Wavelength Function and Diffraction Orders Explained

[anakat-]

an someone explain to me the symbol "m" in dsin$$\theta$$=m$$\lambda$$,
where m is the order of diffraction (or whatever it's called). I am using a fluorospectrometer at which the sin$$\theta$$ is always equal to 1. This instrument can fix the excitation $$\lambda$$. The main point is that scattering of the 1st and second order is observed.

Can somebody PLS explain to me what it means to be in the "1st and/or 2nd order". ie How does this pertain to the actual wavelength function.. I understand that it can be the 1st and 2nd minima after the 1st maxima but am having troubles seeing the big picture.

Another point to consider is that in any absorption spectra, the shifts (delta cm-1) in the peak are constant and I know this can be explained by the equation above. What I am looking for, is an explanation as to why the shifts are constant?

Thank you :tongue:

 

[transience]

The best way that I can think of to explain this is by example. A spectrometer spatially resolves the spectrum of the light source that you are analysing with it. If you take a source that has a narrow bandwidth like a c.w. laser then the spectrum of the laser will only have a single line, corresponding to the wavelength of the laser. If you then put this source into the spectrometer you may see not one line but several corresponding to the different diffraction orders. Generally the higher order diffraction peaks are much less intense so depending upon your setup you may not see them at all.