I think the things but hi thank you very much for listening to this last talk so my name is my name is 7 so far so and form part of the laboratory Physics Department of charming University China so our group 1 of the best group during holography research in China so

recently we developed a new security technique so it's it is the topic of of my talk today so professor she gave a brief introduction on the 1st day of the conference so now I'm going to give some details Introduction

some my talk includes 1 brief introduction of the holograms and photonic crystal and went to the technique of fabricating tools the crystal into photo resist Master strange applying photonic-crystal insecurity packing material

so I think everybody here knows that holograms have been used in security for use a decade or so at the beginning and they are very effective but later on because the normal horrible and fabrication technique is simple so many people learned how to make normal hollow-gram so that security power is fading so to solve the problem encryption

techniques developed since 1993 there are some techniques have been used to i as our knowledge and our group is the 1st part the proposed the encryption technique in the world so

what's Fotona crystals there are some natural photonic crystals such as open and butterfly wings research but they can't be used so when we talk about photonic-crystal we talk about artificial crystals made by people and to make it in dielectric materials and to periodic refractive index distributions so the left period is around my from interests Michael range so there

are different methods to fabricate photonic photonic-crystal of among them the holographic method is known as the most critical 1 with the advantage of fast produce production and low cost and able to make a large area from increased crystals so the method of talk hormone homographic uh fabrication is to use multiple laser beam to form Trudy Austria the interference pattern so that the the pattern all the right to this is a 3 D photonic crystal made by computer simulations so when the pattern is recorded in the photo resist and then you eliminate the crystal with the laser beam you can have a special interference patterns so if you want to have a typical interference pattern you need to fabricate a typical but only a crystal structure so you'll have to know how to arrange multiple being so from this equation we can see I is the intensity distribution of the interference pattern and k Our wave vectors they presented that laser beam so if you know K and you you know how many layers of being you need to form a special patterns and that the the orientations of the paired

so according to the book solid state physics we know the digitalization the reciprocal lattice vectors and we vector this they and this kind of relations and also G. has in relation with primitive reciprocal lattice vector and also primitive reciprocal lattice vectors as a relation with primitive crystal lattice vectors

so for tool dimension of photonic crystal so we have this simple so we we need only true primitive reciprocal lattice vectors that P 1 P 2 and and then we can calculate K K. 1 K. 2 case we so it shows that to form the tool dimensional photonic-crystal you at least need street being and by solving this equation we can get the orientation of the so

so for example if we want to make a hexagonal patterns then after this theoretical work we can get that to we need and these 3 beings with this configuration so students are symmetrically arranged with 120 degree between each other and with the same angle to the normal of the place so that the the angle of the entire is also very important because it is determines the lattice constant 1 that is consonant is important this is there is a

picture of that taken from from from the experiment is shows we used 3 different angles that will wait human nature of the crystal we can get these 3 pet diffraction patterns so how

to get this optical arrangement is very difficult to and registry beings with exactly which this oracle orientations metadata this alignment with cost distortion to photonic crystal scratched the structure so this is developed by our studies of very simple optical system we we fabricated on each and we it has 3 identical gratings and 2 when new to buy 1 laser being we get 3 beings with traveling with and with with the same angle to the optical axis then it forms an have had signal lattice pattern and then recorded into 4 2 and 4 to exist this

is the whole system optical system that the the beam is expanded and column inches and the men made their way Chile and and according to conferences for and the image on the right to use the scanning electron micro in each obtained from our experiments so we

made this and structure into packing material so as 8 is some areas on the material then we applied

it taking 2 I would be enriched sort package and you know in China many Chinese have have problems because of and inability so it's very important for Chinese Chinese government to that people use this kind of sort by there are many solids and manufactured by private produces they they have no idea in the sort at all so uh so we did this book it is very very important to let people know what kind of a package of sort you should so it's very

simple to identify the code just use of energy in a laser pointer and inserted through a piece of white paper maybe you can you can see 6 spot light spot so this this this idea at at the height of the Fe cations is very simple so

in conclusion of this new technique it's conflict has context coding process because it needs theoretical would and he needs the design of the optical system otherwise income make it so this technique it is very difficult to be indicated by owned the other side and the decoding process is very simple and it can be done at anywhere and by anybody thank You can

thank and the image this that there's some questions I just want to ask polarization of the light when you have 3 main yeah that here it has the effect to the foot of the structure by yeah we're we have conclusion about it but this application in it has no effect not not obvious effect so it is like question what I don't understand what they're small so you mean that the photo then that but on crystal the idea that there is no there's the case I I was the what what model used for predicting what the universe beings will look like a mathematical model yeah yeah yeah man that was something do you can use a very we just use that equation question of us i would like to thank you ladies and gentlemen of this moment session but you have spent the intentions intense attention and thank you also for months the outcome which but you will have lost more to you and I'm issue safe trip back home and would like to see you once more the room and if a and