Crystal optical system provided training interference device

FIELD: optical systems.

SUBSTANCE: training interference device provided with crystal optical system has clarifier, crystal-optic bema-splitting system and observation screen. Beam-splitting system has two Iceland spar crystals. Main cross-section planes of the crystals coincide to meet the condition that spatial shift of non-ordinary e-beam in the first crystal is compensated by opposite shift of e-beam in the second crystal. The result of such a coincidence is the light-gathering fringe pattern in form of set of prolonged and bright ellipse-shaped interference bands elongated along line of section of observation screen by main cross-sectional plane of crystals. Path of bands illustrates the basic dependence of Iceland spar crystal refractivity on direction of propagation of e-beam inside crystal. Crystal system is put into motion being lateral to light beam is performed by acting on adjusting screw of the device and changes in deformation of fringe pattern can be revealed. Device allows observing and juxtaposing results of overlapping of two light beams in the same field of view which beams change strongly for mutual coherence degree.

EFFECT: simplified production process; simplified adjustment procedure.

6 dwg

 

Renowned educational interference device with a crystal of Iceland spar (see patent [1]).

The advantage of training the interference of the device with a crystal of Iceland spar is its simplicity and accessibility. The device allows to obtain an interference pattern from two point sources of light are shifted one relative to another in the transverse direction. These sources are formed by passing the primary focus plane-polarized laser beam through a crystal of Iceland spar. When the linear polarization of the laser beam in a diagonal plane of the crystal and the focusing of the primary beam in the output it faces in this area due to the double refraction are two point source of monochromatic light of the same strength. These sources are incoherent, because coming from them the light waves polarized in mutually perpendicular planes. During the mixing of vibrations to a single plane through the Polaroid analyzer and the diagonal orientation of the analyzer overlapping in the plane of observation beams become the maximum extent coherent and can interfere. Generated by device interference pattern can be used to measure the wavelength of light.

A serious drawback of the study interferenz the organizational unit with a crystal of Iceland spar reduce to the following features of this device:

1. Although the formation of two coherent sources based on double refraction in the crystal, features and physical laws of this complex and important for optical theory and practical applications of physical phenomena during the operation of the instrument is absolutely not identified, are not used and remain hidden from the observer. In particular, is hidden the most important feature, which is that the refractive index of necrystal for the extraordinary beam (e-beam) in a complicated manner depending on the direction of propagation of the beam inside the crystal.

2. However, the generated device interference pattern has microscopic dimensions, and this picture can be observed only in individual terms, viewing it in the eyepiece.

These material weaknesses deprived offer educational interference device with crystal optics system. The device is simple and affordable. It is a fast device that forms the longest and vivid picture in the form of a family of strips of two-beam interference elliptical shape elongated along the line of dissection of the screen of the observation plane of the main section of the crystal. This picture can be seen in the large room on the big screen. Very significantly, that the course of stripes pattern sludge is ustrinum the change in the refractive index of the crystal for e-beam with the direction of propagation of the beam inside the crystal.

Consider the training device of the interference of the device with crystal optics system. Optical diagram of the device shown in figure 1,and the course of the rays inside the crystal system is detailed in figure 1,b, a photograph of the instrument is given in figure 2.

In figure 1,and contains the following parts:

1 is a helium-neon laser LH-75, generating monochromatic radiation with a wavelength of λ =6328 E; 2 - eyepiece with an increase of 10xfrom educational microscope; from the eyepiece turned the collective lens, and the remaining therein eye lens is used as a focusing lens large optical power (in the case of the laser, giving narrower than LH-75 beam, you should use a stronger lens, for example short-focus lens from educational microscope); 3, 4 - two crystal Icelandic sword approximate thickness t, i.e., t1t28 mm from the training sets of polarized light (it is desirable that the crystals had a good transparency and were of uniform thickness); the crystals are put and fix so that the plane of their major sections coincided, and the direction of the optical axes of the crystals in the lower part of figure 1,marked by arrows b 00, proved to be symmetrical with respect to the line BB ("antiparallel" location crystals); eyepiece 2 deploy so that the eye of his lens acatalasemia crystal 3 at a distance of about 0.5 cm from the outer surface of the crystal; in the case of ocular eyepiece lens with an increase of 10xfocal length of lens F=1.5 cm, so if the thickness of the crystal, t=0.8 cm the laser beam is focused near the second surface; 5 - enshrined in the disk, the screen Polaroid analyzer from a training set of polarization of light; 6 - another Polaroid, mounted in thin-walled annular frame with a handle, which can serve as an orientation indicator of Polaroid; Polaroid 6 sets instead of Polaroid 5 at a greater distance from the crystal; 7 - screen monitor.

Figure 1,b shows the course of the ordinary ray (o-ray) and extraordinary ray (e-ray) for the case of normal incidence of the primary beam on the input facet of the crystal optics system: the angle of incidence of the beam on the input facet of AA crystal 3 is i=0° . The plane of the main section of crystals 3 and 4 coincide with each other and with the plane of figure 4,b and the plane of oscillation in falling on the line AA pleapositive laser beam is angle λ =45° with the plane of Fig 1,b (diagonal arrangement). Therefore, the fluctuation of the intensity vectorin the incident on the crystal 3 light beam can be represented as a sum of two mutually perpendicular oscillations of the same amplitude and the same phase (they are represented by points to the arrows on the left in figure 1,b). This separation is real is by the crystal (point and the arrow inside the crystal), in relation to which point fluctuations are common, and the arrow is extraordinary.

When evaluating the optical difference of course Δ o - and e-rays are output from crystal optics system should take into account that the angle β rejection e-beam relative to the o-beam is small enough. Neglecting the small difference of the geometric paths of the o - and e-rays, we get

Here, naboutis the refractive index of a crystal of Iceland spar for the o-beam; no=const=1,66, and neis the refractive index of the crystal for e-beam; nedepends on the angle i and is set within n

min
o
nenowhere n
min
o
=1,49. For the evaluation of neuse

the equation of wave normals Fresnel. Following [ 2, 3]; record the value resulting from the equation of wave normals, in the form of approximate equality

where- the angle between the departments of the optical axis 00 and e-beam inside the crystal. At normal incidence of the primary beam on the line AA have ≅ 48° . Then from (2) we get ne=1.57 and from (1) we have t=8 mm Δ ≅ 1,44 mm, the order of interference To=Δ /λ in the light of a helium-neon laser (λ =0,6328 μm) for the Central part of the interference field (i=0° ) will make up To≅ 2300. This means that the necessary degree of temporal coherence of overlapping rays will be observed only at high monochromaticity of the illuminating beam. Valid spectral width δ λ illuminating beam will be determined by the known relation (see, for example, [ 4] )

When the lighting device is Not+Ne laser LH-75, this condition is satisfied, that allows to achieve high-contrast interference pattern.

The basis of the instrument is crystal optics system consisting of two crystals of Iceland spar close thickness, folded together so that the plane of their major sections coincided with the "antiparallel" the location of the crystals (see figure 1,b). Crystal optics system is pressed to the standard square retractable metal plate 50× 50 mm2and 1 mm thick with flanges and secured in the disk to the screen in the form of a wide rim with a rack, the Central part of the frame with crystal optics system can be rotated at a desired angle around the axis of the light puck is. The slide plate has a Central hole with a diameter of 5 mm to pass translucent crystal optics system of the light beam and two lateral holes, threaded screws M3, for clamping screws. Clamping is carried out using a rectangular plate of size 17× 50 mm2and a thickness of 1 mm, also having in its middle part which transmits the light beam hole in the form of a rectangle of size 10× 20 mm and two side smooth round holes with a diameter of 4 mm under the fastening screws M3 length of 20 mm (see figure 2). To the inner surface of the invoice, a metal plate glued strip of thin and soft material, excluding the distorting effect of this plate in contact with the surface of the relatively soft crystal CaCO3. Hour drive-screens fixed in the slider of the optical bench and influencing existing slider adjusting screw, you can make minor smooth movement crystal optics system in a direction transverse with respect to the axis of the illuminating beam. Slight change in thickness of the crystals and their homogeneity within a narrow illuminated channel inside the crystals leads in this case to the corresponding small change in the phase shift Δ ϕ =2π Δ /λ overlapping on the screen there is placed the rays. Each additional change Δ ϕ δ λ =π corresponds to the transition from the picture with the Central bright spot to an additional picture with a Central dark spot (see photos 3, the transition from a) to b)) and the displacement of the fringes on papolos around the interference field.

The Polaroid analyzer 5 (see Fig 1,a) in a standard rectangular mandrel is fixed in the second disk, the screen and positioned near the first CD of the screen with the crystals (see picture 2). In this case, the entire light beam, piercing crystal optics system and forming an interference field, entirely passes through the Polaroid analyzer 5 and the interference pattern fills the entire light field on the screen surveillance (see interferogram figure 3(a, b); the photos were taken when removing screen monitoring 7 from the device to the l=3.3 m; width of the interference field is 0.6 meters). The transition from Fig.± 3,and Fig.± 3,b corresponds to a small transverse displacement of the crystal optics system.

Kind of elliptical course of the interference curves in the picture is due to an important feature polarised diakopoulos crystals, which consists in the following. The refractive index of the crystal CaCO3for the ordinary ray is a constant that does not depend on the direction of the o-ray NR the three crystal (n o=const=1,66), whereas the refractive index of the CaCO3for the extraordinary beam at the same angle i of incidence of the primary beam on the crystal depends on the azimuth α the plane of incidence of the beam. In strongly converging the primary light beam incident on the input face AA of the crystal 3 (see Fig.1,b), there are rays of all sorts of directions within a certain solid angle δ Ω . The axis of this solid angle is oriented normally to the brink AA, and the angles of incidence vary for different rays of the beam in the range of 0≤ i≤ imax. Select from this beam set of rays along the conical surface forming which shall constitute one and the same angle i with the line AA. For all these rays have i=const, but the azimuthal angle α their planes of incidence is different in the range of 0° ≤ α ≤ 360° . Due to the dependence of ne=ne(α ) the difference between the refractive δ n=no-newith the change of the azimuthal angle α changes accordingly. Therefore, the difference of the stroke Δ interfering rays, defined by equation (1), and the magnitude of the phase shift Δ ϕ =2π Δ /λ also change with α . This leads to the fact that the interference curves do not have the correct view of the rings. Right ring would be observed in the case of independence, p is snasti refraction Δ n from the azimuth of the plane of incidence, i.e., if for arbitrary angle of incidence i=const respected conditions Δ nα =no-ne=const and Δ α =const. In effect, the same dependence of nefrom α Δ nα =no-neconst and Δ α ≠ const. Therefore, the interference curves, the formation of which satisfies the obvious condition Δ =const, appropriately deformed, stretched along the line of dissection of the screen of the observation plane of the main section of crystal optics system. Thus, the originality in the course of the interference curves lead to the unique and important conclusion that ne=ne(α ).

Educational interference device with crystal optics system has a second Polaroid analyzer 6 in the form of a system of two circular glass plates with a diameter of 44 mm round Polaroid film of the same size between them. Polaroid 6 is fixed in a narrow iron ring handle (outer ring diameter 53 mm, inner - 45 mm, thickness 5 mm, arm length - 60 mm). Before working with Polaroid 6 disc screen with Polaroid 5 installed near crystal optics system, is removed from the light beam and remove from the scheme of the device, and the analyzer uses a Polaroid camera 6, which is installed at a greater distance l1from crystals. In this case the e Polaroid 6 covers only part of the light field on the screen of observations at the same time you can see two parts of the field. Comparing the pictures seen in these parts of the light field, it is possible to draw important conclusions about the role of the output Polaroid analyzer 6 and, moreover, about the nature of light waves. In the part of the light field, which is formed by rays passing (out) Polaroid, o - and e-rays are polarized in mutually perpendicular planes and therefore they are incoherent and unable to interfere. This is external to the frame of the Polaroid part of the light field interference will not occur, anyway Polaroid 6. Second, internal to the frame of the Polaroid 6 of the light field formed by the rays passing through the analyzer 6, which reduces vibrations of the o - and e-components to a single plane. This provides partial coherence and the possibility of the formation of interference fringes in this part of the light field. The degree of coherence is maximum in case of equality of the amplitudes of the interfering oscillations, i.e. the diagonal orientation of the Polaroid 6. While in the inner part of the light field occurs the system is a high-contrast interference fringes. In images 4 (a, b) and figure 5 (C, d, e, f) the patterns obtained when uninstalling Polaroid 6 at a distance of l10,9 m Images figure 5 (C, D, E, f) made with the removal of l10,4 m Given cartinasardegna illustrate important regularity, namely, that the degree of mutual coherence of the beams that have passed through a Polaroid 6 and, accordingly, the contrast of interventional picture significantly changes when you rotate the Polaroid. It is maximum at a diagonal orientation, when the amplitude of the o - and e-components are the same. It is zero when the amplitude (intensity) of one of the components is equal to zero. The transition from the maximum contrast of the picture (the pictures in figure 4,b, 5 (d, G, e, e)) to zero (photos 4 and 5 (in, In, d, E) corresponds to the rotation of the Polaroid 6 around the axis of the light beam at 45° . When performing experience the amount of necessary rotation it is easy to determine on good seems to be in view of the provisions of the handle frame of the Polaroid 6. When switching from the picture in figure 4,and to the patterns in figure 4,b, 5,b, 5,g, 5,d and 5,the angle of rotation is respectively 45, 90, 135, 180 and 225° . The same can be set according to the position of the label in the form of small dark circle, which is adjacent to the inner edge of the shadow from the frame of the Polaroid and appears in the presence of a small vyboinki near the edge of one of the round glasses this Polaroid.

Literature

1. The decision to grant a patent on the invention of my previous application No. 2001126629/28 (028326), author of Amstislavsky N.E., title of the invention: interference Educational device with crystal Islan the ski spar.

2. Melancholy N.M. Methods of studying the optical properties of crystals. - M., 1970, p.52.

3. Modern crystallography. - M., 1981, v.4, s.

4. D.V. sivukhin the General course of physics. Optics. - M., Nauka, 1980, s.

5. Saveliev IV Course of General physics. Vol.2. - M., Nauka, 1978, s-347.

Educational interference device with crystal optics system consisting of lighting parts in the form of a helium-neon laser, giving pleapositive radiation, and short-focus lens, the beam splitting crystal optics system in combination with the Polaroid analyzer and screen monitoring, characterized in that the beam-splitting system contains two crystal of Iceland spar installed so that the plane of the main sections of the crystals are the same, provided that the direction of the optical axes of the crystals are symmetric with respect to the input face crystal optics system, then the spatial offset of the extraordinary (e-beam relative to the ordinary (o-) of the beam in the first crystal is compensated in the opposite direction of the offset e beam in the second crystal, which causes the overlap of the o - and e - beams at the output of crystal optics system and the diagonal orientation of the Polaroid analyzer provides a high degree of spatial coherence of perekryvaya is on the screen of the monitoring light beams and receive elongated and bright interference pattern in the form of the ellipsoid of interference fringes, elongated along the line of dissection of the screen of the observation plane of the main section of the crystals, a move which illustrates the fundamental theory and practical applications of the phenomenon of double refraction dependence of the refractive index of the crystal for e-beam from the direction of its propagation inside the crystal, the effect on the adjusting screw of the device allows transversely to the light beam moving crystal system and detect small changes in the thicknesses of the crystals within a narrow illuminated channel within the system and associated small changes of the phase shift Δϕ intersecting rays through observation of the dynamics of deformation of the interference pattern is consistent with a transition from the picture with the Central bright spot to an additional painting with a Central dark spot and the displacement of the fringe pattern in strips across the field of view at each change Δϕ δϕ=πand replacement Polaroid analyzer with a wide rim on the Polaroid with narrow rim when establishing Polaroid at a greater distance from the crystals allows to detect important differences in the effect of overlapping of the two beams with the oscillations of the same frequency and phase, but what is happening in mutually perpendicular planes, from the case of overlapping the same light beams, but the fluctuations, reduced to one plane.



 

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