Diffraction on bird feather - Witamy na polskich stronach projektu 衍射对鸟的羽毛- witamy Na polskich施projektu

Diffraction on bird feather - Witamy na polskich stronach projektu 衍射对鸟的羽毛- witamy Na polskich施projektu Diffraction at bird feather Tatjana Saptsina tns@fian.smr.ru Lebedev Institute Samara Branch, Samara, Russia What interesting can you see in the case you had found a bird feather and you have a laser pointer? You can carry out a simple but very fine experiment on diffraction that shows some properties of the coherent light () and gives information about the structure of a bird feather. About diffraction effects. Diffraction is the phenomenon of waves flowing round the obstacles. It can be easily observed with the waves at the water surface. Visible light being the wave process can go around the obstacle too. , Bird feather Bird feather is very complicate biological object. Its properties widely vary depending on the species of bird and the kind of feather or down for a particular bird. (). Experiment The following items and conditions are necessary for carrying out this experiment: 1. dark room. 2. smooth light wall (the white is the best) is needed. Your can use the sheet of the white paper of proper size, A1, for example. You can make experiments in the evening time or in the room without windows. 3. bird feather. 4. laser pointer 5. peace of plasticine 6. table or chair for maintaining of all staff. The laser pointer and the diffraction object (a bird feather) should be placed as it is shown at the picture. The pointer and feather are fixed with peaces of plasticine. During the maintaining process you should be careful and put the plasticine taking into account the way you will easily clean it out after the experiment. The distance between pointer and feather may be small (up to 1 cm), and the best distance between feather and the screen is 2-3 meters. You can shift the feather across the laser beam, finding the most clear diffraction pattern. Some samples of feather and parts of them could be compact and do not transmit the light. In this case it is reasonable to direct the beam through very edge of the feather. As well there may be damaged parts that can distort the structure of the diffraction pattern and it will be better to avoid them. The safety measures During the experiment carrying out the researchers should be aware of the safety use of the laser pointer. The safety measures for this experiment are the following: laser beam should go at the level significantly below the eyes one in order to exclude the occasional getting into an eye. The unwanted strike of low capacity laser can cause the temporary dazzle, the temporary garbling of the color sensing and even the damaging of the inner eye muscles that control the size of eye pupil. Results. Looking to the diffraction patterns we can find some regularity in the light spots structure. The appearance of diffraction patterns of various feathers slightly differ in details. It can be easily determined at least two periodic structures in the pattern, those are caused by two king of elements in complicate texture of bird feather. It is possible to measure the distances between light spots on the picture for both regularity and estimate the arrangement of the elements of the bird feather. Measuring the periods of the diffraction picture and the distance between the feather and the screen (wall) it is possible to find the size of feather structure elements. Let is designate: the distance between the feather and the screen as L, period of the diffraction pattern – D wave lenghth of laser pointer radiation - , period of the feather structure responsible for this pattern - d Then d can be approximately calculated from the formula: d = ,,D/L for example, for , = 0,66 micron, L = 2 m, D = 6 cm, d = 22 micron. It is a rooster feather Discussion After carrying out you experiments you can compare obtained results with ours. Table 1. The value of the periodic structures of poultry feather. Species d, , d,, 12 1 Rooster 22 146 2 Hen 23.6 170 3 Duck 89 203 4 Goose 21 203 The results show that bird feather has the structure with two scales and two directions. The smaller one has the period of several microns, and larger one is of the order of hundred of microns. Looking at the feather through the lens you can understand what features of feather structure cause those diffraction patterns. Diffaction pattern of of poultry feather. Duck Rooster Hen Goose