Fiber launching for galvo scanning

[masterpj]

Hi Everyone,

It's been quite a while.
Lately i've been experimenting with fibers again for things other then using it with my spectrometer.

I followed a guide from les laser lab on youtube to use a visual fault locator combined with a fiber i had laying around (800um) to launch the VFL into a fiber collimator I once bought.. including a fiber collimator with X Y adjust.
I did not commit yet to coupling my own laser where I know the quality of the beam of in the fiber (potentially the cause of issue)

What I found was a quite large spot size with an "alright divergence", using a telescope in a sort of janky measure (a Linos Beam-Expander 2-8X).. could give me a small beam and naturally a horrendously large starting beam so that was out of the question).

I was wondering what kind of fiber diameters are used for those external laser heads that go to the galvos and what I could have been doing wrong.
Is the source of a cheap visual fault locator just so bad that the resulting spot is quite large or was I using too large of a fiber?

[atomd]

Two important things:

• fault detector lunches beam into both core and cladding. To make sure you're only seeing core beam at the output, make 3 turns with the fiber before using it.
• 800um fiber is hugely multimode even in the IR, not even talking about vis. If you don't want to worsen the beam quality, you should match M^2 of fiber to your source. For single mode sources (very low power laser diodes and DPSS laser) you need fiber with single digit um core. For high power laser diode, standard "single mode" fiber with 50um core should be fine

To coupled laser diodes into fiber without loosing too much "diameter" you need to circularize the beam with C-lenses and shape it to the proper cone. And as always remember that coupling is lossy and if you'll try to pump single mode visible fiber expect to lose around 20-40% even on perfect source (4 glass-air transitions on collimators, two glass-air transitions on fiber ends + mismatch).

[VDX]

... from broken CW-fiber-lasers I've got a bunch of IR-laserdiodes with attached 105µm fibers ... the stronger IR-pump-diodes in multi-kW-Fiberlasers with powers of some hundred Watts use 200µm fibers.

If you need some pieces for testing, I could mail you pieces of the 105µm fibers ore something kike 1 meter long chunks of "common" glass fibers with diameters between 200-600µm ...

[masterpj]

... from broken CW-fiber-lasers I've got a bunch of IR-laserdiodes with attached 105µm fibers ... the stronger IR-pump-diodes in multi-kW-Fiberlasers with powers of some hundred Watts use 200µm fibers.

If you need some pieces for testing, I could mail you pieces of the 105µm fibers ore something kike 1 meter long chunks of "common" glass fibers with diameters between 200-600µm ...

Yes please!
Is there a reason to go glass over quartz? From what im seeing it's only the sturdyness that's the difference with quartz being more expensive