49FREQUENCY MODULATION SPECTROSCOPY- A REVIEWFrequency Modulation is the change of carrier frequency proportional to information modulating signal. Frequency modulation spectroscopy is optical heterodyne system capable of sensitive and rapid detection of absorption and dispersion features. This spectroscopy is used to detect the trace gas; to measure the moisture activity; and to inspect the parenteral vial.som_subhra_ghosh@yahoo.co.inReview312012Spectroscopy,Frequency,LaserPriyadarshini.Ch,Somsubhra Ghosh,Somsubhra Ghosh,N. Parthiban,David BanjiNalanda College of Pharmacy, Nalgonda, Andhra Pradesh, India – 508001,Nalanda College of Pharmacy, Nalgonda, Andhra Pradesh, India – 508001,Nalanda College of Pharmacy, Nalgonda, Andhra Pradesh, India – 508001,Nalanda College of Pharmacy, Nalgonda, Andhra Pradesh, India – 508001,Nalanda College of Pharmacy, Nalgonda, Andhra Pradesh, India – 508001