Weidong Chen obtained his PhD degree from University of Lille 1 (France) in 1991. He has been a Lecturer at University of the Littoral Opal Coast (France) since 1993. He became a full Professor of Optics in 2003. His research mainly focuses on the developments of photonic instruments for optical sensing and metrology of atmospheric species (trace gases, aerosols). He has published over 160 peer-reviewed articles in scientific journals, conference proceedings and books. He has won several awards for his developments of a Fourier transform THz spectrometer, a laser sideband far-infrared spectrometer and an infrared laser instrument based on difference-frequency generation. Dean Venables is a lecturer in chemistry at University College Cork, Ireland. He obtained his PhD from Yale University in 2001 with a study of the low frequency motions of liquids using ultrafast terahertz spectroscopy. Since 2003, his research has focused on developing and applying spectroscopic instruments to quantify trace gases and to characterize the optical properties of aerosols in the atmosphere. His work has explored and expanded the use of broadband optical cavities in the visible and ultraviolet and to aerosols. His group’s research includes laboratory, chamber, and field experiments and the group has participated in numerous international campaigns. Markus W. Sigrist obtained his PhD degree from ETH Zürich (Switzerland) in 1977. From 1996 until his retirement in 2013 he was Professor of Experimental Physics at ETH heading a group active in laser spectroscopy and sensing. His research focused on infrared laser development and spectroscopy emphasizing applications ranging from trace gas detection to medical sensing. He has authored or co-authored over 190 publications in reference journals and several book chapters and books. He is a fellow of the Optical Society (OSA) and OSA Traveling lecturer, and acts as Foreign Expert at the Chinese Academy of Sciences.