Reply To: Diffraction theory

[Akhil Dutt Vijayakumar]

 

Hi,

Thanks for the follow-up,

I can add some more clarification on this aspect.

The spectrometer design shown here uses a transmission grating and this configuration is called Littrow spectrometer. Here the grating is already placed at an angle, also the incident light angle is equal to diffraction angle (α = β = 33.367°). 

In this specific setup, the angled grating (33.367°) allows the diffracted beam (-1st order) to retrace its path back through the same collimating and focusing lens. This simplifies alignment and reduces the number of optical components needed.

In the Littrow configuration the -1st order typically has the highest intensity compared to other orders, maximizing signal strength at the detector. Also, the -1st order is further away from the undiffracted beam and scattered light, minimizing their interference with the desired signal.

In general, the -1 order is preferred in spectrometers demanding high intensity and stray light reduction in the diffraction pattern, but depending on the configuration and type of spectrometer(reflection or transmission) other diffraction orders (+1 and higher orders) are also used.

Hope you understand clearly.

Akhil