Second harmonic generation (SHG) is an effective technique for surface probing. By SHG, monolayer adsorbtion can be detected. With different input/output beam polarizations the SHG can yield information on the average orientation of molecular adsorbates. Surface symmetry measurements can be performed rotating the sample around the surface normal. By using tunable lasers, SHG is applicable for surface-specific monolayer spectroscopy. SHG option could be ordered as an extention to Sum Frequency Generation (SFG) spectrometer.