Difraksi Fresnel.docx

DIFRAKSI FRESNEL Difraksi Fresnel difraksi Frensel adalah kasus khusus di mana cahaya yang masuk diasumsikan paralel dan gambar pesawat diasumsikan berada pada jarak yang sangat besar dibandingkan dengan objek difraksi. difraksi Fresnel mengacu pada kasus umum di mana orang-pembatasan yang santai. Hal ini membuat jauh lebih kompleks matematis. Beberapa kasus dapat ditafsirkan dengan cara empiris dan grafis yang wajar untuk menjelaskan beberapa fenomena yang diamati.

Difraksi Fresnel : Celah Tunggal The more accurate Fresnel treatment of the single slit gives a pattern which is similar in appearance to that of the Fraunhofer single slit except that the minima are not exactly zero.

Fresnel Diffraction: Opaque Strip Jenkins & White's treatment is the best I've found. Below is a sketch from J&W which is in best agreement with what we see with the diffraction pattern from a human hair.

Fresnel Geometry For the Fresnel case, all length parameters are allowed to take comparable values, so all must be included as variables in the problem. The usual geometry assumes a monochromatic slit source and the problem is set up in terms of a parameter v as defined below. This parameter is used with the Cornu spiral or a table of elliptical intgrals.

The Cornu Spiral The Cornu spiral is a graphical aid for evaluating the Fresnel integrals which show up in the evaluation of the diffraction intensities for the Fresnel diffraction of the light from a slit. It lends itself to the calculation of diffraction from slits, barriers, and opaque strips.

Diffraction by Opaque Barrier

The beam of a laboratory helium-neon laser was spread with a telescope eyepiece and directed at a machined metal edge. The diffraction pattern was photographed on a screen approximately four meters from the edge. Barrier diffraction must be handled by the techniques of Fresnel diffraction. One way to approach the calculation is by use of the Cornu spiral. Diffraction by Opaque Edges The beam of a laboratory helium-neon laser was spread with a telescope eyepiece and directed at machined metal edges. The diffraction pattern was photographed on a screen approximately four meters from the edge. This is diffraction from the corner of a double-edged razor blade. This diffraction pattern is from the cutout in the razor blade imaged above. Barrier diffraction must be handled by the techniques of Fresnel diffraction. One way to approach the calculation is by use of the Cornu spiral.

Diffraction by Pinhead

The beam of a laboratory helium-neon laser was spread with a telescope eyepiece and directed at the head of an ordinary straight pin. The diffraction pattern was photographed on a screen approximately four meters from the edge. Barrier diffraction must be handled by the techniques of Fresnel diffraction. One way to approach the calculation is by use of the Cornu spiral. Diffraction by Opaque Barrier The diffraction pattern produced by monochromatic light and an opaque edge includes light which penetrates into the geometric shadow and an alternating pattern of bright and dark fringes outside the shadow.

Opaque Circle An opaque circular disk gives a concentric ring diffraction pattern similar to the circular aperture, but in addition it has a bright spot in the center referred to as either Poisson's spot or Fresnel's spot. It seems more appropriate to name it after Fresnel since he developed the theory. Halliday and Resnick have the best picture of it I have found. In fact, Poisson strenuously objected to having it named after him because it was observed after an objection he raised to Fresnel's thesis - i.e. that Fresnel's calculation would imply such a bright dot and it hadn't been seen. This initiated a search for it and it was quickly found.