I am trying to measure the transmittance spectrum through a liquid sample using a visible-NIR spectroscopy (a spectrometer connected to a fiber optics and a collimating lens at the end), with tungsten-halogen light source (through another collimating lens) passing through the sample before reaching the lens connected to the spectrometer. From what I understand, transmittance can be calculated by dividing the measured spectrum with the light source spectrum.
I am able to measure the spectrum (intensity vs. wavelength) of light passing through the sample. However, when I tried to measure the source spectrum without the sample, the intensity exceeds the maximum that can be detected at all wavelengths (so the plot just shows the maximum intensity).
There is also an attenuator (screw) on the light source, which I can use to lower the intensity of light. But if I attenuate it further so that the light source spectrum without sample is measurable, the intensity through the sample will be very low that it is very close to 0.
Is there any suggestion on how to get the light source spectrum at high intensity?
I am thinking of getting the light source spectrum with high attenuation, so the intensity will be within the range that can be measured, and then scale the spectrum up using a constant based on the attenuation levels. For example, turn the attenuation screw by half-full rotation, measure the spectrum, then turn it more by half-rotation and measure the spectrum, and then find the scaling constant by dividing the two spectra. But I tried to measure two spectra at different attenuation levels, but the scaling is not constant across different wavelengths.
Am I on the right track? Or the spectra could not be simply scaled up by some constants?