Lenses
2024-1-3
Definition:
It is a transparent optical device that affects the wavefront curvature of light.
Figure 1: Focus and defocus of a lens.
Optical lenses contain a transparent medium through which light enters from one side and exits from the other. The function of a lens is to change the wavefront curvature of light, that is, to focus or defocus the light. For example:
A collimated beam with an approximately planar wavefront is transformed into a curved wavefront, and the beam is focused to a focal point. At this time, the lens acts as a focusing lens, as shown in Figure 1(a).
The same lens as above can also convert a divergent beam into a collimated beam, in which case the lens acts as a collimating lens. In Figure 1(a), it is assumed that the light beam is incident from the right side.
A lens with a concave surface can turn a collimated or convergent beam into a divergent beam, as shown in Figure 1(b). This lens can also be used to convert an otherwise divergent beam into a collimated beam.
Although the change in beam radius is often thought of as the lens equation, the fundamental equation for a lens is actually the change in wavefront curvature, because changes in wavefront curvature cause changes in the beam radius of light after it passes through the lens. (The direction of energy propagation is usually perpendicular to the direction of the wave front) as shown in Figure 2.
Figure 2: Wavefront curvature change of focusing lens. Red and blue represent the strength and positive and negative of the electric field at a certain moment. The assumed wavelength is much larger than the actual wavelength.
It is a transparent optical device that affects the wavefront curvature of light.
Figure 1: Focus and defocus of a lens.
Optical lenses contain a transparent medium through which light enters from one side and exits from the other. The function of a lens is to change the wavefront curvature of light, that is, to focus or defocus the light. For example:
A collimated beam with an approximately planar wavefront is transformed into a curved wavefront, and the beam is focused to a focal point. At this time, the lens acts as a focusing lens, as shown in Figure 1(a).
The same lens as above can also convert a divergent beam into a collimated beam, in which case the lens acts as a collimating lens. In Figure 1(a), it is assumed that the light beam is incident from the right side.
A lens with a concave surface can turn a collimated or convergent beam into a divergent beam, as shown in Figure 1(b). This lens can also be used to convert an otherwise divergent beam into a collimated beam.
Although the change in beam radius is often thought of as the lens equation, the fundamental equation for a lens is actually the change in wavefront curvature, because changes in wavefront curvature cause changes in the beam radius of light after it passes through the lens. (The direction of energy propagation is usually perpendicular to the direction of the wave front) as shown in Figure 2.
Figure 2: Wavefront curvature change of focusing lens. Red and blue represent the strength and positive and negative of the electric field at a certain moment. The assumed wavelength is much larger than the actual wavelength.
