Phase-shift Cavity Ring-down Technique for Detection of NO2 in PPM Concentration

  • Cherry Dhiman Jamia Millia Islamia, New Delhi
  • Mohd. Shahid Khan Jamia Millia Islamia, New Delhi
  • M.N. Reddy Laser Science and Technology Centre, Delhi
Keywords: Phase-shift cavity ring-down spectroscopy, high reflectivity, laser diode, broadband, PS-CDRS technique


A phase-shift cavity ring-down spectroscopy (PS-CRDS) experimental set-up has been established using a broadband diode laser for the measurement of phase shift due to absorption of NO2 in a sealed off cavity ring-down cell. The PS-CRDS technique is verified by optimising various parameters of CRDS cavity and excitation laser. The PS-CRDS signals were measured on the first harmonics using a lock-in-amplifier. The square modulated laser pulses were used in the experiment to obtain the decay time. Measurements of the signal strengths at different CRDS cavity lengths wre also carried out to verify the detection sensitivity for ppm level concentration measurement of trace gases.

Defence Science Journal, Vol. 64, No. 5, September 2014, pp.426-430, DOI:

Author Biographies

Cherry Dhiman, Jamia Millia Islamia, New Delhi
Ms Cherry Dhiman received her BSc (H.) Physics from Deen Dayal Upadhayaya college, Delhi University and MSc (Physics) from Punjabi University, Patiala. She is currently pursuing her PhD at Jamia Milia Islamia, New Delhi. She received JRF from DRDO in 2009 and gained research experience in the area of laser spectroscopy. She is currently working as a project assistant on a DRDO-funded project at Jamia Milia Islamia, New Delhi.
Mohd. Shahid Khan, Jamia Millia Islamia, New Delhi
Dr Mohd. Shahid Khan did his MSc Physics (Material Science) from Jamia Millia Islamia (JMI), New Delhi, in 1992. He received his PhD (Physics) from JMI in 2002. He is presently working as Assistant Professor at Jamia Millia Islamia, New Delhi. He has authored/co-authored over 35 research publications. He has supervised/co-supervised two research students for their PhD. His areas of research are : Laser spectroscopy, non-linear optics and computational molecular and nanoscience.
M.N. Reddy, Laser Science and Technology Centre, Delhi
Dr MN Reddy obtained his MSc and MPhil in Physics from Central University of Hyderabad, Hyderabad, and PhD in Laser High Resolution Spectroscopy of Rydberg Atoms from IIT, Kanpur. He is scientist ‘G’ and divisional head of Advanced S&T and Photonics Division at LASTEC, Delhi. He established Adaptive Optics Group at LASTEC and headed the Group several years for the development of many indigenous Adaptive Optics technologies for real-time compensation of high power laser beam aberrations. His present R&D activities include development of laser-based sensors for stand-off detection of explosives and mines and High Power Fiber Lasers for Directed Energy Systems.
How to Cite
Dhiman, C., Khan, M. S., & Reddy, M. (2014). Phase-shift Cavity Ring-down Technique for Detection of NO2 in PPM Concentration. Defence Science Journal, 64(5), 426-430.
Chemical Science & Technology