agree with dr Abdullah Hasan Jabbar

I am agree with dr Abdullah Hasan Jabbar

I don’t know

Yes you can again there are Plasmon related stuff or as Abdullah mentioned the surface properties (such as adsorption ). As the fundamentals say , energy has to be pumped to materials for them th switch stated and give away photons at different E=h * frequency . In your case this frequency is different from the pump frequency (Nd:Yag or others)

I agree with Aparna

Is the thickness of the thin film is enough to get the phase-matching condition and coherent length which is required for this nonlinear phenomenon??

I agree with Dr. Abdullai

Second harmonic generation (also called frequency doubling or abbreviated SHG) is a nonlinear optical process, in which two photons with the same frequency interacting with a nonlinear material are effectively "combined" to generate new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons. Second harmonic generation, as an even-order nonlinear optical effect, is only allowed in media without inversion symmetry.

Read further: https://en.wikipedia.org/wiki/Second-harmonic_generation

Thank Harry Barton Essel

For these basic knowledge related with the question

regard

Raad