Polarized Light

Light Polarization Objective: Observe the Light Polarization, understand the kinds of the polarized light. Grasp the way of produce and test to the polarized light. Equipment He-Ne lasing light emitter(1), polaroid filter(2), pedestal(2), optical-electrical converter(1). Theory: Kinds of the polarized light: 1). Natural Daylight: If in the plane which is perpendicular to the direction of light travel, the direction of vibration of light vector is changing irregularly, and the probability of occurred on all sides is equivalent, the mean amplitude of tide on all sides are equivalent, this kind of light is named Natural Daylight. 2). Partially Polarized Light: If the mean amplitude of tide of light vector on some sides are comparatively large, and the other sides are comparatively small, this kind of light is named Partially Polarized Light. 3). Linearly Polarized Light: If light vector vibrates along by a fixed direction, this kind of light is named Linearly or Plane Polarized Light. 4). Elliptical Polarized Light: If the measurement and direction of light vector are changing regularly, in the plane which is perpendicular to the direction of light travel, the extremity movement locus of light vector is a ellipse, this kind of light is named Elliptical Polarized Light. 5). Circularly Polarized Light : When the measurement of light vector in the Elliptical Polarized Light is unchangeable, only the direction is changing regularly, the extremity movement locus of light vector is a circle, this kind of light is named Circularly Polarized Light. Polarization by Use of a Polaroid Filter A Polaroid filter is able to polarize light because of the chemical composition of the filter material. The filter can be thought of as having long-chain molecules that are aligned within the filter in the same direction. During the fabrication of the filter, the long-chain molecules are stretched across the filter so that each molecule is (as much as possible) aligned in say the vertical direction. As unpolarized light strikes the filter, the portion of the waves vibrating in the vertical direction are absorbed by the filter. The general rule is that the electromagnetic vibrations which are in a direction parallel to the alignment of the molecules are absorbed. The alignment of these molecules gives the filter a polarization axis. This polarization axis extends across the length of the filter and only allows vibrations of the electromagnetic wave that are parallel to the axis to pass through. Any vibrations which are perpendicular to the polarization axis are blocked by the filter. Thus, a Polaroid filter with its long-chain molecules aligned horizontally will have a polarization axis aligned vertically. Such a filter will block all horizontal vibrations and allow the vertical vibrations to be transmitted. On the other hand, a Polaroid filter with its long-chain molecules aligned vertically will have a polarization axis aligned horizontally; this filter will block all vertical vibrations and allow the horizontal vibrations to be transmitted. Formula

If the lineally-polarized (plane-polarized) light is incident onto the polarizer, then the intensity of the transmitted light I will depend upon the angle a between the direction of the light polarization and the orientation of the polarizer as follows: I = I0cos2a When the light from light source with linear polarization is incident onto the rotating polarizer. As a result the intensity of light spot on the screen behind the polarizer is varied harmonically depending on the angle between the polarization direction and polarizer angle. Make a set that the flat electro-magnetic wave propagating in the positive direction along the axis x. In this case the equation of such a wave can be written as: Ex = 0, Ey = E0cos(wt - kx), Ez = 0; Hx = 0, Hy = 0, Hz = H0cos(wt – kx); where k=w/c is the wave constant, c is the velocity of the light. As we can see from the animation there is no oscillation of electric and magnetic components of wave in the direction x (Ex= Hx = 0). This means the the electromagnetic wave is the transverse one. This is one of the principle differences of electromagnetic wave as compared to the wave of mechanical stresses. Another principle of electro-magnetic wave propagation is that the vectors E and H oscillate in phase, i.e. they achieve the maximum value in the same points of the space. Details Linearly Polarized Light's Production and test 1).Open the He-Ne lasing light emitter, set the polaroid filter A before the light source, adjust the hight of the light source and filter, let the light source irradiates the center of the opticalelectrical converter when though the filter, the microammeter appears reads. 2).Turn the filter, the lumen output by transmission appears the changing of power, that is because the lasing light emitter produces the Partially Polarized Light, so it needs to turn the filter to the most powerful lumen output, to get the largest read from the microammeter. 3).Set another polaroid filter B before the filter A, observe the changing of electric current when turn around the filter B, adjust the filter B to make the electric current zero, named extinction position, remember the position B0 which the pointer on the filter B points. Matters Need Attention Make the test-bed steady; keep the light source at the center of the optical-electrical converter all along; reading the result until the pointer stop completely;turn off the power and arrange the equipments to the original position when finish the test.

Scores

ESL-183RW

A;

184RW

A;

184LS

B;

ENGL-151A

C;

MATH-188 Pre-Calculus

A;

101A Calculus

A;

101B Calculus

A;

159 Introduction to Statistics

C;

PHYS-121 Introduction to Physics II

B;

SOC-101 Introduction to Sociology

C;

MUS-102 Music Appreciation

B;