Test 4 Optics

What is the maximum E vector?

Amplitude

What is polarization?

Orientation of the E field

Is the E field parallel or perpendicular to the dipole?

parallel

All of the E vectors in one plane is said to be

Plane polarized

Plane polarized example

• When light becomes plane-polarized, the oscillation of the electric field is restricted to a single plane. For example, if the light travels along the x-axis, the E vector might be restricted to oscillate in the yz-plane, with all its variations confined to one direction.

What is responsible for most optical phenomena and it is the only field relevant to polarization?

Electric (E) field

Polarization by anisotropic substances

n and absorption will also vary for any given direction depending on the orientation of the E vector (plane of polarization)

Birefringent crystals

If a crystal has one optic axis it is called birefringent or doubly refractive since for a ray traveling at an angle to the optic axis n will differ depending on whether the E vector is parallel or perpendicular to the plane which contains both the ray and the optic axis

What are the two birefringent crystals

quartz and calcite

O rays are polarized

perpendicular to the plane

E rays are polarized

parallel to the plane

If you have a sphere larger than the ellipsoid that means that

you have positive birefringence because the sphere is larger than the ellipsoid

What is negative birefringence?

The e (extraordinary) rays are larger than the o rays (ordinary)

Birefringent materials only

change the speed of transmission and shift the image of light of one E vector orientation relative to the other

What is dichroism

additional property of birefringent crystals that have selective absorption of light depending on E vector orientation

What is a natural dichroic crystal, also what was originally for birefringence as Nicol prism?

the natural dichroic crystal is tourmaline. but the Nicol prism is two pieces of calcite

parallel E vectors passes freely while

those E vectors perpendicular are strongly absorbed

J sheet polarizer

Microscopic needle-shaped dichroic herapathite crystals were mixed into nitrocellulose which was pulled into thin sheets. This aligned the herapathite crystals with all of their optic axes in one direction.

H sheet polarizer

A sheet of polyvinyl alcohol is stretched in one direction which aligns the long hydrocarbon molecules in the direction of stretch. The sheet is then impregnated with iodine which attaches to the hydrocarbon molecules and forms dipolar iodine chains of the same orientation. The iodine chains absorb the component of the E vector in their direction of alignment and only the E vectors perpendicular to this orientation are fully transmitted.

Pass Axis

The axis that allows a particular orientation of light to pass through is known as the pass axis . If the pass axis on a polaroid sheet is vertical, it will only fully transmit light with a vertical polarization. Light of different orientations (that is not parallel or perpendicular to the pass axis) will be partially transmitted and absorbed. Light of an orientation perpendicular to the pass axis will be fully absorbed. The maximum amount of light that can pass through a polarizer is 50 percent of the original intensity of the light.