Graphene, a single atomic layer of carbon atoms arranged in a honeycomb lattice, has unique electronic structure. Light matter interaction is particularly strong in graphene. We exploit this interaction in the visible to infrared regime for graphene based optoelectronic device. We use optical pump terahertz (THz) probe spectroscopy to reveal hot carrier behavior in graphene. This hot carrier behavior is very important to understand the effect of optical excitation on graphene and might lead to efficient solar energy conversion. We also exploit the strong light matter interaction in THz regime to make graphene based THz modulator. Other 2D materials also have unique properties different from their bulk counterparts. Transitional metal dichalcogenide (TMD), usually labelled as MX2 (M - Mo, W; X - S, Se), becomes direct bandgap semiconductor when it is thinned down to one single layer. Here we show that by investigating the MoSe2/graphene heterostructure using optical spectroscopy and scanning tunneling spectroscopy (STS) we can determine the giant exciton binding energy in MoSe2. This large exciton binding energy is a direct consequence of strong coulomb interaction in 2D, and the understanding of which is important for efficient photocurrent extraction.