EM27/SUN

EM27/SUN
Dr. Michael Gisi, Bruker Optik GmbH
May 30, 2014
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EM27/SUN
•  RockSolid™ pendulum FTIR-Spectrometer
•  Resolution: 0.5 cm-1, double-sided
•  RT-InGaAs Detector (NIR)
•  470 x 630 x 350 cm
•  Mass: ~25 kg incl. tracker
May 30, 2014
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New-developed Solar-Tracker
•  Total weight: <5 kg
•  Beam diameter: 40 mm
•  High resolution
•  Optical feedback by
Cam-Tracker principle:
Gisi et al.: Camtracker: a new
camera controlled high
precision solar tracker system
for FTIR-spectrometers,
AMT 2011.
May 30, 2014
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Internal setup
Adjustable aperture stop
(default: 5mm)
Camera for CamTracker
Field
stop and
detector
TCP/IP
24V
USB
Internal source
May 30, 2014
Space for gas cell (5cm) + T-sensor
Preliminary data - do not redistribute
EM27/SUN: Solar NIR spectra
2 Detector options:
CO2 CH4
•  Narrow: 5000-11000cm-1
CO
•  Wide: 4000-11000cm-1
Note: Wide-band-detector has
lower SNR (~x2)
O2
For analysis results
see: Gisi et al.:
XCO2-measurements with a
tabletop FTS using
solar absorption
spectroscopy
AMT 2012
May 30, 2014
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Sampling Ghost Artifacts
EM27/SUN has the new linear laser diodes
however: no possibility to adjust comparator level
In addition: EM27/SUN not in conditioned environment:
→ influences on electronics by temperature
Typical GPR-values ~ 2-4
May 30, 2014
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Interpolation of zero crossings
Current electronics (“M16”)
enables linear interpolation of
descending zero crossings
from ascending crossings:
Ghost
May 30, 2014
No Ghost when
interpolation enabled
Parent
signal
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Interpolation of zero crossings
Side-effects may be lower sampling position accuracy
due to linear interpolation:
•  Statistical errors in interpolation position
→ Noise in spectra
No significant increase of SNR observed even when
exposed to vibrations.
•  Systematic sampling position errors due to
systematic OPD-dependent change of scanner speed
→ kind of „OPD-dependent Ghost“
How strong are these distortions?
May 30, 2014
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Inspecting pendulum movement
Scanner-velocity deviation (Hz)
Using spectrometer‘s „Real-Time Diagnostics“ Java-applet:
Scanner position (½λ)
May 30, 2014
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Real time-diagnostics
Animation
Scanner Speed: 10kHz
May 30, 2014
Tapping on table with finger
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Influence on interpolation
Systematic increase of speed
causes systematic missampling in this IFG-range
However: Effect is small, here about 0.0002λHeNe @10kHz
(for comparison: original ghosts of IFS125HR were ~ 0.01 λHeNe)
In addition: further optimization possible (by user) by adapting
mirror reversal parameters and increasing reversal-range.
May 30, 2014
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Knocking on spectrometer:
May 30, 2014
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Interpolation of zero crossings
•  Interpolation of descending zero crossings may be a good
way to remove sampling ghost-artifacts.
•  Influences on spectra are estimated to be very small.
•  Further (spectrometer-dependent) optimizing possible
Contact me…
(e.g.: It is very hard to get Java-applet running on due to Java security
settings)
May 30, 2014
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Thank you
Comments,
Questions,
….
May 30, 2014
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www.bruker.com
For research
use only. Not for use in diagnostic procedures. Copyright © 2010 Bruker Optics. All rights reserved.
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30, 2014
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