There is a confocal Raman equipment at our lab. The full laser (633 nm) power is 25 mW. I am worried that too intensive laser would damage the tubes. According to experience, what are the appropriate parameters such as laser power and exposure time for CNTs.
It is near a damaging threshold, but you can clearly see it in your spectra, so if you start with power slightly lower and than will increase it, you can test it for your equipment and CNTs you have. The time is not so high, around 1 sec is good for clear spectra and fractions of second are good for imaging, if you don't need a clear spectra in each point.
here is our article about laser damage in structures containing SWCNT:
Carbon Nanotubes on Polymeric Microcapsules: Free‐Standing Structures and Point‐Wise Laser Openings
AM Yashchenok, DN Bratashov, DA Gorin, MV Lomova, AM Pavlov, ...
Advanced Functional Materials 20 (18), 3136-3142
Really this can depend on the thermal contact to the substrate. In general, you can ease the thermal load for raman measurement by for example embedding the sample in a KBr disk, as is commonly used for FTIR spectroscopy
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