Types and applications of waveplates
2023-12-4
The most common waveplates are quarter-waveplates (λ/4 plates) and half-waveplates (λ/2 plates), in which the phase retardation differences in the two linear polarization directions are π/2 and π respectively, and the corresponding phase propagation The distances are λ/4 and λ/2 respectively.
Here are some important conclusions:
If the beam is linearly polarized and the polarization direction is along one axis of the waveplate, then the polarization direction does not change.
If the incident polarization state does not coincide with any axis and the waveplate is a half-waveplate, then the polarized light is still linearly polarized, but the polarization direction is rotated. If the angle between linearly polarized light and the axis is 45°, then the polarization direction is rotated 90°.
If the angle between the incident polarized light and the axis is 45°, circularly polarized light can be obtained by passing through the quarter waveplate. (Other linearly polarized light will become elliptically polarized light.) Conversely, circularly polarized light can be linearly polarized by passing through a quarter-waveplate.
In a laser cavity, single-frequency operation can be achieved by placing two quarter-waveplates on either side of the gain medium (see twisted mode technique). Depolarization losses can be reduced by placing a half-waveplate between the laser crystal and the cavity mirror. A combination of half-waveplates and polarizers can be used to achieve an output coupler with adjustable transmittance.
Waveplates are usually made of quartz crystal (SiO2) because of its high transparency over a wide range of wavelengths and its high optical quality. There are other materials available (for other wavelength ranges) such as calcite (CaCO3), magnesium fluoride (MgF2), sapphire (Al2O3), mica (a silica material) and some birefringent polymers.
Here are some important conclusions:
If the beam is linearly polarized and the polarization direction is along one axis of the waveplate, then the polarization direction does not change.
If the incident polarization state does not coincide with any axis and the waveplate is a half-waveplate, then the polarized light is still linearly polarized, but the polarization direction is rotated. If the angle between linearly polarized light and the axis is 45°, then the polarization direction is rotated 90°.
If the angle between the incident polarized light and the axis is 45°, circularly polarized light can be obtained by passing through the quarter waveplate. (Other linearly polarized light will become elliptically polarized light.) Conversely, circularly polarized light can be linearly polarized by passing through a quarter-waveplate.
In a laser cavity, single-frequency operation can be achieved by placing two quarter-waveplates on either side of the gain medium (see twisted mode technique). Depolarization losses can be reduced by placing a half-waveplate between the laser crystal and the cavity mirror. A combination of half-waveplates and polarizers can be used to achieve an output coupler with adjustable transmittance.
Waveplates are usually made of quartz crystal (SiO2) because of its high transparency over a wide range of wavelengths and its high optical quality. There are other materials available (for other wavelength ranges) such as calcite (CaCO3), magnesium fluoride (MgF2), sapphire (Al2O3), mica (a silica material) and some birefringent polymers.
