Post by g***@gmail.comPost by Phil HobbsPost by g***@gmail.comThis is not much of a question, just local wisdom.
I use Thor labs lens tubes to couple a diode laser onto
a diffraction grating, single bounce, Littrow?
I've been having problems with getting the coupling,
"just right". I'm setting a lens position with a thread,
as I'm adjusting the lens position the "spot"
(of lasing) is moving around, (In the phase space of the
grating angle) Some tubes are better
some worse... I've been trying to figure it out.
Anyway a single layer of teflon tape..
(on the thread of the lens tube)
seems to have made the whole operation much better.
I'm adding teflon to every lens from now on.
Should I send an email to Thor labs?
George H.
Interesting. It's reasonably well documented by the Yoders and
Vukobratoviches und so weiter that you don't get good lens centring with
just a threaded clamp ring, even with a fixed ring on the other side.
Yoder recommends a loose thread and a plain section machined to a
precision running fit inside the outer tube.
Yoders and Vukobrat... ? This?
https://www.amazon.com/Opto-Mechanical-Systems-Design-Fourth-Two/dp/1439839778/ref=dp_ob_title_bk
I have no good texts on holding optics. (Is there something cheaper?)
I have Yoder's second and third editions of that book, which seems to be
continuing to grow--the third ed. is a single volume about the size of
AoE.
Yoder and Vukobratovich are sort of the classical go-to guys when you
want someone to write a book chapter, like Smith on lenses or Breault on
stray light and black surfaces. So there's a bunch of their stuff in
places like the OSA Handbook of Optics, or volume 4 of Accetta &
Shumaker's SPIE IR and EO systems handbook which you can get free on
dtic.mil). It takes a bit of google-fu to find it, but if you search
on the quoted full title of the volume and specify
site:http://www.dtic.mil, it comes right up:
<http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA364024&Location=U2&doc=GetTRDoc.pdf>
Smith & Chetwynd's "Foundations of Ultraprecision Mechanism Design" is a
good read, as are Timoshenko's "Theory of Plates and Shells" and Anees
Ahmad's CRC book that I can't find at the moment. You're already a fan
of R. V. Jones's "Instruments and Experiences", so I don't need to tell
you about that one.
Post by g***@gmail.comI mostly learn by doing it wrong.
You and all the rest of us besides. ;)
Post by g***@gmail.com(I can tell you how not to hold an interferometer beam splitter, I'm
not sure what the right way is.)
Post by Phil HobbsI imagine that the problem you describe might have to do with some
threads being looser than others or having a slightly wrong pitch, so
that the axis of the tube describes a cone as you screw it in and out.
Yeah I don't know. One of these lens tubes,
https://www.thorlabs.com/thorproduct.cfm?partnumber=LT230P-B
I was thinking that the lens or the laser diode might not be centered...
but mucking about changing lenses and diodes did nothing much.
Post by Phil HobbsIf the Teflon tape doesn't screw up the dimensional stability of the
assembly, that sounds like a great trick.
I've only done four lasers this way, but so far it's awesome...
(well compared to before, like running without 5 lb weights on your
feet. :^)
I sawed off the lens tube tool and put it on a stick so I could adjust the lens
w/o having to remove the grating. Here's some pic's
https://www.dropbox.com/sh/6bacov4nceh0md6/AADqlAZk6NhhBJGOOf87EHSZa?dl=0
So I'm putting a force on the lens as well as a rotation, maybe that's
enough to steer the beams a bit?
Originally I'd add some tape to those lenses that were a bit loose....
more friction. The friction in these tubes is made by an O-ring.
Post by Phil HobbsI've used the Thor lens tubes also, but I usually use the 30-mm
Microbench or Thor cage-and-rod systems for tweaking stuff. One tip is
to ditch the Thor rods and use 6 mm precision centreless-ground rod from
McMaster-Carr or Microbench. The Thor ones appear convenient, since
they have tapped holes on the ends so you can join them together with a
set screw, but the resulting rod is so floppy as to be virtually
useless. Precision rod is easy to cut by using a grinder to notch it,
gently bending it back and forth till it breaks, then cleaning up the ends.
Huh, and the bending doesn't warp the good part of the rod?
I guess I'd grind the whole diameter of the rod. Angle grinder and cut-off wheel.
I usually notch it down all round by about half the radius. There's no
residual bend in the rest of it.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net