museum of Optics shows animated movies on Holography and Lasers custom-produced by a professional Russian video studio using original content. The material contains some basic information， and the guide is available for answering the visitors’ questions about more specific matters. These movies have been very popular among the visitors in each show.
4〓From mirrors and gratings to holography
Holography itself is the highest point of wave optics. It cannot be implemented without some basic knowledge. If we want to go beyond showing holograms and to explain the nature of these "magic images"， we need some complementary exhibits that help explain the basics of optics. First of all， we suggest including some geometrical optical elements in the show such as lenses， prisms and various mirrors（i.e. ancient bronze， modern adaptive mirrors and even Chinese "magic" mirrors）.
Secondly， a demonstration of interference phenomena is essential. The easiest way to show it is through dynamic Moire patterns that can be made interactive. Also， we use double pulse holograms with "frozen" interference patterns （i.e. well-known holograms with deformed surfaces， or the flows of heated air around electric bulb）. Some of our exhibitions included demonstrating classical interference （e.g. Young’s double-slit experiment and Fresnel’s bi-prisms） for any visitors that would be interested. Interactive models of Mach-Zehnder and Michelson interferometers are used in the exhibition to demonstrate the applications of interference. Thirdly， we explain diffraction principles by using a wide range of diffraction gratings： transmissive， reflective， echelette， etc. Showing laser beam diffraction on the opaque round disc， so called Poisson spot， is always very spectacular to visitors. Special attention is payed to spectral properties of diffraction gratings because this leads to a discussion on the color components of white light. This conversation is continued in the interactive monochromatic room and near the dedicated wall with colorful shadows. The latter is one of the most attractive photo zones of the museum and exhibitions.
This approach of using exhibits describing each of the principles in addition to content directly related to the concept of holography has been proven very efficient.
5〓Interact rather than observe
A proverb goes： "Tell me and I will forget， show me and I may remember， involve me and I will understand". This is why we encourage people to interact with the exhibition rather than just observe. Visitors are supposed to be active throughout the exhibition so that they may have a better understanding and a deeper lasting impression. The interactive part of the exhibition allows to involve the emotional component into the process of thinking and understanding of holography and various properties of light. This corresponds the STEAM methods where Art-component adds to the rational knowledge.
The interaction with a holographic exhibit is achieved by using moving lights， holding the holograms in hands and comparing it with a real object. Also suggesting to the visitor to move within the three dimensional space where the holographic image is visible adds to the interactive involvement. These interactions are basic and attractive to the visitor. For instance， a special artistic exhibit consisting of a patchwork of many hologram pieces has been created as a human figure statue rotating on a turntable. The visitors use their phone torches and try to find the hidden images. For this， they have to find the right direction of light and the angle of view.
The plasma "Tesla Balls" （Figure 1） glow in the so-called "mysterious" form. The light in these balls can be controlled. During the guide’s explanations about the properties of plasma， visitors can interact with this exhibit and immediately see the effect. Pictures on the retroreflecting and luminescent walls （Figure 2） produce an impression on the visitor and form a positive opinion about the exhibition in general. These exhibits allow visitors to draw with the torch of their mobile phones and to "freeze" people shadows. [Figure 1 "Tesla Balls" in the Museum of Optics]
Keywords Art and science， science communication， holography， interactive exhibition， cognitive visualization， STEAM education
0〓Introduction
Scientific thinking has been developing over time into structured knowledge constantly bringing in new properties， principles， laws and concepts. Classification has resulted in a complex structure which cannot be assimilated as it is but instead has to be gradually taught. In turn， this is becoming a challenge as knowledge is to be transferred to more and more people. Thus， multiple schools of thought appeared in various areas.
Optics is a science which existed as a separate branch as early as in ancient Greece and Rome， and has widely developed ever since. "The appearance of antique optics can be seen it the works of Archytas and it comes to its peak in the works of Euclid and Ptolemy. Archimedes， Hero， Diocles and Theophrastus also were significant thinkers."[1] Optics has always been related to something that humans can witness through their vision and therefore this is why it was born very early as a branch of science. It also allows the combination of both visual and theoretical aspects because concepts can be proved. Throughout the centuries new and more sophisticated ideas were included in optics. Nowadays it looks just as most other sciences. However， the visible element remains its great advantage.
Education has much evolved during the past decades. For instance， alongside regular classes and conventional lectures， we can now see innovative methods of education： the educational process may include online courses administered through web pages of your browser or mobile phone applications in STEM-based classes which allow to master sciences together with technologies， engineering and mathematics. Such methods are used for education of adults as well.
However， there is another way to propagate scientific knowledge to general public， namely， through scientific shows and exhibitions. There are various exhibition concepts that can be implemented by the organizers of such events. These can be broadly classified into two groups： interactive and not interactive. Interactive techniques can be further based on a method of edutainment which motivates people to explore science through some kind of amusing interaction. This can be specifically appropriate for optical shows as visualization can be implemented. The interactive shows "Light Mysteries" and "Magic of Light" were based on this interaction of the visitors with the state-of-the-art innovations in visualization and light. These shows have holography as their core element and most of the exhibits are in some way related to holography. The purpose of this article is to show the benefits and advantages of the methods used in these shows and it describes the basic underlying principles of the shows as well as an assessment of the results.
1 From STEM to STEAM via holography
Over the past 20 years， interest in STEM education has been growing all over the world. It has been widely recognized that science education， instead of being focused exclusively on future scientists or engineers， should equally be diffused to the majority of young people and adults resulting in science-aware citizens able to cope with the complex challenges of modern technological societies and economic growth. In addition to STEM， a new initiative， STEAM， that is STEM plus arts， has been adopted in many educational systems as arts can definitely assist to the critical process of creativity and innovation combining rational thinking with the intuitive and inspirational approach of art in a very effective method of science communication. In view of these new principles of education， we consider "holography" as a valuable STEM/STEAM tool， as its theory and practice encompass and transverse most major fields of the disciplines involved.
The series of interactive shows "Images of Light"， under various marketing names， aims to trigger the interest of young people and adults in STEAM by exploring the properties of light and human vision through their relation to holography and stereoscopy and vice versa. In their implementation， various tools of communication are used for the introduction of optical phenomena to non-scientific visitors of various age groups and， through the raise of public interest in science and general inquisitiveness， evolves a new type of educational process.
Conventional holographic shows normally consist of analog and digital holograms， artistic holographic installations， multi-channel holograms and other parts. This approach is useful for a first introduction or a broader exposure to holography but cannot provide a deeper understanding of its essence. Combining holography display with demonstrations of other optical phenomena in one show guarantees a more elaborate and educative interactive involvement of visitors. In this case， holography becomes the key core technique for the explanation of various phenomena of wave optics， such as interference， diffraction， and polarization. Moreover， in addition to direct artistic expression with the use of holography as a medium， display holography indirectly connects art and science， for instance， in the case of optical clones of original historical artworks or of holograms depicting a cognitive visualization of scientific principles and information.
2〓Role of guides for the show
When conceiving a show， it is very important to let a person go through and explore it. The visitor can either explore it on his own or in a tour with a specially trained guide. According to our experience， most visitors are interested in getting into rather complex things related to holography （that is， the process of producing a hologram）， therefore， a guide service becomes necessary. It is important for an exhibition to communicate the general concept to a visitor in a proper manner. A leaflet cannot contain information that would be appropriate for every person， an audio guide and QR codes that can be placed near exhibits have the same drawback. However， guide service allows to prepare a method of giving different exhibit descriptions to different age groups. A talk appears to be the most effective way of communication， and this has been proved by numerous feedback reports in the Optics Museum of ITMO University in St. Petersburg.
The designated guide can instantly observe the visitor’s reaction and change the style， speed and language of the tour. In this way， questions can also be addressed just as they arise during the tour. Another important advantage of providing guide service is that it makes the show "alive" and more interesting.
For all these reasons， our shows employ specially trained guides who will learn the basic principles first and then ask specialists about some specific cases. The selection process is very important because the guide has to have both theoretical knowledge of the subject and communicative skills as well as linguistic fluency in order to attract the visitors. For the Museum of Optics of ITMO University and within the "Images of Light" shows we have found young people of the same age as visiting students to be the best guides. This can be attributed to their motivation for learning， interest and openness in communication. This effect is measured by a system of "likes" which allows visitors to rate the guide by giving a "like" card.
3〓History of 3D and true holography
There are many misconceptions and biases around the things that we cannot touch or feel. This can be clearly seen from the public views on holography. Mass media and big companies often use the term "hologram" in order to refer to the various techniques which have no relation or even reference to holograms. This is why people tend to wrongly consider holograms as lenticulars[2]， Pepper’s ghost setup， mirror mirages， holho constructions and other various kinds of projections[3]. In order to eliminate those misconceptions， visitors are invited to see a retrospective and various types of 3D techniques. Thus， in our shows we set a sequence of the following objects： stereoscopes， anaglyphs， chromadepths， lenticulars， "scratch-holograms" and various pseudo-holographic projection systems. This is our adopted approach in practice and we consider it to be a very effective method for helping people realize what really is holography and what is not. These exhibits allow the guide to visually show the difference between holographic and non-holographic methods of 3D visualization. Besides static objects， the exhibitions include demonstrations of short 3D videos on anaglyph， lenticular and polarized 3D displays. When running a 3D movie， the guide can explain the basic principles of the technology. The same is with the animated 3D "holho" setup that is often called holographic. In terms of spatial allocation within an exhibition， this part of the exhibition with various 3D exhibits can come either before or after the strictly holographic part.
In order to further elaborate in the holographic origination technique， we demonstrate various optical setups illustrating hologram recording processes. In practice， this results in two holographic setups used in the Museum of Optics： Leith’s and Denisyuk’s. The differences and the similarities of these two setups are very important to demonstrate for explaining holography， lasers， interference， diffraction and other associated phenomena.
In parallel with demonstrating hardware holographic setups， the Museum of Optics shows animated movies on Holography and Lasers custom-produced by a professional Russian video studio using original content. The material contains some basic information， and the guide is available for answering the visitors’ questions about more specific matters. These movies have been very popular among the visitors in each show.
4〓From mirrors and gratings to holography
Holography itself is the highest point of wave optics. It cannot be implemented without some basic knowledge. If we want to go beyond showing holograms and to explain the nature of these "magic images"， we need some complementary exhibits that help explain the basics of optics. First of all， we suggest including some geometrical optical elements in the show such as lenses， prisms and various mirrors（i.e. ancient bronze， modern adaptive mirrors and even Chinese "magic" mirrors）.
Secondly， a demonstration of interference phenomena is essential. The easiest way to show it is through dynamic Moire patterns that can be made interactive. Also， we use double pulse holograms with "frozen" interference patterns （i.e. well-known holograms with deformed surfaces， or the flows of heated air around electric bulb）. Some of our exhibitions included demonstrating classical interference （e.g. Young’s double-slit experiment and Fresnel’s bi-prisms） for any visitors that would be interested. Interactive models of Mach-Zehnder and Michelson interferometers are used in the exhibition to demonstrate the applications of interference. Thirdly， we explain diffraction principles by using a wide range of diffraction gratings： transmissive， reflective， echelette， etc. Showing laser beam diffraction on the opaque round disc， so called Poisson spot， is always very spectacular to visitors. Special attention is payed to spectral properties of diffraction gratings because this leads to a discussion on the color components of white light. This conversation is continued in the interactive monochromatic room and near the dedicated wall with colorful shadows. The latter is one of the most attractive photo zones of the museum and exhibitions.
This approach of using exhibits describing each of the principles in addition to content directly related to the concept of holography has been proven very efficient.
5〓Interact rather than observe
A proverb goes： "Tell me and I will forget， show me and I may remember， involve me and I will understand". This is why we encourage people to interact with the exhibition rather than just observe. Visitors are supposed to be active throughout the exhibition so that they may have a better understanding and a deeper lasting impression. The interactive part of the exhibition allows to involve the emotional component into the process of thinking and understanding of holography and various properties of light. This corresponds the STEAM methods where Art-component adds to the rational knowledge.
The interaction with a holographic exhibit is achieved by using moving lights， holding the holograms in hands and comparing it with a real object. Also suggesting to the visitor to move within the three dimensional space where the holographic image is visible adds to the interactive involvement. These interactions are basic and attractive to the visitor. For instance， a special artistic exhibit consisting of a patchwork of many hologram pieces has been created as a human figure statue rotating on a turntable. The visitors use their phone torches and try to find the hidden images. For this， they have to find the right direction of light and the angle of view.
The plasma "Tesla Balls" （Figure 1） glow in the so-called "mysterious" form. The light in these balls can be controlled. During the guide’s explanations about the properties of plasma， visitors can interact with this exhibit and immediately see the effect. Pictures on the retroreflecting and luminescent walls （Figure 2） produce an impression on the visitor and form a positive opinion about the exhibition in general. These exhibits allow visitors to draw with the torch of their mobile phones and to "freeze" people shadows. [Figure 1 "Tesla Balls" in the Museum of Optics]