 Hi, I'm Zor. Welcome to a new Zor education. I would like to finish basically my representation of holography. The first lecture, previous lecture, was about hologram of a particular point light. So whenever you have a point light, I have explained how the image of this point light can be recorded and later on reproduced. Today I would like to talk about how the whole hologram of some object, complicated object, can be created. Again, I will not talk about much technical details, only the principle. So, now let me just remind you that whenever you have a point light and it goes to all the different directions, the light goes into all different directions, let's assume that this is a monochromatic light of the wavelength lambda. So whenever we have parallel rays of light of the same monochromatic light of the same wavelength, we will have some interference picture. This interference picture can be recorded, because there are bright and light spots, bright and dark spots. So some kind of a chemical compound, which contains silver or something like this, is used. So the bright spots, whenever they are bright, will modify this compound and the silver spot will be in that particular case. And whenever the white interference picture results in a dark spot on the screen, the dark spot will be actually dark. And then, when there is no light anymore, there is no point light anymore, we are using the same parallel lights of the same wavelengths, of the same monochromatic light. And whenever they are reflecting from the silver spots, from the mirrors, according to the Huygens principle, they will emit light into all different directions. But in this spot, there will be the concentration of light, because all these rays from these little mirrors will be in phase, because that's how interference picture was created in the first place. So if you just come up to this particular lecture without the previous one, I do suggest you to stop and watch the previous lecture on the same website, Unisor.com. So you will go to the Physics 14 course, the chapter is called Waves, and within the waves there will be a menu with holography, and there will be a previous lecture, which is a hologram the point light hologram. So that explains whatever I was just very, very briefly repeated. So we know how to recreate the point light from this particular image created when it used to be here. So when there is no point light, we are still using these parallel lights to recreate the bright spot, which represents this particular point in space. Point light. Okay, now let's talk about object. We don't have a point light, we have an object. Okay, how can we recreate the image of this object when it's no longer there? Well, again, first we have to really create its image, image of this object in such a way that will allow us to recreate its image in space whenever it's no longer there. Okay, so here's how can we do it. We will use a very, very similar principle. Let's have some kind of parallel rays of light which would be illuminating this object. Now, every point where the light comes, it will reflect this light in some way. Some brighter, some darker, and reflection again will be in all the different points. From each point, the reflected light will go into all different directions. So every one of these points can now be considered as a point light. So it's reflected by the surface of this object light which goes into all the different directions. That's exactly what we need, because all these will be of the same monochromatic light of the same wavelengths, but in all the different directions and the reflected from these surface lights will go to the surface of our screen. And they are coming from all the different phases, obviously. Now, whenever you have a different set of rays, also parallel of the same monochromatic light we will have some kind of interference picture between these lights, which are called reference beam, if you wish, between the reference beam and all the reflected lights from each point. Now, if it was one point, point sword, point light as in the previous lecture, the interference picture would be circles. In this case, interference picture would be God only knows what. However, it will reflect this object, its geometry, how each point is basically emitted the light. So this screen will contain a picture of each particular point source as some kind of an interference picture between reflected from this point light and the parallel reference beam. And then we will do exactly the same as we will do with the point light. So whenever this object is no longer there, we will use the same reference beam. It will reflect from little mirrors, which we have created during the creation of the image of the object. In the first stage, it will reflect and again, exactly as it was in the previous lecture, every point light would be recreated in space exactly where it was forming basically an object which is no longer there. So this is a very simple continuation of whatever I was talking in the previous lecture about. If we know how to recreate a point light, we know how to recreate two point lights, three point lights, or infinite number of point lights. So whenever we have an object every point of the surface of this object, if it's lit by some kind of monochromatic light of this wavelength becomes a point light. And we know that this point light will be recreated if we will do this trick with reference beam and record interference picture in some kind of a chemical compound with little pieces of silver creating in the bright spots. So this is just a simple continuation of whatever we know about as creating a hologram of a point light. All we do right now is creating a hologram of many point lights. And again, each point light is recreated exactly where it was relative to a screen. So those which were further will be closer recreated. What's interesting is that the picture created here would correspond basically to a picture as if it was seen by a person who is here and looking on this particular object from this side. But it will see certain things on a different distance and at different angles and that what makes the whole thing looking like 3D. Because how do we see the 3D? Why do we see something in the three dimensions? Well, because we have two eyes and they have different angles and the object has different distances between us and different points of this object and different distances means that we have to change the angle between the eyes, etc. So it all somehow goes into our brain and that's how we see it as a 3D. So the same thing here. So if the person is here then he would see maybe there is a little pithole to look then it will see this object basically in three dimensions. All because every point of that source when illuminated by illuminating beam it's called illuminating beam. So every point of the surface of this object becomes a point light. And then we are recreating this point light using exactly the same technique as I was explaining in the previous lecture. So why don't you read the description of this lecture, textual description. So that might actually make the whole thing a little bit better. I did not go into any technical details about this like what exactly kind of compound is used to record the interference picture as a photograph basically. But you understand that whatever you see here will have nothing to do with the photograph because photograph is actually whenever if you have an object you have photo camera here. So all lights go through the lens and then to some kind of either memory chip or some kind of photographic equipment or whatever. So that's why everything is seen from one point. And all of these rays are not difference. I mean we don't see the difference in distance between this and this or difference between angles whenever we see this from this, the same thing. But here this thing is actually reflecting the distance of every point. And if you will look at the screen where this recording actually is done you will see just dots bright and or silver maybe some reflective reflective dots and dark dots and that's all we have. But it's enough to recreate this picture of object if lit by the same parallel monochromatic light. Okay so again go to unizord.com and go to this lecture that's part of the Physics 14 chapter is called Waves and in the waves you will see hologram part where this is the second lecture. But the previous, the first lecture of the same hologram chapter that is the most important one and I do suggest it to basically go through both of these lectures to really understand the principle. And again it's only the principle it's no technical implementation there are many different waves of how we can implement this. For example how to implement these and these parallel lights of the same monochromatic light of the same wavelengths. Well actually it's arranged from one laser. Laser goes this way then there is some kind of a half transparent mirror partially transparent mirror so some goes here and some reflected here. Now we can have a real mirror at some angle and this would be reflected so this would be illuminating object and this would be reference, rays of light. Something like this can be arranged. Again I do have a picture in the textual description of this record. Now I didn't mention it but unizord.com is totally free there are no advertisements so you can just use it it will without any hesitation. Well thanks very much I'm very glad that I have finished this particular hologram chapter of the waves and then I will switch to completely different part of the course, Physics 14 which is called atoms. So I will talk about atoms and atom structure etc but that's in the future. So thanks very much and good luck.