FTIR-的基本原理和结构.pptVIP

The signal we see at the detector is called the the interferogram. For a simple example: only 1 wave, we see that this results in a sine wave function on the detector. A broad band source (many different waves) and will produce the second, much more complex interferogram (shown is one half of the “double sided” interferogram we usually see when using a our spectrometer). The strong point of the signal on the far right is where all of the light is in phase at ZPD often called the “centerburst”. As the moving mirror moves away from ZPD, the different wavelengths grow more and more out of phase and the signal becomes less intense. The interesting thing is any point in this pattern holds all of the intensity information from each of the individual waves which created it. However, we are used to looking at spectrum, and therefore we have to calculate the spectrum from this pattern. We will talk more about this in a minute. The “X” scale of the interferogram plot is measured in “data points”. These points correspond to the position of the moving mirror (i.e., the path difference) measured at regularly spaced intervals. So lets look at how we actually go about collecting the interferogram so that we can calculate the spectrum. Okay, so now we have the perfect interferogram. What good is that if we can’t interpret it. In order to obtain the spectrum, we use something called Fast Fourier Transformation. A method which calculates the frequencies and their intensity present from the interferogram. This is not too difficult when there is only 1 wave (the sine function is directly related to the frequency), but becomes more complex when more waves are present. However, with the powerful computers available today, these calculations can be done in milliseconds. Here we show the example for 3601 waves (from 4000 to 400 cm-1, 1 data point resolution. The interferogram shown is a double sided interferogram which basically has the same information in the right part as