Laser beams
2023-12-17
Definition:
A beam of light traveling in one direction.
In most cases, the light radiated by a laser is a laser beam. That is, the radiation beam propagates in a specific direction, and the optical power is concentrated on a small area of several square millimeters.
The laser beam is very close to the Gaussian beam. The cross-section of the Gaussian beam intensity can be described by the Gaussian equation, and its width will change in the propagation direction. The size of a beam changes very little when it is very wide, whereas the size of a tightly focused beam changes very quickly.
Figure 1: Electric field distribution near the focus of a Gaussian beam. Here the beam radius is slightly larger than the wavelength and the beam divergence angle is large.
Typically laser beams have high spatial coherence and therefore high beam quality. Therefore, the laser beam has good focusing performance and can form a collimated beam with a very low beam divergence angle.
The optical bandwidth of a laser beam is usually small and therefore the temporal coherence is high. One disadvantage of high coherence is the tendency to form mottled patterns.
The power of a laser beam is almost constant when propagating in transparent media, but will attenuate rapidly in absorbing or scattering media. Non-isotropic media (where the refractive index of the medium changes locally) can also distort the shape of the laser beam.
This may be caused by thermal effects caused by thermal lenses in the gain medium.
Some lasers operate in continuous mode, but the laser beam consists of a series of pulses, typically millions or even billions of pulses per second (see Pulse Repetition Rate).
Most laser beams are linearly polarized, that is, the electric field oscillates in a direction perpendicular to the direction of propagation. The polarization state of the laser radiated by some lasers is uncertain.
A sufficiently powerful visible laser beam is visible when traveling through the air. Because the light beam propagates in the air and is scattered by dust particles and density fluctuations, the scattered light reaches the eye, so the light beam is visible.
When a laser beam is directed at a diffusely scattering object, such as a white screen, a brighter point is seen on the screen because most of the light power is scattered to this one point.
A beam of light traveling in one direction.
In most cases, the light radiated by a laser is a laser beam. That is, the radiation beam propagates in a specific direction, and the optical power is concentrated on a small area of several square millimeters.
The laser beam is very close to the Gaussian beam. The cross-section of the Gaussian beam intensity can be described by the Gaussian equation, and its width will change in the propagation direction. The size of a beam changes very little when it is very wide, whereas the size of a tightly focused beam changes very quickly.
Figure 1: Electric field distribution near the focus of a Gaussian beam. Here the beam radius is slightly larger than the wavelength and the beam divergence angle is large.
Typically laser beams have high spatial coherence and therefore high beam quality. Therefore, the laser beam has good focusing performance and can form a collimated beam with a very low beam divergence angle.
The optical bandwidth of a laser beam is usually small and therefore the temporal coherence is high. One disadvantage of high coherence is the tendency to form mottled patterns.
The power of a laser beam is almost constant when propagating in transparent media, but will attenuate rapidly in absorbing or scattering media. Non-isotropic media (where the refractive index of the medium changes locally) can also distort the shape of the laser beam.
This may be caused by thermal effects caused by thermal lenses in the gain medium.
Some lasers operate in continuous mode, but the laser beam consists of a series of pulses, typically millions or even billions of pulses per second (see Pulse Repetition Rate).
Most laser beams are linearly polarized, that is, the electric field oscillates in a direction perpendicular to the direction of propagation. The polarization state of the laser radiated by some lasers is uncertain.
A sufficiently powerful visible laser beam is visible when traveling through the air. Because the light beam propagates in the air and is scattered by dust particles and density fluctuations, the scattered light reaches the eye, so the light beam is visible.
When a laser beam is directed at a diffusely scattering object, such as a white screen, a brighter point is seen on the screen because most of the light power is scattered to this one point.
