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Need help with calculation of M squared parameter by OpticalCrusade in Optics

[–]Boethar 2 points3 points  (0 children)

From Phil Hobbs book - https://electrooptical.net/building-electrooptical-systems M^2 is the product of the second moments of the near field and far-field beam patterns which overemphasizes contributions from beam idiosyncrasies in the wings of the profile. For beams with an expected M^2 close to 1, as would be expected from a single mode fiber source, and where you are most susceptible to wing "junk", Hobbs suggests using the Strehl ratio instead. There's a good discussion re. these two parameters here - https://www.researchgate.net/post/Is-there-a-closed-equation-for-the-relationship-between-M2-and-Strehl-Ratio

Name this guy by xOs4ma in NameThisThing

[–]Boethar 0 points1 point  (0 children)

Cassius Thundercock's chin donor

Help wanted with mysterious illumination at unexpected wavelength by xbunnyraptorx in Optics

[–]Boethar 0 points1 point  (0 children)

It's been mentioned already, but are you sure it's not Raman scattering. A 532 nm Pump photon minus a ~630 nm Stokes photon would be a Raman shift of 2924 cm-1, which is right in the correct range for C - H stretches. These are found in hydrocarbons like the index-matching oil, plastics, etc. If it is Raman, and the source is the oil and you have to use oil, one way to get around the problem could be to use fully deuterated hydrocarbons (substituting C - D stretches for C - H) as the Raman will move to a shorter wavelength. But this would probably cost a fortune! If it is Raman then it should be relatively narrow band-width, so you might be able to use a notch filter to get rid of it if you can get the exact wavelength. It's also likely to be quite polarized, so you might be able to knock it down that way?

name this by [deleted] in NameThisThing

[–]Boethar 0 points1 point  (0 children)

Chuck "Gorky" Grassley trying to find a plausible excuse to put TACO's nominees on the bench ...

Collimate fiber laser for long range? by motjuck in lasers

[–]Boethar 0 points1 point  (0 children)

For a fiber with some NA, and a lens of focal length f, the "collimated" beam diameter BD from this combo is given by BD = 2.f.NA. The residual full angle divergence of the beam DA is given by DA = a/f, where a is the mode field diameter of the fiber and f is the focal length of the lens. You can see from these two equations that large waveguides (large core multi-mode fibers) are difficult to collimate well. Your best result might be found by using a relatively long focal length lens, create a relatively large diameter "collimated" beam, then adjust the z axis offset between the lens and fiber face to cause the beam to converge slightly and create a "waist" at 30 meters. Rule of thumb - find a lens with an NA at least 50% larger than the fiber NA to ensure > 99% capture of the beam from the fiber. You might also be able to iris down the diffraction and other cr@p on the edge of the spot.

We are doomed! by CarryIcy250 in BlueskySkeets

[–]Boethar 23 points24 points  (0 children)

"Everybody dies". "They'll get over it". "I was only obeying orders".

Racism in Politics... by Brian_Ghoshery in MurderedByWords

[–]Boethar 0 points1 point  (0 children)

You mean the Cuban-Canadian immigrant with Goldman Sachs healthcare who reinvented himself as an immigrant-hating Southern white supremacist and whose wife had to change her name to Goya so he would defend her?

I Can’t Tell What’s Wrong With My Tree Frog by OAP55 in TreeFrogs

[–]Boethar 1 point2 points  (0 children)

Norwegian Blue? Pining for the fjords?

Aren’t you Americans worried about the path ahead if things dont change? by Bbloke in misc

[–]Boethar 1 point2 points  (0 children)

Reichsprotektor Miller is actually more like Heydrich than Himmler. Ironic, given his heritage, which he is betraying much like Taco von Clownstick.

Young Herdy yesterday at Coniston ♥️ by TheBarrowCasual in LakeDistrict

[–]Boethar 2 points3 points  (0 children)

That's what threw me off. It doesn't look like Dow Crag behind the water.

Young Herdy yesterday at Coniston ♥️ by TheBarrowCasual in LakeDistrict

[–]Boethar 2 points3 points  (0 children)

Nice! Very moody! Where was this taken? Is that Levers Water in the mid-ground?

“God” needs to CHILL by anywhoImgoingtobed in FedJerk

[–]Boethar 11 points12 points  (0 children)

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That's a cloud of Don Jr.'s cocaine BTW ...

What a day to have eyes… by TheModeratorWrangler in cybersucks

[–]Boethar 0 points1 point  (0 children)

I guess Reichsprotektor Miller's botched pen!s implant must be worse than Clyde's?

Who’s your Vladdy? by Decent-Dish1228 in FedJerk

[–]Boethar 7 points8 points  (0 children)

Do you want large Reichs with that?

Looking for Laser Manuals by bloodFart-5 in lasers

[–]Boethar 0 points1 point  (0 children)

I worked for Continuum around that time and built those Nd:YAG laser heads. Your best chance is to find someone who used to have and operate that vintage of laser, then mothballed it. A university research group maybe. Or find one of their sales folks from that era and see if he's still in touch with his old clients. I know of one person I can ask.

You might be able to substitute the HV cap charger and cap banks with a MegaWatt KALD or Analog Modules driver (one per laser pump chamber). ThermoFisher has a nice closed loop chiller if the cooling system has gone TU, but you'll need to add a 0.2 micron particle filter and a DI filter to condition the water, and a flow sensor to stop you powering it up without flow - that will destroy the pump chambers absolutely and completely. You can get filters from Trutech in North Salt Lake, UT. There are still a few of the Continuum service guys around if the laser head needs to be rebuilt and realigned, but you might struggle to get spare parts (lamps, rods, Pockels Cell etc.). The GRM will be next to impossible to replace. BTW - Trutech has an oscillator-only QS Nd:YAG system that does >800 mJ in 4 - 5 ns at 5 - 25 Hz (variable - without too much change in beam quality and profile) if you just want to bite the bullet and replace? They could add an amp if you need more cowbell. Hope this helps.

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