I'm waiting on a replacement. My first unit was damaged in shipment. I received an email this evening from ATI saying that the new unit is in final tests and will ship next week.
A selection of the correspondence between Analog Technologies (AT) and me (P):
P: The beam is NOT circular but elliptical (minor axis=2mm, major axis=6 mm).
It seems that there is a simple lens, and NO anamorphotic prisms in the module
.........Spatial-filtering of an extreme elliptical beam is almost impossible
.........it would be beneficial if one could remove all optics from the module, in order to use the raw beam.
AT: Yes, the beam is elliptical. It can be reshaped by the prism or a fiber into circular beam, but the power will be lower, possibly by a factor of 50%
...........Do we have to make them into circular beams by using fiber or prism?
...........Can the raw beam be used directly? If yes the case, our laser cost will be lower
........... the lens could be removed but TEC underneath the lens housing might be destroyed, since the TEC is fragile.
....: ......We can offer another solution - a fiber coupled laser.
............The beam will be pure single transverse mode (through a single mode fiber).
P: ......Single transverse mode" is not sufficient. We also need "single temporal mode" (that means: "single frequency", "only one longitudinal mode")
.......... As written..... a "polarization maintaining, single mode fiber" is needed.
AT: ........The PM (Polarization maintaining) fiber is not expensive. The cost is in the alignment. Such fibers have very small aperture, difficult to be aligned with. The coupling efficiency is low.
Paulos,
What focal length lens and pinhole diameter did you use in your spatial filter? Lenox Laser said they could try to make an elliptical pinhole when I talked to them a couple of years ago.
Thanks. It's nice to see a laser company actually talking to an individual. This seems to be the exception rather than the rule (compared to Coherent or Spectra-Physics, for example), especially if someone (such as myself) should be so foolish as to bring up the subject of "price."
One thing that I don't understand is why they say a prism would reduce output by ~50%. If it's just the elliptical beam that's causing the problem, why not pass the output through a pair of coated anamorphic prisms? At Thorlabs, they have pairs of AR coated prisms (650nm to 1050nm) for only $126.00. That's item number PS871-B at www.thorlabs.com
These are for unmounted prisms, though. They offer them already mounted for a price of $310.00, which seems like a better way to go. In my catalog, they show photographs of an elliptical beam from a Hitachi 635nm diode "before" and "after," and the results look very good. They say the average throughput is 95%.
The company Lenox Laser is very personable and I think they are great. I use their Blox and rods for optical mounts and rail set ups. Very nice because of the re-design benifits. If you ever played with and Erector set you will know what I mean. If you talk to them tell them I said hi, John Pecora. They know me there.
If the beam is eliptical, couldn't you pass the beam through a glass rod of proper diameter and distance from the exit of the laser to "stretch" the beam in the direction wanted thus causing and output that is symetrical? I have seen this technique used for Benton holorams to create a "slit" of light and thus you do not have to waste too much beam as in using a masked slit. Just a thought.
Anamorphic prisms are the way to go. But if you are trying to save a couple of bucks you can use a pair of cylindrical lenses. Simply choose two positive lenses with the ratio of focal lengths equal to the ratio of the beam width to height. Mine work well. I got mine from Edmund.
I agree with Colin, that "Anamorphic prisms are the way to go".
Casix (www.casix.com) sells a pair of them for $35.00 (Part No: ANP0001).
John (Klayer),
I do not think that an elliptical pinhole is the best solution.
The flexibility of the setup would be affected negatively. My opinion is that one should keep the setup as simple and flexible as possible.
John (Pecora),
the glass rod would reshape, but NOT FILTER the beam.
AND a recent e-mail from Analog Technologies:
"....We are considering:
1. We will make a new laser with elliptical beam, but it will allow to have the lens adjusted and removed by the users.
2. We will use a PM fiber after the laser beam. The output will have possibly 10mW, circular Gaussian beam, TM00 mode.
The former will increase the cost by about $80, the latter by $300
Can you tell us is this ok? ...."
Have you tried simply using the larger axis as the beam dia in a pin hole calculation? I have heard reports this actually works very well with only a light loss in power.
I would prefer a internal anamorphic prism than any fibers but that is simply my preference.
Note that the throughput is not given for the Casix prisms. They use a single layer of MgF2 for the AR coatings.
The Thorlabs prisms use high-performance multilayer coatings to achieve ~95% throughput. If it were me, I wouldn't try to save a few dollars by using inferior coatings.
As for a 10mW fiber-coupled laser, it would be far cheaper and easier to use a surplus HeNe (assuming a wavelength ~635nm is needed).