Gaussian beam and focusing versus geometrical optics

This is why there is a discrepancy between the behavior of a Gaussian beam and a point source in this scenario. In summary, a Gaussian beam passing through a lens will have two waists, one at the front focus and another at the back focus, in contrast to a point source which only has one focus. This is due to the wave optics nature of a Gaussian beam and the limitations of geometrical optics.
  • #1
fisico30
374
0
Hello Forum,

if we take a Gaussian beam whose waist occurs at the front focus of a positive lens, we will see that the Gaussian beam will have another waist at the back focus of the lens...

That seems to be in contradiction with what happens in geometrical optics: if we place a point source (diverging beam) at the front focus of a positive lens the beam will be perfectly collimated after the lens...there is no focusing whatsoever. But using a Gaussian beam we have a focusing at the back focal point...

Is my observation correct?


Thanks
fisico30
 
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  • #2
Yes, your observation is correct. When a Gaussian beam passes through a lens, it will create a focus at both the front and back focal points. This is a result of the wave optics nature of a Gaussian beam, where it can be described as a superposition of plane waves. In geometrical optics, the rays of light can only have one focus when they pass through a lens.
 

1. What is the difference between Gaussian beam and geometrical optics?

Gaussian beam and geometrical optics are two different models used to describe the behavior of light. Gaussian beam describes the propagation of light as a wave, while geometrical optics describes it as a ray. In Gaussian beam, the light intensity is distributed in a bell-shaped curve, while in geometrical optics, the light is considered to travel in a straight line.

2. How does Gaussian beam behave when it is focused compared to geometrical optics?

When a Gaussian beam is focused, it maintains its beam width and intensity distribution, while the beam waist (the point of minimum width) shifts to a smaller size. On the other hand, in geometrical optics, when light is focused, the rays converge at a single point. This means that the beam width and intensity distribution change as the light is focused.

3. What is the importance of Gaussian beam and focusing in optical systems?

Gaussian beam and focusing are important in optical systems because they allow us to accurately predict the behavior of light. The Gaussian beam model is especially useful in describing the propagation of laser beams, which are commonly used in various scientific and technological applications. Focusing, on the other hand, is essential for directing and concentrating light in specific areas, such as in microscopy and laser cutting.

4. Can Gaussian beam and geometrical optics be used interchangeably?

No, Gaussian beam and geometrical optics cannot be used interchangeably as they represent different models of light behavior. While they may produce similar results in some cases, each model has its own limitations and is applicable in different scenarios. It is important to use the appropriate model depending on the specific characteristics of the light and the optical system being studied.

5. How does the size of a Gaussian beam change as it propagates compared to geometrical optics?

In Gaussian beam, the beam width increases as it propagates, while in geometrical optics, the beam width remains constant. This is because in Gaussian beam, the beam width is determined by the beam waist and the distance from the waist, while in geometrical optics, the beam width is determined by the aperture of the optical system. This means that in Gaussian beam, the beam can spread out over a larger area, while in geometrical optics, the beam remains concentrated.

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