User Guide to the Jb95 Spectral Fitting Program
G. Calibration, normalization and linearization procedures
Most spectroscopic data will need to be normalized and calibrated (linearized)
prior to any detailed analysis. The calibration is usually based on a relative
frequency reference and performed by simultaneously recording the marker fringes
from, for instance, a Fabry-Perot cavity. A procedure is described to generate a
normalized and linearized data file under these conditions. In this procedure, it
is assumed that the signal file is named PmtF, that of the reference
cavity marker file is MarkersF, and that of the laser power is
PwdF.
1. Calibration
- Select the
MANIPULATION/CALNORMLINEAR dialog.
- Run the peak-finding (PEAK FIND)
procedure on the MarkersF file.
- Display the MarkersF channel and depress the t key from the
MAIN WINDOW to display the file
positions found. The file positions are only shown in the MED and RAW data views.
- Correct problems using P to erase or add marker positions.
2. Normalization - Toggle the display status
off for the MarkersF channel and the display status on for thePwdF
channel. Make sure PwdF is the active channel.
- Shrink the view and position the cursor cross hair over a region
representative of the average power across the scan.
- Depress the h key to determine average voltage value. This factor is
used as the normalizing factor.
- Reposition the cursor in a region where laser was blocked to
determine the voltage for power zero. Depress the l key to determine the
average voltage value for zero power. Note that depressing the W key
will zero both the h and l values. Display the PmtF
channel to make sure it is zero when the laser is blocked. If not, use the
OFFSET option in the MANIPULATION/CONVERSION dialog to manually offset this
file.
- Select the MANIPULATION/CALNORMLINEAR dialog. If the h
and l values are not displayed in the REFER (h) and OFFSET (l) fields, enter 0 in either field and they should be updated.
- Edit the filenames fields in the NORMALIZATION section to read
IN FLNM PmtF
OUT FLNM PmtFn
NORM FLNM PwdF
- Normalization of the PmtF file will be done using the following
formula:
PmtFn[n] = PmtFn * Vh / [PwdF[n] - Vl].
Depress the NORM button. - Note that the %CUT is defined on the
power channel as a percentage of the voltage range between the h and
l values. Regions of the spectrum where powers fall below this value will
not be normalized and are set to zero.
- Also, in some cases, you may
want to smooth the power channel file prior to normalization. Use the FFT SMOOTH
option in the MANIPULATION/CONVERSION dialog prior to normalization.
3. Linearization - Edit the filenames fields in the
LINEARIZATION section to read,
IN FLNM PmtFn
OUT FLNM PmtFnl
- Check that the value
for PTS/FSR is the same as that for AVE PTS/FSR shown in the CALIBRATION section.
- Check that the FINAL MARKER number is the same as the # MKS in
the CALIBRATION section.
- Check the FSR value.
- Depress LINEARIZE.
- Select the ANALYSIS OPTIONS dialog and enter PmtFnl in a channel
filename. Check the DSP STAT box and set the page values and TYPE
fields for each view.
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