"Pressure Tuned" PST etalon!

[Merlin66]

In the Patent # 7149377 (copy in Library), there's details of the PST tuning arrangement.
Figs 13 and 14 tell the story.
"tuned by applying counterbalanced compressive forces....to the etalon" - "tuned by changing the optical length of the (etalon)cavity"
What is means in reality is that the etalon is squeezed to reduce the gap between the etalon plates - the spacers being "resilient" enough to bounce back to their original thickness when the pressure is released.
The smaller the gap, the further the tuning moves towards the red part of the spectrum.
The "sweet spot" I think is therefore due to the angular off-set of the incoming beam and any non uniform distortions of the spacers.
At no time is the etalon "tilted"......

[Merlin66]

Joe,
The easiest way would be to attach a .pdf file with the patent and I'll check and transfer to the Library.
Thanks,
(Uploading PDF's is now OK)

[colinsk]

07149377.pdf
7149377

[PEterW]

Why do we get a bar of on band then? Even pressure would act like the new pressure tuner? Most thinly polished glass materials are going to be very resilient, not going to deform much if at all.... Unless they are using the same stuff they mounted the pentaprism with....

Cheers

PEterW

PS I will give the patents a glance.... Have a good drink first.... Patent speak sometimes is hard to decipher!

[marktownley]

It's the foam gaskets / o-rings that deform, then etalon plates aren't perfectly parallel...

[colinsk]

It has been my opinion that the orange silicon gaskets compress the spacers in the etalon. If the pressure is uneven then you would have problems. Manufacturing spaces is not an easy task and it could be that the spacers are not even to start with.

Parallelism in the etalon space is crucial to having full field of view on band. I am surprised that the spacers are compressible enough to make a change in bandwidth but that is a good reminder at how sensitive these measurements are.

When we have to remove the pin and tighten the compression to get on band it is the result of the orange silicone gaskets compressing over time.

[Merlin66]

Colin,
That Patent is already in the Library.

[Merlin66]

Peter, Mark, Colin, Rusty,
The whole basis behind the Coronado/Lunt Patent is the fact that they have "invented" a commercial method of producing accurate air-spaced etalons. The spacers, their number, position, size and their accuracy come in for special mention. They claim that the use of a 1/6 plate thickness to diameter gives stability and the resilience of the foam etc is consistant......

[colinsk]

I just added this one to my on line library:

http://www.designerinlight.com/solar/so ... 054518.pdf

[colinsk]

Peter, Mark, Colin, Rusty,
The whole basis behind the Coronado/Lunt Patent is the fact that they have "invented" a commercial method of producing accurate air-spaced etalons. The spacers, their number, position, size and their accuracy come in for special mention. They claim that the use of a 1/6 plate thickness to diameter gives stability and the resilience of the foam etc is consistant......

Yes, that is the claim. After thousands of units I am not sure I believe them. Old school etalons were much thicker and had only 3 spacers so the plates did not get warped during contacting. I talked to all of the current designers and none of them would confirm their or others spacing designs. I worked very hard on a diagram that I chose not to include in Resonant Spaces Part I because it is only a guess. I'll search for it and if I can find it I'll attach it to this thread.

[swisswalter]

Hi Colin

the time a took a apart the LS50 etalon there where 5 or six spacers ( I have to check the pics). Patents are not written to give you all (important) informations ;-)

[PEterW]

Interesting patents. The bending caused by the coatings, the preference of soft coatings to minimise this is something I was not aware of. 1/6 thickness is pretty common for substrates that don't flex. If we had some numbers for the relativises and spacer dimensions we could play the numbers with the youngs modulus of the spacers and estimate the forces required to do the tuning. It maybe that the range allows them to make etalons with a wider range and then tighten them up different amounts to bring them on band.
I had also not come across reentrant etalons with risers, I wonder if any of our current products contain any? I might have come across a device made with them that spectrally separated optical fibre signals, don't remember the name of the company that had made them though, cool bit of kit though.
Surface roughness less than 0.5nm, now you're talking! I have a colleague who has optically contacted things together and he says sometimes it works first time, sometimes not.... Black art.
There appear to be a few more etalon filter patents out there that we are missing from the library?

Thank for an entertaining evenings read!

PEterW