MNL-1007 REV A
12
Resolution
There are several definitions for resolution. In FT-IR, nominal resolution is often defined as the reciprocal of the maximum OPD.
Practically, resolution is defined as the minimum spacing between two consecutive wavelength (
Δλ
) / wavenumber (
Δν
) points that
can be fully resolved. Two neighboring spectral features of equal height and width are said to be resolved if there is a dip of at least
20% between the two maxima.
The Signal to Noise Ratio (SNR) of the system is directly proportional to resolution (
Δν
) [
𝑆𝑁𝑅 ∝ Δ𝜐
] [1].
Advanced Settings
Gain Settings
The NanoQuest module has an internal Analog to Digital Converter (ADC) that converts the interferogram data (analog current
detected by the photodetector) to a digital signal.
NanoQuest has two main gain settings:
•
Transmission
: optimum gain setting corresponding to the coupled power in a typical transmission setup.
•
Reflection
: optimum gain setting corresponding to the coupled power equivalent of 1/32 of the coupled power in a typical
transmission setup.
The conversion ratio can be adjusted to:
1.
Avoid saturation of the amplifiers: saturation leads to signal clipping and attenuation.
2.
Enhance the SNR: using the
Transmission
gain option for diffuse Reflection measurements degrades the optimum SNR by a
factor between 3-5 depending on the optical power coupled from the reflection setup.
Apodization
The interferogram can be multiplied by one of several different apodization functions to make a gradual decay to zero values at both
sides of the interferogram, and hence to smooth the spectrum.
