Question unclear. From your question it appears you have prepared a sample (thin film) by RF sputtering and later you are trying to characterize it by some spectroscopic technique (like UV-Visible or Raman) I believe. And you seem to have some difficulty in interpreting the results. Am I correct?

Could you rephrase your question in a better way.

According to De Broglie's hypothesis (wave particle duality), light and matter exhibit both particle behavior and wave behavior. Also wavenumber and energy are directly related. Narrow range of wavenumbers could mean narrow range of energies used. Hope it helps.

Ravi sir,

Actually bombarding the surface with broad ion beam source there are regular ordered nanopatterns formed having  some wavelengths over the surface.. My problem was some papers they have mentioned about short or 'narrow range of wavelengths'. Plz explain me.. As Ms Deepika replied to the answer there are not single wane length here may be some wavelength variation among the patterns.

It is possible that the description is used in the context of order.  In my work on laser abated perovskites thin films, the infrared spectra were extremely broad.  Only with annealing and the appropriate atmosphere did the infrared spectra become similar to crystalline bulk material.

Further, if the electronic properties of the material are significantly different near the surface -more conducting,  compared to the bulk then the infrared spectra will be more reflecting near surface vibrational properties since the skin depth -the depth to which infrared radiation can penetrate the material, is reduced.

Note - this is for infrared spectroscopy.