Sensitivity enhancement at 594.8 nm atomic transition of Cl I for chloride detection in the reinforced concrete using LIBS.

A new atomic line at 594.8 nm of neutral chlorine (Cl I) has been used as a marker to quantify the amount of chloride present in the concrete sample using Laser Induced Breakdown Spectroscopy (LIBS). Although, the relative intensity of the 594.8 nm line is 1000-fold less than that of the most commonly used intense atomic line of Cl I at 837.5 nm reported in the literature, the limit of detection of chlorine achieved with our set-up in the concrete sample using the new line is comparable with the 837.5 nm. This clearly indicates that the sensitivity of the LIBS system for detection of chlorine in concrete sample using 594.8 nm is at least 1000-fold more than the one using 837.5 nm, which can be attributed to the characteristic less self absorption. LIBS data for different concentration of chloride content in concrete sample was also carried out and a calibration curve was drawn. The excitation scheme for 594.8 nm line is also proposed in this work.

Laser-induced photoacoustic detection of ozone at 266 nm using resonant cells of different configuration.

A highly sensitive pulsed photoacoustic (PA) spectrometer with different PA cell geometries was designed and fabricated in our laboratory to determine ozone detection at ppb level. The comparative performance and merits of these custom made cells were studied. The excitation source of PA spectrometer is a nanosecond pulsed laser at 266 nm (fourth harmonic of Nd:YAG laser) and a sensitive electret microphone as a photoacoustic detector. The sensitivity optimization of the PA system with different experimental parameters including the resonant acoustic modes of the 3 PA cells was carried out for the detection of ozone. The minimum detection limit for ozone achieved under our experimental conditions, with 3 PA cells were 10, 31 and 26 ppbV for cells designated as cell # 1, cell # 2 and cell # 3, respectively. This limit of ozone detection achieved in our work is quite appreciable to be able to detect ozone under safe permissible limits and the sensitivity achieved in our case is an order of magnitude better than earlier reports using sophisticated laser system like quantum cascade laser.

Photoacoustic spectrometry for trace gas analysis and leak detection using different cell geometries.

A photoacoustic (PA) spectrometer with high selectivity and sensitivity has been developed for trace gas analysis and for the detection of gas leak at part per trillion by volume (pptV) level. This PA system comprises of a resonant photoacoustic cell, a pulsed line tunable CO(2) laser as an excitation source and a sensitive electret microphone as a photoacoustic detector with an option to trigger the safety alarm system for early warning of gas leaks. In this work, three resonant PA cells with various geometries have been developed at our laboratory for the detection of photoacoustic signal using pulsed laser system and their comparative performance have been studied. As a special application of this PA system, the detection of sulfur hexa fluoride (SF(6)) gas using these three cells has been carried out for optimizing the sensitivity. Besides this, our PA system can very well be applied for pollution monitoring and detection of hazardous gases in a noisy environment.