Question

Distinguish between half wave plate and quarter wave plate

Answer 1

Half Wave Plate

The half wave plate can be used to rotate the polarization state of a plane polarized light as shown in Figure 1.

Suppose a plane-polarized wave is normally incident on a wave plate, and the plane of polarization is at an angle q with respect to the fast axis, as shown. After passing through the plate, the original plane wave has been rotated through an angle 2q.

A half-wave plate is very handy in rotating the plane of polarization from a polarized laser to any other desired plane (especially if the laser is too large to rotate). Most large ion lasers are vertically polarized. To obtain horizontal polarization, simply place a half-wave plate in the beam with its fast (or slow) axis 45° to the vertical. The l/2 plates can also change left circularly polarized light into right circularly polarized light or vice versa. The thickness of half waveplate is such that the phase difference is 1/2 wavelength (l/2, Zero order) or certain multiple of 1/2-wavelength [(2n+1)l/2, multiple order].

Quarter Wave Plate

Quarter wave plate are used to turn plane-polarized light into circularly polarized light and vice versa. To do this, we must orient the wave plate so that equal amounts of fast and slow waves are excited. We may do this by orienting an incident plane-polarized wave at 45° to the fast (or slow) axis, as shown in Figure 2. When a l/4 plate is double passed, i.e., by mirror reflection, it acts as a l/2 plate and rotates the plane of polarization to a certain angle, i.e., 90°. This scheme is widely used in isolators, Q-switches, etc.

The thickness of the quarter waveplate is such that the phase difference is 1/4 wavelength (l/4, Zero order) or certain multiple of 1/4-wavelength [(2n+1)l/4, multiple order].

Answer 2

Answer:

The quarter-wave plate, which converts linearly polarized light into circularly polarized light. Half-wave plate, which shifts the polarization direction of linearly polarized light,

Explanation:

1. Half wave plates and quarter wave plates are fundamentally different from one another because half wave plates prefer to modify the polarisation direction of linearly polarised light, while quarter wave plates tend to change linearly polarised light into circularly polarised light.
2. A half wave plate is a birefringent material which changes the phase between two perpendicular polarisation by π or half a wave. While a quarter wave plate is a birefringent material which changes the phase between the same two polarisation by π/2.
3. A half wave plate can be used to convert one linear polarisation to another, or one circular polarisation to another While a quarter wave plate is can be used to convert linear polarised light to circularly polarised light

Hence these points makes differences between the half wave plate and quarter wave plate.

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