Lasers of different wavelengths in visible and infrared regions have been used as excitation source to study graphene. If you need Raman spectra of graphene for characterization of graphene (to assess the number of layers, concentration and type of defects etc) then you will have to compare Raman spectra of your graphene with some Raman spectra of graphene which already exist in the literature. Find a nice publication which investigates the issue in which you are interested for example how the Raman spectrum depends of the number of graphene layers. Then you have to measure the Raman spectra of your graphene using the same laser, spectral range where the Raman shift is registered, resolution etc as in the publication in order to compare the spectra.

You may even ask the people who will perform the Raman spectra measurements whether they can reproduce the technique described in the publication you found. Reasonable number of scans should be found by people who operate the Raman spectrometer, usually this number depends on the level of noise which you find acceptable i. e. important spectral features (for example signatures of phonons) must be more pronounced than the noise.

Laser power is an important parameter. Too much power can damage graphene. Other important parameters are the temperature at which the Raman spectra are measured and substrate at which graphene is placed.

Dr Sunil, may helpful to you

www.researchgate.net/figure/a-FT-IR-and-b-FT-Raman-spectra-of-graphite-and-graphene-oxide-materials_fig1_318396906/amp

www.researchgate.net/figure/FT-Raman-spectra-of-multi-walled-carbon-nanotube-MWCNT_fig4_271309127/amp

you can check my papers you will get all the informations you need

I am familiar with above mention materials. up to 3500 cm-1 is okay.

i got very good results with a 488 nm laser. calculation of defect density and layer number needs wavelength value as input. so it's very important.