What Is Beam Calculation?
In general, the fundamental mode radiation field emitted by a laser resonator, the amplitude distribution of its cross-section follows a Gaussian function, so it is called a Gaussian beam.
- In general, the fundamental mode radiation field emitted by a laser cavity, the amplitude distribution of its cross section follows
- The query about the spot size actually asks the beam waist diameter or beam waist radius. The beam waist refers to the place where Gaussian light is transmitted in absolute parallel. Radius refers to the cross-section of Gaussian light, where the maximum amplitude is taken as the origin, and the amplitude drops to 0.36788 times the origin, which is 1 / e times. Because Gaussian light is symmetrical about the origin, 1 / e A circle is formed, and the radius of the circle is the radius of the cross-section of the light spot; if the cross-section at the beam waist is taken into consideration, the radius at this time is the beam waist radius. Along the light spot, the envelope of the radius of each place is a hyperboloid, which has an asymptote. The transmission characteristics of Gaussian beams are diffused at a specific angle along the propagation direction at a distance. This angle is the far-field divergence angle of the beam, which is the angle between a pair of asymptotes. It is proportional to the wavelength and its beam waist radius. It is inversely proportional. Therefore, the smaller the beam waist radius, the faster the light spot will diverge; the larger the beam waist radius, the slower the light spot will diverge.
- We can see with the photosensitive film, at close range,
- Amplitude distribution characteristics
- From the expression of the Gaussian beam, we can get:
- On the z-section, its amplitude changes according to the Gaussian function, as shown in the figure. The distance from the optical axis when the amplitude decreases to 1 / e of the maximum value in the beam cross section
- The theoretical basis for our calculation of the collimation system is the formula for the transmission characteristics of Gaussian beams. For a lens with a linearity much larger than the input spot, the input light can be regarded as a point light source, and its far-field divergence angle is the point light source. "Edge line" included angle; so we can simply use geometric optics to calculate the spot size and maximum working distance of the collimation system according to the specific parameters of the lens.
- From the Gaussian function, we can calculate the loss of light energy when the clear aperture is large. It is not that when the diameter of the clear region is equal to or slightly larger than the spot diameter, the light energy can pass completely. In fact, the loss at this time Up to 0.6dB. A simple estimate is to make the diameter of the clear light twice or more than the spot size. [2]