Appendix 1: Etalon Alignment
Fabry-Perot Fringe pattern
For definiteness, we assume that we start with an
interference maximum at the center of the pattern. The
center spot is the nth order interference fringe. The ring
surrounding the center spot is the (n – 1)th order ring, and
the ring just outside that is the (n - 2)nd order fringe and so
on. Increasing the plate separation increases the
interference order of the center spot to become the n + 1st,
so the center spot expands outward to become the first
ring. The first ring expands outward to become the second
ring, … .
Alignment: If as you move your eye to the left, and you observe the innermost spot or ring is
growing larger, the plate separation is greater to the left than at the center. If as you move your
eye to the left, and you observe the inner most spot or ring is growing smaller, the plate
separation is smaller to the left than at the center.
If the plate separation is larger to the left, tighten the left side adjustment screws. If these screws
are already very tight, loosen the right side adjustment screws.
If as you move your eye to the left, and you observe the inner most spot or ring as growing
larger, the plate separation is greater to the left than at the center.
Continue to the vertical (up-down axis). Optimize. Return to the horizontal. Repeat until you as
satisfied. DO NOT OVER TIGHTEN THE SCREWS. DO NOT USE ANY TOOLS TO
TIGHTEN THE SCREWS.
Remove the camera and observe the green ring pattern. If the rings breathe (grow
and contract) as you move your line of sight left and right and up and down, then
the alignment needs to be refined. There are three alignment screws on the face of
the etalon nearest to the magnet. Tighten and loosen each screw in turn as you
move your head back and forth along a line perpendicular to the line joining the
other two screws. (Tighten and loosen; do not just tighten!! Use finger tightness
only. Do not use tools to tighten the screws. Damage may result if tools are used.
Read the alignment appendix for more details.) When you no longer observe the
rings growing and contracting, move on to the next step.
STOP HERE.
Align.1
Appendix 1: Etalon Alignment
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Haidinger fringe
From Wikipedia, the free encyclopedia
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Haidinger fringes are interference fringes formed by the interference of monochromatic and
coherent light to form visible dark and bright fringes. Fringe localization is the region of space
where fringes with reasonably good contrast are observed.
Haidinger fringes are fringes localized at infinity. Also known as fringes of equal inclination,
these fringes result when light from an extended source falls on a thin film made of an optically
denser medium. They are also observed in Fabry-Pérot and Michelson interferometers. They can
be observed by introducing a converging lens between the film and observation plane with focus
of the lens lying in observation plane.
1. Fizeau fringes: Definition from Answers.com
www.answers.com › Library › Science › Sci-Tech Dictionary
Fizeau fringes ( fz frinjz ) ( optics ) Interference fringes of monochromatic
light from interference in a geometrical situation other than plane parallel
http://www.ing.iac.es/Astronomy/observing/manuals/html_manuals/wht_instr/taurus/subse
ction1.6.0.3.4.html
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Optical alignment of etalons
Alignment procedures for a sophisticated etalon: The final process in setting up an etalon is
the optical alignment of the etalon plates (i.e. setting the plates parallel). This should be carried
out when the etalon is first loaded, and then checked during the observing run, preferably every
day.
Align.2
Appendix 1: Etalon Alignment
Note that before the etalon can be accurately aligned, the etalon compartment should have been
flushed with dry nitrogen for at least an hour.
The etalon is aligned by moving it into the light-table position, illuminating it with an arc lamp
mounted below the light-table, and viewing the Fabry-Perot ring pattern from above. The access
hatches should not be opened during this process, as this will disturb the controlled environment
of the etalon compartment. Instead, there are two slides above and below the light table. The
slide below the light table covers a diffusing screen. Remove this slide, and bolt the calibration
lamp unit to the underside of the light table. Then remove the slide above the light table, which
covers a viewport. Note that in order to move the top slide, it will be necessary to use an electric
screwdriver (or similar) to depress a catch in the top left hand corner of the slide.
If you switch the calibration lamp on, and the etalon is servoing correctly, you should now be
able to see the Fabry-Perot ring pattern through the top viewport. As you move your head from
side to side across the etalon, the ring pattern will appear to contract or expand if the etalon
plates are not parallel. The basic aim of the alignment process is to minimise this variation in
ring radius, by adjusting the offsets applied to the CS100 servo channels. The CS100 should be
set to local control during the alignment process, as for the initial servoing of the etalon.
First move your head from side to side along the X axis of the etalon, and adjust the COARSE X
PARALLELISM control on the CS100 to minimise the expansion or contraction of the rings as
the head is moved. Then move along the Y axis, and adjust the COARSE Y PARALLELISM.
The orientation of the X and Y axes is marked on the top of the light-table. The FINE Z control
should now be used to make a ring just appear in the centre of the field and the alignment
process should be repeated observing this ring and adjusting the X and Y FINE PARALLELISM
controls. This small central ring is very sensitive to departures from parallelism, so provides an
accurate indication of alignment. Some
Thu Apr 7 00:29:52 BST 1994
Fabry-Perot alignment using a video camera
Alfred T. Goble and S. Maleki »View Author Affiliations
Applied Optics, Vol. 26, Issue 11, pp. 2063-2063 (1987)
http://dx.doi.org/10.1364/AO.26.002063
View Full Text Article
Acrobat PDF (294 KB)
Align.3
Appendix 1: Etalon Alignment
Journal of Physics E: Scientific Instruments Volume 2 Number 11 Create an
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G L Rogers 1969 J. Phys. E: Sci. Instrum. 2 1006 doi:10.1088/0022-3735/2/11/432
A device for aligning a large Fabry-Perot etalon
G L Rogers
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Tag this articleFull text PDF (297 KB)
AbstractReferences
NOTES
By using a small pentagonal prism scanning the face of a large Fabry-Perot etalon, an observing
telescope placed laterally can detect very small changes in ring size and facilitate exact
adjustment.
Green line: Find zero field line shape. Turn field on for center three and fit to model. Fit
outside six to model. Try for 435 and 405
Use exposure time to adjust image saturation.
Kinematic mount for FP.
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Appendix 1: Etalon Alignment
Align.5