beam expander logic

[steve001]

This app with graphical presentation will be useful in the discussion
gausian beam rev 2.0.xls

Use I.E or another browser that has Macromedia Flash installed to see the graphical presentation

 

[justinjja]

This clipping concept is Interesting... it makes me wonder what kind of beam you would get with a 1m focal length collimating lens that is only 1mm wide. :undecided:

I would think you would get a 1mm beam with excelent divergence.
but it would require a huge laser lol,
and about 99% of the power would be lost

 

[Jubathoph]

I concur doctor. I have tried similar from a 75mm lens from binoculars. The lens had a 2ft. Focal length and I used it to colimate a 445. The result on the opposite wall was a perfect circle same diameter as the lens surrounded by huge blue ellipse.

 

[Bluefan]

Clipping the beam creates a top head profile, which diverges as a sinc profile, which has a higher divergence than a gaussian profile (which diverges to a gaussian) with the same beam diameter.
Simple fourier optics. This isn't geometrical optics Jubathoph, that's where you go wrong.
Cyparagon: the 1mm aperture will be the limiting factor, that determines the beam diameter and it creates a top head profiile.

 

[lazeristasUVISIR]

my cents :shhh:

The expander is used to expand a beam of the finished laser (like a DPSS green laser with a ~1mm beam). A simple design is a combination of a negative (divergent) lens and a positive (focusing) lens.

The collimation is mostly done for laser diodes with a very big divergent. Mostly a single aspehric lens is sufficient to get a good beam. Though collimated beam sizes are not large (<15 mm) as good optics for large NA & diameter are very expensive.

"If that is correct, would having a collimating lens designed to be say, 1 inch away from an axix module work in the same way? "

Yes. Some tricks should be done to correct a laser diode astigmatism.

A philosophical question:
What do you call a collimated laser beam? :na:

(The answer should give an insight about a relationship between a focal length, a beam diameter, and the farthest focusing distance within Gaussian optics.)

 

[steve001]

my cents :shhh:

The expander is used to expand a beam of the finished laser (like a DPSS green laser with a ~1mm beam). A simple design is a combination of a negative (divergent) lens and a positive (focusing) lens.

The collimation is mostly done for laser diodes with a very big divergent. Mostly a single aspehric lens is sufficient to get a good beam. Though collimated beam sizes are not large (<15 mm) as good optics for large NA & diameter are very expensive.




Yes. Some tricks should be done to correct a laser diode astigmatism.

A philosophical question:
What do you call a collimated laser beam? :na:

(The answer should give an insight about a relationship between a focal length, a beam diameter, and the farthest focusing distance within Gaussian optics.)

What is an infinite conjugate ?

 

[lazeristasUVISIR]

What is an infinite conjugate ?

In the geometrical optics design an object (or an image) is put at infinity then the image (or an object) are in the lens focal plain, and rays come (go way) parallel. Lens formula 1/f = 1/s1 + 1/s2 (with s2=infinity)

The laser optics does not follow geometrical optics as a beam diffraction should be considered especially for small beams.

 

[Jubathoph]

Bluefan interresting point on Fourier approach vs geometric approach. My exposure to the math behind this stuff is limited to the undergrad version as taugt to Mech Engineering undergrad. Sometimes we simplify things in the name of practicallity. What I can say however is that for my 445, uwhich is pretty far from Gaussian profile nomatter what lens you use, the longer FL lenses outperform even if there is some clipping. If you recall I tried out a 8mm FL lens a while back which had a NA of .5; in the review I could not comment on relative performance. Finally I got a 405 G1 and was very disappointed in the relative divergence especially because the two are so close in price once you get the Jrob mod for the G1. For DPSS or single mode lasers this may be very different.

As far as beam expanders go, you can build some awesome adjustable assemblies from Thorlabs or Newport. Lenses cost 35 each, tube and adjustable lens mount cost 100 for total cost Around 190 for a 2" assembly. I am speccing one right now for a 7 diode handheld.

 

[steve001]

As far as beam expanders go, you can build some awesome adjustable assemblies from Thorlabs or Newport. Lenses cost 35 each, tube and adjustable lens mount cost 100 for total cost Around 190 for a 2" assembly. I am speccing one right now for a 7 diode handheld.

Will you be using ThorLabs stackable optic tubes ?

 

[steve001]

In the geometrical optics design an object (or an image) is put at infinity then the image (or an object) are in the lens focal plain, and rays come (go way) parallel. Lens formula 1/f = 1/s1 + 1/s2 (with s2=infinity)

The laser optics does not follow geometrical optics as a beam diffraction should be considered especially for small beams.

Me no understand ? Did I answer the question correctly ?

 

[electron]

@ Cyparagon

Very nice pics, I have always loved what beam expanders can do; well done!