similarly, it was seen that the intensity of 13th harmonic in indium plasma was much higher as compared to its neighboring harmonics. this was quite surprising because this kind of effect was never seen in gas harmonics. upon careful investigations, it was pointed out by the researchers that this harmonic enhancement happens when the energy of a particular harmonic order matches with a strong transition present in the plasma. for example, it was observed that in tin, there exists a very strong transition 4d 5s 5p p → 4d 5s 5p (d) d at 26.27 ev and this transition has a high oscillator strength (gf value) of 1.52. the energy of this transition corresponds to 17th harmonic with 800 nm excitation wavelength. similarly, in indium, there exists a strong transition 4d5s → 4d 5s 5p at 19.92 ev with a high gf value of 1.11. the energy of this transition corresponds to 13th harmonic with 800 nm excitation wavelength. this enhancement in a particular harmonic order is most commonly known as resonant high harmonic generation (rh). apart from tin and indium, rh has been observed in many other plasmas such as chromium, manganese, antimony etc. presence of such resonances makes plasma makes plasma harmonics very different from gas harmonics. the enhanced harmonic efficiency of a given harmonic order can be useful for the development of narrowband tabletop xuv light sources. these type of sources can be very helpful in various types of spectroscopy techniques.