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Diffraction Grating

A project log for Handheld VNIR Spectrometer

A small portable spectrometer that can be used in the field to collect spectral data.

adamAdam 07/19/2016 at 16:010 Comments

For the diffraction grating I used a 600 l/mm holographic concave diffraction grating that I bought off of Alibaba for around $90. The concave surface of the grating serves to both collimate and focus the light eliminating the need for mirrors. This grating was design for use in a monochromator, measuring a single wavelength at a time using an exit slit, where the grating would be rotated about its central axis to change the wavelength of light impinging on the exit slit. However I found it does a fine job as a polychromator even though it is not flat field corrected.

Below you can see the highly detailed technical drawing and specs that came with the grating describing it's optical properties.

Zooming in on the drawing scribbled on the masking tape is the proper setup for the entrance and exits slits and the angle between them.

From what I can decipher, the entrance slit should be placed 94mm from the center axis of the grating while the exit slit, or in my case the CCD, should be placed 100mm from the grating at a 61.6 angle from the entrance slit arm.

As you can see from the images below the surface of the grating isn't in perfect condition, but it still does the job.

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