The Importance of Temperature Stability

This is a forum to share experiences and ideas about holography.
John Sonley

The Importance of Temperature Stability

Post by John Sonley »

Earlier in the year, when it was a lovely English summers day - yes, the sun really does shine in northern England, Jem and I had a hugely unsuccessful day - not a single one of our attempts produced even the slightest indication of a holographic image.
We put the failure down to temperature changes as the bright sun heated the whole of Jem's workshop

I thought I'd do a few calculations to get a feel of how critical temperature stability is for the time duration of a holographic exposure. I didn't get down to fancy maths incorporatung cubical expansion, just bog-standard linear expansion

I assumed a typical support for a mirror could be a 0.5 metre length of stainless steel rod

The calculations revealed that a 0.02 deg.C change in temperature of that rod over the exposure time of the hologram would cause a movement of one quarter of a wavelength of red light - which would give rise to a dim holographic image, twice that temperature change - no hologram at all!
The equivalent figure for green light is 0.018 deg. C

If you could find a source of invar rod, the problem reduces by a factor of ten

If someone out there is more in-tune with undertaking this type of determination for whole structures, please check my approximations as I'l sure there'll be synergistic and converse effects to consider


Brgds

John
Colin Kaminski

The Importance of Temperature Stability

Post by Colin Kaminski »

I used to have a metal table behind an uninsulated wall facing south. I could use an interferometer to measure the thermal expansion of the steel top. I would suggest setting up an interferometer and measuring the changes. Solid fringes are solid fringes...
Sergio

The Importance of Temperature Stability

Post by Sergio »

I've got similar results with aluminum, 0.014°C for half wavelength/half metre and not so far from steel...so the climate on lab need to be controlled and Michelson interferometre conditioned to not expansion cancel the fringe movement mutually, suppose these movement visually is veeeryy slow so plot graphic temperature vs fringe movement is desirable.
Joe Farina

The Importance of Temperature Stability

Post by Joe Farina »

As I recall, Jem was previously making holograms on a wood floor in a shed. This would probably be the major factor affecting stability in that situation, but it looks like he solved the problem by bypassing the wood floor and supporting the table directly from the underlying concrete.

Say for example you have a wood floor made up of planks that are three feet long. As the moisture content and temperature of the wood fluctuate over a very short period of time, the wood will very likely twist or warp. The longer the wood, the more it will warp. In addition, all the neighboring and connected wood planks will be "doing their thing" as well, and these disturnabces will likely be transferred to other planks and thence to the table.

As for temperature, yes, that's important also. I went to considerable lengths in my lab to stabilize temperature by enclosing the table (the whole room actually) with two-inch styrofiam, with sealed edges. The lasers and electric baseboard heaters are on the other side of the styrofoam. And I have an accurate digital thermostat for the heaters. I got the thermostat from a Canadian company -- the Canadians sure do seem to know a lot about heating :wink:
dave battin

The Importance of Temperature Stability

Post by dave battin »

my vote goes totally to the Michelson interferometer for testing purposes, by expanding the fringes enough, lets say projected on a wall now mark the dark band in two places
on the wall. now watch these fringes closely and see if they drift/wiggle/hop/and return to the marked lines on the wall, if they don’t return to the same position or shift more then 1/2 way(during exposure time) to your marks, you have a problem, and you can now start to investigate your situation...............


John did'nt you make a movie of this ?
John Sonley

The Importance of Temperature Stability

Post by John Sonley »

dave battin wrote:my vote goes totally to the Michelson interferometer for testing purposes, by expanding the fringes enough, lets say projected on a wall now mark the dark band in two places
on the wall. now watch these fringes closely and see if they drift/wiggle/hop/and return to the marked lines on the wall, if they don’t return to the same position or shift more then 1/2 way(during exposure time) to your marks, you have a problem, and you can now start to investigate your situation...............


John did'nt you make a movie of this ?
- on Facebook I put a movie of some of my H2s

Hi Dave - and thanks for all the other comments and of course you're absolutely right the interferometer tells you whether you have stability or not .... after all the ideas that try, the yes or no arbiter is the MI
The reason for the posting was simply an interest in quantifying the magnitude of temperature changes; it also adds strength to case for having short exposure times.
Although I haven't seen the changes Jem has incorporated in his workshop, I've seen photos and his support now goes through the wooden floor right down to bedrock - he's sent me photos of his really bright holograms with his new set-up.

I'm fortunate in having a below-ground basement holography lab with a concrete floor which I don't heat when producing holograms and whilst the basement temperature drops to about 50 deg F during the winter, I am able to produce bright H2 image plane holograms with exposures of up tp 30 seconds reliably and up to 50 seconds less reliably

Jem, myself and a new member to our group, Laker - who lives quite close to me plan to meet-up in a month or so to swap notes


Dave
John Klayer

The Importance of Temperature Stability

Post by John Klayer »

I don't know why I didn't think about the temperature change before with my cave holography. Here I thought it was the C315 going goofy. I thought after the two green LEDs lit everything was good to go. I couldn't understand why lately I've been getting better results after a long warm up time for the laser. It wasn't the laser warming up; it was the longer aluminum bar I'm now using for supporting the reference fiber stabalizing to the 55F cave temperature from the 100F Georgia summer.
John Sonley

The Importance of Temperature Stability

Post by John Sonley »

Thanks for the comment John - although I could do with a little of that warmth here - it's cold wet and grey today!

It's difficult to predict absolute effects of temperature change, every set-up will be different but as Dave Battin said a few postings ago - the Michelson Interferometer tells the truth ............. stable fringes, good holograms ... unstable fringes, don't waste good film

BRgds

John
John Klayer

The Importance of Temperature Stability

Post by John Klayer »

I'm going to try to let my apparatus temperature stabalize for a couple of days in the cave over this weekend. I plan to put it in the cave sometime Friday night or Saturday morning then come back on Monday to make a few shots. Now I'm starting to worry about condensation as the cave is at or near 100% humidity. Maybe I wont install the laser and optics till Monday.
John Sonley

The Importance of Temperature Stability

Post by John Sonley »

Hi John - my basement lab is dampish as it's below ground level and not drylined but it is non-condensing and I keep a small portable dehumidifier running to keep the RH to circa 75%.
One hidden benefit of a moist atmosphere is that it prevents holo film curling up and so makes temporary lamination on to glass easy - which is sometimes not the case in warmer dryer atmospheres
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