[RASMB] interference optics

[Tom Laue]

Hi-
The underlying cause of the jitter is the fact that the source and 
detector are referenced mechanically to different spots on the XLI 
frame, and that the thermal baseplate is flexible. The bulk of the 
vertical shift comes from thermal gradients in the vicinity of the 
condensing lens (at the bottom of the chamber). These gradients result 
in the lens "tipping" relative to the source, and give rise to both a 
vertical component and a slight 'rotational' shift to the fringes (i.e. 
the vertical shift is not quite uniform across the image). The TI/RI 
noise will remove most of the effects, with the 'rotational' shift not 
being quite as reproducible as the purely vertical 'breathing' shift.
If you shut off the thermo-electric modules (not recommended), the bulk 
of the vertical displacement is eliminated. The time constant for the 
shifts is on the order of minutes.
Some years back we built a new source and condenser lens mount which 
decreased the breathing motion from tenths of a fringe to hundredths of 
a fringe. Kristian Schilling has built a similar mount.
Best wishes,
Tom

On 1/15/2013 12:41 PM, Ute Curth wrote:
> Dear all,
>
> I hope you had a good start in 2013 and some of you can possibly give 
> me advice on a problem with our Xl-I machine.The raw data of  our 
> interference optics show (and always showed) such an enormous vertical 
> jitter that it is hard to judge whether the sample sediments at all 
> and where the meniscus is located (see attached file). Whereas, after 
> subtraction of TI and RI noise the data look quite nice, I am 
> wondering what the reason of this jitter is. Has anyone an idea about 
> its possible source and how I can get rid of it?
>
> Thank you in advance
>
> Ute
> -- 
> PD Dr. rer. nat. Ute Curth
> > Medizinische Hochschule Hannover
> > Strukturanalyse
> > OE 8830
> > Carl-Neuberg-Str. 1
> > 30625 Hannover
> > Germany
> >
> > Tel.: +49-511-5329372
> > Fax : +49-511-5325966
>
>
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-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
Durham, NH 03824-3544
Phone: 603-862-2459
FAX:   603-862-0031
E-mail: Tom.Laue at unh.edu
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