The " Kama Suthra " guide to 445nm LD positioning
On the learning curve path for optics, I have come to the understanding regarding the Fast and Slow Axis nature of the 445nm LD. I was puzzled because in setting up my test bed-“ Copper is Proper “….the only way I was able to get the prisms to correct the astigmatic beam of the 445 was to align the stripe …horizontally to the prism pair…or so I thought !!!!!!!
Let me explain….when one looks at the colliminated ( FL @ 4mm ) beam of the 445 at 12 Meter….I saw a rectangular output of 14mm tall by 43mm wide. OK….so I logically assume that the Fast Axis, the axis which has more divergence was represented by the 43mm wide portion of the beam profile. And conversely…the Slow Axis was therefore the 14mm wide portion of the beam. When I placed the anamorphic prism pair ( Per Zoof’s template ) in front of the LD output…the beam was corrected. At 12Meter…the resultant beam profile was a square geometry of 14mm. Perfect. Per Pseudonomen’s 137 Divergence calculator….that works out to 1.0 mRad. So…contrary to all I have read…and patient and teaching PM’s from Dave, p!t8ull, and RedlumX ….I said NO…the Fast Axis must strike the prisms…HORIZONTALLY…a logical conclusion based on what works and what I observed.
Well…not so in the “ Alice in Wonderland “ of laser optics !!! It turns out that this beam is a “ Shape Shifter” The beam…just after it leaves the LD IS a ellipse…long axis going up and down….VERTICAL…At this point…the LD IS orientated so the Slow Axis is going up and down….and the Fast Axis is going from side to side. So… with NO prisms…and with a Collimination lens in the beam path…
At 10cm from the LD output....the beam profile looks like " l "
At75cm from the LD output….the beam profile looks like " o "
At 300cm from the LD output...the beam profile looks like " -- "
So what does ALL this mean ?? Simply this….For a Axis module with a 445nm LD pressed in or a bare 445nm diode inserted into a Brass mount ( like the one from LSP/Dave with the LD secured in its holder)…and with the Collimination lens attached….the beam will appear to be a rectangle…..at 12 Meters…this bar will typically be 14mm x 43mm. The correct radial position for the Axis module or bare diode is when the 43mm dimension of the rectangle projection is horizontal. This position is where the prism set corrects the Fast Axis. This position delivers a square geometry…at 12 Meters. What happens at 20 Meters…not as square….but still OK.
A variable for ALL Graphic Laser Show venues is…How far from the projector will the beam strike the termination plane ??? Big Variable !!!!!....but for my guess…..I would speculate that a range from 5 to 30 Meters would be normal. This is just my SWAG !!....Unless you are at Disney or Stone Mountain !!! For my needs…12 Meters is typically the max. The first prism in the prism set can be adjusted to deliver the optimal geometry for your needs. For all you behind me on the learning curve ( If any )….this blah, blah explaination is intended.
Most of this info has been presented before....although NOT in the unique way I have presented my thoughts ( Read mental meanderings ). Thanks for reading and hope this helps anyone else !!!!
Research presented from " Terrawatt Labs "
CDBEAM 2/2011
Last edited by CDBEAM; 02-03-2011 at 12:07.
Reason: A small tweak
Beam Axiom #1 ~The Quantum well is DEEP ! Photons for ALL !!
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Beam Axiom #2 ~Yes...As a matter of fact...I DO wear tinfoil on my head !!
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Beam Axiom #3 ~Whe'n dout...Po ah Donk awn et !!
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Beam Axiom #4 ~A Chicken in every Pot, and a Laser Lumia in every Livingroom !!
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Beam Axiom #5 ~"Abstract Photonic Expressionism"....is "Abstractonimical" !!
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Beam Axiom #6 ~ "A Posse ad Essea" ~ From being possible to being actual ...is the beam target !