Model 428 User’s Manual APPENDIX F – SPECTRAL CALCULATION
Bristol Instruments, Inc. 68
APPENDIX F – SPECTRAL CALCULATION
The spectrum of the input signal can be recovered by using the query “:CALC2:DATA?”
The response will be the spectral intensity in scientific notation for each of the 16384
spectral frequency bins.
The uncorrected wavelength in nanometers for any spectral point m can then be
calculated using the formula:
For a model 428A,
Ref
is equal to 632.9909nm; for a model 428B,
Ref
is equal to
632.9914nm.
To accurately compute the wavelength, the dispersion of air and internal calibration
factors must be taken into account.
The dispersion of air can be approximated by:
Where the wavelength is in units of nanometers, the temperature, T, is in units of degrees
Celsius (C) and the pressure, P, is in units of millimeters of mercury (mmHg).
The temperature and pressure can be queried using “:FETCH:SCAL:ENV?”.
The dispersion corrected vacuum wavelengths can then be computed as:
The internal wavelength calibration coefficient can be queried using “:CALC2:WCOE?”.
To calculate the x-axis values in frequency, invert the wavelength values and multiply
them by the speed of light, 299792458m/s.
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