What formulas are used to calculate absorption spectra?

To calculate single absorption spectra ΔA we register two consecutive probe pulse spectra and use the following formulas.

Single Probe Channel

ΔA=log10(I0 sample/Iex sample)

Dual Probe Channel (Probe-Reference)

ΔA= log10[(I0 sample/Iex sample)x(Iex reference/I0 reference)]

where

Iex sample – intensity of probe light after the sample when the excitation light was incident on the sample (pump on signal)

I0 sample – intensity of probe light after the sample when the excitation light was blocked by optical chopper (pump off signal)

Iex reference – intensity of light in the reference channel when the excitation light was incident on the sample (pump on reference)

I0 reference – intensity of light in the reference channel when the excitation light was blocked by optical chopper (pump off reference)

After that multiple absorption spectra are averaged to give single line in 3D absorption-time-wavelength surface.

Note: Helios has an option first to average separately all spectral intensities over specified time and then calculate ΔA.