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Hi James,

I think it is a good idea to use a diffuser if possible if you want the highest wavelength precision and stability. The exact shape and position of the lamp lines depends on the way the slit is illuminated. Using a diffuser minimises any variation caused when changing the lamp for example, reducing systematic errors and making the calibration more consistent long term. My lamps for the latest LHIRES upgrade with the servo control came with translucent sleeves round them. (The ones for the ALPY did not as they illuminate the slit indirectly via a reflective diffuser screen)

Robin

To: Robin,

RE:"I think it is a good idea to use a diffuser if possible if you want the highest wavelength precision and stability."

Yea I never liked the idea of a "naked" bulb with possible flicker, inhomogeneity, or otherwise strange behavior when the thermal/voltage conditions vary, staring back at the CCD chip/slit, so I left the final diffuser I used and tested on the lamp as seen in the diagram shown below:

I made sure the Ar-Ne lamp could not damage this "diffuser" by melting or being too hot. It fits very snugly on the lamp and is fairly robust as seen above.
Thanks for all the advice!

James