Polarization of laser emission
2024-5-26
Definition:
Definition: The direction of electric field vibration of the laser beam.
In most cases, the emitted light from a laser is polarized. Usually linearly polarized, that is, the electric field oscillates in a specific direction perpendicular to the propagation direction of the laser beam.
. Some lasers (for example, fiber lasers) do not produce linearly polarized light, but other stable polarization states, which can be converted into linearly polarized light using a combination of appropriate wave plates.
If it is broadband radiation and the polarization state is related to the wavelength, the above method cannot be used.
In some special cases, a radially polarized beam can be generated, that is, the polarization direction in the beam cross section is radial.
Usually, radially polarized radiation is obtained by first polarizing light through some optical elements, or it can also be obtained directly from a laser.
The advantage of this method is that it can avoid depolarization losses and can be applied to solid-state bulk lasers.
Polarized laser radiation is required in many applications. For example:
Nonlinear frequency conversion where phase matching is satisfied only in one polarization direction
Two laser beams are required for polarization coupling (see polarization combining)
Processing of laser beams in polarization-dependent devices, such as interferometers, semiconductor optical amplifiers, and optical modulators
There are also some lasers (many fiber lasers) whose emitted light is not polarized. This does not mean that the laser outputs unpolarized light. The power of the two polarization components is equal at any time, and their amplitudes are completely irrelevant.
It's just that the polarization state is very unstable, for example due to temperature fluctuations, or changes between different directions. In order to obtain completely unpolarized light, some optical devices that eliminate polarization are needed.
Figure 1: Different polarization states of laser radiation, with several pulses propagating from left to right.
The degree of polarization of linearly polarized light is characterized by the polarization extinction ratio (PER), which is defined as the ratio of the power in the two polarization directions, in decibels. It can be obtained by measuring the power that changes with the direction after the light passes through the polarizer. The extinction ratio of the polarizer must be greater than the extinction ratio of the laser beam.
Definition: The direction of electric field vibration of the laser beam.
In most cases, the emitted light from a laser is polarized. Usually linearly polarized, that is, the electric field oscillates in a specific direction perpendicular to the propagation direction of the laser beam.
. Some lasers (for example, fiber lasers) do not produce linearly polarized light, but other stable polarization states, which can be converted into linearly polarized light using a combination of appropriate wave plates.
If it is broadband radiation and the polarization state is related to the wavelength, the above method cannot be used.
In some special cases, a radially polarized beam can be generated, that is, the polarization direction in the beam cross section is radial.
Usually, radially polarized radiation is obtained by first polarizing light through some optical elements, or it can also be obtained directly from a laser.
The advantage of this method is that it can avoid depolarization losses and can be applied to solid-state bulk lasers.
Polarized laser radiation is required in many applications. For example:
Nonlinear frequency conversion where phase matching is satisfied only in one polarization direction
Two laser beams are required for polarization coupling (see polarization combining)
Processing of laser beams in polarization-dependent devices, such as interferometers, semiconductor optical amplifiers, and optical modulators
There are also some lasers (many fiber lasers) whose emitted light is not polarized. This does not mean that the laser outputs unpolarized light. The power of the two polarization components is equal at any time, and their amplitudes are completely irrelevant.
It's just that the polarization state is very unstable, for example due to temperature fluctuations, or changes between different directions. In order to obtain completely unpolarized light, some optical devices that eliminate polarization are needed.
Figure 1: Different polarization states of laser radiation, with several pulses propagating from left to right.
The degree of polarization of linearly polarized light is characterized by the polarization extinction ratio (PER), which is defined as the ratio of the power in the two polarization directions, in decibels. It can be obtained by measuring the power that changes with the direction after the light passes through the polarizer. The extinction ratio of the polarizer must be greater than the extinction ratio of the laser beam.
