[RASMB] Dark interference fringe pattern

[Hayes, David]

Hi Arne,

 

I will let more knowledgeable people give possible reasons for the dark
fringe patterns (Walter Stafford once told me an XLI was once focused on
the second order fringes instead of the first order fringes, but I think
he saw what that looked like and I only heard about it), but as a lab
with an XLI fully upgraded to Proteome Lab version, I wanted to say that
our interference system works better than what is seen in your screen
shots.  

In older systems there was a brightness and contrast setting, but in
newer systems there is no brightness or contrast control:  it is
supposed to be automatic.  My XLI has the same laser setting screen as
in your screen shot (no brightness or contrast control).  However, for
standard double sector cells without interference slits on the top
window, my laser duration is set to 0.1 degree.  I can use 0.2 degrees,
but the fringes look too bright and washed out.  My fringes would be
completely oversaturated at 0.6 degrees duration which is on your screen
shot.  With the thin slit window holders (sold by Spin Analytical) my
duration is set to 1.2 degrees since the slits control the light
intensity and the brightness of the fringes is always a little too
bright by my judgment and I wish I still had the contrast/brightness
controls.

 

Our friendly Beckman maintenance man, Sam Fishpaw, would never leave a
PM visit with fringes looking like this.

 

David Hayes

 

________________________________

From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org]
On Behalf Of Rufer, Arne
Sent: Thursday, April 29, 2010 9:35 AM
To: rasmb at rasmb.bbri.org
Subject: [RASMB] Dark interference fringe pattern

 

Dear colleagues,

 

we recently encounter problems with the interference optical system on
our XLI (upgraded to Proteome Lab version) in that the fringe pattern
looks very dark (please see attached screenshots). Beckman field service
recommended to us to clean the lenses in the laser housing of the
monochomator arm (which we did paying attention to reinstall the lens in
the correct orientation) and to clean/exchange the filter above the
condensor lens. While intermittantly the brightness/contrast of the
fringe pattern improved, we are back to "very dark" after trying to
further clean things up. What remains also is a concentric interference
pattern superimposed to the expected fringes, which you can see on the
left side of the fringe patttern in the second screen shot. This ghost
pattern is also visible when we look at the scallop position or an empty
cell hole.

Any suggestion as to how we can get our machine back to normal would be
greatly apprecieated.

 

Best regards,

 

Arne

 

 

 

 

 

 

 

Dr. Arne Rufer

F. Hoffmann-La Roche AG

PROBMO Optical Spectroscopy

065/207

CH-4070 Basel

Tel: 0041-(0)61-6882126

arne.rufer at roche.com

 




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