Mitsubishi ML520G71...Red Holy Grail or Flashlight Fail ??

[planters]

Yes. I think that has been the source of my confusion. Its the terminology that got between us. Is anyone knife edging these (in the classical sense)? Or is everyone stacking them?

[CDBEAM]

I'm gonna jump in here....( Wada suprise ) !! These diodes are simular to the 445's...and I was just experimenting. The farfield (uncorrected )beam MUST be a horizontal bar. Only when the LD is in this orientation can the cylinderical lenses operate properly and expand the Slow Axis...of course this assumes that the C-lenses are in the normal orientation.
So....with the LD in this correct orientation, when one closely examines the beam geometry as the beam propagates from the colli lens outward....the initial geometry is a small VERTICAL bar, The range to which I am refering to is between 0 mm to 45mm. As the beam propagates outward, the bar changes from a vertical bar to a point geometry. I assume this is the point where the SA = FA. Past the distance of 45 mm....the geometry of the beam evolves to a horizontal bar.

The range of 0 to 45 mm is where we will be positioning our knife edge. SO....the knife edge must be in the standard orientation....NOT a vertical stackage. At the plane where the knife edge will be, the beam geometry looks to be a vertical bar....about 1mm wide by 2mm tall...so a standard knife edge will provide the most compact combination of two beams. As in ll not = I think I am correct on this !!! To those who have experimented with the G71....Let me know !!!!!!!!!!

Note: We have now entered the next phase of this project....being beam combining for a dual or quad set up !!! More fun !!!

Beam

[taggalucci]

Sounds right to me CDBeam

What I find interesting about the || knife-edged nearfield is how (almost) irrelevant it is in the far field i.e. whilst the 2 beams start off being very side by side in the near field, by the far field they are practically superimposed on each other. If knife-edged perfectly parallel to each other at 1mm spacing, in theory the combined far field would be literally 1mm wider than a single beam (though this difference may be lessened by the cylinder lenses (if I'm thinking correctly).

I'm still confused by the terms slow and fast axis. I always think of the most divergent as being the fast axis, though I believe this is different to what you've said above. All I know is that it is the most divergent axis we correct by expanding to reduce divergence. And though this appears initially to be counter productive (in the near field), it is most productive in the far field, with a smaller beam achieved.

[CDBEAM]

Tag....Perhaps this is so because each individual beam diverges into the adjacent beam. After all...the beams start their tandem travel....in an almost contiguous state !! So why would not appear that in the farfield they have done the " Vulcan Mind Melt " hahaha....and look to be a single geometry !!! All this thinking has caused the need for some cartoon relief !!! For my friends in Merry ole England !!!! BEAM

Note:..As far as Fast Axis vs Slow Axis.....the nomenclature is counter to common sense.....We are expanding the Slow Axis.....Not reducing the Fast Axis....took me months to get my head around this !!!

[planters]

That is what I had thought. I am doing some bench testing to simulate the optical "events" during knife edging ( I do not yet have the components others have for actual experiments with these diodes or the facility with a straight forward optical design program). It looks as if two beams offset by the knife edge by 0.5mm need to be set to DIVERGE by an amount roughly equal to their off axis position to cancel and co-align in the far field. So, beams knife edged 0.5mm apart (and that will eventually grow to 4mm) will require the second beam to be 1.0mm offset for a 5mm combined near field spread. Now this is very rough, but the requirement to diverge seems pretty clear. This might be the first time this property has significance because of the unusual characteristics of these diodes with their very narrow slow axis and their very large divergence. If this holds, the achievable power density on the scanner might be higher than first thought.

[taggalucci]

Because of the superimposition brought about by each beam diverging into its neighbour, the potential power density is limited to how small one can get the most diverging axis in the nearfield combined with the magnification power of the correction optics which is a product of the diode's aspect ratio.

Theoretically, the nearfield dimensions (quoted as 1mm) of the divergent axis could be smaller than half the dimensions (quoted as 2mm) of the least divergent, provided the collimation lens can get close enough to the diode face and if such optics were possible. This could result in a knife-edging offset measured in um and mean that the expanded beam would be smaller in the nearfield.

[planters]

The fast axis achieves a larger dimension than the slow when they both simultaneously encounter the radially symmetrical collimator. It has expanded more, so just like the effect of the cylinders down stream, which expand the beam and slow the divergence, the beam then diverges less in that axis.

[planters]

Because of the superimposition brought about by each beam diverging into its neighbour, the potential power density is limited to how small one can get the most diverging axis in the nearfield combined with the magnification power of the correction optics which is a product of the diode's aspect ratio.

As I understand you , I would agree. However, what I am speculating is that a simple "four x 4mm beams means 16mm"is not a given. I think the limit is set by the tightness of the knife. Obviously, the current size of the collimator is arbitrary. If reduced in a thought experiment to essentially adjacent to the diode the extremely small beam dimensions would allow far tighter knife edging and some distance down stream the 4mm beams would be only microns offset and the same correction optics are not going to do some crazy shuffle and blow the beam up to 16mm. Right?

[CDBEAM]

YIKES !!! I gotta digest those above statements !!! Could be awhile !!!! HAHA BEAM.....AND after my thinkin....I will likely resemble the pic below !!!

God Bless you R.Crumb !!

Note: Seriously....thanx for the above points......THIS is a very interesting dialogue !!!

[planters]

There is no such thing as a free lunch. ENTROPY RULES!

However, consider for a moment that these diode's emitters are releasing energy at aprox 1MW/cm. Really! And the energy density on our scanners is more like 10W/cm! Aside from the losses due to optical aberrations, we are in no way cheating any physical laws if we reduce the dilution effect of Knife edging. In commercial systems, arrays in diode bars deliver KW/cm because their emitters are more closely spaced not because they are driven harder. Some time ago, kiyoukan was on to something when he considered a positive first cylinder, to allow tighter knife edging at the first focus. Unstable, tricky and complicated? Maybe so, but this may be a significant target to allow more power on smaller and faster scanners.