We have a SPEX 1680B double monochomator that is badly out of alignment. I have set it to 0 nm and shined a He-Ne laser through it. I have aligned it vertically. The laser beam goes through the ends fine. However, when we start to the align the gratings, that is when we have problems. I can align it at 530 nm, but when I move the monochromator to red (613-630 nm), the light no longer goes all the way through and it starts missing the second set of mirrors. I can then align it on red, and the same thing happens when I go to green. Are their any sort of tricks to align this double monochromator or does anyone know what we are doing wrong here?
Dear Ross! It seem to me that that You fill rather free with laser wavelength values: if You have diode pumped Nd3+ SHG laser the wavelength value is 532nm. If red laser is HeNe the wavelength is 632,8nm. Double monochromator can have high spectral resolution and the tuning with Your above selected wavelength occurs to be rough (incorrect).
My best regards
Clarification: The HeNe laser was used to calibrate the 0 nm position. Once the gratings were aligned, we used a Xe lamp and spectrometer to try and do a calibration using other wavelengths.
I don't have any experience with that monochromator. I envy your opportunity to work with it. Hope you solve your problem and have fun using it.
Does the drive use a sine bar to linearise the wavelength adjustment, and is this operating correctly? The two gratings need to track one another for light to propagate all the way through.
If the vertical alignment of either of the gratings is too far out, the image of the input slit may "walk-off" either the intermediate slit, or the exit slit, as the wavelength is tuned.
Adjust the first grating to centre the image of the input slit on the intermediate slit, then adjust the second grating to image the intermediate slit on the output slit.
See section 4.2 and figure 2 in the document linked below.
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/OSD/1680.pdf
According to my experience, Double monochromator can have high spectral resolution, but you can solve your problem by using 2 gratings . Adjust one by one i.e first grating to the centre of the chosen image and then adjust the second grating to the same image .This the beast way but you must have a patience. Thank you
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