laserbeams and microscopes

[abacus49]

My son has a question for his science class and I am not knowledgable about the subject so I am looking for some help.

 

Can a microscope make the beam from a laser more powerful?

[Cap'n Refsmmat]

A lens can focus the beam onto a smaller point, but it can't make it more powerful - you'd have to somehow add more energy to it to do that.

[swansont]

A lens can focus the beam onto a smaller point, but it can't make it more powerful - you'd have to somehow add more energy to it to do that.

 

Well, you increase the intensity, since you have the same power in a smaller area, and you could interpret that as making it more powerful. The region getting the light has seen an increase in power.

[Sisyphus]

It would focus the beam (and therefore make it more intense but in a smaller area) right by the eyepiece, but it would spread out after that. It would no longer be a "beam," just like a regular flashlight the color of the laser.

[swansont]

It would focus the beam (and therefore make it more intense but in a smaller area) right by the eyepiece, but it would spread out after that. It would no longer be a "beam," just like a regular flashlight the color of the laser.

 

That's true of a single lens. With a microscope/telescope setup, i.e. the lenses separated by the sum of their focal lengths, you'd change beam sizes but the beam would have its normal divergence. A collimated beam would not diverge, and the size will change by the ratio of the focal lengths. We do this in the lab — collimate a beam coming out of a fiber, and then expand it to fill the window of the vacuum chamber (about 37mm), and also take a free-space beam and make it smaller to fit into a small aperture on an optoelectrical component. In both cases the beams continue to propagate with very little divergence (or convergence).