Trajectory of a laser beam

I think your thoughts are correct. But now your using theory as to how small a linear ray of light is, you could argue that down to the atom. What advantage do you get by tracking individual rays against considering one 2 micron ray?

Well, for instance, if the 2 micron ray impignes over a surface patterned with a 1 micron reflective-nonreflective pattern, the "part" of the ray that goes over the reflective part will reflect, and the other part will not...is this correct? In principle, should be, but somehow, I do not feel so sure. Might some kind of interference occur in this latter case among the individual linear beams that I would be considering? But even in this case, the model of "individual buch of linear beams" to characterize the 2 micron beam would still be useful (and correct, provided interactions between those are allowed).

Thanks again for your interest.

Me thinks someone should mention that it would depend the media your beam passes through; as well as other outside influences such as gravity. Does anyone remember 'red shift'.

Dear Guest,

Your light beam will diverge - and quickly too - if your exit aperture is effectively 2 microns. Modeling the beam as a bundle of parallel rays will not accurately represent the beam configuration. Modeling the beam as a cone is more appropriate for simple geometric ray-tracing calculations.

If you wish to include the effects of interference on a rough surface, your problem is vastly more complicated and may need to be computed stochastically or modeled using wavelets.

To calculate the divergence of the cone, assume your laser's (or your laser's optics') exit aperture as a circular, 2-micron hole, and the laser's wavelength as 632.8 nm (helium-neon wavelength. Yours may be different). The divergence of the beam, in radians, is expressed by the following relation:

where θ_R is the beam divergence, in radians (R stands for 'Rayleigh' btw),

λ is the laser's wavelength, in meters (632.8 x 10^-9 m),

and

d is the exit aperture diameter, in meters (2 x 10^-6 m).

Using the above values, we get θ_R = sin^-1(1.22 × 632.8e-09 / 2 e-06) radians,

or

θ_R = 0.396 rad,

or

θ_R = 22.706 degrees!

Yes, the configuration of your beam is most definitely a cone.

Hope this helps.

-e

Are you talking about a laser diode made of many diode lasers (note the difference) in an array? If so, you have to remember that the light from such a device is not linear and is not coherent. At the very least, you need a lot of optics to get the beam linear (as we expect lasers to be) and more to get in coherent.

I think you are going to have to consider the wave nature of light. When it strikes a surface, there will be interference effects that cannot be modeled with a ray tracing model.

I all you want is a trajectory why cant you use a light sensitive product .. they once used film to detect radiation. the rays would leave marks on the unexposed plate. If a chemical sensitive to the laser were applied to a plate or paper and stationed at progressively further distances 2,4,8,16 ..... then it would be fairly easy to see and calculate the trajectory and the tendency toward scattering. Lil lowbrow i know but just a thought.

I'll lowbrow you one better... Take up smoking. It'll show you exactly what's happening with the beam!

OOh ooh.

Hey ma! I'm smoking for science!

Finally a good reason.

cr3

"Honest, mom! Tobacco smoke doesn't work as well!"

Mollify her by promising to smoke a hookah.

If it's not a theoretical exercise, but only for practical trace, use some form of haze or smoke, or run it though some colloid like watered milk or something

Well, if you're using a true laser, the waves are pretty much parallel. At a width of two microns, you still should be able to see a spot on a target. If you need to know what the expansion rate of the beam is, contact the laser maker. That's one of the most fundamental parameters by which the laser is sold.

Also, when the light is coherent (All waves in phase with each other), it would seem you can think of it as a single beam - not a bundle.