Optics: how gather and align light from a scene?

[Betelgeuse_LA]

TL;DR Summary

Engineering micromechatronical systems

Dear forum,

I want to capture the light from a rectangular area by a monochromator in order to analyze the average intensity of the entire area, at specific wavelengths.
The monochromator is at a fixed distance from the scene.

What type of arrangement do I need (lens, collimator?, et.c.) ? From what I understand, a collimator is required to parallelize the light reflecting from the scene, because it must hit on the devices's grating as a parallel bundle. Also, the scene is not a point source, but a finite area reflecting light in any direction. And the distance to it is finite, as mentioned.
Many thanks in advance

 

[Drakkith]

My first thought is to use a two lenses. One to focus the light from the scene, the 2nd to undo the focusing and collimate it. However, with the width of the area so large compared to the distance between it and the monochromator there might be trouble fitting the two lenses in and still getting the FoV needed.

 

[Baluncore]

I want to capture the light from a rectangular area by a monochromator in order to analyze the average intensity of the entire area, at specific wavelengths.

How will you illuminate the surface?
Is the area to the side of the rectangle available for optics or illumination?

I would consider a pair of 45° diagonal mirrors (each 206 x 160 mm) as the first stage. The 160 mm x 320 mm rectangle could be broken in two and overlain, by a 100% diagonal mirror, with a 50% diagonal mirror, to combine the two halves. The result would be a 160 mm square beam. The 50% beam splitter would provide for illumination and observation from different directions.

 

[Gleb1964]

I assume that monochromator already has input slit and collimator inside. The task should be formulated like the light from rectangle object scene should be: 1) averaged and 2) delivered to monochromator input slit 3) and fill the entrance numerical aperture. In other words light should fit the acceptance etendue of the monochromator.
For example, a relay optics (lens) forming en real image of the object scene at the end of an waveguide or integrating sphere, where the light is mixed and feeding into monochromator input slit. Waveguide or integration sphere can efficiently mix the light from the different areas of scene and change the shape factor.
Scene has rectangle shape and cannot be simply projected into monochromator slit without significant losses.