Virtual Point Source of Laser Beam?

[Ed Wesly]

"The usual trick is to call the laser manufacturer and ask for the waist location."

Shall do! Thanks!

[Laserman532]

The usual trick is to call the laser manufacturer and ask for the waist location. When I was a FSE for a pulsed laser company, this was a common question. It may not be on the common data sheet, but the engineers WILL know it. If not, they can get it. For an application like holography, most sales engineers will get you the data, even on a used laser.


Steve

if it is a cavity with a flat HR, couldn't one determine the beam waste location by knowing the radius of curvature of the OC mirror if cavity length is known?

[mixedgas]

if it is a cavity with a flat HR, couldn't one determine the beam waste location by knowing the radius of curvature of the OC mirror if cavity length is known?

Yes, You can do that by hand.

Also, the PSST simulator I mentioned does just that, and a lot more. It draws the beam diameter vs distance graph for inside the cavity as well. Fun to play with!

Steve

[frostypaw]

The attached paper is helpful for those who wish to try spatial filtering for RGB Projection as well.

Steve

That perked my ears up, working out how to calculate the size of the waist i.e. w(0) is fascinating but then i'll try to buy a proper aperture. Shall try and get my head around it. This forum really is an educational resource, many thanks

[Eidetic]

Spatial filtering is used to remove the diffraction effects that travel along with laser beams, mostly caused by particles on optics upstream. The size of the pinhole used should be as large as possible to clean the beam adequately. Using equations to calculate the beam waist and choosing a pinhole based on that will likely get you a much smaller pinhole than is really needed. That can result in diffracted rings around the beam, and makes it very difficult to keep the beam going perfectly through the pinhole. Also, a laser that's not a symmetrical gaussian shape at the source needs a pinhole large enough to pass the long axis without the effects just mentioned, while small enough to adequately filter the light in the short axis direction. Holographers have historically struggled with spatial filtering, but using as large a pinhole as possible makes the technique easy and convenient.

[frostypaw]

You're very right after doing the maths - but the range in waist sizes was interesting too which must affect things upstream as well and hence the amount of beam unavoidably lost doing it with the combined beam.

I shall continue to gaze longingly at atenlaser's absolutely beautiful beam profile with that molybdenum aperture.